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Guide to
CONCRETE
OVERLAYS
Sustainable Solutions for Resurfacing and Rehabilitating Existing Pavements
May 2014
THIRD EDITION
ACPA publication TB021.03P
On the Cover
source: Todd Hanson, Iowa DOT source: Jim Cable, Iowa State University source: Randell Riley, Illinois chapter, ACPA
source: Kevin Merryman, Iowa DOT source: The Transtec Group source: Todd Hanson, Iowa DOT
Technical Report Documentation Page
1. Report No.
2. Government Accession No.
3. Recipient’s Catalog No.
ACPA Publication TB021.03P
4. Title and Subtitle
5. Report Date
Guide to Concrete Overlays: Sustainable Solutions for Resurfacing and
Rehabilitating Existing Pavements (3rd edition)
May 2014
6. Performing Organization Code
7. Author(s)
8. Performing Organization Report No.
Dale Harrington and Gary Fick
9. Performing Organization Name and Address
10. Work Unit No. (TRAIS)
National Concrete Pavement Technology Center
Institute for Transportation, Iowa State University
2711 South Loop Drive, Suite 4700
Ames, IA 50010-8664
11. Contract or Grant No.
12. Sponsoring Organization Name and Address
13. Type of Report and Period Covered
American Concrete Pavement Association
500 New Jersey Ave., NW
7th Floor
Washington, DC 20001
14. Sponsoring Agency Code
15. Supplementary Notes
16. Abstract
The primary goal of this guide is to fill the knowledge gap about concrete overlays so that pavement owners can
confidently include concrete overlays in their toolbox of pavement solutions and make more informed decisions about
designing and constructing them. Another goal is to help owner agencies understand and appreciate the versatility of
concrete overlay solutions. This is not a complete step-by-step manual, nor does it provide prescriptive formulae or
specifications for designing and constructing concrete overlays. Rather, as the title suggests, this booklet provides expert
guidance that can supplement practitioners’ own professional experience and judgment. In particular, since the 2nd edition
was published, this edition enhances original material with updated information on the following topics:
•Evaluating existing pavements to determine if they are good candidates for concrete overlays
•Selecting the appropriate overlay system for specific pavement conditions
•Managing concrete overlay construction work zones under traffic
•Accelerating construction of concrete overlays when appropriate
17. Key Words
18. Distribution Statement
Pavements – concrete overlays – resurfacing – pavement preservation –
pavement rehabilitation
19. Security Classification (of this
report)
20. Security Classification (of this
page)
21. No. of Pages
145 plus front matter
and Notes page
22. Price
Unclassified.
Unclassified.
Form DOT F 1700.7 (8-72) Reproduction of completed page authorized
Guide to Concrete Overlays
Sustainable Solutions for Resurfacing
and Rehabilitating Existing Pavements
Third Edition, May 2014
Authors
Dale Harrington, Snyder & Associates, Inc.
Gary Fick, Trinity Construction Management Services, Inc.
Contributing Technical Authors
Amanda Bordelon, PhD, University of Utah
James Cable, PhD, P.E., Cable Concrete Consultation LC
Dan DeGraaf, P.E., Michigan Concrete Paving Association
Nigel Parkes, PNA Construction Technologies, Inc.
Randell Riley, P.E., Illinois Chapter, American Concrete Pavement Association
Rob Rodden, P.E., American Concrete Pavement Association
Jeff Roesler, PhD, P.E., University of Illinois at Urbana-Champaign
Julie Vandenbossche, PhD, P.E., University of Pittsburg
Project Coordinator
Melisse Leopold, Snyder & Associates, Inc.
Managing Editor
Marcia Brink, National Concrete Pavement Technology Center
Copyeditor
Carol Gostele, Birch Tree Editing
Technical Illustrator
Luke Snyder, Snyder & Associates, Inc.
Design and Layout
Mina Shin
Abbreviations
AASHTO American Association of State Highway and
Transportation Officials
ACI American Concrete Institute
AC PA American Concrete Pavement Association
ASR alkali-silica reactivity/reaction/reactive
ASTM American Society for Testing and Materials
CRCP continuously reinforced concrete pavement
CTE coefficient of thermal expansion
FAQ frequently asked question
FHWA Federal Highway Administration
FRC fiber-reinforced concrete
FWD falling weight deflectometer
IRI International Roughness Index
JPCP jointed plain concrete pavement
M-E PDG Mechanistic-Empirical Pavement Design Guide
MRD material-related distress
MUTCD Manual on Uniform Traffic Control Devices
NCHRP National Cooperative Highway Research Program
PCA Portland Cement Association
PCC portland cement concrete
SCM supplementary cementitious material
TRB Transportation Research Board
TCP traffic control plan
For More Information
Tom Cackler, Director
Marcia Brink, Senior Editor
National Concrete Pavement Technology Center
Iowa State University Research Park
2711 S. Loop Drive, Suite 4700
Ames, IA 50010-8664
515-294-9480
www.cptechcenter.org/
mbrink@iastate.edu
Mission
e mission of the National Concrete Pavement Technology Center
is to unite key transportation stakeholders around the central goal of
advancing concrete pavement technology through research, technology
transfer, and technology implementation.
For Additional Copies
e American Concrete Pavement Association is distributing this
guide. For additional copies, contact your local ACPA chapter or
affiliated state paving association (www.acpa.org/ournetwork); ask for
ACPA publication no. TB021.03P.
About This Guide
is guide is a product of the National Concrete Pavement Technology
Center (CP Tech Center) at Iowa State University, with funding from
the American Concrete Pavement Association. It is the third edi-
tion of the Guide to Concrete Overlays since 2007. Complementary
publications by the CP Tech Center include the Guide to the Design
of Concrete Overlays Using Existing Methodologies (October 2012),
Guide to Concrete Overlays of Asphalt Parking Lots (October 2012),
and Preservation and Rehabilitation of Urban Concrete Pavements Using
in Concrete Overlays: Solutions for Joint Deterioration in Cold Weather
States (anticipated publication June 2014). e entire series of con-
crete-overlays related documents is on the CP Tech Center’s website,
www.cptechcenter.org/.
Acknowledgments
e CP Tech Center gratefully acknowledges the generous financial
support of the American Concrete Pavement Association regarding the
development and printing of this guide. Without the association’s sup-
port, there would be no third edition. In addition, the CP Tech Center
and the authors wish to thank the knowledgeable, experienced, and
dedicated concrete pavement experts, both public and private, who
served on the Technical Advisory Committee and contributed to the
development of this guide. e committee consists of the following
people:
Gina Ahlstrom, P.E., FHWA
Andy Bennett, Michigan Department of Transportation
Tom Burnham, P.E., Minnesota Department of Transportation
Jim Cable, PhD., P.E., Cable Concrete Consultation LC
Dan DeGraaf, P.E., Michigan Concrete Paving Association
Jim Duit, Duit Construction Co., Inc.
Jim Grove, P.E., Senior Project Engineer, FHWA
Todd Hanson, P.E., Iowa Department of Transportation
Kevin Maillard, P.E., OHM Advisors
Kevin Merryman, P.E., Iowa Department of Transportation
Randell Riley, P.E., Illinois Chapter, ACPA
Robert Rodden, P.E., ACPA
Jeff Roesler, PhD, P.E., University of Illinois at Urbana-Champaign
Gordon Smith, P.E., Iowa Concrete Paving Association
Mark Snyder, PhD, P.E., Pennsylvania Chapter, ACPA
Shannon Sweitzer, P.E., North Carolina Turnpike Authority
Sam Tyson, P.E., Federal Highway Administration
Jeff Uhlmeyer, P.E., Washington State Department of
Transportation
Julie Vandenbossche, PhD, P.E., University of Pittsburgh
Leif Wathne, P.E., American Concrete Pavement Association
Matt Zeller, P.E., Concrete Paving Association of Minnesota
Disclaimers
Neither Iowa State University nor this document’s authors, editors, designers, illustrators, distributors, or technical advisors make any representations or warranties, expressed or implied, as to the accuracy of information
herein and disclaim liability for any inaccuracies.
Iowa State University does not discriminate on the basis of race, color, age, religion, national origin, sexual orientation, gender identity, sex, marital status, disability, genetic testing, or status as a U.S. veteran. Inquiries can
be directed to the Director of Equal Opportunity and Diversity, Iowa State University, 3680 Beardshear Hall, 515-294-7612.
v
Guide to Concrete Overlays
Contents
List of Figures .................................................................................... ix
List of Tables .................................................................................... xii
Ch 1. Introduction ................................................................. 1
Two Concrete Overlay (Resurfacing) Options ........................................ 2
Bonded Overlay Option ................................................................. 2
Unbonded Overlay Option ............................................................3
Benefits of Concrete Overlays .............................................................3
History of Concrete Resurfacing ........................................................4
Improvements in Concrete Resurfacing Technology .............................. 4
Sustainability ...................................................................................... 5
Asset Management through Resurfacing Solutions ...............................5
Preventive Maintenance ..................................................................6
Minor Rehabilitation ...................................................................... 6
Major Rehabilitation ......................................................................6
Lessons Learned from Recent Concrete Overlay Projects ....................6
Project Evaluation and Selection ..................................................... 6
Concrete Overlay Design ................................................................7
Plans and Specifications .................................................................. 7
Sequence of Construction and Maintenance of Traffic .................... 7
Concrete Overlay Construction ...................................................... 8
Ch 2. Evaluating Pavements and Selecting Solutions.......9
Pavement Evaluation Process ............................................................ 11
Historical Data and Future Projections (Desk Review) .................12
Visual Examination (On-site Review) ........................................... 12
Existing Support and Localized Distress ....................................12
Vertical Constraints .................................................................. 14
Profile Grade.............................................................................14
Pavement Coring ..........................................................................15
Optional Analyses .........................................................................15
Deflection Testing ..................................................................... 16
Alternative Means of Determining Support Conditions ............. 16
Roughness and Surface Friction Tests ........................................17
Condition Assessment Profile .......................................................17
Pavement Evaluation Report .........................................................17
Selecting Appropriate Concrete Overlay Solution ............................... 17
Ch 3. Overview of Concrete Overlay Options ...................25
Bonded Concrete Overlay on Asphalt Pavements .............................26
Application and Uses ....................................................................26
Performance .................................................................................27
Keys to Success ............................................................................. 27
Overlay Process.............................................................................27
Pavement Evaluation ................................................................27
Overlay Design ......................................................................... 27
Construction ............................................................................ 28
Future Repairs ..........................................................................29
Key Resources ...............................................................................29
Bonded Concrete Overlay on Composite Pavements ........................30
Application and Uses ....................................................................30
Performance .................................................................................31
Keys to Success ............................................................................. 31
Overlay Process.............................................................................31
Pavement Evaluation ................................................................31
Overlay Design ......................................................................... 31
Construction ............................................................................ 32
Future Repairs ..........................................................................33
Key Resources ...............................................................................33
Bonded Concrete Overlay on Concrete Pavements ...........................34
Application and Uses ....................................................................34
Performance .................................................................................34
Keys to Success ............................................................................. 35
Overlay Process.............................................................................35
Pavement Evaluation ................................................................35
Overlay Design ......................................................................... 36
Construction ............................................................................ 36
Future Repairs ..........................................................................37
Key Resources ...............................................................................37
Unbonded Concrete Overlay on Asphalt Pavements .........................38
Application and Uses ....................................................................38
Performance .................................................................................39
Keys to Success ............................................................................. 39
Overlay Process.............................................................................39
Pavement Evaluation ................................................................39
Overlay Design ......................................................................... 39
Construction ............................................................................ 40
Future Repairs ..........................................................................41
Key Resources ...............................................................................41
Unbonded Concrete Overlay on Composite Pavements .....................42
Application and Uses ....................................................................42
Performance .................................................................................43
Keys to Success ............................................................................. 43
Overlay Process.............................................................................43
Pavement Evaluation ................................................................43
Overlay Design ......................................................................... 43
Construction ............................................................................ 44
Future Repairs ..........................................................................45
Key Resources ...............................................................................45
Guide to Concrete Overlays
vi
Contents, continued
Unbonded Concrete Overlay on Concrete Pavements ...................... 46
Application and Uses ....................................................................46
Performance .................................................................................47
Keys to Success ............................................................................. 47
Overlay Process.............................................................................47
Pavement Evaluation ................................................................47
Overlay Design ......................................................................... 47
Construction ............................................................................ 48
Future Repairs ..........................................................................49
Key Resources ...............................................................................49
Ch 4. Concrete Overlay Design ..........................................51
Concrete Overlay Design Variables ................................................... 51
Existing Pavement Characterization ..............................................51
Surface Considerations .............................................................51
Structural Considerations .........................................................52
Traffic Characterization ............................................................. 52
Material Properties ....................................................................52
Climatic Factors ........................................................................53
Distress Mode ........................................................................... 53
ickness Design Selection ........................................................... 53
Background of Design Methodologies ......................................53
ACPA BCOA Method .............................................................. 53
BCOA-ME Method..................................................................55
1993 AASHTO Guide Method ................................................55
AASHTO Pavement ME Design Guide Method ......................56
ACPA StreetPave Method .........................................................56
Slabs with Optimized Geometry and OptiPave2™ Design
Software ................................................................................ 57
Design Considerations for Bonded Overlay Systems ........................57
Bonded Overlays of Asphalt and Composite Pavements ...............57
Bonded Overlays of Concrete Pavements ......................................58
Design Considerations for Unbonded Overlay Systems ..................... 58
Unbonded Overlays of Concrete Pavements ................................. 59
Suitability of Existing Pavement as a Base ................................. 59
Interlayer .................................................................................. 59
Drainage of Interlayer ............................................................... 60
Joint Design..............................................................................61
Unbonded Overlays of Asphalt Pavements ....................................62
Unbonded Overlays of Composite Pavements .............................. 62
Plan Development ............................................................................ 62
Engineering Survey ..........................................................................62
Survey Methods ............................................................................ 62
Laser Scanning .............................................................................63
Measurement and Payment Items for Concrete Overlays .................. 63
Establishing Plan Quantity for Overlay Concrete .........................63
Typical Costs of Concrete Overlays .................................................. 64
Miscellaneous Design Details ........................................................... 64
Curb and Gutter Details ............................................................... 64
Leaving the Existing Curb in Place ...........................................64
Removing Curb and Gutter ......................................................64
Overlay Curb ............................................................................ 64
Vertical Grade Changes ................................................................65
Overhead Clearance ................................................................. 65
Barriers and Rails ..................................................................... 65
Safety Edge .............................................................................. 65
Cross Road Drainage Structures ...............................................65
Cross Slope and Superelevation ................................................65
In-place Pavement Structures ........................................................ 66
Plate Dowel Details ......................................................................66
Corrosion Resistance ................................................................67
Plate Dowel Installation for Construction Joints Formed with a
Bulkhead (Form) ...................................................................67
Plate Dowel Installation in Slipform or Full-depth Saw Cut
(Butt-type) Construction Joints ................................................ 67
Dowel Installation for Contraction Joints .................................68
Transitions .................................................................................... 69
Mill and Fill Transitions for Bonded Concrete Overlays ............ 69
Transition Details for Bonded Concrete Overlays ..................... 69
Transition Details for Unbonded Concrete Overlays ................. 70
Widening and Lane Addition ....................................................... 71
Typical Drainage Outlets for Interlayers ....................................... 73
Rural Conditions ...................................................................... 73
Urban Conditions ..................................................................... 74
Ch 5. Concrete Overlay Materials and Mixtures ............... 75
Primary Concrete Materials .............................................................. 75
Cementitious Materials ................................................................75
Aggregates ....................................................................................75
Admixtures ................................................................................... 76
Conventional Concrete Mixtures......................................................76
Low w/cm Ratio ........................................................................... 76
Adequate Air Void System ............................................................ 76
Accelerated Mixtures ........................................................................ 76
Other Materials ................................................................................ 77
Structural Fibers for Concrete Overlays ........................................77
Separation Layer Materials ............................................................ 78
Asphalt Separation Layer ..........................................................78
Nonwoven Geotextile Separation Layer ....................................79
vii
Guide to Concrete Overlays
Contents, continued
Dowel Bars and Tiebars ................................................................80
Joint Sealant .................................................................................80
Curing Compound ....................................................................... 80
Ch 6. Concrete Overlay Strategies in Work Zones ...........81
Objectives of Work Zone Management ............................................81
Safety............................................................................................82
Traffic Flow .................................................................................. 82
Cost Effectiveness ......................................................................... 82
Work Zone Space Considerations ..................................................... 82
Conventional Paving Equipment Clearances ................................82
Reducing Clearances ...............................................................83
Other Clearances .......................................................................... 85
Construction Traffic Control ............................................................ 85
Concrete Overlay Staging .................................................................85
Two-Lane Highway under Traffic ................................................. 85
Temporary Safety Fillet .............................................................86
Pilot Cars for Continuous Production ......................................86
Examples of Staging Sequences .....................................................86
Two-Lane Highway Expanded to ree Lanes under Traffic ......... 86
Four-Lane Divided Highway without Crossovers and under
Traffic ........................................................................................... 87
Ch 7. Construction of Concrete Overlays ..........................99
Key Points for Concrete Overlay Construction .................................99
Bonded Overlays: Ensuring Proper Bond .......................................102
Unbonded Overlays: Installation of Geotextile Interlayer Fabric ..... 103
Placing Dowel Baskets ....................................................................104
Curing Concrete Overlays .............................................................. 105
Sawing Joints ..................................................................................105
Accelerated Construction ............................................................... 105
Opening Overlay to Traffic ............................................................. 106
Minimizing Early Loading Fatigue Damage .................................106
Strength Conversions ................................................................. 106
Strength Criteria for Opening Bonded Overlay Systems ............106
Bonded on Concrete ...............................................................106
Bonded on Asphalt .................................................................106
Strength Criteria for Opening Unbonded Overlay Systems.........106
Repairs of Concrete Overlays .........................................................107
Repairs of Bonded or in Unbonded Concrete Overlays .......... 107
Repairs of Full-Depth Unbonded Concrete Overlays ..................108
Appendix A. Evaluation and Selection Tables ................ 109
Appendix B. Reconstruction Options for Concrete .........111
In-place Recycled Concrete as a Processed Base Material ................ 111
Rubblization of Concrete Pavement ...............................................111
Crack and Seat (Not Recommended) .............................................112
Appendix C. Fiber Reinforcement ................................... 113
Why Fibers? ...................................................................................113
Types of Fibers ............................................................................... 113
High-volume Macro Synthetic Fiber Mixtures................................114
Construction Considerations When Using Fibers ...........................114
Appendix D. Laser Scanning Survey ............................... 11 6
Roadway Surface 3-D Laser Scanning ............................................116
Scanning Applications to Pavements ..............................................116
Planning Items to Be Considered ...................................................116
Data Analysis .................................................................................117
Static Scanning Operation .............................................................. 118
Mobile 3-D Laser Scanning ............................................................ 118
Mobile Mapping Operations ..........................................................118
Appendix E. Factors for Constructing Concrete
Overlays Under Traffic .................................................... 119
Appendix F. Stringless Paving Operation .......................127
Horizontal and Vertical Control Requirements and System
Limitations ................................................................................. 127
ree-step Process for Stringless Paving .......................................... 128
Existing Stringless Control Systems ................................................129
System No. 1 ............................................................................. 129
System No. 2 ............................................................................. 130
System No. 3 ..............................................................................130
Stringless System Equipment Selection Criteria ..............................131
Appendix G. Considerations for Developing Project
and Supplemental Specifications ................................ 132
General ..........................................................................................132
Contractor Submittal Considerations ......................................... 132
Scheduling and Conflicts ............................................................132
Limitations of Operations ..........................................................132
Method of Measurement and Basis of Payment ..........................132
Materials ........................................................................................ 132
Separation Layer for Unbonded Overlays ...................................133
Construction .................................................................................. 133
Preoverlay Repairs .......................................................................133
Bonded Concrete Overlays Over Concrete .............................133
Bonded Concrete Overlays Over Asphalt ................................ 133
Unbonded Overlays Over Concrete ........................................ 133
Unbonded Concrete Overlays Over Asphalt ...........................133
Guide to Concrete Overlays
viii
Contents, continued
Surface Cleaning.........................................................................133
Bonded Concrete Overlays Over Concrete or Asphalt ............133
Unbonded Concrete Overlays Over Concrete or Asphalt ........133
Concrete Placement .................................................................... 133
Grade Control ........................................................................ 133
Overlay Placement .................................................................. 133
Liquid Membrane Curing...........................................................134
Joint Sawing ...............................................................................134
General ................................................................................... 134
Joint Width ............................................................................134
Joint Seal ................................................................................134
Timing ...................................................................................134
Bonded Overlays Over Concrete ............................................134
Bonded Overlays Over Asphalt ...............................................134
Unbonded Overlays ................................................................ 134
Appendix H. Suggested Owner-Contractor Meetings
to Ensure a Quality Product .........................................135
Prebid Meeting Check List .............................................................135
Prebid Meeting ...............................................................................135
Prepour/Preconstruction Review Checklist ..................................... 135
Appendix I. Innovative Methods for Accelerated
Concrete Overlay Construction .................................... 138
References .........................................................................141
Bibliography ......................................................................144
ix
Guide to Concrete Overlays
List of Figures
Figure 1. Typical concrete overlay (before and after concrete
overlay placement) ....................................................... 1
Figure 2. Types of concrete overlays ............................................ 2
Figure 3. Milling concrete (left) and milled surface (right) .......... 3
Figure 4. Forty-six states where concrete overlays have been
constructed (shaded in blue)......................................... 4
Figure 5. Appropriate preservation solutions at various stages
of pavement service life ................................................ 5
Figure 6. Typical bonded and unbonded concrete solutions
at various stages of pavement service life ....................... 6
Figure 7. Pavement evaluation process, with examples of
existing pavement conditions ..................................... 10
Figure 8. Examples of existing pavement conditions, from a
condition assessment profile ....................................... 11
Figure 9. Visual inspection for MRD deterioration at the edge
of pavement ............................................................... 13
Figure 10. Moderate ASR cracking along the perimeter of slab ... 13
Figure 11. D-cracked pavement .................................................. 14
Figure 12. Typical joint deterioration with HMA patch ............. 14
Figure 13. Dynamic cone penetrometer ...................................... 16
Figure 14. Selecting appropriate concrete overlay solution
for asphalt pavements ................................................. 18
Figure 15. Selecting appropriate concrete overlay solution for
composite pavements ................................................. 20
Figure 16. Selecting appropriate concrete overlay solution for
concrete pavements .................................................... 22
Figure 17. Bonded concrete overlay of fair or better asphalt
pavement with surface distresses (previously called
ultra-thin whitetopping) ............................................. 26
Figure 18. Bonded overlay of asphalt pavement ........................... 26
Figure 19. SH-119 in 1991 prior to placement of an bonded
concrete overlay .......................................................... 27
Figure 20. SH-119 in 2009 after 18 years of service .................... 27
Figure 21. Longitudinal joints should be arranged to avoid
wheel paths ................................................................ 28
Figure 22. Bonded concrete overlay of fair or better condition
composite pavement with asphalt surface distresses .... 30
Figure 23. Bonded overlay of asphalt ........................................... 30
Figure 24. Existing composite pavement ..................................... 31
Figure 25. Bonded on composite pavement................................. 31
Figure 26. Bonded concrete overlay of good condition concrete
pavement with surface distresses ................................. 34
Figure 27. Bonded concrete on concrete ..................................... 34
Figure 28. Photo of concrete pavement with shotblast surface
prior to concrete overlay in 1994 ................................ 35
Figure 29. ree-inch concrete bonded overlay (photo dated
2013) ......................................................................... 35
Figure 30. Width of transverse joint in bonded concrete
overlay on concrete pavement should be equal to or
greater than width of crack in existing pavement ........ 36
Figure 31. Crack cage over concrete pavement crack ................... 37
Figure 32. Unbonded concrete overlay (previously called
conventional whitetopping) of poor-to-deteriorated
condition asphalt pavement ........................................ 38
Figure 33. Unbonded concrete overlay of asphalt pavement ........ 38
Figure 34. Poor to deteriorated asphalt pavement to be
resurface ..................................................................... 39
Figure 35. Poor to deteriorated asphalt pavement resurfaced
with unbonded concrete overlay ................................. 39
Figure 36. Consider asphalt rut depth when determining
saw-cut depth ............................................................. 41
Figure 37. Unbonded concrete overlay of poor-to-deteriorated
condition composite pavement ................................... 42
Figure 38. Unbonded overlay of composite ................................. 42
Figure 39. Composite pavement prior to unbonded concrete
overlay ........................................................................ 43
Figure 40. Unbonded concrete overlay over composite
pavement ................................................................... 43
Figure 41. Consider asphalt rut depth when determining
saw-cut depth ............................................................. 45
Figure 42. Unbonded concrete overlay of poor condition
concrete pavement ...................................................... 46
Figure 43. Unbonded concrete on concrete ................................. 46
Figure 44. Route D35 existing pavement in poor condition ........ 47
Figure 45. Route D35 5-inch unbonded overlay ......................... 47
Figure 46. Overlay design factors that affect one another ............ 51
Figure 47. Illustration of structural capacity loss over time
and with traffic ........................................................... 56
Figure 48. Width of overlay joint saw cut must be greater than
the crack width in the existing pavement .................... 58
Guide to Concrete Overlays
x
Figure 49. Upper sketch shows concrete overlay locking up
with old pavement (keying), and lower sketch shows
interlayer separates overlay from existing pavement. ... 59
Figure 50. Geotextile fabric separation layer ................................ 60
Figure 51. White geotextile fabric interlayer ................................ 60
Figure 52. Overlay blowup where expansion joint should have
been cut over existing concrete expansion joint .......... 60
Figure 53. Asphalt stripping of interlayer .................................... 61
Figure 54. Tapered plate dowel baskets in transverse contraction
joints and football-shaped plate dowels for slipformed
longitudinal construction joints.................................. 61
Figure 55. Higher shrinkage restraint in joint intersection
with round dowel (left) versus joint intersection
with plate dowel (right) .............................................. 61
Figure 56. Digital terrain model acquired through laser
scanning ..................................................................... 63
Figure 57. Concrete overlay cost by thickness ..............................64
Figure 58. Milling detail when leaving the existing curb in
place ........................................................................... 64
Figure 59. Milling detail when removing and replacing curb ........ 64
Figure 60. Detail of curb overlay ................................................. 64
Figure 61. Concrete curb overlay ................................................. 64
Figure 62. Typical safety edge for concrete overlay without
paved shoulder ........................................................... 65
Figure 63. Dowel options in superelevation areas ........................ 65
Figure 64. Concrete overlay with standard manhole .................... 66
Figure 65. Diamond-shaped plate dowels in fixed-formed
construction joints (right side) and football-shaped
dowels by slipforms .................................................... 66
Figure 66. Detail of construction joint plate dowel for
fixed-form paving ....................................................... 67
Figure 67. Taper-shaped construction joint plate dowel using
fixed forms ................................................................. 67
Figure 68. Detail of construction joint plate dowel for slipform
paving ........................................................................ 67
Figure 69. Slots being cut to accept the football-shaped plate
dowels ........................................................................ 67
Figure 70. Detail of plate dowel for contraction joint .................. 68
Figure 71. Plan view of roadway with plate dowels ...................... 68
Figure 72. Mill and fill transition for concrete overlay of
concrete pavement ...................................................... 69
Figure 73. Mill and fill transition for concrete overlay of asphalt
or composite pavement .............................................. 69
Figure 74. New transition tapers used to meet bridge approach
slabs or maintain clearance under bridges with bonded
overlay of concrete pavement ......................................69
Figure 75. New transition tapers used to meet bridge approach
slabs or maintain clearance under bridges with
bonded overlay of asphalt pavement ........................... 69
Figure 76. New transition tapers used to meet bridge approach
slabs or maintain clearance under bridges with
unbonded overlay of concrete pavement ..................... 70
Figure 77. New transition tapers used to meet bridge approach
slabs or maintain clearance under bridges with
unbonded overlay of asphalt pavement ....................... 70
Figure 78. Temporary granular transition to existing side
road/driveway ............................................................. 70
Figure 79. Asphalt wedge transition to existing side
road/driveway ............................................................. 70
Figure 80. Bonded overlay of concrete pavement with
widening unit ............................................................. 71
Figure 81. Bonded overlay of asphalt or composite pavement
with widening unit ..................................................... 71
Figure 82. View of tiebars for concrete overlay widening unit ........71
Figure 83. Unbonded overlay of concrete, asphalt, or
composite pavement with widening unit .................... 72
Figure 84. Bonded or unbonded overlay of asphalt or composite
pavement (previously widened with asphalt or concrete,
and to be widened again with new concrete overlay) .. 72
Figure 85. Unbonded overlay of concrete, asphalt, or composite
pavement with full concrete lane addition .................. 72
Figure 86. Interlayer outlet for concrete overlay shoulder ............ 73
Figure 87. HMA interlayer outlet for asphalt shoulder ................ 73
Figure 88. Geotextile interlayer outlet with new paved shoulder
(concrete or asphalt) ................................................... 73
Figure 89. Drainage of separation layer (interlayer) into an
existing underdrain system when existing curb is
removed and replaced ................................................. 74
Figure 90. Drainage of separation layer fabric into intake
when curb is not removed .......................................... 74
Figure 91. Synthetic fibers (1.5 in. to 2.25 in.) ............................ 77
Figure 92. Geotextile separation layer .......................................... 79
Figure 93. Light-colored geotextile fabric used as a separation
layer for an unbonded overlay .................................... 79
List of Figures, continued
xi
Guide to Concrete Overlays
Figure 94. Managing work zones effectively involves
balancing several priorities .......................................... 81
Figure 95. Stringline paver .......................................................... 83
Figure 96. A three-track, zero-clearance paver placing concrete
along a median barrier ................................................ 83
Figure 97. A typical four-track paver modified to three tracks,
providing zero clearance in a C/G situation
in Oklahoma .............................................................. 83
Figure 98. Controlling paving profile using a moveable stringline
on the adjacent lane ................................................... 84
Figure 99. Controlling paving profile using a paver ski on the
adjacent lane .............................................................. 84
Figure 100. Stringless paver ........................................................... 84
Figure 101. Zero clearance stringless paver .................................... 84
Figure 102. Vertical traffic control panels may be used to mark
pavement edge dropoff ............................................... 86
Figure 103. Centerline safety edge fillets for overlays
3 in. (50 mm) or greater ............................................. 86
Figure 104. Overlay of two-lane roadway with paved shoulders
(conventional paver) ................................................... 88
Figure 105. Overlay of two-lane roadway with granular shoulders
(conventional paver) ................................................... 90
Figure 106. Overlay of two-lane roadway with minimum
granular shoulders (zero-clearance paver) .................... 92
Figure 107. Overlay of two-lane roadway widening to three
lanes with paved shoulder (conventional paver) .......... 94
Figure 108. Overlay of four-lane roadway with paved shoulders
(conventional paver) ................................................... 96
Figure 109. Compare the surface texture of the nonshotblasted
area (upper left half of image) to the roughened
surface texture on the shotblasted section of
pavement (under the pen) ........................................ 102
Figure 110. Overlap of nonwoven geotextile material section ...... 103
Figure 111. Fastening nonwoven geotextile fabric to existing
concrete pavement .................................................... 103
Figure 112. Paving on top of nonwoven geotextile materials ........ 104
Figure 113. Paving on top of white geotextile fabric interlayer .... 104
Figure 114. Dowel basket anchor nails should be placed on
the downstream side of the basket relative to the
direction of pavement ............................................... 104
Figure 115. Manually verifying dowel placement ........................ 104
Figure 116. Removing overlay panels .......................................... 107
Figure 117. Finish and cure of concrete overlay repair ................. 107
Figure 118. Typical concrete pavement milling operation ........... 107
Figure 119. Typical concrete pavement milling operation ........... 107
Figure 120. Typical concrete pavement millings from milling
operation .................................................................. 108
Figure 121. Recycled concrete aggregate ...................................... 111
Figure 122. Rubblized concrete pavement ................................... 111
Figure 123. Fibers in concrete mix .............................................. 113
Figure 124. Fibers added at plant (left) and bags tossed into
ready-mix truck (right) .............................................. 114
Figure 125. Finished concrete overlay with synthetic fibers ......... 115
Figure 126. Balling fibers ............................................................ 115
Figure 127. Typical mobile scan project workflow ....................... 117
Figure 128. Pavement DTM/detail ............................................. 117
Figure 129. Pavement cross section detail .................................... 117
Figure 130. Static laser scanner.................................................... 118
Figure 131. Mobile laser scanner ................................................. 118
Figure 132. Mobile scanner onboard quality control
operation area ........................................................... 118
Figure 133. Paving machine control ............................................ 127
Figure 134. Survey existing surface to develop and build
database.................................................................... 128
Figure 135. ATV with GPS and laser profile ...............................128
Figure 136. Total robotic station ................................................. 129
Figure 137. System 1—Stringless paving operation using total
stations and reference points ..................................... 129
Figure 138. Computer controls on paving machine..................... 129
Figure 139. Rotating laser over reference points .......................... 130
Figure 140. System 2 paving machine ......................................... 130
Figure 141. System 2—Stringless paving operation using GPS,
a rotating laser, and reference points ......................... 130
Figure 142. GPS base station mobile or fixed .............................. 131
Figure 143. GPS paver control system ......................................... 131
Figure 144. System 3—Stringless paving operation using GPS .... 131
List of Figures, continued
Guide to Concrete Overlays
xii
List of Tables
Table 1. Recommended Optional Testing ................................ 15
Table 2. Subgrade Soil Types and Approximate Support
Values ......................................................................... 17
Table 3. Possible Preoverlay Repairs on Existing Asphalt
Pavement in Preparation for Bonded Overlay ............. 28
Table 4. Possible Preoverlay Repairs on Existing Composite
Pavement in Preparation for Bonded Overlay ............. 32
Table 5. Possible Preoverlay Repairs on Existing Concrete
Pavement in Preparation for Bonded Overlay ............. 37
Table 6. Possible Preoverlay Repairs on Existing Asphalt
Pavement in Preparation for Unbonded Overlay ........40
Table 7. Possible Preoverlay Repairs on Existing Composite
Pavement in Preparation for Unbonded Overlay ........44
Table 8. Typical Transverse Joint Spacing ................................. 48
Table 9. Possible Preoverlay Repairs on Existing Concrete
Pavement in Preparation for Unbonded Overlay ........49
Table 10. Summary of Current Overlay Design Software .......... 54
Table 11. Typical Weight and ickness for Geotextile
Interlayer .................................................................... 60
Table 12. Typical Adjustment Factors for Estimating Overlay
Cubic Yard Plan Quantities ........................................ 63
Table 13. Size and Spacing of Plate Dowels for Construction
Joints .......................................................................... 66
Table 14. Size and Spacing of Plate Dowels for Contraction
Joints .......................................................................... 66
Table 15. e Effect of Aggregate Gradation on Mixture
Properties ................................................................... 75
Table 16. Slab ickness and Opening Strength ........................ 77
Table 17. Summary of Fiber Types ............................................. 78
Table 18. Michigan DOT Asphalt Separation Layer Gradation..78
Table 19. Geotextile Separation Layer Material Properties ......... 79
Table 20. Concrete Overlay Work Zone Management
Considerations ........................................................... 81
Table 21. Concrete Paving Construction Practices for
Overlays ..................................................................... 99
Table 22. Distress Types and Severity Levels Recommended
for Assessing Concrete Pavement Structural
Adequacy ................................................................. 109
Table 23. Distress Types and Levels Recommended for Assessing
Asphalt and Composite Pavement Structural
Adequacy ................................................................. 110
Table 24. Considerations for Concrete Overlay Construction
under Traffic ............................................................. 119
Table 25. Applicability, Pros, and Cons of Various Accelerated
Construction Methods ............................................. 138
1
Guide to Concrete Overlays
Ch 1. INTRODUCTION
Chapter 1.
INTRODUCTION
e need has never been greater for engi-
neered strategies to preserve and maintain
the nation’s pavements. With shrinking
budgets, ever-increasing traffic volumes and
loads, and the critical emerging focus on
infrastructure sustainability and pavement
preservation, highway agencies are being
asked to do more with less in managing their
pavement networks. Concrete overlays can
serve as sustainable and cost-effective solu-
tions for improved management of pavement
assets, including preservation, resurfacing, and
rehabilitation. In addition, they contribute
to more sustainable construction practices by
preserving and extending pavement service for
years beyond the original design life. Many
concrete overlays have been in service for
decades, effectively extending the life of the
original pavement structures for 30 years or
more.
To ensure that concrete overlays provide
durable, long-lasting maintenance and
rehabilitation solutions, good design and
construction practices must be followed.
ese include designing an overlay that is
appropriate for the situation, accomplishing
appropriate pre-overlay repairs and prepara-
tion of the existing pavement, and using good
construction practices like proper jointing and
curing. With thorough planning, work zones
can be managed to accommodate these activi-
ties without sacrificing project safety, traffic
flow, or cost effectiveness.
Despite a demonstrated history of hundreds
of successful concrete overlay projects, some
agencies and contractors have hesitated to
design and construct them. One reason may
be a lack of understanding of engineered con-
crete overlays. e primary goal of the Guide
to Concrete Overlays series, therefore, is to
fill the knowledge gap and answer pavement
owners’ questions so that they can confidently
include concrete overlays in their toolbox of
pavement solutions and make more informed
decisions about designing and construct-
ing them. e first (Harrington et al. 2007)
and second (Harrington 2008) editions of
this guide described concrete overlay types,
applications, and issues related to design and
construction. is third, expanded edition
enhances the original material with updated
information:
• Evaluating existing pavements to determine
if they are good candidates for concrete
overlays
• Selecting the appropriate overlay system for
specific pavement conditions
• Managing concrete overlay construction
work zones under traffic
• Accelerating construction of concrete over-
lays when appropriate
Like the first and second editions, however,
this guide is not a complete step-by-step man-
ual, nor does it provide prescriptive formulae
or specifications for designing and construct-
ing concrete resurfacing projects. As the title
suggests, this booklet provides expert guid-
ance that can supplement practitioners’ own
professional experience and judgment.
Another goal of this guide is to help owner
agencies understand and appreciate the versa-
tility of concrete overlay solutions. A common
misconception is that concrete overlays are
limited to projects that require long-term
solutions (20 to 35 years) and that other
options may be better suited for short-term
solutions (5 to 15 years). Another is that over-
lays are expensive or difficult to build, or are
niche solutions with limited applicability. In
actuality, however, the following statements
are true:
• Concrete overlays can be designed to cost
effectively accommodate all combinations
of design life and traffic loading. eir
thickness can vary from 2 to 10 inches
or greater, depending on the existing
pavement condition, anticipated traffic,
available funding, and desired design life.
• Concrete overlay solutions exist for
all pavement types (concrete, asphalt,
and composite [asphalt surfacing over
concrete]).
• Concrete overlay solutions exist for all
pavement conditions; see Figure 1. Because
concrete distributes traffic loads over a wide
area, the underlying pavement does not
experience highly concentrated stresses. As
a result, as long as the original pavement
remains stable and uniform, a concrete
overlay can be placed.
Figure 1. Typical concrete overlay (before [left] and after concrete overlay placement)
Guide to Concrete Overlays
2
Ch 1. INTRODUCTION
Two Concrete
Overlay (Resurfacing)
Options
As Figure 2 illustrates, there are two options
regarding concrete overlays: bonded and
unbonded. is guide uses the general term
“concrete resurfacing” when collectively dis-
cussing both bonded and unbonded concrete
overlay solutions.
Bonded overlays are designed as part of the
pavement thickness, whereas unbonded over-
lays are essentially new pavement on a stable
base (existing pavement). Bonded overlay
options require that the existing pavement
be in good to fair structural condition. e
overlay helps eliminate surface distresses, with
the new overlay and existing pavement act-
ing as a monolithic pavement. Unbonded
overlay options add structural capacity to the
existing pavement system and do not require
bonding to the existing pavement. Unbonded
overlays can be placed on poor or even deterio-
rated pavements that are uniform. As shown
in Figure 2, both bonded and unbonded
overlays can be placed on existing asphalt,
composite, or concrete pavements.
Bonded Overlay Option
e purpose of bonded concrete overlays is to
add structural capacity and eliminate surface
distresses on existing pavements that are in
good to fair structural condition. Bonded
overlays generally provide resurfacing solu-
tions for routine or preventive pavement
maintenance and for minor rehabilitation.
Bonded concrete overlays are relatively thin
(2–6 in. [50–150 mm]). Bonded together,
the overlay and the existing pavement per-
form as one monolithic pavement. Bonding
between the overlay and the existing pave-
ment is essential. e bond ensures that the
overlay and existing pavement perform as
one structure, with the original pavement
continuing to carry a significant portion of
the load. All bonded overlay projects, there-
fore, are carefully designed and constructed
to achieve and maintain a bond between the
overlay and the existing pavement.
Factors that affect the performance of the
resurfaced pavement include the structural
integrity of the underlying pavement, the
effectiveness of the bond, the ability of the
two layers to move monolithically to maintain
the bond, and overlay jointing and curing
techniques.
e key to achieving desired performance is
to ensure the two structures—the existing
pavement and the overlay—behave as one
structure. erefore, it is important to under-
stand movement-related properties, such as
expansion and contraction properties, of both
the existing pavement and the overlay. For
example, for a bonded concrete overlay of an
existing concrete pavement, the coefficient of
thermal expansion (CTE) of the overlay con-
crete mixture should be similar to or less than
that of the existing concrete pavement.
Most bonded overlay projects are more chal-
lenging than unbonded overlay projects.
erefore, it is important to pay close atten-
tion to details in this guide.
Figure 2. Types of concrete overlays
Bonded Overlay Option Unbonded Overlay Option
In general, bonded resurfacing is used to eliminate surface
distress when the existing pavement is in good structural
condition.
Bonding is essential, so thorough surface preparation is
necessary before resurfacing.
In general, unbonded resurfacing is highly reliable, with
longer design life than rehabilitation with asphalt.
Minimal preresurfacing repairs are necessary for unbonded
resurfacing.
(Preventive Maintenance/Minor Rehabilitation)
OVER ASPHALT
(Minor/Major Rehabilitation)
OVER COMPOSITE
OVER CONCRETE
3
Guide to Concrete Overlays
Ch 1. INTRODUCTION
Unbonded Overlay Option
e purpose of an unbonded overlay is to
restore structural capacity to an existing
pavement that is moderately to significantly
deteriorated. Unbonded overlays are minor or
major rehabilitation strategies.
e term “unbonded” simply means that
bonding between the overlay and the under-
lying pavement is not needed to achieve the
desired performance (i.e., the thickness design
procedure does not consider the existing
pavement as a structural component of the
surfacing layer). us, the overlay performs as
a new pavement, and the existing pavement
provides a stable base. When the underlying
pavement is asphalt or composite, partial or
full bonding between the concrete overlay
and the underlying asphalt layer should not
cause a problem. In fact, such bonding gener-
ally adds some load-carrying capacity to the
system. So, unbonded concrete overlays on
existing asphalt or composite pavements are
not rigorously designed and constructed to
prevent bonding between the layers.
When the underlying pavement is concrete,
however, unbonded concrete overlays are
carefully designed and constructed to prevent
bonding between the two concrete layers.
at is because any bonding between the two
concrete layers may stress the overlay and
result in undesired reflective cracking.
Benefits of
Concrete Overlays
Agencies that regularly construct concrete
overlays derive several benefits:
1. Concrete overlays consistently provide cost-
effective solutions.
a. Dollar for dollar, they are one of the
most effective long-term pavement
preservation and major rehabilitation
options for existing pavements.
b. Because of the wide range of overlay
thicknesses that can be used, combined
with the preoverlay work required,
concrete overlays provide cost-effective
solutions for almost any pavement type
and condition, desired service life, and
anticipated traffic loading.
2. Concrete overlays can be constructed
quickly and conveniently.
a. e existing pavement does not need to
be removed. In fact, it is factored into
the overlay design to continue to help
carry some of the traffic load.
b. In most cases, minimal preoverlay
repairs are necessary.
c. Concrete overlays are placed using nor-
mal concrete pavement construction
practices.
d. Many concrete overlays can be opened
to traffic within a day of placement.
Nondestructive strength indicators, like
maturity testing, enable engineers to
take advantage of this benefit.
e. Accelerated construction practices can
be used. is guide provides useful
FAQ—Can concrete pavement actually be milled efficiently?
Yes. While not commonly done, several large projects in the recent past have utilized
milling as a means to remove up to 4 inches of the existing concrete pavement prior to
constructing a concrete overlay, as shown in Figure 3, or, in limited cases, to repair an
existing concrete overlay. Modern milling machines can effectively remove concrete at
production rates similar to asphalt pavement; efficiency and production are influenced
primarily by the depth of cut and hardness of the aggregate.
recommendations for coupling concrete
overlay construction with accelerated
construction techniques.
3. Concrete overlays are easy to maintain.
a. Repairing concrete overlays, especially
thin overlays, is usually much easier
than repairing a section of conventional
pavement.
b. in overlays constructed without
reinforcement can be easily and eco-
nomically milled out and replaced with
a new concrete surface.
c. Utility repair locations can be restored
to original surface elevation and ride
quality with ease.
4. Concrete overlays are an effective means
to enhance pavement sustainability by
improving surface reflectance (albedo),
increasing structural longevity, enhancing
surface profile stability, and maintaining
ride quality.
5. Concrete overlays can serve, in and of
themselves, as complete preventive main-
tenance, preservation, or rehabilitation
solutions.
Figure 3. Milling concrete (left) and milled surface (right)
Guide to Concrete Overlays
4
Ch 1. INTRODUCTION
History of Concrete
Resurfacing
Use of portland cement concrete (“concrete”)
to resurface existing pavements can be traced
to as early as 1901. By the mid-1980s, many
new concrete overlays were being constructed,
and the technology was rapidly maturing into
a standard practice in some agencies. A 1994
National Cooperative Highway Research
Program (NCHRP) Synthesis of Practice 204
showed that a relatively low-maintenance
service life of 20 years can be expected and
that many resurfacings have provided 30 to 40
years of service.
With the inclusion of data from NCHRP
Syntheses 99 and 204 (1982, 1994) the
American Concrete Pavement Association’s
(ACPA) National Concrete Overlay Explorer
(2013a) provides the best historical informa-
tion on the use of concrete overlays in the
United States. is database documents the
construction of 1,152 concrete overlays in
the United States from 1901 through 2012.
Concrete resurfacings have undergone an
impressive growth, which is evident in the
number of documented resurfaced highways
in service in the last three decades. Between
1980 and 2010, five times as many con-
crete overlay projects were constructed per
decade as were constructed in the previous six
decades.
is growth is evidence that concrete over-
lays are a good investment for highway
agencies seeking an additional preservation
or major rehabilitation alternative. Jointed
plain and reinforced concrete overlays in
service throughout the country are bonded,
Figure 4. Forty-six states where concrete overlays have been constructed (shaded in blue)
unbonded, and partially bonded overlays of
concrete pavements. Many plain and a few rein-
forced overlays also are in service as overlays of
asphalt concrete pavements, especially in heavy
trucking corridors. Concrete overlays have been
successfully constructed in 46 different states;
see Figure 4.
Improvements in
Concrete Resurfacing
Technology
Many of the changes and improvements in
the technology foreseen in the earlier reviews
have been realized as the highway community
has cooperated in working for better design
procedures, construction guidelines, and
specifications for all types of concrete overlays.
Among the major advances has been the
better definition of how the existing pavement
should be evaluated and prepared for a con-
crete overlay. Another has to do with improved
methods of placement of concrete overlays,
improved design methodologies, and synthetic
fiber technology. Fiber-reinforced concrete
resurfacings have been on the increase because
they contribute to the performance of thin
concrete resurfacing. e improved perfor-
mance comes from the increase in concrete
structural integrity through improved tough-
ness and durability of the concrete. Major
research projects have been completed, pro-
viding long-term solutions of bonded and
unbonded overlays of concrete and hot mix
asphalt (HMA) pavements. ese efforts,
along with pricing factors and a national focus
on training outreach and technical guidance
development, have led to more acceptance
and increased use of high-quality concrete
overlays.
Not surprisingly, concrete resurfacings share
two design requirements with on-grade
concrete pavements: they require uniform
support conditions and management of
movement if satisfactory performance is to
be realized. Nearly all the documented cases
of premature overlay failure can be traced to
some violation of these requirements, often
a result of incorrect assessment of the exist-
ing pavement. For this reason, the evaluation
of the existing pavement is paramount to
determine if uniform support and movement
control of the underlying pavement and inter-
face layer exist or can be cost-effectively made
to exist. If so, will a bonded concrete overlay
act as a monolithic unit with the underlying
pavement and provide the structural capacity,
load transfer, and drainage system required
to meet the design life? If not, an unbonded
overlay will be necessary to meet the same
criteria but with a slightly different approach
toward overlay thickness, drainage, and verti-
cal constraints.
Concrete resurfacing can be either a pres-
ervation fix or a rehabilitation fix. With a
preservation fix, the resurfacing is normally
completed with a bonded overlay over exist-
ing pavement that is in good or fair condition
or repaired or milled to bring it to that
condition. e preservation fix represents
the lowest possible cost with possible small
amounts of localized failures (<1 percent)
within the design life. For a rehabilitation fix,
the resurfacing is normally completed with an
unbonded overlay over poor or deteriorated
materials. To have a successful overlay, not
only should the good and poor characteris-
tics of the existing pavement be understood,
but the level of expected success for dollars
expended must be realistic. e initial costs
can be minimized, but a shorter performance
and greater need for additional maintenance
in the future is normally the result, or the
initial costs can be greater with greater perfor-
mance and reduced follow-up maintenance.
Minor cracking and localized failures should
be expected when placing a concrete overlay
on existing pavements. is should not be
viewed as a lack of performance, but rather
as a cost-effective treatment that may require
some further maintenance. In many cases, it
will be more cost effective to anticipate some
maintenance costs for a concrete overlay
rather than go overboard on preoverlay repair
costs in an attempt to prevent any cracking or
localized failures.
5
Guide to Concrete Overlays
Ch 1. INTRODUCTION
Sustainability
Many agencies are emphasizing sustainability
in their pavement management decisions.
Quantifying the impact of pavement deci-
sions on the primary sustainability factors of
(1) environment, (2) society, and (3) econom-
ics is nearly impossible. We can, however,
look at the sustainable benefits of concrete
overlays from a qualitative perspective and
conclude the following:
• Preserving the existing pavement has a
minimal impact on the environment (no
waste products are produced).
• User delays during construction are
reduced as compared to reconstructing a
pavement.
• Concrete overlays are capable of maintain-
ing their smoothness for many years, which
provides a benefit to society.
• Concrete overlays typically have a lower
life-cycle cost than asphalt overlays of
equivalent design life.
Concrete overlay pavement systems can be
sustainable for a wide range of design life
choices. Rather than removing and recon-
structing the original pavement, the owner
maintains and builds equity in it, realizing
a return on its original investment as long
as the original pavement remains part of the
system.
For these and other reasons, concrete overlays
are cost-effective, sustainable solutions. ey
provide societal benefits in the form of reli-
able load-carrying capacity and fewer and
shorter disruptions to traffic for pavement
resurfacing and rehabilitation.
Asset Management
through Resurfacing
Solutions
Simply put, asset management involves a
strategic and systematic approach to manag-
ing pavements; it relies heavily on pavement
management data and life-cycle cost analysis.
Pavement management and pavement pres-
ervation activities have become extremely
important in managing and accounting for
investments in highway pavements.
First, a little explanation to eliminate
confusion. For the last half century, “pave-
ment rehabilitation” has been defined as
a functional or structural enhancement of
a pavement, which produces a substantial
extension in service life, by substantially
improving pavement condition and ride qual-
ity. Over the last decade, the Federal Highway
Administration (FHWA) has been a strong
proponent and supporter of the concept of
cost effectively preserving the country’s road-
way network. is has helped in the recent
years to spur a nationwide movement of
“pavement preservation” and “asset manage-
ment” programs.
A number of definitions for the terms reha-
bilitation and preservation have existed for
years, and these terms are constantly misused
or incorrectly used interchangeably. e fol-
lowing descriptions are promoted by FHWA.
Pavement preservation is a strategy, a net-
work-level, long-term program to enhance
pavement performance by using an inte-
grated, cost-effective set of practices that
extends pavement life, improves safety, and
meets motorist expectations without recon-
struction. Pavement rehabilitation is defined
as a structural or functional enhancement
of a pavement that produces a substantial
extension in service life. To preserve a pave-
ment, it must be maintained and at times
rehabilitated. As shown in Figure 5, pavement
preservation is considered preventive mainte-
nance plus minor rehabilitation.
What is the difference between concrete
resurfacing and concrete overlays? Resurfacing
is a generic term for providing a new or
fresh surface on the existing pavement and
is considered mainly a preservation (preven-
tive maintenance and minor rehabilitation)
strategy. Concrete resurfacing consists of both
bonded and unbonded concrete overlays. It
is an integral component of a comprehensive
asset management approach, because it cost
effectively extends pavement life and improves
both functional and structural characteristics.
e variety, flexibility, and cost effectiveness
of concrete resurfacing, using overlay options,
make resurfacing an excellent solution for a
Figure 5. Appropriate preservation solutions at various stages of pavement service life
Preventive
Maintenance
Pavement Preservation
Reconstruction
Minor
Rehabilitation
Major
Rehabilitation
Maintenance
Pav
ement Condition
Time
Poor
Good
Rehabilitation
Guide to Concrete Overlays
6
Ch 1. INTRODUCTION
full spectrum of pavement needs. Figure 6
represents a typical pavement condition curve
over the life of a pavement. e preventive
maintenance, minor rehabilitation (together,
the preservation window), and major reha-
bilitation zones are noted where bonded and
unbonded overlays can be used to restore
pavement to the original or better condition.
Preventive Maintenance
Preventive maintenance is a major component
of pavement preservation. Basically, it consists
of extending the service life of structurally
sound pavements by applying cost-effective
treatments to the surface or near the surface.
Bonded concrete overlays of approximately 2
to 4 inches provide excellent preventive main-
tenance strategies for all types of pavements.
Minor Rehabilitation
Minor rehabilitation is used when structural
capacity needs to be restored to a pavement
but major rehabilitation is not required. One
of the major advantages of concrete overlays
as a preservation solution is that they increase
the pavement’s structural capacity, even if that
is not the primary objective of the preserva-
tion activity. Bonded and unbonded concrete
overlays of 4 in. (102 mm) provide excellent
minor rehabilitation solutions.
Major Rehabilitation
For pavements needing structural improve-
ment, major rehabilitation is the approach
typically used. Major rehabilitation calls for
structural enhancements that extend the
service life of an existing pavement and/or
improve its load-carrying capability. Bonded
concrete overlays up to 6 to 7 inches are not
uncommon, and unbonded overlays from 6
to 10 inches have been the norm.
To show the significance of concrete overlays
as a rehabilitation strategy, the American
Association of State Highway and
Transportation Officials (AASHTO) (2007)
recently stated that “thin unbonded concrete
overlays, 4–5 in. [100–125 mm] in depth,
have proven to be a rehabilitation option for
composite (asphalt over concrete) pavements
that exhibit significant deterioration. When
properly designed and constructed, unbonded
concrete overlays have been shown to increase
load-carrying capacity and extend pavement
life.”
Lessons Learned
from Recent
Concrete Overlay
Projects
To ensure that concrete overlays provide
durable, long-lasting maintenance and reha-
bilitation solutions, basic good design and
construction practices must be followed.
ese include designing an overlay that is
appropriate for the situation, accomplishing
appropriate preoverlay repairs and preparation
of the existing pavement, and using good con-
struction practices like proper jointing and
curing. With thorough planning, work zones
can be managed to accommodate these activi-
ties without sacrificing project safety, traffic
flow, or cost effectiveness.
Like its predecessors, this third edition of
the Guide to Concrete Overlays is the result
of collaboration between state departments
of transportation (DOTs), industry, and
academia to further enhance the state of the
practice for the design and construction of
concrete overlays. Many of the updates to this
edition are a result of the Concrete Overlay
Field Application Program conducted by
Iowa State University’s National Concrete
Pavement Technology Center (CP Tech
Center) under a cooperative agreement with
the FHWA. rough this program, expert
teams visited 26 sites in 18 different states,
and concrete overlay projects were either con-
structed or scheduled for construction in nine
states. Many lessons were learned while assist-
ing agencies with the design and construction
of concrete overlays, which prompted the
development of this updated edition. A sum-
mary of the key lessons learned is provided
below:
Project Evaluation and
Selection
Lessons learned regarding project evaluation
and selection include the following:
• Utilize coring, falling weight deflectometers
(FWDs), and “as built” plans to investigate
existing pavement layer conditions and
thicknesses to determine what type of over-
lay is appropriate for a given roadway.
• If existing asphalt will be milled, take cores
of asphalt to ensure that adequate (mini-
Figure 6. Typical bonded and unbonded concrete solutions at various stages of pavement service life
Preventive
maintenance
Bonded
on Asphalt
or
Composite
Bonded
on
Concrete
Unbonded
on
Concrete
Unbonded
on Asphalt
or
Composite
Minor
rehabilitation
Major
rehabilitation
Reconstruction
Existing p
avement condition
before treatment
Time
7
Guide to Concrete Overlays
Ch 1. INTRODUCTION
mum 3-inch) asphalt depth will remain
after milling as a design minimum and to
allow loaded concrete trucks to travel on
the milled surface with minimal damage
to it.
• In freeze-thaw climates and/or areas with
expansive soils, evaluate existing pave-
ment in spring and summer to identify
critical pavement distresses that need to be
accounted for in the overlay design.
• Identify all vertical constraints (bridges,
utilities, loop vehicle detectors, curbs, bar-
riers, ramps and driveways, guardrails, and
other structures) that may impact construc-
tion and develop a plan to mitigate them.
Concrete Overlay Design
Lessons learned regarding design include the
following:
• During the early phases of design, consider
all partial and full detour options and their
impact on construction.
• Choose the most appropriate overlay type
(bonded or unbonded) to meet existing
pavement conditions and anticipated future
traffic loadings.
• For unbonded overlays over concrete in
nonarid climates, provide a positive drain-
age path for surface moisture to exit the
interlayer bond breaker (separation layer)
to prevent interlayer erosion under heavy
traffic loadings.
• In designs for unbonded overlays over
concrete, compare asphalt or geotextile
interlayer (separation layer) costs, construc-
tion time, and performance.
• Determine transition lengths from the
existing profile elevation to the top of the
concrete overlay profile elevation on exist-
ing profile constraints, final roadway design
speeds, length and type of traffic control to
be used, and final open-to-traffic speeds.
• Utilize cubic yard and square yard payment
items. Square yard covers placement, and
cubic yard covers material, which reduces
contractor risk and cost while paying for
concrete used to fill surface irregularities.
• Based on construction economics and
expected overlay performance in designs for
unbonded overlays over concrete, correct
irregularities in cross slope and profile by
varying the thickness of concrete, not the
depth of the asphalt bond breaker (separa-
tor layer). Deeper transverse joint sawing
may be necessary to achieve T/3, but final
overlay performance will be enhanced.
• In designs for bonded overlays over asphalt,
exercise care when milling the asphalt to
prevent leaving a thin asphalt lift, which
can cause delamination.
• Consider two potential overlay quantity
design options:
◦For minimal preliminary work and cost
▪Do no preliminary surveys other than
measuring wheel-rut depth and pave-
ment cross slope at 500-foot intervals.
▪Develop design profiles of centerline
and pavement edges.
▪Estimate the quantity of concrete
required to meet the profiles and pro-
vide minimum thickness at centerline
and edges of pavement.
▪Add a reasonable percentage to the
concrete quantity to account for place-
ment tolerance, construction losses,
and surface/cross-section irregularities
and establish the “new theoretical”
plan quantity. Some states use 15 to
20 percent, depending on the thick-
ness of the overlay and the amount
of pavement cross-slope correction
desired. e thinner the overlay and
the higher the cross-slope correction,
the higher the percentage. Some states
add a maximum overrun of 2 to 3
percent to the “new theoretical” plan
quantity.
◦For optimization of concrete quantities
▪Conduct nine-shot cross sections at
50-foot intervals to map the existing
surface.
▪Develop a design centerline pro-
file and cross slope that optimizes
pavement smoothness, maintains
minimum overlay depth at centerline,
and optimizes concrete quantities.
▪Limit the contractor to an additional
percent of the quantity identified by
the desired cross section and design
profile. Some states use 6 to 8 percent,
depending on the thickness of the
overlay.
• Evaluate the impacts of removing/replac-
ing medians or existing curbs versus their
retention in terms of construction time,
cost, and future performance.
• Carefully review the construction sequence
and maintenance of traffic in conjunction
with joint layout. In some cases, tied lon-
gitudinal construction joints can interfere
with the maintenance of both public and
contractor traffic.
• Develop the construction sequence to meet
closed-road or through-traffic maintenance
in conjunction with joint layout and design
for turn lanes and shoulder concrete work.
• Develop staging plans that allow for the use
of paving equipment between existing con-
crete railings and temporary safety-related
barrier walls.
• Design transitions and bridge-approach
pavement sections to minimize hand place-
ment and detailed jointing plans.
• Determine the type and amount of surface
preparation required based on agency pri-
oritization of the following goals:
◦Pavement smoothness
◦Concrete quantity
◦Matching existing surface features
◦Maintaining minimum cross slopes
◦Removing unstable existing pavement
layers
◦Vertical clearance site conditions
◦Bond enhancement between existing and
overlay pavement layers
Plans and Specifications
Lessons learned regarding plans and specifica-
tions include the following:
• Reduce plan sets to necessary quanti-
ties, design details, plan/profile data (not
sheets), and survey control information.
• Require the use of vibrator frequency mon-
itor recorders on the paver.
• Utilize standard concrete mixes and matu-
rity measurements to control opening
of intersections and access points. Use
accelerated concrete mixtures only when
necessary.
• When existing surface milling is required,
clearly define the purpose, vertical and
cross-slope limits, and required existing
surface survey accuracy.
Sequence of Construction
and Maintenance of Traffic
Lessons learned regarding construction
sequencing and traffic maintenance include
the following:
• Hold a public preconstruction meeting to
communicate traffic control impacts and
identify public concerns that should be
addressed by the contractor and highway
agency during construction.
• Minimize the number of gaps for inter-
sections and driveways to provide for
uninterrupted paving.
Guide to Concrete Overlays
8
Ch 1. INTRODUCTION
• Consider paving plans that allow tempo-
rary access for adjacent property owners
where possible and accommodate their
daily needs.
• Clearly state the criteria for lane closures
and allow for contractor alternative sugges-
tions to meet the criteria.
• Provide for alternative detour routes to
be used in the case of unforeseen circum-
stances (crashes, wide loads, equipment
breakdowns, etc.).
• Jointly with the contractor, develop a traffic
control plan that allows sufficient room for
construction operations and keeps the trav-
eling public and pedestrians safe.
• Anticipate and mitigate temporary drainage
issues caused by milling operations.
• In the case of construction of single-lane
overlays with 24-hour pilot car operations
on a two-lane road, apply the following
construction suggestions:
◦Allow multiple construction zones
separated by two miles between flag-
ger stations. e 2-mile work zone area
requirement is the distance between
flagger stations versus the outermost
warning signs.
◦Consider using a 3.5-mile paving work
zone and allow the contractor to close
local crossings in the work zone only
when those in the adjacent zone are
open.
◦Allow the contractor to propose methods
and materials to construct temporary
access ramps (in use for less than one
month).
◦Encourage construction of bridge work,
transition sections, subdrains, pavement
patching, side ditch drainage work, and
earthwork prior to staged surface prepa-
ration and paving operations.
◦Delete centerline safety wedge construc-
tion where pilot car operations are used
24/7 through the work area.
◦Allow for equipment work on shoulders
and side ditches to proceed in the same
area as a lane closure employed for other
prepaving work.
◦Where bridge approaches and road inter-
sections are immediately adjacent to each
other, encourage use of extended tem-
porary barrier-rail lengths and three-leg
traffic signal setups to reduce construc-
tion/traffic delays.
Concrete Overlay
Construction
Lessons learned regarding construction
include the following:
• Require contractor development of a
comprehensive paving plan to address con-
struction and public impacts.
• When necessary, accelerate all construction
processes to minimize public impact. Limit
contract stage work times to emphasize the
need for accelerated work if that is the goal
of the contract.
• Where load transfer is called for in wheel
paths only, use separate partial dowel bas-
kets for each wheel path and do NOT cut
the basket shipping wires.
• When anchoring dowel baskets, consider
the use of uniform thicknesses of separa-
tion layer, adequate numbers of anchors,
and the relationship of anchor length and
shot force to the separation layer depth and
material; minimize the head of concrete in
front of the paver. Monitor dowels behind
the paver for location, orientation, and
depth.
• Utilize software such as HIPERPAV to
anticipate paving or curing problems and
mitigate their impact on operations.
• Minimize the temperature differential
between the existing pavement surface
and the concrete overlay during placement
and curing. is is especially critical dur-
ing cool-weather paving for the following
reasons:
◦When a bonded concrete overlay is
placed in cooler weather, the day/night
temperature differential will cause move-
ment in the existing pavement; it will
expand during the day and contract at
night. To prevent cracking in the over-
lay, the overlay must reach saw strength
before the underlying pavement’s night-
time contraction. Specifying a minimum
overlay mix temperature of 65°F has
proven to be helpful in mitigating this
set-time issue.
◦In addition, when a concrete overlay is
placed in cooler weather, the concrete
can set from the bottom up, delaying the
sawing window. Temporarily covering
the overlay with plastic after paving helps
the concrete to set properly, allowing for
timely sawing.
is guide provides updated guidance for the
design, construction, and maintenance of
concrete overlays, which should be adapted
to fit local conditions and policies. Successful
performance of any pavement rehabilitation
method requires that design, materials, and
construction be considered as complementary
processes.
9
Guide to Concrete Overlays
Ch 2. EVALUATION & SELECTION
Chapter 2.
EVALUATING PAVEMENTS AND SELECTING
SOLUTIONS
Evaluating the existing pavement condi-
tion is an important part of the pavement
preservation and rehabilitation process. A
comprehensive evaluation provides valuable
information about the pavement’s condition,
performance capabilities, and limitations,
including the following:
• Identification of all in-situ pavement layers
• Characteristics and behavior of in-place
pavement materials
• Presence, type, and extent of distress
• Structural condition and load-carrying
capacity
• Functional characteristics of the pavement,
such as grades, roughness, friction, and
noise
Several activities can be performed as part of
the pavement evaluation process (see Hall
et al. 2001; Hoerner et al. 2001; NCHRP
2007). Specifics will vary from project to
project, depending on the project type and
relative significance. For the purpose of deter-
mining whether or not a concrete overlay is
a good candidate for an overlay, the process
can be divided into the following mandatory
and optional steps. e steps for pavement
evaluation are shown in Figures 7 and 8 on
the following pages. Appendix A also provides
evaluation tables based on existing pavement
type and condition.
Mandatory evaluation activities include the
following:
• Historical data collection, records review,
and future projections (desk review)
• Visual examination (on-site review)
• Core analysis
• Pavement evaluation report
Optional evaluation activities include the
following:
• Additional tests (including FWD, analyses
of material-related distresses, drainage,
roughness, and surface friction) if the cause
of distress is unknown or if additional
information is needed to determine the
extent of distress
• Condition assessment profile
e evaluation concludes with a profile of the
overall pavement condition assessment. See
Figure 8.
After a pavement has been thoroughly evalu-
ated, then a solution can be selected. In many
cases, either a bonded or unbonded concrete
overlay will be an appropriate and effective
solution. For those pavements for which a
concrete overlay is not appropriate, other
treatment options are discussed in Appendix B.
Guide to Concrete Overlays
10
Ch 2. EVALUATION & SELECTION
Figure 7. Pavement evaluation process, with examples of existing pavement conditions (source: Snyder & Associates, Inc.)
• Type of distress
• Depth of distress
• Verification of thickness for pavement
base/subbase
Initial Evaluation (steps 1–4)
Optional Analyses
Core Analysis
Visual Examination
Concrete Asphalt / Composite
Good
Fair
Poor
Good
Fair
Poor
• Pavement material (including
aggregate CTE), design, age,
thickness, layers
• Existing traffic and performance level
• Design life
• Remaining life
• Desired traffic and performance level
• Desired design life
• Elevations and grade restrictions
• Other historical information
Pavement History and Performance Goals
4
(depending on extent of problems)
(indicated by core analysis)
Conduct if (a) material or durability issues are
indicated, or (b) roadway provides service for
high levels of traffic, especially if a bonded
overlay is being considered.
• Petrography analysis
◦Concrete material-related distress (MRD)
◦Poor air-void system
• Asphalt stripping
• CTE
Conduct if (a) pavement or subgrade support
issues are indicated, or (b) roadway provides
service for high levels of traffic, especially if
a bonded overlay is being considered.
• FWD tests
◦Subgrade/subbase support (k value)
◦Subgrade/subbase variability
◦Pavement properties
◦Load transfer efficiency
◦Presence of voids
◦Asphalt stiffness
◦Concrete flexural strength
• Subgrade tests
◦Freeze-thaw characteristics
◦Shrink-swell characteristics
◦Soil strength (dynamic cone penetration
or standard penetration test)
Conduct if (a) materials or durability issues
are indicated, or (b) roadway provides
service for high levels of traffic, especially if
a bonded overlay is being considered.
4-b. Subsurface Tests
4-c. Surface Texture Tests
4-a. Material-related Tests
Deteriorated Deteriorated
11
Guide to Concrete Overlays
Ch 2. EVALUATION & SELECTION
Concrete Asphalt / Composite
• Corner breaks
• Joint deterioration (severe)
• Tented panels
• Longitudinal cracking
• Pumping/faulting
• Punchout
• MRD (medium to severe)
• Transverse cracking
• Subgrade/subbase condition
• Other
Surface Deficiencies
Structural Deficiencies
Structural Deficiencies
Surface Deficiencies
• Friction loss
• Joint deterioration (low to medium)
• Map cracking (non-alkali-silica
reactivity [ASR])
• Popouts
• Noise
• Scaling
• Roughness (not distress related)
• Plastic shrinkage cracks
• Thermal shrinkage cracks
• IRI
• Other
• Bleeding/flushing
• Block cracking
• Friction loss
• Noise
• Corrugation
• Joint reflective cracking
• Roughness (not distress related)
• Rutting
• Weathering/raveling
• Shoving
• Slippage
• IRI
• Other
• Fatigue (alligator) cracking
• Depressions
• Heaves
• Longitudinal cracking
• Potholes
• Transverse thermal cracking
• Rutting/shoving
• Subgrade /subbase condition
• Other
Pavement
Evaluation
Report
and
Pavement
Condition
Rankings
Initial Evaluation (Step 5)
Condition Assessment Profile
5
Pavement
Evaluation Process
e purpose of evaluating the existing pave-
ment’s condition is to collect details about
any distresses and performance problems that
currently exist and their causes. is informa-
tion helps the owner-agency determine if a
pavement is a good candidate for a concrete
overlay and, if so, the extent of spot repairs
required before an overlay is constructed. e
extent of repairs needed is an important fac-
tor in determining if/when either a bonded
or unbonded overlay will be a cost-effective
solution.
Evaluating the existing pavement’s condition
involves at least three steps:
1. e first step is to review the pavement’s
historical design and performance record—
pavement thickness and other design
attributes, mixture materials and design,
construction date and method, traffic load-
ings, design life, maintenance activities to
date, etc.
Along with looking at the historical
records, this step should include recording
future performance requirements, such as
expected traffic loadings and overlay design
life.
is step should include a determination
of any elevation limits and/or grade restric-
tions that signal potential clearance issues
for overlay construction.
2. e second step is a visual examination of
the pavement’s condition, noting visible
surface and structural distresses.
3. e third step is a more thorough exami-
nation of the pavement structure through
a core analysis. is step will identify
distresses or performance problems that
cannot be determined by a visual exam
alone. Core analyses verify pavement thick-
ness, the subgrade/subbase material and
thickness, and the depth and perhaps type
or cause of distresses.
Based on information learned in steps 1
through 3 (Figure 7), the necessity for addi-
tional evaluation should be considered. For
example, tests related to materials or dura-
bility distresses, possible support problems,
or surface conditions may be necessary.
e following questions can help the pave-
ment owner determine if additional tests are
advisable:
• What is the extent of pavement distresses,
based on the visual evaluation and core
analysis?
• What is the pavement’s expected service
level and life? Major highways with sig-
nificantly high truck volumes and/or long
service life require more extensive and com-
prehensive evaluations than lower-volume
roadways.
Results from all initial evaluation steps should
be recorded in a Condition Assessment
Profile. is profile helps the agency deter-
mine the pavement’s overall condition and
summarize it in a Pavement Evaluation
Report.
Figure 8. Examples of existing pavement
conditions, from a condition assessment profile
Guide to Concrete Overlays
12
Ch 2. EVALUATION & SELECTION
Historical Data and Future
Projections (Desk Review)
e first step is to collect data from office files
and other historical records associated with
the project. e goal is to collect as much
information about the existing pavement as
possible, such as original design data, con-
struction information, subgrade/subbase data,
materials testing data, traffic data, perfor-
mance data, and so on. Possible data sources
for this effort include the following:
• Design reports
• Construction plans/specifications (new and
rehabilitation)
• Materials and soils properties from previous
laboratory test programs and/or published
reports
• Past pavement condition surveys, non-
destructive testing and/or destructive
sampling investigations
• Maintenance/repair histories
• Traffic measurements/forecasts
• Environmental/climate studies
• Pavement management system reports
Discussions with local design and mainte-
nance engineers may also be beneficial and
should be included as participants in the on-
site review process. e information gathered
in this step can be used to divide the pave-
ment into discrete sections with similar design
and performance characteristics.
is step also includes determining future
performance requirements, such as expected
traffic loadings and overlay design life.
Consideration should be made for potential
future traffic generators (i.e., special events,
future development along the route, etc.) that
may impact the thickness design procedure.
Visual Examination
(On-site Review)
With historical information in hand, the sec-
ond step is a visual site inspection to obtain
initial information about the pavement’s
performance and distress issues. Members of
the design team should conduct the visual
examination. At a minimum, the following
items should be reviewed and recorded for
future reference:
Drainage Surveys
Poor drainage conditions are a major cause
of distress in pavement structures. Unless
moisture-related problems are identified and
corrected, the effectiveness of repairs and
overlays will be reduced. As part of a pave-
ment distress survey, the overall drainage
conditions of the existing pavement should
be assessed. Excavation at the edge of the
pavement may provide useful information
regarding trapped water and other drainage
issues. Observations of moisture/drainage
problems (e.g., pumping, corner breaks,
standing water, etc.) may indicate the need
for a more intensive FWD test for the support
value k or a more thorough survey of subsur-
face drainage conditions. e purposes of a
drainage survey are the following:
• Detect and identify moisture-related
distress
• Document prevailing drainage conditions
(e.g., cross slopes, cut/fill areas, depth and
condition of ditches)
• Assess edge-drain conditions
If edge drains are present, their effectiveness
should be evaluated by observing their out-
flow after a rainfall or after water is released
from a water truck over pavement discon-
tinuities. Another way to assess edge-drain
effectiveness is through video inspections
(Daleiden 1998; Christopher 2000). A video
camera attached to a pushrod cable and
inserted into the drainage system at outlets
can locate blockages like rodents’ nests or
areas of crushed pipe. Several states have
adopted edge-drain video inspection in their
pavement evaluation/construction process.
e visual examination should include the
location and inspection of all under-drain
outlets.
It is especially important to determine the
subgrade soil’s freeze-thaw and shrink-swell
characteristics. Soil strength-related tests
using the dynamic cone penetrometer or the
standard penetration test provide useful infor-
mation about subgrade stability.
Possible drainage problems indicated by a
drainage survey may suggest the need for
in-depth analysis of the pavement structure’s
drainability. DRIP (Drainage Requirements
In Pavements), an FHWA computer program,
can assist in such an analysis (Mallela et al.
2002).
Existing Support and Localized
Distress
One key to successful concrete overlays is
ensuring that the underlying pavement and
subgrade/subbase provide uniform support.
Information gained from distress surveys
will have the greatest impact on identifying
necessary spot repairs and selecting appropri-
ate overlays. Pavement distress in the form
of visible defects or deterioration of the
pavement is the most basic indication of an
existing pavement’s current performance and
structural condition. e FHWA publication
Distress Identification Manual for the Long-
Term Pavement Performance Program (2003a)
is useful when identifying pavement distresses
and measuring their severity. Information
obtained in this step will be used to determine
the type and extent of field testing required.
Types of distress are determined primarily
by occurrence and appearance and can indi-
cate the underlying causes of deterioration.
Severity of distress represents the criticality
of the distress in terms of progression; more
severe distresses will require more extreme
rehabilitation measures. e extent of each
distress type and severity level must be mea-
sured when an overlay is considered.
For example, consideration should be given to
any deterioration of an asphalt surface course
(existing asphalt or composite pavement),
because asphalt is a good reflector of underly-
ing problem areas. Examples include subbase/
subgrade problems due to poor drainage,
material-related distresses (MRDs) such as
alkali-silica reaction (ASR) or D-cracking in a
concrete layer, and other defects that result in
isolated expansion or loss of support.
Panel tenting (early stages of blowups)
may indicate the presence of a void under
a concrete panel in an existing concrete or
composite pavement. Sections with significant
tenting can be repaired to relieve the pres-
sure and provide uniform support. If, during
the desk review process, an open graded base
(OGB) is found to be part of the pavement
structure, an FWD analysis is warranted (see
Optional Analyses on page 15) because of the
likelihood of secondary consolidation of the
OGB, which results in nonuniform support
conditions. is FWD testing should be done
prior to the on-site review to assure that the
design team has the information at hand to
assist in evaluating the support conditions.
13
Guide to Concrete Overlays
Ch 2. EVALUATION & SELECTION
Material-related Distress (MRD) in
Existing Concrete Layer
Pavements exhibiting MRD may be viable
candidates for unbonded concrete overlays,
but when MRD is suspected or known to
exist, the extent of present and potential
future distress must be assessed. In many cases
MRD manifests as bottom-up deterioration,
which means that visible distresses may be
minimal to moderate while distresses at the
bottom of the pavement are severe. A quick
and inexpensive method for checking for
bottom-up deterioration is to excavate at the
edge of the pavement at multiple joint loca-
tions and visually inspect for deterioration
that is not visible from the surface; see Figure
9. In all cases where MRD is suspected, how-
ever, laboratory testing as referenced above is
needed to assess the degree of deterioration as
well as the potential for future deterioration.
When a concrete overlay of an MRD pave-
ment is deemed viable, the design life of the
overlay should take into account the remain-
ing life of the existing pavement. e lower
the severity and rate of the MRD, the higher
the chance of longer service life.
Bonded concrete overlays over pavements
with MRD are not recommended due to the
movement of the pavement from the MRD
and subsequent reactive cracking. However,
unbonded concrete overlays have been con-
structed on pavements with MRD for years.
A good example is the 5-inch unbonded over-
lay of a concrete pavement with D-cracking
in the Kansas City metro area on Route D35
(see Figures 44 and 45 in Chapter 3). After
seven years carrying more than 9,000 vehicles
per day, the overlay is in excellent condition.
ere is little, if any, information or research
documenting the condition of existing pave-
ments with MRD before concrete overlay
construction or the performance of unbonded
concrete overlays on pavements with MRD.
e three most common mechanisms that
cause MRD in concrete are alkali-silica reac-
tion, D-cracking, and freezing and thawing;
these mechanisms and their influence on
overlay performance are described below. In
principal, any continued expansion due to
the mechanisms discussed below will likely
shorten the life of an overlay.
Alkali-silica Reaction (ASR)
Alkali–silica reaction is a reaction that occurs
over time between water, alkali-hydroxides
in cement paste, and reactive noncrystalline
silica found in some aggregates (see Figure 9).
is reaction creates an alkali-silicate gel that
absorbs water and expands, exerting expansive
pressure inside the mixture and causing crack-
ing and loss of strength of the concrete.
Alkali-silica reaction requires the presence
of three ingredients: reactive aggregates,
alkali hydroxides in the paste, and moisture.
Expansion rates may vary, causing distress
in years to decades depending largely on the
mineralogy of the aggregates; see Figure 10.
Absence of any one of the three ingredients
will prevent the reaction, but in practice this
may not always be possible.
Reducing the amount of water penetrating
the concrete will slow the reaction, but the
reaction will proceed if the relative humidity
in the pores is greater than approximately 80
percent, which is almost always likely in pave-
ments—even in arid climates. Once cracking
begins in a concrete layer, it is likely that dis-
tress will accelerate because additional water
can penetrate more easily.
FAQ—Can a pavement with MRD be an appropriate candidate for a concrete overlay?
Existing pavements that exhibit MRD should not be considered for a bonded overlay. ey
are, however, potentially viable as unbonded overlay candidates. Nonuniform support and
loss of support are the primary issues to consider when designing an unbonded overlay of a
pavement with MRD. Because MRD requires moisture to develop, further progression can
sometimes be slowed through improved drainage of the existing pavement by retrofitting
pavement edge drains prior to constructing a concrete overlay.
Unless it can be demonstrated that all the
alkalis have been consumed in the exist-
ing pavement, limiting future reactions, it
should be assumed that the existing system
will continue to expand. Suspect concrete
must be evaluated to assess the potential for
future expansion using approaches such as
described in Report on the Diagnosis, Prognosis,
and Mitigation of Alkali-Silica Reaction (ASR)
in Transportation Structures (Fournier et al.
2010). e reduction of subsurface water,
even in slow-acting ASR, is an important
step in the effort to mitigate the ASR dam-
age before replacing the riding surface an
unbonded concrete overlay.
Figure 9. Visual inspection for MRD deterioration at the edge of pavement
Figure 10. Moderate ASR cracking along the perimeter of slabs (source:
[Thomas et al. 2011])
Guide to Concrete Overlays
14
Ch 2. EVALUATION & SELECTION
D-cracking
D-cracking is damage incurred by the propen-
sity for some limestone aggregates to absorb
water when wet, but not release it under dry-
ing conditions because of the small size of
the pores in the aggregate. e particles thus
become saturated and, under freezing condi-
tions, will crack and expand, causing damage
in the mixture. e distress tends to begin at
the bottom of a slab and at joints, and it pro-
gresses inward; see Figure 11.
In extreme cases, all that will be left is rubble.
Evaluation of the risk varies from state to
state, and reference should be made to local
DOT knowledge of whether or not an exist-
ing layer is at risk. Typically, a D-cracking
pavement will need repair in approximately
10 years, although some pavements have
lasted as long as 40 years. If damage has already
started, then it is likely to continue, causing
damage zones at the joints to grow wider
over time, therefore reducing support for any
layer placed above it. Removing and replacing
damaged sections may buy some time, but the
distress will continue to grow in the at-risk
concrete at the interfaces with the repairs.
As with any MRD, the likely remaining life of
the damaged pavement must be accounted for
when considering the design life of a concrete
overlay.
Freezing and Thawing
Concrete that is saturated and subjected to
freezing and thawing cycles will exhibit dam-
age, particularly at the joints. is is largely
due to the expansion of water within the
system as it freezes and the lack of a proper
air-void system (spacing and volume of
air). Typically with a poor air-void system,
the deterioration occurs at the joints where
moisture is most prevalent; see Figure 12.
e damage may continue to progress inward
from the joint as moisture finds its way
through the damaged zone.
Any mitigation strategy that reduces access
of moisture will slow or prevent continued
distress. While an overlay may provide some
degree of insulation, thus reducing the num-
ber of freeze-thaw cycles and slowing damage
rates, the problem will not be eliminated.
For a potential bonded overlay in which the
existing pavement is to be brought to good
condition by spot repairs or milling, it is
important before a selecting an overlay to
periodically check the air content of the exist-
ing pavement in accordance with ASTM C
457. is check should be made at different
depths of the mid-panels of the existing pave-
ment as part of the evaluation process. For
example, if the air content is below 5 percent
and the spacing factor is greater than 0.008
inch, the details of moisture access have to be
examined carefully before a bonded overlay
is considered. is is particularly true if this
condition exists in the lower depths.
For unbonded overlays, where partial- or full-
depth deterioration of the joint is present,
the unsound concrete around the joints can
be removed and replaced with low-strength
concrete (e.g., flowable mortar). No sawing or
reestablishment of the joint is necessary, since
the overlay will be unbonded and cracking in
the existing concrete will not affect the over-
lay. is approach with an unbonded overlay
should be a practical and cost-effective solu-
tion for pavements with freeze-thaw damage
in poor or deteriorated condition. e desired
project life of the overlay must match the
expected life of the existing pavement after
repairs are made.
Vertical Constraints
Constructing concrete overlays will raise the
roadway profile grade unless it is lowered
through mechanical measures such as milling.
Consideration should be given to the effects
of grade change, particularly at bridge under-
passes and approaches, shoulder areas, and
curb and gutter units. Design details for these
situations are included on pages 64, 69, and
70. e visual survey should include a com-
prehensive list of potential vertical constraints
such as the following:
• Bridge structures
• Overhead clearance requirements
• Guard rail, parapet wall, cable barrier, and
median barrier
• Curb and gutter
• Storm sewer inlets
• Intersecting roadways and access drives
• Drainage conduits and culverts
• Foreshoulder slopes and ditches
Profile Grade
A review of the existing profile grade line
should be conducted; areas of significant
deviation will have to be investigated through
analysis of core samples. Evidence of numer-
ous active panel movements in a concrete or
composite pavement may indicate potentially
unstable or nonuniform subgrade support
or MRD. ese, too, will require detailed
pavement analyses to determine the extent of
distress and possible corrective action(s). For
example, if movement is confined to isolated
areas, full-depth repairs in these areas may be
considered. Irregularities in profile (signifi-
cant dips/bumps) should be noted and the
cause(s) should be determined. Typical cross
slope of the existing pavement and the limits
of superelevated curves should be included in
the visual survey.
Figure 12. Typical joint deterioration with HMA patch (source: Trinity
Construction Management Services, Inc.)
Figure 11. D-cracked pavement
15
Guide to Concrete Overlays
Ch 2. EVALUATION & SELECTION
Pavement Coring
It may be difficult to determine the cause(s)
and the extent of the cracking from a visual
inspection alone. Core analyses can supple-
ment information collected from the visual
inspection. is can be done concurrently
with the on-site review or at a later date. Core
frequency and location should be determined
based on the distresses noted during the visual
examination.
At a minimum, two cores per lane per mile
should be obtained to evaluate layer thick-
nesses and pavement condition. Whenever
possible, members of the design team should
be present during the coring to observe the
condition of the pavement layers as they are
cored.
Cores are beneficial in determining layer
thicknesses and identifying the pavement’s
support value; the type and condition of layer
materials; the depth of distress(es); and, if
the existing pavement is full-depth asphalt or
composite, the condition of the existing bond
between layers. For asphalt and composite
pavements, it is critical to evaluate the bond
between lifts and identify stripped layers
to determine whether or not the remain-
ing asphalt (after milling, if any occurs) will
be suitable for the concrete overlay design
assumptions. Cores that penetrate into the
subgrade may show evidence of unstable
conditions, such as the beginning of fine
soil migration into open-graded subbase lay-
ers that can lead to plugging and instability.
Cores also provide samples for possible labo-
ratory analyses.
Optional Analyses
Various factors affect the necessity for and
extent of additional pavement evaluation
tests. Additional testing may be necessary
Table 1. Recommended Optional Testing
Optional Testing Existing Asphalt Pavement Existing Composite Pavement Existing Concrete Pavement
Bonded Unbonded Bonded Unbonded Bonded Unbonded
Falling Weight Deflectometer (FWD)
Modulus of Elasticity (∈) of Asphalt X X
Effective Static Modulus of Subgrade Reaction (k)X X X X X X
Load Transfer Efficiency X X X X
Cores
Stripping (ASTM D 4867) of Asphalt X X X X
Pavement Layer Thickness X X X X X X
Petrographic Examination X1,2 X2X1,3 X2
1 - Entrained air properties when low air content is the suspected cause of observed distress
2 - Identify whether detrimental MRD is present
3 - Determine aggregate type
based on observations noted during the on-
site review and/or analysis of pavement cores;
see Table 1. Roadway type (i.e., primary or
secondary) and reliability of the ensuing
design may drive the decision. For example,
a concrete overlay of a county road with
moderate traffic could be designed with the
information obtained in the first three steps.
Conversely, a divided highway with heavy
traffic may require additional information to
more precisely characterize the existing pave-
ment’s properties.
A thorough pavement condition analysis is
always necessary to assess the applicability
of either a bonded or an unbonded concrete
overlay solution. In general, more informa-
tion about the existing pavement condition
is required when bonded overlay systems are
being considered or designed. ere are sev-
eral reasons for this:
1. Compared to an unbonded overlay, the
performance of bonded concrete overlays
is more dependent on the condition of the
existing pavement
2. Because bonded overlays are relatively
thin, they are somewhat more susceptible
to stresses, and the very nature of a bond
imposes stress.
3. e existing pavement will become part of
a monolithic, overlaid pavement structure
(not just a base for an unbonded overlay),
so it needs to contribute a certain level of
strength and integrity and be capable of
developing and maintaining a bond with
the overlay.
erefore, when evaluating a pavement’s
suitability for a bonded concrete overlay, it
is particularly important to characterize the
existing cross section and pavement char-
acteristics and the type, severity, and extent
of distresses. Laboratory testing may not be
required on every project. Lab tests may be
conducted to confirm or clarify results from
the visual examination, reveal distress mecha-
nisms, and provide additional information
needed to identify feasible treatments (see
pages 18–23.
A detailed engineering evaluation of the
type, degree, and state of MRD may be war-
ranted to determine if an overlay is feasible.
Unbonded overlays on concrete or composite
pavements with MRD can be expected to
have a long life, equal to a full-depth concrete
pavement, if the overlays are designed cor-
rectly, taking into account any nonuniformity
in the existing pavement. For this to be pos-
sible, the rate of MRD progression and the
potential for further deterioration (post con-
crete overlay) needs to be understood.
icker unbonded overlays (6 in. [150 mm]
or greater) have been used successfully on
ASR distressed concrete pavement (alone
or as part of an existing composite pave-
ment) in a variety of climates and for a wide
range of highway classes. ese overlays per-
form extraordinarily well when the reactive
aggregate expansion is near completion, has
slowed its rate of deterioration, or is relatively
uniformly spread throughout the existing
pavement. Extreme variation in the degree
of ASR distress along the length of pavement
FAQ—When are additional analyses really necessary?
In general, additional analysis (testing) to refine design inputs is only necessary when the
existing pavement is in poor condition and/or heavy traffic is anticipated.
Guide to Concrete Overlays
16
Ch 2. EVALUATION & SELECTION
(particularly when distress is concentrated at
the joints), however, can result in nonuniform
support and consequent performance chal-
lenges for the overlay.
Since D-cracking normally occurs at or near
concrete joints, bonded concrete overlays on
concrete pavements with D-cracking (or com-
posite pavements in which the concrete layer
has D-cracking) have had mixed performance
results. Localized joint movement and even
failure can occur in the underlying pavement.
is may cause cracking in the overlay as a
result of the nonuniform base support.
Deflection Testing
Pavement deflection testing is an effective way
to assess a pavement’s structural capabilities.
e data can be used to estimate, through
back-calculation methods, modulus of elastic-
ity and k-value. Again, pavement deflection
tests are not required for all pavements,
especially those in fair or better condition or
on lower-volume roads. When performed, a
minimum of one test per lane per one-half
mile should be conducted.
Several deflection devices are available, but
they all operate in basically the same manner.
A known load is applied to a pavement sur-
face, and the resulting deflection is measured.
e FWD, or any device capable of applying
loads similar in magnitude and duration to
that of a moving wheel load, is commonly
used. Deflection test results are also used to
develop pavement deflection profiles, back-
calculate layer properties, determine load
transfer capabilities, and evaluate the poten-
tial for voids at slab corners.
Alternative Means of
Determining Support Conditions
In some cases, a visual examination and core
analyses provide enough information to
determine if the pavement is a good candidate
for a concrete overlay. Sometimes, however,
particularly in borderline situations, further
analysis is required. One such analysis may
include determination of the subgrade/
subbase support conditions under the pave-
ment in terms of the California bearing ratio
(CBR).
FAQ—Why is optional testing for unbonded overlays necessary when the existing
pavement is characterized as a “high-quality” subbase in the thickness design process?
Even though unbonded overlays are less dependent on the condition of the existing pave-
ment than bonded overlays, there may be circumstances where additional optional testing is
desirable. is is especially the case both for high-volume roadways where design reliability
is critical and for any time that MRD is suspected in the existing pavement.
A low-cost and easy on-site method for
determining the level of support in terms
of CBR is through the use of the dynamic
cone penetrometer (DCP); see Figure 13.
is instrument provides a measure of the
in situ strength of fine-grained and granular
subgrades and granular base and subbase
materials.
A 17.6-lb (8-kg) weight is raised to a height
of 22.6 in. (575 mm) and then dropped, driv-
ing the cone into the soil or other material
being tested. e output is a penetration rate
(PR) expressed in terms of inches (mm) per
blow. (e DCP test method is defined under
ASTM D 6351: Standard Test Method for Use
of the Dynamic Cone Penetrometer in Shallow
Pavement Applications.)
Soil strength-related tests using the DCP, or
the standard penetration test, provide useful
information about subgrade stability.
e benefits of the DCP test include the
following:
• Low cost
• Easy to use—an operator can be trained in
minutes
• Large penetration depth—data can be col-
lected up to 36 inches in depth
• Fast—a large amount of data can be col-
lected and the values converted to CBR
quickly
Although the DCP does not measure density
directly, it may be used to assess the density of
a fairly uniform material by relating density
to PR. In this way, under-compacted or “soft”
spots can be identified.
e CBR value can also be important in terms
of overlay thickness design. Concrete over-
lay design methods for determining overlay
thickness use bearing capacity expressed in
terms of the modulus of subgrade reaction (k).
Although the k-value is difficult to measure,
it can be estimated relatively easily from the
CBR value.
Figure 13. Dynamic cone penetrometer (source: David White,
Iowa State University)
17
Guide to Concrete Overlays
Ch 2. EVALUATION & SELECTION
In Table 2, above, CBR values are associ-
ated with k-values expressed in pounds
per square inch (psi) per inch or pounds
per cubic inch. In the table, both values
are generally associated with subgrade soil
types and support conditions. For projects
designed for light-traffic loads only, or
where extensive soil testing is impractical
or economically unjustified considering
the project scope, the k-value can be esti-
mated. Conservatism is advised in making
such estimates.
Roughness and Surface
Friction Tests
Roughness and surface friction are two
key indicators of the functional perfor-
mance of a pavement: its smoothness for
comfortable ride and its skid resistance
for safety. Roughness testing (expressed
in terms of the International Roughness
Index, IRI) at the project level can be
useful to help identify localized areas of
roughness and to assess the effectiveness
of treatments (pre- and post-treatment
roughness comparisons). Friction (skid
resistance) testing is not commonly con-
ducted for project-level evaluations but
may be meaningful on projects exhibiting
a disproportionate number of wet-weather
crashes.
Condition Assessment Profile
When all aspects of an existing pavement have
been evaluated, the critical distresses and drainage
conditions should be summarized. One useful
way to summarize this information is to plot it
on a condition assessment profile, or strip chart
(Smith et al. 2008). In bar chart form, this profile
visually indicates where various distresses occur
over the length of the project, as well as their
extent and severity. Distresses such as slab crack-
ing, corner breaks, faulting and spalling, and
continuous roughness can be displayed. Areas of
poor drainage or significant changes in topogra-
phy (cut/fill sections) can be overlaid on the strip
charts. Such summaries provide critical insight
into a pavement’s structural and functional per-
formance, helping roadway owners determine if
and when pavement preservation or rehabilitation
activities are appropriate.
Figures 14, 15, and 16 provide a graphical exam-
ple of the pavement and evaluation and overlay
selection processes.
Pavement Evaluation Report
e final evaluation step is summarizing the
results of data collection and analyses in an evalu-
ation report. Any critical nonpavement factors,
such as shoulder condition, ditches, right-of-
way, curves, bridges, ramps, and traffic patterns,
should be identified in the report. Ultimately, this
information will be used in the identification and
selection of appropriate spot repairs and overlays,
as described in the next section.
Selecting
Appropriate
Concrete Overlay
Solution
Several factors should be considered when
selecting the type of concrete overlay solu-
tion. e condition of the existing pavement
is the paramount factor. Generally, existing
pavements in relatively good condition, or
that can be cost effectively brought to good
condition, are candidates for bonded concrete
overlays. In these cases, bonded overlays can
improve functionality (e.g., reduce roughness
or noise or enhance friction) and/or increase
structural capacity (e.g., accommodate antici-
pated increases in truck-traffic loadings).
For example, a pavement in fair to poor func-
tional condition due to rutting and shoving
can be resurfaced with a bonded overlay after
the pavement has been improved to good
condition through spot repairs or milling to
remove deficiencies. e bond between the
overlay and the existing pavement inherently
adds structural capacity. In this situation,
however, it may be just as cost effective to
place a slightly thicker unbonded overlay with
less preoverlay repair work and not have to
depend on the bond.
Generally, existing pavements in poor con-
dition that exhibit significant structural
deterioration are candidates for unbonded
overlays. Moreover, the presence of MRD,
such as alkali-silica reaction ASR or
D-cracking, also suggests the need for an
unbonded overlay or even reconstruction. See
Appendix B for reconstruction options.
Concrete overlays can provide economical
short- and long-term solutions for pave-
ments in a variety of conditions, as shown in
Figures 14–16 on the following pages. Note
that the overlay solutions recommended in
these flowcharts are generally long-term fixes,
on the order of 20 years or more of expected
life.
Table 2. Subgrade Soil Types and Approximate Support Values
Soil Type Support k (psi/in.) CBR
Fine grained; silt and clay-size
particles predominate Low 75 to 120 2.5 to 3.5
Sand and sand-gravel mixture with moderate
amounts of silt and clay Medium 130 to 170 4.5 to 7.5
Sand and sand-gravel mixture
relatively free of plastic fines High 180 to 220 8.5 to 12.0
Notes: CBR (California bearing ratio); 1 psi = 0.0069 megapascal (MPa);
1 psi/in.=0.27 MPa/m
Table is based on information in ACI 330R-08 regarding ranges of values for several types of subgrade soil (Portland
Cement Association 1984; NCHRP 1982) compacted to the specified density.
Guide to Concrete Overlays
18
Ch 2. EVALUATION & SELECTION
Figure 14. Selecting appropriate concrete overlay solution for asphalt pavements
Can milling and minor spot repairs
cost effectively solve deficiencies,
bring the pavement to “Good
Condition,” and meet other
constrants (i.e., vertical clearance,
shoulders, safety rails, foreslopes,
etc.) to allow for bonded overlay?
Can existing or potential unstable
conditions or major deciencies (e.g.,
wet subgrade, asphalt stripping) be
addressed cost eectively with a
combination of preservation
techniques (e.g., milling, retrot
subdrains, full-depth patches) and
other contraints (e.g., vertical
clearence, safety rails, etc.) met with
an adequately thick unbonded
overlay?
Note: Concrete overlay thickness must be appropriately designed consider-
ing estimated trac, desired design life, and budget.
NO
NO
YES
Selecting the Appropriate
Concrete Overlay Solution
for Asphalt Pavements
Pavement is structurally sound but
needs increased structural capacity,
improved surface characteristics
(smoothness, friction, and noise),
surface defects removed, and/or
improved albedo properties.
Good Condition
Bonded Concrete Overlay
Over Asphalt Pavement
Unbonded Concrete Overlay
Over Asphalt Pavement
3 in. min. asphalt
Pavement is structurally sound but
has minor surface distresses such as
potholes, block cracking, or random
thermal cracking. Check for undulat-
ing prole grade to determine if
sub-drainage issues exist. Check
cores to ensure there is no measure-
able stripping or delamination in the
asphalt.
Fair Condition
Pavement has measurable distresses
beyond those described under “Fair
Condition,” such as alligator
cracking, rutting, shoving, slippage,
stripping, and raveling.
Note: Asphalt is a good reector
of underlying distresses such as
poor subbase conditions.
Poor Condition
Pavement exhibits “Poor
Condition” characteristics as
well as signicant deteriora-
tion, raveling, thermal
expansion, stripping, and
structural distresses.
Deteriorated Condition
Additional Repairs
Spot Repairs
Milling and Patching
Can spot surface repairs and/or spot
structural repairs cost effectively
solve deficiencies, bring the
pavement to “Good Condition,” and
meet other constraints (i.e., vertical
clearances, shoulders, safety rails,
foreslopes, etc.) to allow for a
bonded overlay?
Can spot structural repairs and/or
milling cost effectively solve
deficiencies, meet vertical and
structural requirements, and bring the
existing pavement to a condition that
provides a uniform subbase for an
unbonded overlay?
Install subdrains if needed
Joint spacing
Joint spacing
Install subdrains if needed
Milling/Minor Spot Repairs YES
YES
3 in. min. asphalt
3 in. min. asphalt
Concrete overlays can provide
economical short- to long-term
solutions for asphalt pavements.
e recommendations provided
in the following owchart are
generally long-term xes on the
order of 20 years or more of
expected life.
Second, what is the desired pavement life of the overlay,
given the condition of the existing pavement? ird,
what type of overlay (bonded or unbonded) will achieve
the rst two objectives at the lowest life-cycle cost?
Several factors should be considered when selecting
either a bonded or unbonded concrete overlay for an
existing asphalt pavement. Two predominant factors are
the condition of the existing pavement and the extent of
pre-overlay repairs required, if any.
Generally, existing pavements in relatively good or fair condition, or
poor-condition pavements that can be cost-eectively brought to good
condition, are candidates for bonded concrete overlays. Existing asphalt
pavements that cannot be cost eectively returned to good condition are
candidates for unbonded overlays as long as signicant structural repairs to
the existing pavements are not needed. Signicant asphalt deterioration can
be overlaid with concrete as long as unstable and so spots are repaired.
Unless there are unrepairable subsurface issues requiring removal of the
asphalt, it is rare that a unbonded concrete overlay cannot be utilized.
As with any preservation approach, the
principles of asset management are a
cornerstone in selecting the appropriate
concrete overlay solution. ree important
asset management questions need to be
answered as part of the selection process,
for the appropriate concrete overlay
solution to meet the needs of an agency.
First, what is the desired level of service to
be provided by the concrete overlay?
NO
NO
YES
FAQ—What if the existing pavement is not a candidate for a
concrete unbonded overlay? While most pavements can be preserved
with a concrete overlay, there are situations where a concrete overlay
is not appropriate. When this occurs, reconstruction is an alternative.
Reconstruction options include the following:
• Recommended: Mill and ll. Remove asphalt by milling, repair
any subgrade issues, and ll with new concrete pavement.
Recycle asphalt material.
• Permissible in specic situations: When the asphalt is less than
6-in. thick and is in deteriorated condition, the asphalt may be
recycled into the subgrade/subbase through full-depth
reclamation (FDR).
Asphalt surface
Rural
sectionUrban
section
F
A
Q
—
W
h
at i
f
t
h
e existin
g
pavement is not a can
d
i
d
ate
f
or a
c
oncrete un
b
on
d
e
d
over
l
a
y
? W
h
i
l
e most pavements can
b
e preserve
d
w
it
h
a concrete over
l
a
y
, t
h
ere are situations w
h
ere a concrete over
l
a
y
is not appropriate. W
h
en t
h
is occurs, reconstruction is an a
l
ternative.
Reconstruction options inc
l
u
d
e t
h
e
f
o
ll
owin
g
:
•
R
ecommended: Mi
ll
an
d
ll
. Remove asp
h
a
l
t
by
mi
ll
in
g
, repair
a
n
y
su
bg
ra
d
e issues, an
d
ll
wit
h
new concrete pavement.
R
ec
y
c
l
e asp
h
a
l
t materia
l
.
•
P
e
rmi
ss
i
b
l
e
in speci
c situations: W
h
en t
h
e asp
h
a
l
t is
l
ess t
h
an
6
-in. t
h
ic
k
an
d
is in
d
eteriorate
d
con
d
ition, t
h
e asp
h
a
l
t ma
y
b
e
r
ec
y
c
l
e
d
into t
h
e su
bg
ra
d
e/su
bb
ase t
h
rou
gh
f
u
ll
-
d
ept
h
r
ec
l
amation (FDR).
Can milling and minor spot repairs
cost effectively solve deficiencies,
bring the pavement to “Good
Condition,” and meet other
constrants (i.e., vertical clearance,
shoulders, safety rails, foreslopes,
etc.) to allow for bonded overlay?
Can existing or potential unstable
conditions or major deciencies (e.g.,
wet subgrade, asphalt stripping) be
addressed cost eectively with a
combination of preservation
techniques (e.g., milling, retrot
subdrains, full-depth patches) and
other contraints (e.g., vertical
clearence, safety rails, etc.) met with
an adequately thick unbonded
overlay?
Note: Concrete overlay thickness must be appropriately designed consider-
ing estimated trac, desired design life, and budget.
NO
NO
YES
Selecting the Appropriate
Concrete Overlay Solution
for Asphalt Pavements
Pavement is structurally sound but
needs increased structural capacity,
improved surface characteristics
(smoothness, friction, and noise),
surface defects removed, and/or
improved albedo properties.
Good Condition
Bonded Concrete Overlay
Over Asphalt Pavement
Unbonded Concrete Overlay
Over Asphalt Pavement
3 in. min. asphalt
Pavement is structurally sound but
has minor surface distresses such as
potholes, block cracking, or random
thermal cracking. Check for undulat-
ing prole grade to determine if
sub-drainage issues exist. Check
cores to ensure there is no measure-
able stripping or delamination in the
asphalt.
Fair Condition
Pavement has measurable distresses
beyond those described under “Fair
Condition,” such as alligator
cracking, rutting, shoving, slippage,
stripping, and raveling.
Note: Asphalt is a good reector
of underlying distresses such as
poor subbase conditions.
Poor Condition
Pavement exhibits “Poor
Condition” characteristics as
well as signicant deteriora-
tion, raveling, thermal
expansion, stripping, and
structural distresses.
Deteriorated Condition
Additional Repairs
Spot Repairs
Milling and Patching
Can spot surface repairs and/or spot
structural repairs cost effectively
solve deficiencies, bring the
pavement to “Good Condition,” and
meet other constraints (i.e., vertical
clearances, shoulders, safety rails,
foreslopes, etc.) to allow for a
bonded overlay?
Can spot structural repairs and/or
milling cost effectively solve
deficiencies, meet vertical and
structural requirements, and bring the
existing pavement to a condition that
provides a uniform subbase for an
unbonded overlay?
Install subdrains if needed
Joint spacing
Joint spacing
Install subdrains if needed
Milling/Minor Spot Repairs YES
YES
3 in. min. asphalt
3 in. min. asphalt
Concrete overlays can provide
economical short- to long-term
solutions for asphalt pavements.
e recommendations provided
in the following owchart are
generally long-term xes on the
order of 20 years or more of
expected life.
Second, what is the desired pavement life of the overlay,
given the condition of the existing pavement? ird,
what type of overlay (bonded or unbonded) will achieve
the rst two objectives at the lowest life-cycle cost?
Several factors should be considered when selecting
either a bonded or unbonded concrete overlay for an
existing asphalt pavement. Two predominant factors are
the condition of the existing pavement and the extent of
pre-overlay repairs required, if any.
Generally, existing pavements in relatively good or fair condition, or
poor-condition pavements that can be cost-eectively brought to good
condition, are candidates for bonded concrete overlays. Existing asphalt
pavements that cannot be cost eectively returned to good condition are
candidates for unbonded overlays as long as signicant structural repairs to
the existing pavements are not needed. Signicant asphalt deterioration can
be overlaid with concrete as long as unstable and so spots are repaired.
Unless there are unrepairable subsurface issues requiring removal of the
asphalt, it is rare that a unbonded concrete overlay cannot be utilized.
As with any preservation approach, the
principles of asset management are a
cornerstone in selecting the appropriate
concrete overlay solution. ree important
asset management questions need to be
answered as part of the selection process,
for the appropriate concrete overlay
solution to meet the needs of an agency.
First, what is the desired level of service to
be provided by the concrete overlay?
NO
NO
YES
FAQ—What if the existing pavement is not a candidate for a
concrete unbonded overlay? While most pavements can be preserved
with a concrete overlay, there are situations where a concrete overlay
is not appropriate. When this occurs, reconstruction is an alternative.
Reconstruction options include the following:
• Recommended: Mill and ll. Remove asphalt by milling, repair
any subgrade issues, and ll with new concrete pavement.
Recycle asphalt material.
• Permissible in specic situations: When the asphalt is less than
6-in. thick and is in deteriorated condition, the asphalt may be
recycled into the subgrade/subbase through full-depth
reclamation (FDR).
Asphalt surface
Rural
sectionUrban
section
F
A
Q
—
W
h
at i
f
t
h
e existin
g
pavement is not a can
d
i
d
ate
f
or a
c
oncrete un
b
on
d
e
d
over
l
a
y
? W
h
i
l
e most pavements can
b
e preserve
d
w
it
h
a concrete over
l
a
y
, t
h
ere are situations w
h
ere a concrete over
l
a
y
is not appropriate. W
h
en t
h
is occurs, reconstruction is an a
l
ternative.
Reconstruction options inc
l
u
d
e t
h
e
f
o
ll
owin
g
:
•
R
ecommended: Mi
ll
an
d
ll
. Remove asp
h
a
l
t
by
mi
ll
in
g
, repair
a
n
y
su
bg
ra
d
e issues, an
d
ll
wit
h
new concrete pavement.
R
ec
y
c
l
e asp
h
a
l
t materia
l
.
•
P
e
rmi
ss
i
b
l
e
in speci
c situations: W
h
en t
h
e asp
h
a
l
t is
l
ess t
h
an
6
-in. t
h
ic
k
an
d
is in
d
eteriorate
d
con
d
ition, t
h
e asp
h
a
l
t ma
y
b
e
r
ec
y
c
l
e
d
into t
h
e su
bg
ra
d
e/su
bb
ase t
h
rou
gh
f
u
ll
-
d
ept
h
r
ec
l
amation (FDR).
Can milling and minor spot repairs
cost effectively solve deficiencies,
bring the pavement to “Good
Condition,” and meet other
constrants (i.e., vertical clearance,
shoulders, safety rails, foreslopes,
etc.) to allow for bonded overlay?
Can existing or potential unstable
conditions or major deciencies (e.g.,
wet subgrade, asphalt stripping) be
addressed cost eectively with a
combination of preservation
techniques (e.g., milling, retrot
subdrains, full-depth patches) and
other contraints (e.g., vertical
clearence, safety rails, etc.) met with
an adequately thick unbonded
overlay?
Note: Concrete overlay thickness must be appropriately designed consider-
ing estimated trac, desired design life, and budget.
NO
NO
YES
Selecting the Appropriate
Concrete Overlay Solution
for Asphalt Pavements
Pavement is structurally sound but
needs increased structural capacity,
improved surface characteristics
(smoothness, friction, and noise),
surface defects removed, and/or
improved albedo properties.
Good Condition
Bonded Concrete Overlay
Over Asphalt Pavement
Unbonded Concrete Overlay
Over Asphalt Pavement
3 in. min. asphalt
Pavement is structurally sound but
has minor surface distresses such as
potholes, block cracking, or random
thermal cracking. Check for undulat-
ing prole grade to determine if
sub-drainage issues exist. Check
cores to ensure there is no measure-
able stripping or delamination in the
asphalt.
Fair Condition
Pavement has measurable distresses
beyond those described under “Fair
Condition,” such as alligator
cracking, rutting, shoving, slippage,
stripping, and raveling.
Note: Asphalt is a good reector
of underlying distresses such as
poor subbase conditions.
Poor Condition
Pavement exhibits “Poor
Condition” characteristics as
well as signicant deteriora-
tion, raveling, thermal
expansion, stripping, and
structural distresses.
Deteriorated Condition
Additional Repairs
Spot Repairs
Milling and Patching
Can spot surface repairs and/or spot
structural repairs cost effectively
solve deficiencies, bring the
pavement to “Good Condition,” and
meet other constraints (i.e., vertical
clearances, shoulders, safety rails,
foreslopes, etc.) to allow for a
bonded overlay?
Can spot structural repairs and/or
milling cost effectively solve
deficiencies, meet vertical and
structural requirements, and bring the
existing pavement to a condition that
provides a uniform subbase for an
unbonded overlay?
Install subdrains if needed
Joint spacing
Joint spacing
Install subdrains if needed
Milling/Minor Spot Repairs YES
YES
3 in. min. asphalt
3 in. min. asphalt
Concrete overlays can provide
economical short- to long-term
solutions for asphalt pavements.
e recommendations provided
in the following owchart are
generally long-term xes on the
order of 20 years or more of
expected life.
Second, what is the desired pavement life of the overlay,
given the condition of the existing pavement? ird,
what type of overlay (bonded or unbonded) will achieve
the rst two objectives at the lowest life-cycle cost?
Several factors should be considered when selecting
either a bonded or unbonded concrete overlay for an
existing asphalt pavement. Two predominant factors are
the condition of the existing pavement and the extent of
pre-overlay repairs required, if any.
Generally, existing pavements in relatively good or fair condition, or
poor-condition pavements that can be cost-eectively brought to good
condition, are candidates for bonded concrete overlays. Existing asphalt
pavements that cannot be cost eectively returned to good condition are
candidates for unbonded overlays as long as signicant structural repairs to
the existing pavements are not needed. Signicant asphalt deterioration can
be overlaid with concrete as long as unstable and so spots are repaired.
Unless there are unrepairable subsurface issues requiring removal of the
asphalt, it is rare that a unbonded concrete overlay cannot be utilized.
As with any preservation approach, the
principles of asset management are a
cornerstone in selecting the appropriate
concrete overlay solution. ree important
asset management questions need to be
answered as part of the selection process,
for the appropriate concrete overlay
solution to meet the needs of an agency.
First, what is the desired level of service to
be provided by the concrete overlay?
NO
NO
YES
FAQ—What if the existing pavement is not a candidate for a
concrete unbonded overlay? While most pavements can be preserved
with a concrete overlay, there are situations where a concrete overlay
is not appropriate. When this occurs, reconstruction is an alternative.
Reconstruction options include the following:
• Recommended: Mill and ll. Remove asphalt by milling, repair
any subgrade issues, and ll with new concrete pavement.
Recycle asphalt material.
• Permissible in specic situations: When the asphalt is less than
6-in. thick and is in deteriorated condition, the asphalt may be
recycled into the subgrade/subbase through full-depth
reclamation (FDR).
Asphalt surface
Rural
sectionUrban
section
F
A
Q
—
W
h
at i
f
t
h
e existin
g
pavement is not a can
d
i
d
ate
f
or a
c
oncrete un
b
on
d
e
d
over
l
a
y
? W
h
i
l
e most pavements can
b
e preserve
d
w
it
h
a concrete over
l
a
y
, t
h
ere are situations w
h
ere a concrete over
l
a
y
is not appropriate. W
h
en t
h
is occurs, reconstruction is an a
l
ternative.
Reconstruction options inc
l
u
d
e t
h
e
f
o
ll
owin
g
:
•
R
ecommended: Mi
ll
an
d
ll
. Remove asp
h
a
l
t
by
mi
ll
in
g
, repair
a
n
y
su
bg
ra
d
e issues, an
d
ll
wit
h
new concrete pavement.
R
ec
y
c
l
e asp
h
a
l
t materia
l
.
•
P
e
rmi
ss
i
b
l
e
in speci
c situations: W
h
en t
h
e asp
h
a
l
t is
l
ess t
h
an
6
-in. t
h
ic
k
an
d
is in
d
eteriorate
d
con
d
ition, t
h
e asp
h
a
l
t ma
y
b
e
r
ec
y
c
l
e
d
into t
h
e su
bg
ra
d
e/su
bb
ase t
h
rou
gh
f
u
ll
-
d
ept
h
r
ec
l
amation (FDR).
19
Guide to Concrete Overlays
Ch 2. EVALUATION & SELECTION
Can milling and minor spot repairs
cost effectively solve deficiencies,
bring the pavement to “Good
Condition,” and meet other
constrants (i.e., vertical clearance,
shoulders, safety rails, foreslopes,
etc.) to allow for bonded overlay?
Can existing or potential unstable
conditions or major deciencies (e.g.,
wet subgrade, asphalt stripping) be
addressed cost eectively with a
combination of preservation
techniques (e.g., milling, retrot
subdrains, full-depth patches) and
other contraints (e.g., vertical
clearence, safety rails, etc.) met with
an adequately thick unbonded
overlay?
Note: Concrete overlay thickness must be appropriately designed consider-
ing estimated trac, desired design life, and budget.
NO
NO
YES
Selecting the Appropriate
Concrete Overlay Solution
for Asphalt Pavements
Pavement is structurally sound but
needs increased structural capacity,
improved surface characteristics
(smoothness, friction, and noise),
surface defects removed, and/or
improved albedo properties.
Good Condition
Bonded Concrete Overlay
Over Asphalt Pavement
Unbonded Concrete Overlay
Over Asphalt Pavement
3 in. min. asphalt
Pavement is structurally sound but
has minor surface distresses such as
potholes, block cracking, or random
thermal cracking. Check for undulat-
ing prole grade to determine if
sub-drainage issues exist. Check
cores to ensure there is no measure-
able stripping or delamination in the
asphalt.
Fair Condition
Pavement has measurable distresses
beyond those described under “Fair
Condition,” such as alligator
cracking, rutting, shoving, slippage,
stripping, and raveling.
Note: Asphalt is a good reector
of underlying distresses such as
poor subbase conditions.
Poor Condition
Pavement exhibits “Poor
Condition” characteristics as
well as signicant deteriora-
tion, raveling, thermal
expansion, stripping, and
structural distresses.
Deteriorated Condition
Additional Repairs
Spot Repairs
Milling and Patching
Can spot surface repairs and/or spot
structural repairs cost effectively
solve deficiencies, bring the
pavement to “Good Condition,” and
meet other constraints (i.e., vertical
clearances, shoulders, safety rails,
foreslopes, etc.) to allow for a
bonded overlay?
Can spot structural repairs and/or
milling cost effectively solve
deficiencies, meet vertical and
structural requirements, and bring the
existing pavement to a condition that
provides a uniform subbase for an
unbonded overlay?
Install subdrains if needed
Joint spacing
Joint spacing
Install subdrains if needed
Milling/Minor Spot Repairs YES
YES
3 in. min. asphalt
3 in. min. asphalt
Concrete overlays can provide
economical short- to long-term
solutions for asphalt pavements.
e recommendations provided
in the following owchart are
generally long-term xes on the
order of 20 years or more of
expected life.
Second, what is the desired pavement life of the overlay,
given the condition of the existing pavement? ird,
what type of overlay (bonded or unbonded) will achieve
the rst two objectives at the lowest life-cycle cost?
Several factors should be considered when selecting
either a bonded or unbonded concrete overlay for an
existing asphalt pavement. Two predominant factors are
the condition of the existing pavement and the extent of
pre-overlay repairs required, if any.
Generally, existing pavements in relatively good or fair condition, or
poor-condition pavements that can be cost-eectively brought to good
condition, are candidates for bonded concrete overlays. Existing asphalt
pavements that cannot be cost eectively returned to good condition are
candidates for unbonded overlays as long as signicant structural repairs to
the existing pavements are not needed. Signicant asphalt deterioration can
be overlaid with concrete as long as unstable and so spots are repaired.
Unless there are unrepairable subsurface issues requiring removal of the
asphalt, it is rare that a unbonded concrete overlay cannot be utilized.
As with any preservation approach, the
principles of asset management are a
cornerstone in selecting the appropriate
concrete overlay solution. ree important
asset management questions need to be
answered as part of the selection process,
for the appropriate concrete overlay
solution to meet the needs of an agency.
First, what is the desired level of service to
be provided by the concrete overlay?
NO
NO
YES
FAQ—What if the existing pavement is not a candidate for a
concrete unbonded overlay? While most pavements can be preserved
with a concrete overlay, there are situations where a concrete overlay
is not appropriate. When this occurs, reconstruction is an alternative.
Reconstruction options include the following:
• Recommended: Mill and ll. Remove asphalt by milling, repair
any subgrade issues, and ll with new concrete pavement.
Recycle asphalt material.
• Permissible in specic situations: When the asphalt is less than
6-in. thick and is in deteriorated condition, the asphalt may be
recycled into the subgrade/subbase through full-depth
reclamation (FDR).
Asphalt surface
Rural
sectionUrban
section
F
A
Q
—
W
h
at i
f
t
h
e existin
g
pavement is not a can
d
i
d
ate
f
or a
c
oncrete un
b
on
d
e
d
over
l
a
y
? W
h
i
l
e most pavements can
b
e preserve
d
w
it
h
a concrete over
l
a
y
, t
h
ere are situations w
h
ere a concrete over
l
a
y
is not appropriate. W
h
en t
h
is occurs, reconstruction is an a
l
ternative.
Reconstruction options inc
l
u
d
e t
h
e
f
o
ll
owin
g
:
•
R
ecommended: Mi
ll
an
d
ll
. Remove asp
h
a
l
t
by
mi
ll
in
g
, repair
a
n
y
su
bg
ra
d
e issues, an
d
ll
wit
h
new concrete pavement.
R
ec
y
c
l
e asp
h
a
l
t materia
l
.
•
P
e
rmi
ss
i
b
l
e
in speci
c situations: W
h
en t
h
e asp
h
a
l
t is
l
ess t
h
an
6
-in. t
h
ic
k
an
d
is in
d
eteriorate
d
con
d
ition, t
h
e asp
h
a
l
t ma
y
b
e
r
ec
y
c
l
e
d
into t
h
e su
bg
ra
d
e/su
bb
ase t
h
rou
gh
f
u
ll
-
d
ept
h
r
ec
l
amation (FDR).
Can milling and minor spot repairs
cost effectively solve deficiencies,
bring the pavement to “Good
Condition,” and meet other
constrants (i.e., vertical clearance,
shoulders, safety rails, foreslopes,
etc.) to allow for bonded overlay?
Can existing or potential unstable
conditions or major deciencies (e.g.,
wet subgrade, asphalt stripping) be
addressed cost eectively with a
combination of preservation
techniques (e.g., milling, retrot
subdrains, full-depth patches) and
other contraints (e.g., vertical
clearence, safety rails, etc.) met with
an adequately thick unbonded
overlay?
Note: Concrete overlay thickness must be appropriately designed consider-
ing estimated trac, desired design life, and budget.
NO
NO
YES
Selecting the Appropriate
Concrete Overlay Solution
for Asphalt Pavements
Pavement is structurally sound but
needs increased structural capacity,
improved surface characteristics
(smoothness, friction, and noise),
surface defects removed, and/or
improved albedo properties.
Good Condition
Bonded Concrete Overlay
Over Asphalt Pavement
Unbonded Concrete Overlay
Over Asphalt Pavement
3 in. min. asphalt
Pavement is structurally sound but
has minor surface distresses such as
potholes, block cracking, or random
thermal cracking. Check for undulat-
ing prole grade to determine if
sub-drainage issues exist. Check
cores to ensure there is no measure-
able stripping or delamination in the
asphalt.
Fair Condition
Pavement has measurable distresses
beyond those described under “Fair
Condition,” such as alligator
cracking, rutting, shoving, slippage,
stripping, and raveling.
Note: Asphalt is a good reector
of underlying distresses such as
poor subbase conditions.
Poor Condition
Pavement exhibits “Poor
Condition” characteristics as
well as signicant deteriora-
tion, raveling, thermal
expansion, stripping, and
structural distresses.
Deteriorated Condition
Additional Repairs
Spot Repairs
Milling and Patching
Can spot surface repairs and/or spot
structural repairs cost effectively
solve deficiencies, bring the
pavement to “Good Condition,” and
meet other constraints (i.e., vertical
clearances, shoulders, safety rails,
foreslopes, etc.) to allow for a
bonded overlay?
Can spot structural repairs and/or
milling cost effectively solve
deficiencies, meet vertical and
structural requirements, and bring the
existing pavement to a condition that
provides a uniform subbase for an
unbonded overlay?
Install subdrains if needed
Joint spacing
Joint spacing
Install subdrains if needed
Milling/Minor Spot Repairs YES
YES
3 in. min. asphalt
3 in. min. asphalt
Concrete overlays can provide
economical short- to long-term
solutions for asphalt pavements.
e recommendations provided
in the following owchart are
generally long-term xes on the
order of 20 years or more of
expected life.
Second, what is the desired pavement life of the overlay,
given the condition of the existing pavement? ird,
what type of overlay (bonded or unbonded) will achieve
the rst two objectives at the lowest life-cycle cost?
Several factors should be considered when selecting
either a bonded or unbonded concrete overlay for an
existing asphalt pavement. Two predominant factors are
the condition of the existing pavement and the extent of
pre-overlay repairs required, if any.
Generally, existing pavements in relatively good or fair condition, or
poor-condition pavements that can be cost-eectively brought to good
condition, are candidates for bonded concrete overlays. Existing asphalt
pavements that cannot be cost eectively returned to good condition are
candidates for unbonded overlays as long as signicant structural repairs to
the existing pavements are not needed. Signicant asphalt deterioration can
be overlaid with concrete as long as unstable and so spots are repaired.
Unless there are unrepairable subsurface issues requiring removal of the
asphalt, it is rare that a unbonded concrete overlay cannot be utilized.
As with any preservation approach, the
principles of asset management are a
cornerstone in selecting the appropriate
concrete overlay solution. ree important
asset management questions need to be
answered as part of the selection process,
for the appropriate concrete overlay
solution to meet the needs of an agency.
First, what is the desired level of service to
be provided by the concrete overlay?
NO
NO
YES
FAQ—What if the existing pavement is not a candidate for a
concrete unbonded overlay? While most pavements can be preserved
with a concrete overlay, there are situations where a concrete overlay
is not appropriate. When this occurs, reconstruction is an alternative.
Reconstruction options include the following:
• Recommended: Mill and ll. Remove asphalt by milling, repair
any subgrade issues, and ll with new concrete pavement.
Recycle asphalt material.
• Permissible in specic situations: When the asphalt is less than
6-in. thick and is in deteriorated condition, the asphalt may be
recycled into the subgrade/subbase through full-depth
reclamation (FDR).
Asphalt surface
Rural
sectionUrban
section
F
A
Q
—
W
h
at i
f
t
h
e existin
g
pavement is not a can
d
i
d
ate
f
or a
c
oncrete un
b
on
d
e
d
over
l
a
y
? W
h
i
l
e most pavements can
b
e preserve
d
w
it
h
a concrete over
l
a
y
, t
h
ere are situations w
h
ere a concrete over
l
a
y
is not appropriate. W
h
en t
h
is occurs, reconstruction is an a
l
ternative.
Reconstruction options inc
l
u
d
e t
h
e
f
o
ll
owin
g
:
•
R
ecommended: Mi
ll
an
d
ll
. Remove asp
h
a
l
t
by
mi
ll
in
g
, repair
a
n
y
su
bg
ra
d
e issues, an
d
ll
wit
h
new concrete pavement.
R
ec
y
c
l
e asp
h
a
l
t materia
l
.
•
P
e
rmi
ss
i
b
l
e
in speci
c situations: W
h
en t
h
e asp
h
a
l
t is
l
ess t
h
an
6
-in. t
h
ic
k
an
d
is in
d
eteriorate
d
con
d
ition, t
h
e asp
h
a
l
t ma
y
b
e
r
ec
y
c
l
e
d
into t
h
e su
bg
ra
d
e/su
bb
ase t
h
rou
gh
f
u
ll
-
d
ept
h
r
ec
l
amation (FDR).
Can milling and minor spot repairs
cost effectively solve deficiencies,
bring the pavement to “Good
Condition,” and meet other
constrants (i.e., vertical clearance,
shoulders, safety rails, foreslopes,
etc.) to allow for bonded overlay?
Can existing or potential unstable
conditions or major deciencies (e.g.,
wet subgrade, asphalt stripping) be
addressed cost eectively with a
combination of preservation
techniques (e.g., milling, retrot
subdrains, full-depth patches) and
other contraints (e.g., vertical
clearence, safety rails, etc.) met with
an adequately thick unbonded
overlay?
Note: Concrete overlay thickness must be appropriately designed consider-
ing estimated trac, desired design life, and budget.
NO
NO
YES
Selecting the Appropriate
Concrete Overlay Solution
for Asphalt Pavements
Pavement is structurally sound but
needs increased structural capacity,
improved surface characteristics
(smoothness, friction, and noise),
surface defects removed, and/or
improved albedo properties.
Good Condition
Bonded Concrete Overlay
Over Asphalt Pavement
Unbonded Concrete Overlay
Over Asphalt Pavement
3 in. min. asphalt
Pavement is structurally sound but
has minor surface distresses such as
potholes, block cracking, or random
thermal cracking. Check for undulat-
ing prole grade to determine if
sub-drainage issues exist. Check
cores to ensure there is no measure-
able stripping or delamination in the
asphalt.
Fair Condition
Pavement has measurable distresses
beyond those described under “Fair
Condition,” such as alligator
cracking, rutting, shoving, slippage,
stripping, and raveling.
Note: Asphalt is a good reector
of underlying distresses such as
poor subbase conditions.
Poor Condition
Pavement exhibits “Poor
Condition” characteristics as
well as signicant deteriora-
tion, raveling, thermal
expansion, stripping, and
structural distresses.
Deteriorated Condition
Additional Repairs
Spot Repairs
Milling and Patching
Can spot surface repairs and/or spot
structural repairs cost effectively
solve deficiencies, bring the
pavement to “Good Condition,” and
meet other constraints (i.e., vertical
clearances, shoulders, safety rails,
foreslopes, etc.) to allow for a
bonded overlay?
Can spot structural repairs and/or
milling cost effectively solve
deficiencies, meet vertical and
structural requirements, and bring the
existing pavement to a condition that
provides a uniform subbase for an
unbonded overlay?
Install subdrains if needed
Joint spacing
Joint spacing
Install subdrains if needed
Milling/Minor Spot Repairs YES
YES
3 in. min. asphalt
3 in. min. asphalt
Concrete overlays can provide
economical short- to long-term
solutions for asphalt pavements.
e recommendations provided
in the following owchart are
generally long-term xes on the
order of 20 years or more of
expected life.
Second, what is the desired pavement life of the overlay,
given the condition of the existing pavement? ird,
what type of overlay (bonded or unbonded) will achieve
the rst two objectives at the lowest life-cycle cost?
Several factors should be considered when selecting
either a bonded or unbonded concrete overlay for an
existing asphalt pavement. Two predominant factors are
the condition of the existing pavement and the extent of
pre-overlay repairs required, if any.
Generally, existing pavements in relatively good or fair condition, or
poor-condition pavements that can be cost-eectively brought to good
condition, are candidates for bonded concrete overlays. Existing asphalt
pavements that cannot be cost eectively returned to good condition are
candidates for unbonded overlays as long as signicant structural repairs to
the existing pavements are not needed. Signicant asphalt deterioration can
be overlaid with concrete as long as unstable and so spots are repaired.
Unless there are unrepairable subsurface issues requiring removal of the
asphalt, it is rare that a unbonded concrete overlay cannot be utilized.
As with any preservation approach, the
principles of asset management are a
cornerstone in selecting the appropriate
concrete overlay solution. ree important
asset management questions need to be
answered as part of the selection process,
for the appropriate concrete overlay
solution to meet the needs of an agency.
First, what is the desired level of service to
be provided by the concrete overlay?
NO
NO
YES
FAQ—What if the existing pavement is not a candidate for a
concrete unbonded overlay? While most pavements can be preserved
with a concrete overlay, there are situations where a concrete overlay
is not appropriate. When this occurs, reconstruction is an alternative.
Reconstruction options include the following:
• Recommended: Mill and ll. Remove asphalt by milling, repair
any subgrade issues, and ll with new concrete pavement.
Recycle asphalt material.
• Permissible in specic situations: When the asphalt is less than
6-in. thick and is in deteriorated condition, the asphalt may be
recycled into the subgrade/subbase through full-depth
reclamation (FDR).
Asphalt surface
Rural
sectionUrban
section
F
A
Q
—
W
h
at i
f
t
h
e existin
g
pavement is not a can
d
i
d
ate
f
or a
c
oncrete un
b
on
d
e
d
over
l
a
y
? W
h
i
l
e most pavements can
b
e preserve
d
w
it
h
a concrete over
l
a
y
, t
h
ere are situations w
h
ere a concrete over
l
a
y
is not appropriate. W
h
en t
h
is occurs, reconstruction is an a
l
ternative.
Reconstruction options inc
l
u
d
e t
h
e
f
o
ll
owin
g
:
•
R
ecommended: Mi
ll
an
d
ll
. Remove asp
h
a
l
t
by
mi
ll
in
g
, repair
a
n
y
su
bg
ra
d
e issues, an
d
ll
wit
h
new concrete pavement.
R
ec
y
c
l
e asp
h
a
l
t materia
l
.
•
P
e
rmi
ss
i
b
l
e
in speci
c situations: W
h
en t
h
e asp
h
a
l
t is
l
ess t
h
an
6
-in. t
h
ic
k
an
d
is in
d
eteriorate
d
con
d
ition, t
h
e asp
h
a
l
t ma
y
b
e
r
ec
y
c
l
e
d
into t
h
e su
bg
ra
d
e/su
bb
ase t
h
rou
gh
f
u
ll
-
d
ept
h
r
ec
l
amation (FDR).
Can milling and minor spot repairs
cost effectively solve deficiencies,
bring the pavement to “Good
Condition,” and meet other
constrants (i.e., vertical clearance,
shoulders, safety rails, foreslopes,
etc.) to allow for bonded overlay?
Can existing or potential unstable
conditions or major deciencies (e.g.,
wet subgrade, asphalt stripping) be
addressed cost eectively with a
combination of preservation
techniques (e.g., milling, retrot
subdrains, full-depth patches) and
other contraints (e.g., vertical
clearence, safety rails, etc.) met with
an adequately thick unbonded
overlay?
Note: Concrete overlay thickness must be appropriately designed consider-
ing estimated trac, desired design life, and budget.
NO
NO
YES
Selecting the Appropriate
Concrete Overlay Solution
for Asphalt Pavements
Pavement is structurally sound but
needs increased structural capacity,
improved surface characteristics
(smoothness, friction, and noise),
surface defects removed, and/or
improved albedo properties.
Good Condition
Bonded Concrete Overlay
Over Asphalt Pavement
Unbonded Concrete Overlay
Over Asphalt Pavement
3 in. min. asphalt
Pavement is structurally sound but
has minor surface distresses such as
potholes, block cracking, or random
thermal cracking. Check for undulat-
ing prole grade to determine if
sub-drainage issues exist. Check
cores to ensure there is no measure-
able stripping or delamination in the
asphalt.
Fair Condition
Pavement has measurable distresses
beyond those described under “Fair
Condition,” such as alligator
cracking, rutting, shoving, slippage,
stripping, and raveling.
Note: Asphalt is a good reector
of underlying distresses such as
poor subbase conditions.
Poor Condition
Pavement exhibits “Poor
Condition” characteristics as
well as signicant deteriora-
tion, raveling, thermal
expansion, stripping, and
structural distresses.
Deteriorated Condition
Additional Repairs
Spot Repairs
Milling and Patching
Can spot surface repairs and/or spot
structural repairs cost effectively
solve deficiencies, bring the
pavement to “Good Condition,” and
meet other constraints (i.e., vertical
clearances, shoulders, safety rails,
foreslopes, etc.) to allow for a
bonded overlay?
Can spot structural repairs and/or
milling cost effectively solve
deficiencies, meet vertical and
structural requirements, and bring the
existing pavement to a condition that
provides a uniform subbase for an
unbonded overlay?
Install subdrains if needed
Joint spacing
Joint spacing
Install subdrains if needed
Milling/Minor Spot Repairs YES
YES
3 in. min. asphalt
3 in. min. asphalt
Concrete overlays can provide
economical short- to long-term
solutions for asphalt pavements.
e recommendations provided
in the following owchart are
generally long-term xes on the
order of 20 years or more of
expected life.
Second, what is the desired pavement life of the overlay,
given the condition of the existing pavement? ird,
what type of overlay (bonded or unbonded) will achieve
the rst two objectives at the lowest life-cycle cost?
Several factors should be considered when selecting
either a bonded or unbonded concrete overlay for an
existing asphalt pavement. Two predominant factors are
the condition of the existing pavement and the extent of
pre-overlay repairs required, if any.
Generally, existing pavements in relatively good or fair condition, or
poor-condition pavements that can be cost-eectively brought to good
condition, are candidates for bonded concrete overlays. Existing asphalt
pavements that cannot be cost eectively returned to good condition are
candidates for unbonded overlays as long as signicant structural repairs to
the existing pavements are not needed. Signicant asphalt deterioration can
be overlaid with concrete as long as unstable and so spots are repaired.
Unless there are unrepairable subsurface issues requiring removal of the
asphalt, it is rare that a unbonded concrete overlay cannot be utilized.
As with any preservation approach, the
principles of asset management are a
cornerstone in selecting the appropriate
concrete overlay solution. ree important
asset management questions need to be
answered as part of the selection process,
for the appropriate concrete overlay
solution to meet the needs of an agency.
First, what is the desired level of service to
be provided by the concrete overlay?
NO
NO
YES
FAQ—What if the existing pavement is not a candidate for a
concrete unbonded overlay? While most pavements can be preserved
with a concrete overlay, there are situations where a concrete overlay
is not appropriate. When this occurs, reconstruction is an alternative.
Reconstruction options include the following:
• Recommended: Mill and ll. Remove asphalt by milling, repair
any subgrade issues, and ll with new concrete pavement.
Recycle asphalt material.
• Permissible in specic situations: When the asphalt is less than
6-in. thick and is in deteriorated condition, the asphalt may be
recycled into the subgrade/subbase through full-depth
reclamation (FDR).
Asphalt surface
Rural
sectionUrban
section
F
A
Q
—
W
h
at i
f
t
h
e existin
g
pavement is not a can
d
i
d
ate
f
or a
c
oncrete un
b
on
d
e
d
over
l
a
y
? W
h
i
l
e most pavements can
b
e preserve
d
w
it
h
a concrete over
l
a
y
, t
h
ere are situations w
h
ere a concrete over
l
a
y
is not appropriate. W
h
en t
h
is occurs, reconstruction is an a
l
ternative.
Reconstruction options inc
l
u
d
e t
h
e
f
o
ll
owin
g
:
•
R
ecommended: Mi
ll
an
d
ll
. Remove asp
h
a
l
t
by
mi
ll
in
g
, repair
a
n
y
su
bg
ra
d
e issues, an
d
ll
wit
h
new concrete pavement.
R
ec
y
c
l
e asp
h
a
l
t materia
l
.
•
P
e
rmi
ss
i
b
l
e
in speci
c situations: W
h
en t
h
e asp
h
a
l
t is
l
ess t
h
an
6
-in. t
h
ic
k
an
d
is in
d
eteriorate
d
con
d
ition, t
h
e asp
h
a
l
t ma
y
b
e
r
ec
y
c
l
e
d
into t
h
e su
bg
ra
d
e/su
bb
ase t
h
rou
gh
f
u
ll
-
d
ept
h
r
ec
l
amation (FDR).
Guide to Concrete Overlays
20
Ch 2. EVALUATION & SELECTION
Figure 15. Selecting appropriate concrete overlay solution for composite pavements
Can existing or potential unstable
conditions or major deciencies (e.g., wet
subgrade, MRD, faulting) be addressed
cost eectively with a combination of
preservation techniques (e.g., milling,
retrot subdrains, full-depth non-sawed
lean concrete patches)? Can other
constraints (e.g., vertical clearance, safety
rails, etc.) be met with an adequately thick
unbonded overlay? Does the asphalt need
to be completely milled to remove major
deciencies such as stripping and a new
interlayer placed between the underlying
concrete and a new unbonded overlay?
NO
NO
YES
Selecting the Appropriate
Concrete Overlay Solution
f
or Composite Pavements
(Asphalt Over Concrete)
Pavement is structurally sound
but needs increased structural
capacity, improved surface
characteristics (smoothness,
friction and noise), corrected
surface defects, and/or improved
albedo properties.
Good Condition
Bonded Concrete Overlay
Over Composite Pavement
Unbonded Concrete Overlay
Over Composite Pavement
3 in. min. asphalt
Pavement is structurally sound but
has minor surface distresses such
as potholes, block cracking,
random cracking, and thermal
cracking. Check for undulating
prole grade to determine if sub-
drainage or secondary consolida-
tion issues exist. Check cores to
ensure there is no measureable
asphalt stripping or delamination.
Fair Condition
Pavement has measurable distress-
es beyond those described under
“Fair Condition.” ese include
alligator cracking, rutting, shoving,
slippage, stripping, raveling, and
possible MRD (see page 13).
Note: Asphalt is a good reector
of underlying distresses such as a
poor subbase or joint deteriora-
tion in concrete pavements.
Poor Condition
Exhibits “Poor Condition” as well
as signicant surface deterioration,
raveling, and structural distresses.
If severe or potentially severe joint
deterioration from freeze-thaw
damage or material-related distress
(MRD: ASR or D-cracking) is
present and it exists 3 to 4
beyond the joint at nearly every
joint, then the pavement is not
normally a good candidate for an
overlay unless the service life is
reduced.
Deteriorated Condition
Spot Repairs
Milling and Patching
Additional Repairs
Can spot surface repairs and/or spot
structural repairs cost eectively solve
deciencies, bring the pavement to
“Good Condition,” and meet other
constraints (i.e., vertical clearance,
shoulders, safety rails, foreslopes, etc.)
to allow for a bonded overlay?
Can milling and minor spot repairs
cost eectively solve deciencies,
bring the pavement to “Good
Condition,” and meet other
constraints (i.e., vertical clearance,
shoulders, safety rails, foreslopes, etc.)
to allow for a bonded overlay?
Can spot structural repairs and/or
milling (asphalt layers prone to
stripping to be removed) cost
eectively solve deciencies, meet
other contraints (i.e., vertical
clearance, shoulders, safety rails,
foreslopes, etc.), and bring the existing
pavement to a condition that will
provide uniform subbase for an
unbonded overlay?
Install subdrains if needed
Joint spacing
Joint spacing
Install subdrains if needed
Milling/Minor Spot Repairs
YES
YES
NO
YES
Concrete overlays can provide
economical short- to long-term
solutions for composite pavements.
e recommendations provided in
the following owchart are generally
long-term xes on the order of 20
years or more of expected life.
As with any preservation approach,
the principles of asset management
unbonded) will achieve the rst two objectives at
the lowest life-cycle cost?
Several factors should be considered when
selecting either a bonded or unbonded concrete
overlay of an existing composite pavement. Two
predominant factors are the condition of the
existing pavement and the extent of necessary
pre-overlay repairs, if any.
Generally, bonded overlays are appropriate for any composite pavement that is
either in good condition or can be improved cost eectively from fair or poor
condition to good condition. Composite pavements that cannot be repaired
cost eectively to good condition are most likely candidates for unbonded
overlays, provided that the existing pavement can serve as a subbase that
provides relatively uniform support. Signicant deterioration can be overlaid
with concrete as long as unstable and so spots are repaired prior to overlay
construction.
A thorough pavement evaluation should be performed to determine the
condition of the existing pavement and assess the scope of required pre-over-
lay repairs. If material-related distress (MRD: ASR, D-cracking, and/or
freeze-thaw damage) is detected during the pavement evaluation, lab testing
should be performed to assess the extent of MRD (see page 13 for further
guidance on dealing with existing pavements with MRD).
are a cornerstone in selecting the
appropriate concrete overlay solution.
ree important asset management
questions need to be answered as part of
the selection process. First, what is the
desired level of service to be provided by
the concrete overlay? Second, what is the
desired pavement life of the overlay given
the condition of the existing pavement?
ird, what type of overlay (bonded or
Note: Concrete overlay thickness to be appropriately designed considering
estimated trac, desired design life, and budget.
3 in. min. asphalt
NO
3 in. min. asphalt FAQ—What if the existing pavement is not a candidate for an
unbonded concrete overlay? While most pavements can be preserved
with an unbonded concrete overlay, there are situations where an
overlay is not appropriate. When this occurs, reconstruction is an
alternative. Reconstruction options are discussed in Appendix B.
In summary, they include the following:
• Recommended: In-place recycling of the existing pavement to
serve as a base for new pavement or shoulder material.
• Permissible in specic situations: Rubblizing the existing
concrete pavement to serve as a base for new concrete
pavement.
• Not recommended: Crack-and-seat to serve as a base for new
pavement.
Asphalt surface
Rural
sectionUrban
section
ConcreteConcrete
F
A
Q
—
Wh
at i
f
t
h
e existin
g
pavement is not a can
d
i
d
ate
f
or an
un
b
on
d
e
d
concrete over
l
a
y
? W
h
i
l
e most pavements can
b
e preserve
d
w
it
h
an un
b
on
d
e
d
concrete over
l
a
y
, t
h
ere are situations w
h
ere an
over
l
a
y
is not appropriate. W
h
en t
h
is occurs, reconstruction is an
alte
rn
at
iv
e.
Reconstruction o
p
tions are discussed in A
pp
endix B.
I
n summar
y
, t
h
e
y
inc
l
u
d
e t
h
e
f
o
ll
owin
g
:
•
R
ecommende
d
: In-p
l
ace rec
y
c
l
in
g
o
f
t
h
e existin
g
pavement to
serve as a
b
ase
f
or new
p
avement or s
h
ou
ld
er materia
l.
•
P
e
rmi
ss
i
b
l
e
in speci
c situations: Ru
bbl
izin
g
t
h
e existin
g
c
oncrete pavement to serve as a
b
ase
f
or new concrete
p
avemen
t.
•
Not recommended
:
Crac
k
-an
d
-seat to serve as a
b
ase
f
or ne
w
pavemen
t.
21
Guide to Concrete Overlays
Ch 2. EVALUATION & SELECTION
Can existing or potential unstable
conditions or major deciencies (e.g., wet
subgrade, MRD, faulting) be addressed
cost eectively with a combination of
preservation techniques (e.g., milling,
retrot subdrains, full-depth non-sawed
lean concrete patches)? Can other
constraints (e.g., vertical clearance, safety
rails, etc.) be met with an adequately thick
unbonded overlay? Does the asphalt need
to be completely milled to remove major
deciencies such as stripping and a new
interlayer placed between the underlying
concrete and a new unbonded overlay?
NO
NO
YES
Selecting the Appropriate
Concrete Overlay Solution
f
or Composite Pavements
(Asphalt Over Concrete)
Pavement is structurally sound
but needs increased structural
capacity, improved surface
characteristics (smoothness,
friction and noise), corrected
surface defects, and/or improved
albedo properties.
Good Condition
Bonded Concrete Overlay
Over Composite Pavement
Unbonded Concrete Overlay
Over Composite Pavement
3 in. min. asphalt
Pavement is structurally sound but
has minor surface distresses such
as potholes, block cracking,
random cracking, and thermal
cracking. Check for undulating
prole grade to determine if sub-
drainage or secondary consolida-
tion issues exist. Check cores to
ensure there is no measureable
asphalt stripping or delamination.
Fair Condition
Pavement has measurable distress-
es beyond those described under
“Fair Condition.” ese include
alligator cracking, rutting, shoving,
slippage, stripping, raveling, and
possible MRD (see page 13).
Note: Asphalt is a good reector
of underlying distresses such as a
poor subbase or joint deteriora-
tion in concrete pavements.
Poor Condition
Exhibits “Poor Condition” as well
as signicant surface deterioration,
raveling, and structural distresses.
If severe or potentially severe joint
deterioration from freeze-thaw
damage or material-related distress
(MRD: ASR or D-cracking) is
present and it exists 3 to 4
beyond the joint at nearly every
joint, then the pavement is not
normally a good candidate for an
overlay unless the service life is
reduced.
Deteriorated Condition
Spot Repairs
Milling and Patching
Additional Repairs
Can spot surface repairs and/or spot
structural repairs cost eectively solve
deciencies, bring the pavement to
“Good Condition,” and meet other
constraints (i.e., vertical clearance,
shoulders, safety rails, foreslopes, etc.)
to allow for a bonded overlay?
Can milling and minor spot repairs
cost eectively solve deciencies,
bring the pavement to “Good
Condition,” and meet other
constraints (i.e., vertical clearance,
shoulders, safety rails, foreslopes, etc.)
to allow for a bonded overlay?
Can spot structural repairs and/or
milling (asphalt layers prone to
stripping to be removed) cost
eectively solve deciencies, meet
other contraints (i.e., vertical
clearance, shoulders, safety rails,
foreslopes, etc.), and bring the existing
pavement to a condition that will
provide uniform subbase for an
unbonded overlay?
Install subdrains if needed
Joint spacing
Joint spacing
Install subdrains if needed
Milling/Minor Spot Repairs
YES
YES
NO
YES
Concrete overlays can provide
economical short- to long-term
solutions for composite pavements.
e recommendations provided in
the following owchart are generally
long-term xes on the order of 20
years or more of expected life.
As with any preservation approach,
the principles of asset management
unbonded) will achieve the rst two objectives at
the lowest life-cycle cost?
Several factors should be considered when
selecting either a bonded or unbonded concrete
overlay of an existing composite pavement. Two
predominant factors are the condition of the
existing pavement and the extent of necessary
pre-overlay repairs, if any.
Generally, bonded overlays are appropriate for any composite pavement that is
either in good condition or can be improved cost eectively from fair or poor
condition to good condition. Composite pavements that cannot be repaired
cost eectively to good condition are most likely candidates for unbonded
overlays, provided that the existing pavement can serve as a subbase that
provides relatively uniform support. Signicant deterioration can be overlaid
with concrete as long as unstable and so spots are repaired prior to overlay
construction.
A thorough pavement evaluation should be performed to determine the
condition of the existing pavement and assess the scope of required pre-over-
lay repairs. If material-related distress (MRD: ASR, D-cracking, and/or
freeze-thaw damage) is detected during the pavement evaluation, lab testing
should be performed to assess the extent of MRD (see page 13 for further
guidance on dealing with existing pavements with MRD).
are a cornerstone in selecting the
appropriate concrete overlay solution.
ree important asset management
questions need to be answered as part of
the selection process. First, what is the
desired level of service to be provided by
the concrete overlay? Second, what is the
desired pavement life of the overlay given
the condition of the existing pavement?
ird, what type of overlay (bonded or
Note: Concrete overlay thickness to be appropriately designed considering
estimated trac, desired design life, and budget.
3 in. min. asphalt
NO
3 in. min. asphalt FAQ—What if the existing pavement is not a candidate for an
unbonded concrete overlay? While most pavements can be preserved
with an unbonded concrete overlay, there are situations where an
overlay is not appropriate. When this occurs, reconstruction is an
alternative. Reconstruction options are discussed in Appendix B.
In summary, they include the following:
• Recommended: In-place recycling of the existing pavement to
serve as a base for new pavement or shoulder material.
• Permissible in specic situations: Rubblizing the existing
concrete pavement to serve as a base for new concrete
pavement.
• Not recommended: Crack-and-seat to serve as a base for new
pavement.
Asphalt surface
Rural
sectionUrban
section
ConcreteConcrete
F
A
Q
—
Wh
at i
f
t
h
e existin
g
pavement is not a can
d
i
d
ate
f
or an
un
b
on
d
e
d
concrete over
l
a
y
? W
h
i
l
e most pavements can
b
e preserve
d
w
it
h
an un
b
on
d
e
d
concrete over
l
a
y
, t
h
ere are situations w
h
ere an
over
l
a
y
is not appropriate. W
h
en t
h
is occurs, reconstruction is an
alte
rn
at
iv
e.
Reconstruction o
p
tions are discussed in A
pp
endix B.
I
n summar
y
, t
h
e
y
inc
l
u
d
e t
h
e
f
o
ll
owin
g
:
•
R
ecommende
d
: In-p
l
ace rec
y
c
l
in
g
o
f
t
h
e existin
g
pavement to
serve as a
b
ase
f
or new
p
avement or s
h
ou
ld
er materia
l.
•
P
e
rmi
ss
i
b
l
e
in speci
c situations: Ru
bbl
izin
g
t
h
e existin
g
c
oncrete pavement to serve as a
b
ase
f
or new concrete
p
avemen
t.
•
Not recommended
:
Crac
k
-an
d
-seat to serve as a
b
ase
f
or ne
w
pavemen
t.
Can existing or potential unstable
conditions or major deciencies (e.g., wet
subgrade, MRD, faulting) be addressed
cost eectively with a combination of
preservation techniques (e.g., milling,
retrot subdrains, full-depth non-sawed
lean concrete patches)? Can other
constraints (e.g., vertical clearance, safety
rails, etc.) be met with an adequately thick
unbonded overlay? Does the asphalt need
to be completely milled to remove major
deciencies such as stripping and a new
interlayer placed between the underlying
concrete and a new unbonded overlay?
NO
NO
YES
Selecting the Appropriate
Concrete Overlay Solution
f
or Composite Pavements
(Asphalt Over Concrete)
Pavement is structurally sound
but needs increased structural
capacity, improved surface
characteristics (smoothness,
friction and noise), corrected
surface defects, and/or improved
albedo properties.
Good Condition
Bonded Concrete Overlay
Over Composite Pavement
Unbonded Concrete Overlay
Over Composite Pavement
3 in. min. asphalt
Pavement is structurally sound but
has minor surface distresses such
as potholes, block cracking,
random cracking, and thermal
cracking. Check for undulating
prole grade to determine if sub-
drainage or secondary consolida-
tion issues exist. Check cores to
ensure there is no measureable
asphalt stripping or delamination.
Fair Condition
Pavement has measurable distress-
es beyond those described under
“Fair Condition.” ese include
alligator cracking, rutting, shoving,
slippage, stripping, raveling, and
possible MRD (see page 13).
Note: Asphalt is a good reector
of underlying distresses such as a
poor subbase or joint deteriora-
tion in concrete pavements.
Poor Condition
Exhibits “Poor Condition” as well
as signicant surface deterioration,
raveling, and structural distresses.
If severe or potentially severe joint
deterioration from freeze-thaw
damage or material-related distress
(MRD: ASR or D-cracking) is
present and it exists 3 to 4
beyond the joint at nearly every
joint, then the pavement is not
normally a good candidate for an
overlay unless the service life is
reduced.
Deteriorated Condition
Spot Repairs
Milling and Patching
Additional Repairs
Can spot surface repairs and/or spot
structural repairs cost eectively solve
deciencies, bring the pavement to
“Good Condition,” and meet other
constraints (i.e., vertical clearance,
shoulders, safety rails, foreslopes, etc.)
to allow for a bonded overlay?
Can milling and minor spot repairs
cost eectively solve deciencies,
bring the pavement to “Good
Condition,” and meet other
constraints (i.e., vertical clearance,
shoulders, safety rails, foreslopes, etc.)
to allow for a bonded overlay?
Can spot structural repairs and/or
milling (asphalt layers prone to
stripping to be removed) cost
eectively solve deciencies, meet
other contraints (i.e., vertical
clearance, shoulders, safety rails,
foreslopes, etc.), and bring the existing
pavement to a condition that will
provide uniform subbase for an
unbonded overlay?
Install subdrains if needed
Joint spacing
Joint spacing
Install subdrains if needed
Milling/Minor Spot Repairs
YES
YES
NO
YES
Concrete overlays can provide
economical short- to long-term
solutions for composite pavements.
e recommendations provided in
the following owchart are generally
long-term xes on the order of 20
years or more of expected life.
As with any preservation approach,
the principles of asset management
unbonded) will achieve the rst two objectives at
the lowest life-cycle cost?
Several factors should be considered when
selecting either a bonded or unbonded concrete
overlay of an existing composite pavement. Two
predominant factors are the condition of the
existing pavement and the extent of necessary
pre-overlay repairs, if any.
Generally, bonded overlays are appropriate for any composite pavement that is
either in good condition or can be improved cost eectively from fair or poor
condition to good condition. Composite pavements that cannot be repaired
cost eectively to good condition are most likely candidates for unbonded
overlays, provided that the existing pavement can serve as a subbase that
provides relatively uniform support. Signicant deterioration can be overlaid
with concrete as long as unstable and so spots are repaired prior to overlay
construction.
A thorough pavement evaluation should be performed to determine the
condition of the existing pavement and assess the scope of required pre-over-
lay repairs. If material-related distress (MRD: ASR, D-cracking, and/or
freeze-thaw damage) is detected during the pavement evaluation, lab testing
should be performed to assess the extent of MRD (see page 13 for further
guidance on dealing with existing pavements with MRD).
are a cornerstone in selecting the
appropriate concrete overlay solution.
ree important asset management
questions need to be answered as part of
the selection process. First, what is the
desired level of service to be provided by
the concrete overlay? Second, what is the
desired pavement life of the overlay given
the condition of the existing pavement?
ird, what type of overlay (bonded or
Note: Concrete overlay thickness to be appropriately designed considering
estimated trac, desired design life, and budget.
3 in. min. asphalt
NO
3 in. min. asphalt FAQ—What if the existing pavement is not a candidate for an
unbonded concrete overlay? While most pavements can be preserved
with an unbonded concrete overlay, there are situations where an
overlay is not appropriate. When this occurs, reconstruction is an
alternative. Reconstruction options are discussed in Appendix B.
In summary, they include the following:
• Recommended: In-place recycling of the existing pavement to
serve as a base for new pavement or shoulder material.
• Permissible in specic situations: Rubblizing the existing
concrete pavement to serve as a base for new concrete
pavement.
• Not recommended: Crack-and-seat to serve as a base for new
pavement.
Asphalt surface
Rural
sectionUrban
section
ConcreteConcrete
F
A
Q
—
Wh
at i
f
t
h
e existin
g
pavement is not a can
d
i
d
ate
f
or an
un
b
on
d
e
d
concrete over
l
a
y
? W
h
i
l
e most pavements can
b
e preserve
d
w
it
h
an un
b
on
d
e
d
concrete over
l
a
y
, t
h
ere are situations w
h
ere an
over
l
a
y
is not appropriate. W
h
en t
h
is occurs, reconstruction is an
alte
rn
at
iv
e.
Reconstruction o
p
tions are discussed in A
pp
endix B.
I
n summar
y
, t
h
e
y
inc
l
u
d
e t
h
e
f
o
ll
owin
g
:
•
R
ecommende
d
: In-p
l
ace rec
y
c
l
in
g
o
f
t
h
e existin
g
pavement to
serve as a
b
ase
f
or new
p
avement or s
h
ou
ld
er materia
l.
•
P
e
rmi
ss
i
b
l
e
in speci
c situations: Ru
bbl
izin
g
t
h
e existin
g
c
oncrete pavement to serve as a
b
ase
f
or new concrete
p
avemen
t.
•
Not recommended
:
Crac
k
-an
d
-seat to serve as a
b
ase
f
or ne
w
pavemen
t.
Guide to Concrete Overlays
22
Ch 2. EVALUATION & SELECTION
Figure 16. Selecting appropriate concrete overlay solution for concrete pavements
Can spot surface repairs and/or spot
structural repairs cost eectively solve
deciencies, bring the pavement to
“Good Condition,” and meet other
constraints (i.e., vertical clearance,
shoulders, safety rails, foreslopes, etc.)
to allow for a bonded overlay?
NO
NO
Bonded Concrete Overlay
Over Concrete Pavement
Unbonded Concrete Overlay
Over Concrete Pavement
Install subdrains if needed
Intermediate
joint spacing
Match existing underlying
joints with saw-cut full
depth of overlay plus ½ in.
Joint spacing
Install subdrains if needed
Place separator layer
(geotextile or 1-in. min. asphalt)
Note: Concrete overlay thickness to be appropriately designed considering:
estimated trac, desired design life, and budget.
Can existing or potential unstable conditions or
major deciencies (e.g., wet subgrade, MRD,
faulting) be addressed cost eectively through a
combination of preservation techniques (e.g.,
milling, retrot subdrains, full-depth patches, slab
stabilization), and can other constraints (e.g., vertical
clearance, shoulders, safety rails, foreslopes) be
addressed with an adequately thick unbonded
overlay?
YES
YES
Selecting the Appropriate
Concrete Overlay Solution
for Concrete Pavements
Pavement is structurally sound
but needs increased structural
capacity, improved surface
characteristics (smoothness,
friction and noise), corrected
surface defects, and/or
improved albedo properties.
Good Condition
Paement is structurally sound
but has minor surface distresses
such as random cracking,
periodic partial-depth joint
spalling, and shadowing. Check
for undulating prole grade to
determine if sub-drainage issues
or other foundation issues such
as secondary consolidation of an
open-graded base exist.
Fair Condition
Pavement has measurable
surface distresses beyond those
described as “Fair Condition.”
ese include full-depth joint
deterioration, working cracks,
spot structural failures, faulting,
and/or material-related distress-
es (MRD).
Poor Condition
Pavement is in “Poor Condition”
and exhibits signicant surface
deterioration and structural
distresses. If severe or potentially
severe joint deterioration from
freeze-thaw damage or MRD is
present and it exists 3 to 4
beyond the joint at nearly every
joint, then the pavement is not
normally a good candidate for an
overlay unless the service life is
reduced.
Deteriorated Condition
Spot Repairs
Additional Repairs
Can milling and minor spot repairs
cost eectively remove deciencies,
bring the pavement to “Good
Condition,” and meet other
constraints (i.e., vertical clearance,
shoulders, safety rails, foreslopes,
etc.) to allow for a bonded overlay?
Can milling and/or structural repairs
(patching) cost eectively solve
deciencies, bring the existing
pavement to a condition that will
provide uniform support as a
subbase, meet other constraints (i.e.,
vertical clearance, shoulders, safety
rails, foreslopes, etc.), and bring the
existing pavement to a condition that
will provide a uniform subbase for
an unbonded overlay?
If deterioration is also in the bottom
half of the pavement and is located at
the joints, the joints can be milled or
removed full depth and replaced
with lower quality concrete (lean
concrete) with no sawing of the joint.
Cracking in the removed joint will
not aect the performance of an
unbonded overlay due to the
interlayer.
Install full-depth
flowable mortar
patches. No
sawing.
Install full-depth
flowable mortar
patches. No
sawing.
Milling/Minor Spot Repairs
YES
YES
NO
NO
Milling and Patching
Concrete surfaceConcrete surface
Rural
section
Rural
section
Urban
section
Urban
section
FAQ—What if the existing pavement is not a candidate for an
unbonded concrete overlay? While most pavements can be
preserved with an unbonded concrete overlay, there are
situations where an overlay is not appropriate. When this occurs,
reconstruction is an alternative. Reconstruction options are
discussed in Appendix B. Following is a brief summary:
• Recommended: In-place recycling of the existing pavement
and use as a base for new pavement or shoulder material.
• Permissible in specic situations: Rubblizing the existing
concrete pavement to serve as a base for new concrete
pavement.
• Not recommended: Crack-and-seat to serve as a base for
new pavement.
Concrete overlays can provide
economical short- to long-term
solutions for concrete pavements.
e recommendations provided in
the following owchart are general-
ly long-term xes on the order of 20
years or more of expected life.
As with any preservation approach,
the principles of asset management
overlay (bonded or unbonded) will achieve the rst
two objectives at the lowest life-cycle cost?
Several factors should be considered when selecting
either a bonded or unbonded concrete overlay for an
existing concrete pavement. Two predominant factors
are the condition of the existing pavement and the
extent of necessary pre-overlay repairs, if any.
Generally, bonded overlays are appropriate for any
concrete pavement that is either in good condition or
can be improved cost eectively from fair or poor condition to good condition.
Concrete pavements that cannot be cost eectively repaired to a good condi-
tion are candidates for unbonded overlays, provided that the existing
pavement can serve as a subbase that provides relatively uniform support.
Signicant deterioration can be overlaid with concrete as long as unstable and
so spots are repaired prior to overlay construction.
A thorough pavement evaluation should be performed to determine the
condition of the existing pavement and assess the scope of pre-overlay repairs
that may be required. If material-related distress (MRD: ASR, D-cracking,
and/or freeze-thaw damage) is detected during the pavement evaluation, lab
testing should be performed to assess the extent of MRD (see page 13 for
further guidance on dealing with existing pavements with MRD).
are a cornerstone in selecting the appropriate
concrete overlay solution. ree important
asset management questions need to be
answered as part of the selection process, for
the appropriate concrete overlay solution to
meet the needs of an agency. First, what is
the desired level of service to be provided by
the concrete overlay? Second, what is the
desired life of the overlay given the condition
of the existing pavement? ird, what type of
23
Guide to Concrete Overlays
Ch 2. EVALUATION & SELECTION
Can spot surface repairs and/or spot
structural repairs cost eectively solve
deciencies, bring the pavement to
“Good Condition,” and meet other
constraints (i.e., vertical clearance,
shoulders, safety rails, foreslopes, etc.)
to allow for a bonded overlay?
NO
NO
Bonded Concrete Overlay
Over Concrete Pavement
Unbonded Concrete Overlay
Over Concrete Pavement
Install subdrains if needed
Intermediate
joint spacing
Match existing underlying
joints with saw-cut full
depth of overlay plus ½ in.
Joint spacing
Install subdrains if needed
Place separator layer
(geotextile or 1-in. min. asphalt)
Note: Concrete overlay thickness to be appropriately designed considering:
estimated trac, desired design life, and budget.
Can existing or potential unstable conditions or
major deciencies (e.g., wet subgrade, MRD,
faulting) be addressed cost eectively through a
combination of preservation techniques (e.g.,
milling, retrot subdrains, full-depth patches, slab
stabilization), and can other constraints (e.g., vertical
clearance, shoulders, safety rails, foreslopes) be
addressed with an adequately thick unbonded
overlay?
YES
YES
Selecting the Appropriate
Concrete Overlay Solution
for Concrete Pavements
Pavement is structurally sound
but needs increased structural
capacity, improved surface
characteristics (smoothness,
friction and noise), corrected
surface defects, and/or
improved albedo properties.
Good Condition
Paement is structurally sound
but has minor surface distresses
such as random cracking,
periodic partial-depth joint
spalling, and shadowing. Check
for undulating prole grade to
determine if sub-drainage issues
or other foundation issues such
as secondary consolidation of an
open-graded base exist.
Fair Condition
Pavement has measurable
surface distresses beyond those
described as “Fair Condition.”
ese include full-depth joint
deterioration, working cracks,
spot structural failures, faulting,
and/or material-related distress-
es (MRD).
Poor Condition
Pavement is in “Poor Condition”
and exhibits signicant surface
deterioration and structural
distresses. If severe or potentially
severe joint deterioration from
freeze-thaw damage or MRD is
present and it exists 3 to 4
beyond the joint at nearly every
joint, then the pavement is not
normally a good candidate for an
overlay unless the service life is
reduced.
Deteriorated Condition
Spot Repairs
Additional Repairs
Can milling and minor spot repairs
cost eectively remove deciencies,
bring the pavement to “Good
Condition,” and meet other
constraints (i.e., vertical clearance,
shoulders, safety rails, foreslopes,
etc.) to allow for a bonded overlay?
Can milling and/or structural repairs
(patching) cost eectively solve
deciencies, bring the existing
pavement to a condition that will
provide uniform support as a
subbase, meet other constraints (i.e.,
vertical clearance, shoulders, safety
rails, foreslopes, etc.), and bring the
existing pavement to a condition that
will provide a uniform subbase for
an unbonded overlay?
If deterioration is also in the bottom
half of the pavement and is located at
the joints, the joints can be milled or
removed full depth and replaced
with lower quality concrete (lean
concrete) with no sawing of the joint.
Cracking in the removed joint will
not aect the performance of an
unbonded overlay due to the
interlayer.
Install full-depth
flowable mortar
patches. No
sawing.
Install full-depth
flowable mortar
patches. No
sawing.
Milling/Minor Spot Repairs
YES
YES
NO
NO
Milling and Patching
Concrete surfaceConcrete surface
Rural
section
Rural
section
Urban
section
Urban
section
FAQ—What if the existing pavement is not a candidate for an
unbonded concrete overlay? While most pavements can be
preserved with an unbonded concrete overlay, there are
situations where an overlay is not appropriate. When this occurs,
reconstruction is an alternative. Reconstruction options are
discussed in Appendix B. Following is a brief summary:
• Recommended: In-place recycling of the existing pavement
and use as a base for new pavement or shoulder material.
• Permissible in specic situations: Rubblizing the existing
concrete pavement to serve as a base for new concrete
pavement.
• Not recommended: Crack-and-seat to serve as a base for
new pavement.
Concrete overlays can provide
economical short- to long-term
solutions for concrete pavements.
e recommendations provided in
the following owchart are general-
ly long-term xes on the order of 20
years or more of expected life.
As with any preservation approach,
the principles of asset management
overlay (bonded or unbonded) will achieve the rst
two objectives at the lowest life-cycle cost?
Several factors should be considered when selecting
either a bonded or unbonded concrete overlay for an
existing concrete pavement. Two predominant factors
are the condition of the existing pavement and the
extent of necessary pre-overlay repairs, if any.
Generally, bonded overlays are appropriate for any
concrete pavement that is either in good condition or
can be improved cost eectively from fair or poor condition to good condition.
Concrete pavements that cannot be cost eectively repaired to a good condi-
tion are candidates for unbonded overlays, provided that the existing
pavement can serve as a subbase that provides relatively uniform support.
Signicant deterioration can be overlaid with concrete as long as unstable and
so spots are repaired prior to overlay construction.
A thorough pavement evaluation should be performed to determine the
condition of the existing pavement and assess the scope of pre-overlay repairs
that may be required. If material-related distress (MRD: ASR, D-cracking,
and/or freeze-thaw damage) is detected during the pavement evaluation, lab
testing should be performed to assess the extent of MRD (see page 13 for
further guidance on dealing with existing pavements with MRD).
are a cornerstone in selecting the appropriate
concrete overlay solution. ree important
asset management questions need to be
answered as part of the selection process, for
the appropriate concrete overlay solution to
meet the needs of an agency. First, what is
the desired level of service to be provided by
the concrete overlay? Second, what is the
desired life of the overlay given the condition
of the existing pavement? ird, what type of
25
Guide to Concrete Overlays 25
Guide to Concrete Overlays
Ch 3. OVERLAY OPTIONS
Chapter 3.
OVERVIEW OF CONCRETE OVERLAY OPTIONS
As previously described, concrete resurfacing
consists of two options: bonded overlays and
unbonded overlays. Both options are appli-
cable to all existing pavement types—i.e., on
asphalt, composite, and concrete pavements.
is chapter provides an overview of each of
the two concrete overlay options on all exist-
ing pavement types.
Bonded concrete overlay:
1. Bonded on asphalt
2. Bonded on composite
3. Bonded on concrete
Unbonded concrete overlay:
1. Unbonded on asphalt
2. Unbonded on composite
3. Unbonded on concrete
Guide to Concrete Overlays
26
Ch 3. OVERLAY OPTIONS
Bonded Concrete Overlay on Asphalt Pavements
Application and Uses
Bonded concrete overlays on asphalt
pavements
• May be appropriate for asphalt roads,
streets, and intersections in fair or better
structural condition with typical distresses
such as rutting, shoving, slippage, and
thermal cracking; see Figure 18
• Are generally 2–6 in. (50–150 mm) thick
• Rely on the existing asphalt pavement to
provide additional load-carrying capacity,
and bond to the existing asphalt pavement
to form a monolithic section, thereby
reducing stresses and deflections
• Add structural capacity where traffic
loads have increased or are anticipated to
increase
• Eliminate surface defects such as rutting
and shoving
• Improve surface characteristics (friction,
noise, and smoothness)
• Reduce urban heat island effect by increas-
ing pavement surface albedo
Figure 17 illustrates an asphalt pavement that
may be a candidate for a bonded concrete
overlay, along with the kinds of preoverlay
repairs that may be appropriate.
Figure 17. Bonded concrete overlay of fair or better asphalt pavement with surface distresses
(previously called ultra-thin whitetopping)
-
Existing asphalt pavement
with surface distresses
Milled and cleaned
surface
New 2–6 in. (50–150 mm)
bonded concrete overlay
with square panels
Figure 18. Bonded overlay of asphalt pavement
27
Guide to Concrete Overlays 27
Guide to Concrete Overlays
Ch 3. OVERLAY OPTIONS
Performance
Bonded concrete overlays of asphalt pave-
ments have been successfully used in many
states to maintain and rehabilitate asphalt
pavements with surface defects; see Figures
19 and 20. Numerous studies have shown
bonded concrete overlays to offer a durable
surface course provided (1) there is a sufficient
bond between the asphalt surface and concrete
overlay, and (2) the existing asphalt pavement
provides adequate structural support.
Keys to Success
• Milling of existing asphalt may be required
to eliminate or reduce surface distortions of
2 in. (50 mm) or more and to help provide
a good bond.
• Minimal spot repairs may be required.
• A minimum of 3 in. (75 mm) of asphalt
should remain after milling.
• Asphalt surface should be sprinkled with
water when the surface temperature is
greater than 120ºF (49ºC) during overlay
placement.
• A clean surface is critical to achieving an
adequate bond between the overlay and the
underlying asphalt.
• Appropriate panel size should be established
with respect to the thickness of the concrete
overlay and should preferably be sawed in
small square panels.
• Transverse joints must be sawed T/3 (with
special attention to thickened overlay over
asphalt ruts and other nonuniform areas).
• When feasible, design the longitudinal
joints to be outside of the normal wheel
paths.
• No notable stripping or delamination at
tack lines exists in asphalt pavement to
remain after milling.
• inner overlays may shorten the sawing
window; additional saws are likely to be
required.
• Application of curing compound or other
curing methods must be timely and thor-
ough, especially at the edges.
• Sealing joints improves performance.
Overlay Process
e overlay project consists of pavement
evaluation, design, construction, and future
repairs.
Pavement Evaluation
An evaluation of the existing asphalt pave-
ment is necessary to
• Ensure it is structurally adequate to carry
the anticipated traffic loads
• Determine if milling is required and to
what depths
• Establish the bonded overlay design
thickness
For information on pavement evaluation, see
Chapter 2. Asphalt pavements with significant
structural deterioration, inadequate or non-
uniform base/subbase support, or stripping of
asphalt layers due to inadequate drainage are
not good bonded overlay candidates; in such
cases, an unbonded concrete overlay should be
considered.
Overlay Design
Design elements include overlay thickness,
mixture design, joints, and drainage.
Overlay Thickness
e design thickness for bonded concrete
overlays is typically 2–6 in. (50–150 mm),
depending on the desired load-carrying capac-
ity and service life as well as the structural
capacity provided by the underlying pave-
ment. Additional overlay thickness may be
required in transition sections to prevent
movement of the overlay panels adjacent to
the existing asphalt pavement and to reduce
the potential for cracking due to traffic impact
loadings.
e recommended thickness design pro-
cedures are those used by the American
Concrete Pavement Association’s Bonded
Concrete Overlay on Asphalt (BCOA)
ickness Designer (2012) or the BCOA ME
(Vandenbossche 2013). For more informa-
tion on these procedures, see Table 10 in
Chapter 4.
Mixture Design
Conventional concrete mixtures have been
successfully used for bonded concrete overlays
of asphalt pavements. When accelerated open-
ing is desired, conventional concrete mixtures
should be proportioned for rapid strength
gain without increasing shrinkage properties.
For additional information on accelerated
mixtures, see page 76.
e use of high-modulus structural fibers
can improve the toughness and postcracking
behavior of the concrete and help mitigate the
effects of plastic shrinkage cracking, should
it occur. For more information,see discussion
beginning on page 77.
Joint Design
e recommended joint pattern for bonded
overlays of asphalt is small square panels,
typically in the range of 3–8 ft (0.9–2.4 m),
to reduce differential movement between the
concrete overlay and asphalt and to reduce
curling and warping stresses. It is recom-
mended that the length and width of joint
squares in feet be limited to 1.5 times the
overlay thickness in inches. In addition,
if possible, longitudinal joints should be
arranged so that they are not in the wheel
Figure 19. SH-119 in 1991 prior to placement of an bonded concrete
overlay (source: Ron Youngman, CO/WY chapter, ACPA)
Figure 20. SH-119 in 2009 after 18 years of service (source: Ron
Youngman, CO/WY chapter, ACPA)
Guide to Concrete Overlays
28
Ch 3. OVERLAY OPTIONS
path; see Figure 21. e use of tiebars or
dowels is not necessary because of the small
panel size.
Studies performed in Iowa on low-volume
roadways with bonded concrete overlays of
asphalt pavement have shown that, on aver-
age, only 5 percent of the contraction joints
were cracked after 10 years. ese results
indicate that there are potential cost savings
that could be realized on similar low-volume
roadways, either by increasing the slab
dimensions or by reducing the concrete over-
lay thickness.
In the past, bonded overlays less than or
equal to 6 inches thick have typically left
the joints unsealed. Studies performed by
Figure 21. Longitudinal joints should be arranged to avoid wheel paths
2 ft x 2 ft panels
wheel paths joint in wheel path
3 ft x 3 ft panels Traffic
direction 6 ft x 6 ft panels
Outer Shoulder
Outer Shoulder
Outer Shoulder
Outer Shoulder
4 ft x 4 ft panels
12 ft 12 ft
the Minnesota DOT (MnDOT 2013) have
shown improved performance when joints are
sealed. Because the concrete overlay is bonded
to the underlying asphalt pavement, moisture
that is allowed to infiltrate open joints has
nowhere to drain, eventually weakening the
bond and resulting in premature cracking of
the slabs.
Drainage
Stripping or delamination in the upper 3
inches of the remaining asphalt layer to be
overlaid can lead to premature failure of the
bonded concrete overlay. During evaluation
and design of a bonded concrete overlay
project, existing subgrade drainage should
be evaluated, as would be done with asphalt
Table 3. Possible Preoverlay Repairs on Existing Asphalt Pavement in Preparation for Bonded
Overlay
Existing Pavement Distress Spot Repairs to Consider
Rutting ≥ 2 in. (50 mm) Mill
Rutting < 2 in. (50 mm) None or mill
Shoving, slippage Mill
Crack width ≥ maximum coarse aggregate
size used in the concrete overlay mixture
Fill with flowable fill.
Crack width < maximum coarse aggregate
size used in the concrete overlay mixture
None
Low- to medium-severity pothole Remove loose material and fill integrally with the concrete
overlay.
High-severity pothole and/or areas
needing full-depth repair
To prevent a single overlay panel from bonding to both
asphalt and concrete, make full-depth repairs across a full
lane width with concrete and adjust the transverse joint
spacing in the concrete overlay to match the location of
the underlying patch. The full lane width prevents trying to
match a longitudinal joint for a partial lane patch.
resurfacing. If necessary, steps should be taken
to ensure adequate drainage in the future (i.e.,
retrofit edge drains, free draining shoulder
materials, geotextiles, etc.).
When underdrains are present, they should
be cleaned, video inspected, and repaired as
necessary.
Construction
Construction steps include preoverlay repairs,
milling, surface cleaning, concrete placement,
curing, joint sawing, and sealing.
Preoverlay Repairs
Before the milling operation commences,
areas with potholes; localized, moderate-
to-severe alligator cracking; or loss of base/
subgrade support will require partial or
full-depth spot repairs to provide uniform
bonding and to achieve the desired load-
carrying capacity and long-term durability; see
Table 3.
e milled surface should be inspected for
isolated pockets of deterioration that require
further repairs. For isolated areas that have
a high number of wide transverse thermal
cracks, a decision needs to be made whether
to bridge the cracks with the bonded overlay
or to clean and fill the cracks. Concrete can
span normal asphalt longitudinal and trans-
verse cracks. Filling old cracks with sand,
flowable fill, or other appropriate material is
necessary only for cracks that have an opening
greater than the maximum-size aggregate used
in the overlay.
Milling
In general, milling should be minimized
because it results in loss of structural support.
ere is no reason to mill off good asphalt
that can contribute to composite action and
continue to help carry traffic loads.
Typically, milling all asphalt surfaces to
improve bonding is not required. e main
objectives of milling prior to placing a bonded
overlay are (1) to remove significant surface
distortions that contain soft asphaltic mate-
rial, which would result in an inadequate
bonding surface; (2) to reduce high spots
to help ensure minimum overlay depth and
reduce the quantity of concrete needed to fill
low spots; and (3) to match curb or adjacent
structure elevations.
Matching existing features or minimizing the
vertical change in profile grade will often be
the primary criteria for determining the mill-
ing depth. When this is the case, a thorough
evaluation of the thickness and condition of
the existing asphalt pavement must be per-
formed to assure that the remaining asphalt to
be overlaid is sound and thick enough to pro-
vide structural support for carrying loads.
29
Guide to Concrete Overlays 29
Guide to Concrete Overlays
Ch 3. OVERLAY OPTIONS
When milling the existing pavement to a
specific profile and/or cross slope is being
considered, assure that there is adequate pave-
ment depth to maintain a minimum 3 inches
of sound asphalt for bonding after the milling
is completed.
Most surface distresses can be removed
through milling. Milling may be used where
surface distortions are 2 in. (50 mm) or
greater. e amount of asphalt removed
depends on the types and severity of distresses
and the thickness of the asphalt. Milling can
be used to remove gross irregularities that
would cause quantity overruns in the volume
of concrete needed for the overlay; it is not
necessary to obtain a perfect cross section
or to completely remove ruts. If a stripped
(loose) layer of asphalt is encountered, it
must be completely removed to provide a
sound structural layer for bonding. e mini-
mum thickness of structurally sound asphalt
required for bonding is 3 inches.
Construction traffic—specifically, trucks
loaded with concrete—can cause significant
damage to the remaining asphalt pavement.
An adequate layer of asphalt is required to
prevent delamination, thus ensuring that
the asphalt will function as a load-carrying
portion of the composite section (not as
a separation layer or shear plane, as in an
unbonded overlay). Some construction traf-
fic, however, can be placed on the milled
surface to identify any loose material (i.e.,
partial lifts, deteriorated asphalt, isolated
areas of stripping, etc.) remaining after the
milling operation. All unsound areas should
be removed prior to performing any further
operations.
While the milling machine is on site, it is
important that the pavement surface be
inspected to determine if additional milling is
required.
Surface Cleaning
Following repairs, the asphalt surface should
be cleaned to ensure adequate bonding
between the existing asphalt surface and the
new concrete overlay. Adequate bonding is
very important to the performance of this
type of overlay. Cleaning may be accom-
plished by first sweeping the asphalt surface,
then cleaning with compressed air. If material
is subsequently tracked onto the pavement
surface, the surface must be re-cleaned.
Pressure washing should be considered only
when dust control is mandated or when mud
has been tracked onto the milled surface. In
no case should water or moisture be allowed
to stand on the asphalt pavement prior to
overlay placement. To prevent contamination,
it is important to avoid a lengthy lag time
between final surface cleaning and paving.
Concrete Placement
When the surface temperature of the asphalt
is at or above 120°F (49°C), sprinkling the
surface with water can reduce the temperature
and minimize the chance of early-age crack-
ing. No standing water should remain on the
surface at the time the overlay is placed. Water
trapped in the milled surface can be blown off
with compressed air.
Once the surface of the existing asphalt
pavement has been prepared, paving is accom-
plished using either conventional fixed-form
or slipform construction. Because of the non-
uniform thickness of concrete, the concrete
material is bid on a cubic-yard basis. Some
states also include a bid item for placement on
a square-yard basis.
Curing
Curing is especially critical on a bonded
concrete overlay because its high surface
area-to-volume ratio makes the thin concrete
overlay more susceptible to rapid moisture
loss. Within 30 minutes of placing the over-
lay, curing compound should be applied at
twice the standard rate. e finished product
should appear as a uniformly painted solid
white surface, with the vertical faces along the
edges of the overlay also thoroughly coated.
Joint Sawing
Timely joint sawing is necessary to prevent
random cracking. Joint sawing should com-
mence as soon as the concrete has developed
sufficient strength so that joints can be cut
without significant raveling or chipping.
Lightweight early-entry saws may be used to
allow the sawing crew to get on the pavement
as soon as possible. With typical joint spacing
of 3 to 6 feet, extra saws will likely be needed
to avoid random cracking. Transverse joints
can be sawed with conventional saws set to a
depth of T/3. Transverse joint saw-cut depths
for early-entry sawing should not be less than
1.25 in. (31 mm). Longitudinal joints should
be sawed to a depth of T/3.
Joint Sealing
Contraction and construction joints should
be filled with a hot-poured joint sealant (the
use of backer rod is not recommended).
Future Repairs
Bonded concrete overlays on asphalt may be
easily repaired using full-panel replacement.
Another option is simply to mill and inlay
with concrete. Do not patch with asphalt,
because the adjacent concrete panels will
move and break the bond. If a panel is dis-
tressed but the ride quality of the pavement is
not compromised, the panel should be left in
place. If a ride-quality problem develops, the
panel should be replaced before any pieces of
concrete become loose from the overlay.
Key Resources
ACI Committee 325 (2006); ACPA (1999);
MnDOT (2013); Rasmussen and Rozycki
(2004); Vandenbossche (2013)
Guide to Concrete Overlays
30
Ch 3. OVERLAY OPTIONS
Figure 22 illustrates a composite pave-
ment that may be a candidate for a bonded
concrete overlay, along with the kinds of pre-
overlay repairs that may be appropriate.
Bonded Concrete Overlay on Composite Pavements
Figure 22. Bonded concrete overlay of fair or better condition composite pavement with asphalt
surface distresses
Existing composite pavement
with asphalt surface distresses
Milled and cleaned
surface
New 2–6 in. (50–150 mm)
thick bonded concrete overlay
with square panels
Application and Uses
Bonded concrete overlays on composite
(asphalt on concrete) pavements
• May be appropriate for composite roads,
streets, and intersections in fair or better
structural condition with typical distresses
such as rutting, shoving, slippage, and ther-
mal cracking; see Figure 23
• Are generally 2–6 in. (50–150 mm) thick
• Rely on the existing asphalt pavement to
provide additional load-carrying capacity,
and bond to the existing composite pave-
ment to form a monolithic section, thereby
reducing stresses and deflections
• Add structural capacity where traffic loads
have increased or are anticipated to increase
• Eliminate surface defects such as rutting
and shoving
• Improve surface characteristics (friction,
noise, and smoothness)
• Reduce urban heat island effect by increas-
ing pavement surface albedo Figure 23. Bonded overlay of asphalt
31
Guide to Concrete Overlays 31
Guide to Concrete Overlays
Ch 3. OVERLAY OPTIONS
Performance
Bonded concrete overlays have been success-
fully used in many states to maintain and
rehabilitate composite pavements with surface
defects; see Figures 24 and 25. e key to
long-term performance is ensuring the two
structures—the existing composite pavement
and the overlay—move as one structure.
Keys to Success
e following actions will help ensure a suc-
cessful project:
• An effective bond between the layers of the
composite pavement is necessary.
• A quality bond between the concrete over-
lay and the composite pavement system is
beneficial.
• Milling of existing asphalt may be required
to eliminate or reduce surface distortions of
2 in. (50 mm) or more and to help provide
a good bond.
• A minimum of 3 in. (75 mm) of asphalt
should remain after milling.
• Minimal spot repairs may be required.
• e asphalt surface should be sprinkled
with water when the surface temperature is
greater than 120ºF (49ºC) during overlay
placement.
• A clean surface is critical to achieving an
adequate bond between the overlay and the
underlying asphalt.
• An appropriate panel size should be estab-
lished with respect to the thickness of the
concrete overlay, and it should preferably be
sawed in small square panels.
Figure 24. Existing composite pavement (source: James Cable, Iowa
State University)
Figure 25. Bonded on composite pavement (source: James Cable,
Iowa State University)
FAQ—What if the existing concrete pavement has MRD below the asphalt surface?
Material-related distresses such as D-cracking, alkali-silica reaction, and freeze-thaw
joint deterioration can sometimes be difficult to detect in the underlying concrete pave-
ment. ese distresses can lead to a loss of support and premature failure of the bonded
concrete overlay. Caution should be used when considering a bonded overlay when these
conditions are present. Improving the drainage of the subgrade/subbase below the exist-
ing concrete (i.e., retrofit edge drains) can slow the progression of MRDs and potentially
extend the life of a proposed bonded concrete overlay.
• Transverse joints must be sawed T/3 (with
special attention to thickened overlay over
asphalt ruts and other nonuniform areas).
• When feasible, design the longitudinal
joints to be outside of the normal wheel
paths.
• inner overlays may shorten the sawing
window; additional saws are likely to be
required.
• Application of curing compound or other
curing methods must be timely and thor-
ough, especially at edges.
• Sealing joints may improve performance.
• No notable stripping or delamination at
tack lines should exist in asphalt pavement
to remain after milling.
Overlay Process
e overlay project consists of pavement
evaluation, design, construction, and future
repairs.
Pavement Evaluation
An evaluation of the existing asphalt pavement
is necessary (1) to ensure it is structurally
adequate to carry the anticipated traffic loads,
(2) to determine required milling depths, and
(3) to establish the bonded overlay design
thickness. For general information on pave-
ment evaluation, see Chapter 2.
Composite pavements are not good candi-
dates for bonded overlays of less than 6 in.
(125 mm) if they display any of the following
problems:
• Significant structural deterioration, inade-
quate or uneven subgrade/subbase support,
poor drainage conditions, or stripping or
delamination of asphalt layers
• Problems in the underlying concrete (pos-
sibly reflected in the asphalt layer) due to
MRD
• Indications of possible future durability
problems
Overlay Design
Design elements include overlay thickness,
mixture design, joints, and drainage.
Overlay Thickness
e design thickness for bonded concrete
overlays is typically 2–6 in. (50–150 mm),
depending on the desired load-carrying
capacity and service life as well as the struc-
tural capacity provided by the underlying
pavement.
Guide to Concrete Overlays
32
Ch 3. OVERLAY OPTIONS
e recommended thickness design pro-
cedures are those used by the American
Concrete Pavement Association’s Bonded
Concrete Overlay on Asphalt (BCOA)
ickness Designer (2012) or the BCOA ME
(Vandenbossche 2013). For more informa-
tion on these procedures, see Table 10 in
Chapter 4.
Mixture Design
Conventional concrete mixtures have been
successfully used for bonded concrete overlays
of asphalt pavements. When accelerated open-
ing is desired, conventional concrete mixtures
should be proportioned for rapid strength
gain without increasing shrinkage properties.
For additional information on accelerated
mixtures, see page 76.
e use of high-modulus structural fibers
can improve the toughness and postcracking
behavior of the concrete and help mitigate the
effects of plastic shrinkage cracking, should it
occur. For more information, see page 77 and
Appendix C.
Joint Design
e recommended joint pattern for bonded
overlays of asphalt is small square panels, typi-
cally in the range of 3–8 ft (0.9–2.4 m), to
reduce differential movements between the
concrete overlay and asphalt and to reduce
curling and warping stresses. It is recom-
mended that the length and width of joint
squares in feet be limited to 1.5 times the
overlay thickness in inches. In addition,
if possible, longitudinal joints should be
arranged so that they are not in the wheel
path. e use of tiebars or dowels is not neces-
sary because of the small panel size.
In the past, bonded overlays less than or equal
to 6-inches thick have typically left the joints
unsealed. Studies performed by the Minnesota
DOT (2013) have shown improved perfor-
mance when joints are sealed. Because the
concrete overlay is bonded to the underlying
asphalt pavement, moisture that is allowed to
infiltrate open joints has nowhere to drain,
eventually weakening the bond and resulting
in premature cracking of the slabs.
Drainage
Stripping or delamination in the upper 3
inches of the remaining asphalt layers to be
overlaid can lead to premature failure of the
bonded concrete overlay.
During evaluation and design of a bonded
concrete overlay project, existing subgrade
drainage should be evaluated, as would be
done with asphalt resurfacing. If necessary,
steps should be taken to ensure adequate
drainage in the future (i.e., retrofit edge
drains, free draining shoulder materials, geo-
textiles, etc.).
When underdrains are present, they should
be cleaned, video inspected, and repaired as
necessary.
Construction
Construction steps include preoverlay repairs,
milling, surface cleaning, concrete placement,
curing, joint sawing, and sealing.
Preoverlay Repairs
Before the milling operation commences,
areas with potholes; localized, moderate-
to-severe alligator cracking; or loss of base/
subgrade support will require partial or full-
depth spot repairs with asphalt to provide
uniform bonding and to achieve the desired
load-carrying capacity and long-term durabil-
ity; see Table 4.
Existing Pavement Distress Spot Repairs to Consider
Rutting ≥ 2 in. (50 mm) Mill
Rutting < 2 in. (50 mm) None or mill
Shoving, slippage Mill
Crack width ≥ maximum coarse aggregate
size used in the concrete overlay mixture
Fill with flowable fill.
Crack width < maximum coarse aggregate
size used in the concrete overlay mixture
None
Low- to medium-severity pothole Remove loose material and fill integrally with the concrete
overlay.
High-severity pothole and/or areas needing
full-depth repair
To prevent a single overlay panel from bonding to both
asphalt and concrete, make full-depth repairs across a full
lane width with concrete and adjust the transverse joint
spacing in the concrete overlay to match the location of
the underlying patch. The full lane width prevents trying to
match a longitudinal joint for a partial lane patch.
Table 4. Possible Preoverlay Repairs on Existing Composite Pavement in Preparation for
Bonded Overlay
e milled surface should be inspected for
isolated pockets of deterioration that require
further repairs. For isolated areas that have
a high number of wide transverse thermal
cracks, a decision needs to be made whether
to bridge the cracks with the bonded over-
lay or to clean and fill the cracks. Concrete
can span normal asphalt longitudinal and
transverse cracks. Filling old cracks with fly
ash slurry, concrete grout, flowable mortar,
or other appropriate material is necessary
only for cracks that have an opening greater
than the maximum-size aggregate used in the
bonded overlay.
Panel tenting (early stages of blowups) may be
an indication that there is a void under exist-
ing panels. Sections with significant tenting
should be repaired to relieve the pressure and
provide uniform support before construction
of a bonded overlay.
If there is vertical movement of the underlying
concrete adjacent to a crack, the movement
can be stopped by replacing or retrofitting
the joint. e crack can also be controlled
without repairing the underlying pavement by
adding fibers to the mixture or, in some cases,
by placing reinforcing steel over the joint in
the overlay. Typically, 36-in. (900-mm) long
no. 4 bars are stapled to the existing pavement
at 30-in. (750-mm) spacings perpendicular to
the crack.
Milling
In general, milling should be minimized
because it results in loss of structural support.
ere is no reason to mill off good asphalt
that can contribute to composite action and
continue to help carry traffic loads.
Typically, milling all asphalt surfaces to
improve bonding is not required. e main
objectives of milling prior to placing a bonded
overlay are (1) to remove significant surface
distortions that contain soft asphaltic mate-
rial, which would result in an inadequate
bonding surface; (2) to reduce high spots
to help ensure minimum overlay depth and
reduce the quantity of concrete needed to fill
low spots; and (3) to match curb or adjacent
structure elevations. Milling may also be
considered to roughen the surface, which will
likely enhance bonding.
Matching existing features or minimizing the
vertical change in profile grade will often be
the primary criteria for determining the mill-
ing depth. When this is the case, a thorough
evaluation of the thickness and condition of
the existing asphalt pavement must be per-
formed to assure that the remaining asphalt to
be overlaid is sound and thick enough to pro-
vide structural support for carrying loads.
33
Guide to Concrete Overlays 33
Guide to Concrete Overlays
Ch 3. OVERLAY OPTIONS
When milling the existing pavement to a
specific profile and/or cross slope is being
considered, assure that there is adequate pave-
ment depth to maintain a minimum 3 inches
of sound asphalt for bonding after the milling
is completed.
Most surface distresses can be removed
through milling; see Table 4. Milling may
be used where surface distortions are 2 in.
(50 mm) or greater. e amount of asphalt
removed depends on the types and severity
of distresses and the thickness of the asphalt.
e objective of milling is to remove gross
irregularities that would cause quantity over-
runs in the volume of concrete needed for the
overlay; it is not necessary to obtain a perfect
cross section or to completely remove ruts. If
a stripped (loose) layer of asphalt is encoun-
tered, it must be completely removed to
provide a sound structural layer for bonding.
e minimum thickness of structurally sound
asphalt required for bonding is 3 inches.
Construction traffic—specifically, trucks
loaded with concrete—can cause significant
damage to the remaining asphalt pavement.
An adequate layer of asphalt is required to
prevent delamination, thus ensuring that
the asphalt will function as a load-carrying
portion of the composite section (not as
a separation layer or shear plane, as in an
unbonded overlay). When possible, however,
some construction traffic should be placed
on the milled surface to identify any loose
material (i.e., partial lifts, deteriorated asphalt,
isolated areas of stripping, etc.) remaining
after the milling operation. All unsound areas
should be removed prior to performing any
further operations.
While the milling machine is on site, it is
important that the pavement surface be
inspected to determine if additional milling is
required.
Surface Cleaning
Following repairs, the asphalt surface should
be cleaned to ensure adequate bonding
between the existing asphalt surface and the
new concrete overlay. Adequate bonding is
very important to the performance of this
type of overlay. Cleaning may be accom-
plished by first sweeping the asphalt surface,
then cleaning with compressed air. Pressure
washing should be considered only when
dust control is mandated or when mud has
been tracked onto the milled surface. In no
case should water or moisture be allowed to
stand on the asphalt pavement prior to over-
lay placement. To prevent contamination,
it is important to avoid a lengthy lag time
between final surface cleaning and paving.
Concrete Placement
When the surface temperature of the asphalt
is at or above 120°F (49°C), sprinkling the
surface with water can reduce the temperature
and minimize the chance of early-age crack-
ing. No standing water should remain on
the surface at the time the overlay is placed.
Water trapped in the milled surface can be
blown off with compressed air.
Once the surface of the existing asphalt
pavement has been prepared, paving is
accomplished using either conventional fixed-
form or slipform construction. Because of
the nonuniform thickness of concrete, the
concrete material is bid on a cubic-yard basis.
Some states also include a bid item for place-
ment on a square-yard basis.
Curing
Curing is especially critical on a bonded
concrete overlay because its high surface
area-to-volume ratio makes the thin concrete
overlay more susceptible to rapid moisture
loss. Within 30 minutes of placing the over-
lay, curing compound should be applied at
twice the standard rate. e finished product
should appear as a uniformly painted solid
white surface, with the vertical faces along the
edges of the overlay also thoroughly coated.
Joint Sawing
Timely joint sawing is necessary to prevent
random cracking. Joint sawing should com-
mence as soon as the concrete has developed
sufficient strength so that joints can be cut
without significant raveling or chipping.
Lightweight early-entry saws may be used to
allow the sawing crew to get on the pavement
as soon as possible. With typical joint spacing
of 3 to 6 feet, extra saws will likely be needed
to avoid random cracking. Transverse joints
can be sawed with conventional saws set to a
depth of T/3. Transverse joint saw-cut depths
for early-entry sawing should not be less than
1.25 in. (31 mm). Longitudinal joints should
be sawed to a depth of T/3.
Joint Sealing
Contraction and construction joints should
be filled with a hot-poured joint sealant (the
use of backer rod is not recommended).
Future Repairs
Bonded concrete overlays on composite pave-
ments may be easily repaired using full-panel
replacement. Another option is simply to mill
and inlay with concrete. Do not patch with
asphalt, because the adjacent concrete panels
will move and break the bond. If a panel is
distressed but the ride quality of the pavement
is not compromised, the panel should be left
in place. If a ride-quality problem develops,
the panel should be replaced before any pieces
of concrete become loose from the overlay.
Key Resources
ACI Committee 325 (2006); ACPA (1999);
MnDOT (2013); Rasmussen and Rozycki
(2004); Vandenbossche (2013)
Guide to Concrete Overlays
34
Ch 3. OVERLAY OPTIONS
Bonded Concrete Overlay on Concrete Pavements
Figure 26. Bonded concrete overlay of good condition concrete pavement with surface distresses
Existing concrete pavement
with surface distresses
Prepared surface
Monolithic pavement with
new concrete surface
Application and Uses
Bonded concrete overlays on concrete
pavements
• May be appropriate for concrete pavements
in good structural condition and with lim-
ited surface distresses; see Figure 27
• Are generally 2–5 in. (50–125 mm) thick
• Eliminate surface defects such as extensive
scaling or surface cracking and/or improve
surface characteristics like friction, noise,
and smoothness
• Enhance structural capacity to accommo-
date increase in traffic loads
Performance
When properly considered, designed,
specified, and constructed, bonded concrete
overlays of concrete pavements have been suc-
cessfully used for many years as a means of
strengthening existing concrete pavements, Figure 27. Bonded concrete on concrete
Figure 26 illustrates a concrete pavement that
may be a candidate for a bonded concrete
overlay, along with the kinds of preoverlay
repairs that may be appropriate.
35
Guide to Concrete Overlays 35
Guide to Concrete Overlays
Ch 3. OVERLAY OPTIONS
providing a new smooth surface, and repairing
surfaces with surface defects such as scaling,
high steel, plastic shrinkage cracks, etc.; see
Figures 28 and 29.
ey do not, however, have as high a success
rate as other types of concrete overlays, pri-
marily because of the increased attention to
detail required in all phases that is sometimes
overlooked in the execution of a project. e
goal is to ensure the layers are bonded and
react monolithically to loads. e design,
specification, construction, and field supervi-
sion of any proposed bonded overlays over
concrete require a commitment to proper
technique. For best results, projects should be
supervised by engineers and contractors expe-
rienced with this technology. Special attention
needs to be given to the following items to
prevent premature failure:
• A proper assessment of whether or not an
existing concrete pavement is an appro-
priate candidate for the technique is
imperative. A majority of failures of bonded
concrete overlays on concrete pavements
are the result of improper assessment of the
existing pavement.
• e existing concrete pavement must be in
good condition or brought to good condi-
tion and cleaned effectively in order for
the overlay and existing pavement to bond
monolithically. If debonding occurs, it leads
to structural failure in the form of fatigue
cracking.
• Proper specifications or supplemental speci-
fications adapted for the specific project are
necessary.
• Poor or improper surface preparation and
cleaning may also lead to debonding and
cracking.
• e thermal compatibility (assessed by
coefficient of thermal expansion, or CTE)
between the overlay and existing pavement
needs to be addressed. Differential aggre-
gate movement between the overlay and
existing pavement can lead to debonding of
the overlay.
• Inadequate curing and/or using oversized
slab dimensions will induce higher curl-
ing and warping stresses that can stress
the bond between the layers and lead to
debonding.
Keys to Success
e following actions will help ensure a suc-
cessful project:
• Existing concrete pavement should either
be in good condition or be cost effectively
brought to good condition through repairs
or milling.
• e existing pavement surface must be pre-
pared to enhance bonding to the overlay.
• e overlay’s aggregate thermal properties
(CTE) must be similar to (or lower than)
those of the existing pavement to minimize
shear stress in bond.
• Working cracks in the existing pavement
should be repaired (or the overlay should be
sawed over the crack) to prevent the crack
from reflecting through the overlay.
• Existing joints must be in fair condition or
repaired.
• inner overlays may shorten the sawing
window.
• Transverse joints in the overlay must be
sawed full depth plus 0.50 in. (12 mm),
and longitudinal joints must be sawed to a
depth of at least T/2.
• Joints in the overlay must align with those
of existing pavement because the structure
must move monolithically.
• e width of transverse joints in the over-
lay must be equal to or greater than the
underlying crack width at the bottom of
the existing transverse joint (see the follow-
ing page).
• An application of a curing compound or
other curing methods must be timely and
thorough, especially at the edges.
• To minimize curling and warping stresses,
some agencies have successfully created
smaller overlay panels by sawing additional
transverse and longitudinal joints in the
overlay between the matched joints.
Overlay Process
e overlay project consists of pavement
evaluation, design, construction, and future
repairs.
Pavement Evaluation
An evaluation of the existing concrete pave-
ment is necessary to ensure that it is a good
candidate for a bonded overlay and that,
once resurfaced, it will be structurally sound
enough to carry anticipated traffic loads. For
general information on pavement evaluation,
see Chapter 2.
If an existing concrete pavement exhibits
cracking from expansion caused by MRD,
such as ASR or D-cracking, it is not a good
candidate for a bonded concrete overlay
(see page 13 for a discussion of MRD). An
unbonded overlay may be considered.
Figure 28. Photo of concrete pavement with shotblast surface prior to
concrete overlay in 1994 (source: Todd Hanson, Iowa DOT)
Figure 29. Three-inch concrete bonded overlay (photo dated 2013)
(source: Todd Hanson, Iowa DOT)
Guide to Concrete Overlays
36
Ch 3. OVERLAY OPTIONS
Overlay Design
Design elements include overlay thickness,
mixture design, joints, and drainage.
Overlay Thickness
A bonded concrete overlay relies on the
existing concrete pavement as an integral
structural component to carry traffic loading.
e overlay is bonded to the existing con-
crete pavement to form a monolithic section,
thereby reducing stresses and deflections.
Under certain conditions, a mill and inlay
can be used if the existing pavement has
significant surface issues but is structurally
sound and the subbase/subgrade is stable
(Harrington et al. 2014).
e design thickness for bonded concrete
overlays is typically 2–5 in. (50–125 mm),
depending on the desired load-carrying
capacity and service life as well as the struc-
tural capacity provided by the underlying
pavement. Some states, such as Colorado,
have used 6-in. (150-mm) bonded overlays
on high-traffic roads.
ickness is commonly determined using
an established design procedure such as the
AASHTO Guide for Design of Pavement
Structures (AASHTO 1993, 1998). Agencies
are becoming increasingly familiar, however,
with the procedure in the Mechanistic-
Empirical Pavement Design Guide (M-E PDG)
(AASHTO 2008) as well. For more informa-
tion, see Table 10 in Chapter 4.
Mixture Design
Conventional concrete mixtures have been
successfully used for bonded concrete overlays
of concrete pavements. When accelerated
opening is desired, conventional concrete
mixtures should be proportioned for rapid
strength gain without increasing shrinkage
properties. For additional information on
accelerated mixtures, see page 76.
e use of high-modulus structural fibers
can improve the toughness and postcracking
behavior of the concrete and help mitigate the
effects of plastic shrinkage cracking, should it
occur. For more information, see page 77 and
Appendix C.
Regarding concrete aggregate, several issues
should be considered:
• A well graded aggregate will reduce the
water and paste content of the mixture,
thus reducing potential shrinkage and curl-
ing, as well as the related risk of debonding.
• e maximum aggregate size of the overlay
concrete should be one-third of the overlay
thickness.
• Aggregate with CTE similar to or lower
than that of the existing concrete pave-
ment will help ensure the two layers move
together, thus reducing stresses at the bond
interface.
• Pore space in the aggregate should be
fully saturated before batching (moisture
condition greater than saturated-surface-
dry); otherwise, the aggregate will tend to
pull water from the mixture at early ages,
increasing the possibility of shrinkage,
which can lead to debonding.
Joint Design
e bonded overlay joint type, location,
and width must precisely match those of the
existing concrete pavement in order to cre-
ate a monolithic structure. Matched joints
eliminate reflective cracking and ensure that
the two layers of the pavement structure
move together, helping maintain bonding. To
minimize curling and warping stresses, some
agencies have successfully created smaller
overlay panels by sawing additional transverse
and longitudinal joints in the overlay between
the matched joints.
An important element in transverse joint
design is joint dimensions. e depth should
be full depth plus 0.50 in. (13 mm). To pre-
vent debonding, the width of the transverse
joint should be equal to or greater than the
width of the underlying joint or crack in the
existing pavement; see Figure 30.
e width of the existing underlying
pavement crack may be determined by spot-
excavating along the pavement edge. (If the
pavement system experiences expansion and
the overlay pushes against itself because the
width of the transverse overlay joint is less
than the width of the underlying existing
pavement crack, debonding may occur.)
Some agencies believe that T/2 is sufficient for
longitudinal joint depth. Others recommend
sawing longitudinal joints full depth plus 0.50
in. (13 mm) to cut through the bond line.
Tiebars, dowel bars, or other embedded steel
products are not used in bonded concrete
overlays to minimize restraint forces in the
bond.
Except for joint design, bonded overlays on
existing continuously reinforced concrete
pavements (CRCP) are designed, prepared,
and constructed the same way as bonded
concrete overlays on jointed plain concrete
pavements (JPCP). Transverse joints are not
cut in bonded concrete overlays over CRCP
pavements. Acceptable cracking will occur
in the bonded overlay, typically (but perhaps
not immediately) over existing cracks in the
CRCP.
Drainage
During evaluation and design of a bonded
concrete overlay project, existing subgrade
drainage should be evaluated, as would be
done with asphalt resurfacing. If necessary,
steps should be taken to ensure adequate
drainage in the future (i.e., retrofit edge
drains, free draining shoulder materials, geo-
textiles, etc.).
When underdrains are present, they should
be cleaned, video inspected, and repaired as
necessary.
Construction
Construction steps include preoverlay repairs,
milling, surface cleaning, concrete placement,
curing, and joint sawing.
Preoverlay Repairs
Preoverlay repairs of certain distresses may be
necessary to achieve the desired load-carrying
capacity and long-term durability. e surface
should be inspected for isolated pockets of
deterioration that require repairs; see Table 5.
For isolated areas that have wide random
cracks or working joints, full-depth repairs
may be necessary. When cracks (particularly
working cracks) exist in the pavement to be
resurfaced, reflective cracking will almost
Figure 30. Width of transverse joint in bonded concrete overlay on concrete pavement should
be equal to or greater than width of crack in existing pavement
Note: Overlay joint width shall be equal to or
greater than crack in the existing slab.
If “X” is 0.50 in. (13 mm) or greater, the underlying
crack width in the existing slab should be
measured. If crack is 0.25 in. (6.4 mm) or greater,
and existing pavement does not have dowel bars,
the joints should be evaluated to determine if load
transfer rehabilitation is required to eliminate
faulting. If there are numerous joints of this type,
the existing pavement may not be a good
candidate for a bonded overlay.
Width of new
overlay
transverse joint
Concrete
overlay
Underlying crack
in existing slab
Saw cut in
existing slab (X)
Overlay joint
37
Guide to Concrete Overlays 37
Guide to Concrete Overlays
Ch 3. OVERLAY OPTIONS
Table 5. Possible Preoverlay Repairs on Existing Concrete Pavement in Preparation for
Bonded Overlay
Existing Pavement Distress Spot Repairs to Consider
Random cracks Reflective cracking is likely if no repairs are made; use crack cages or
full-depth repairs for severe cracks
Faulting Slab stabilization
Pumping Slab stabilization
Asphalt patch Replace with concrete patch to ensure bonding
Joint spalling Partial-depth repair
Scaling Remove with cleaning
always occur. Crack cages over existing non-
working cracks have been successfully used to
prevent reflective cracking; see Figure 31.
When voids are detected under existing slabs,
the slabs should be stabilized through grout
injection or other methods. Asphalt patches
should be removed and replaced with con-
crete patches (or simply filled with concrete
at the time of overlay placement) to ensure
bonding of the concrete layers.
A consideration in performing repairs is
whether or not movement in the underlying
pavement will cause movement in the overlay.
Any movement in the overlay that does not
occur at matched joints could contribute
to debonding and subsequent failure of the
overlay.
Surface Preparation
Surface preparation of the existing concrete
pavement is accomplished to produce a
roughened surface that will enhance bonding
between the two layers. A variety of surface
preparation procedures may be used, includ-
ing shotblasting, milling, high water-pressure
blasting, and sandblasting.
Figure 31. Crack cage over concrete pavement crack (source: James Cable)
e most commonly used and most effective
surface preparation procedure is shotblasting.
Although milling will roughen the concrete
pavement surface, milling should not be used
solely for that purpose because of its potential
for causing surface microcracking and fractur-
ing the exposed aggregate. If milling is used
to lower the pavement elevation, any resulting
microcracking should be removed by shot-
blasting or high water-pressure blasting.
Surface Cleaning
Following surface preparation, the concrete
surface should be cleaned to ensure adequate
bonding between the existing concrete surface
and the new concrete overlay. Cleaning may
be accomplished by sweeping the concrete
surface, followed by cleaning in front of the
paver with compressed air. If material is sub-
sequently tracked onto the pavement surface,
the surface must be re-cleaned. Paving should
commence soon after cleaning to minimize
the chance of contamination.
Vehicles should be limited on the existing
surface after it is prepared. If it is absolutely
necessary to have vehicles on the existing
concrete, care should be taken that they do
not drip oil or other contaminants that could
compromise the bond.
Concrete Placement
Grade adjustments may be made to ensure
the required thickness of the concrete.
Conventional concrete paving practices and
procedures are followed for bonded concrete
overlays. A bonding grout or epoxy coating
of the existing surface to enhance bond is not
required.
Curing
Curing is especially critical on a bonded
concrete overlay because its high surface-area-
to-volume ratio makes the thin concrete
overlay more susceptible to rapid moisture
loss. Within 30 minutes of placing the overlay,
curing compound should be applied at twice
the standard rate. e finished product should
appear as a uniformly painted solid white sur-
face, with the vertical faces along the edges of
the overlay also thoroughly coated.
Joint Sawing
Timely joint sawing is necessary to prevent
random cracking. Sawing should begin as
soon as the concrete is strong enough that
joints can be cut without significant raveling
or chipping.
If lightweight early entry saws are used for
transverse joints, it must be remembered that
the depth of the saw cut must be the thickness
of the overlay plus 0.5 inch and the width of
the saw cut must be equal to or greater than
the width of the underlying joint or crack
in the existing pavement. is may require
resawing the transverse joint with a conven-
tional saw to meet these requirements.
To help match transverse joint locations, place
guide nails on each edge of the existing pave-
ment at the joints; after the overlay is placed,
mark the joint with a chalk line connecting
the guide nails.
Future Repairs
e recommended repair option for bonded
concrete overlays on concrete is full-panel
replacement. Concrete panels are easily
removed and replaced. Another option is sim-
ply to mill and inlay with concrete. If a panel
is cracked or otherwise distressed but the ride
quality of the pavement is not compromised,
the panel may be left in place.
Key Resources
ACI Committee 325 (2006); ACPA (1990a);
Trevino et al. (2004)
Guide to Concrete Overlays
38
Ch 3. OVERLAY OPTIONS
Unbonded Concrete Overlay on Asphalt Pavements
Figure 32 illustrates an asphalt pavement that
may be a candidate for an unbonded concrete
overlay, along with the kinds of preoverlay
repairs that may be appropriate.
Figure 32. Unbonded concrete overlay (previously called conventional whitetopping) of poor-to-deteriorated
condition asphalt pavement
Existing deteriorated
asphalt pavement
New unbonded overlay
Need for milling determined based
on degree of surface distortions
Application and Uses
Unbonded concrete overlays on asphalt
pavements
• May be appropriate for asphalt pavements
with significant deterioration such as
severe rutting, potholes, alligator crack-
ing, subgrade/subbase issues, shoving, and
pumping; see Figure 33
• Are generally 4–11 in. (100–280 mm) thick
(JPCP or CRCP)
• Are essentially designed as a new concrete
pavement on a stable base course, assuming
an unbonded condition between the layers
• Restore or increase the structural capacity
of existing pavement
• Eliminate surface defects such as rutting
and shoving
• Improve surface characteristics (friction,
noise, and smoothness)
• Reduce urban heat island effect by increas-
ing pavement surface albedo Figure 33. Unbonded concrete overlay of asphalt pavement
39
Guide to Concrete Overlays 39
Guide to Concrete Overlays
Ch 3. OVERLAY OPTIONS
Performance
Unbonded overlays of asphalt pavements
have been successfully used in many states,
with more than 30 years of good-to-excellent
performance in states such as California and
Iowa. See Figures 34 and 35. Unbonded
overlays over asphalt do not require extensive
preoverlay repairs, but spot repairs of certain
areas may be necessary to minimize local-
ized failures. ough this overlay type does
not rely on bonding, some partial bonding
between the overlay and existing asphalt pave-
ment may occur and can contribute to better
performance of the pavement.
Keys to Success
e following actions will help ensure a suc-
cessful project:
• Milling of existing asphalt may be required
to eliminate surface distortions of 2 in. (50
mm) or more.
• Full-depth repairs should be considered
only at isolated spots where structural
integrity needs restoring.
• Concrete patches in the existing asphalt
pavement surface should be separated from
the overlay with a thin layer of geotextile
fabric or other bond breaker.
• Shorter joint spacing in the overlay can
help reduce curling and warping stress.
• Joints should be sawed in the overlay as
soon as possible because the sawing window
may be shorter than it typically is for full-
depth pavements.
• e asphalt surface should be sprinkled
with water when the surface temperature is
greater than 120ºF (49ºC) during overlay
placement.
Figure 34. Poor to deteriorated asphalt pavement to be resurface
(source: Todd Hanson, Iowa DOT)
Figure 35. Poor to deteriorated asphalt pavement resurfaced with
unbonded concrete overlay (source: Kevin Merryman, Iowa DOT)
• Partial bonding between the overlay and
the asphalt layer of the existing composite
pavement is acceptable and may improve
load-carrying capacity.
• No notable asphalt stripping should exist in
the asphalt after milling.
Overlay Process
e overlay project consists of pavement
evaluation, design, construction, and future
repairs.
Pavement Evaluation
An evaluation of the existing asphalt pave-
ment is necessary to ensure it is a good
candidate for an unbonded overlay. e objec-
tives of the evaluation are to (1) estimate the
existing pavement’s structural contribution as
a subbase, (2) determine the type and extent
of preoverlay repairs, and (3) characterize key
inputs to the overlay design (e.g., the founda-
tion support value should be determined to
establish a thickness design that accounts for
the contribution of the asphalt layer[s]).
Asphalt pavements are good candidates for
unbonded overlays if the existing asphalt
layer(s) can provide, or can be cost-effectively
repaired to provide, a uniform, stable platform
for the overlay.
For general information on pavement evalua-
tion, see Chapter 2.
Overlay Design
Design elements include using the existing
pavement as a base, overlay thickness, mixture
design, joints, and drainage.
Existing Pavement as Base
In an unbonded overlay design, the existing
asphalt pavement is considered as a stable
base, and the overlay is designed essentially as
a new concrete pavement. e design assumes
an unbonded condition between the layers.
ere are two approaches to assessing the
potential structural contribution of the exist-
ing asphalt pavement to the new pavement
system. e approach in the AASHTO Guide
for Design of Pavement Structures (AASHTO
Design Guide) (1993, 1998) considers the
modulus of subgrade reaction (k-value). e
M-E PDG (AASHTO 2008) considers both
friction and k-value.
Overlay Thickness
Unbonded overlay thicknesses typically range
from 4 to 11 in. (100 to 280 mm). Unlike
bonded overlays where there is a minimum
thickness of asphalt required for structural
support, the existing asphalt need only pro-
vide a stable and uniform subbase for the
unbonded overlay. Regardless of whether the
asphalt will be milled because of vertical con-
straints or remain in its existing condition, the
minimum thickness of asphalt to be overlaid
must be adequate to provide a stable working
platform capable of withstanding all antici-
pated construction traffic (specifically, trucks
loaded with concrete); this would typically be
3–4 inches of remaining asphalt or equivalent
support from other underlying materials such
as a chip seal surface(s).
Portions of a project with significantly differ-
ent existing pavement and subbase conditions
can be broken into separate sections and
designed to specifically address those given
conditions.
e AASHTO Design Guide (1993, 1998)
and M-E PDG (AASHTO 2008) provide
design procedures. For more information, see
Chapter 4.
Guide to Concrete Overlays
40
Ch 3. OVERLAY OPTIONS
Mixture Design
Conventional concrete mixtures have been
successfully used for unbonded concrete over-
lays of asphalt pavements. When accelerated
opening is desired, conventional concrete
mixtures should be proportioned for rapid-
strength gain without increasing shrinkage
properties. For additional information on
accelerated mixtures, see Chapter 7.
Joint Design
e load transfer design is the same as for new
concrete pavements. Doweled joints are used
for unbonded overlays of pavements that will
experience significant truck traffic, typically
pavements 7 in. (175 mm) and thicker.
For overlays equal to or less than 6 in. (150
mm) thick, the maximum spacing in feet is
1.5 times the slab thickness in inches.
For overlays greater than 6 in. (150 mm), a
maximum joint spacing in feet of 2 times the
slab thickness in inches is often recommended
for unbonded overlays. A 7-in. (175-mm)
overlay would thus receive a maximum 14-ft
(4.3-m) joint spacing. e maximum recom-
mended spacing is typically 15 ft (4.6 m).
For situations where the design requires
mechanical load transfer across the joints and
the pavement is less than 7 inches in thick-
ness, conventional dowels cause slipform
paving clearance problems. Smaller diameter
dowels do not significantly help the clear-
ance issue and may not provide long-term
load transfer because of potential socketing in
concrete. One solution that should be con-
sidered is the use of structural fibers to help
hold cracks and joints together. Additionally,
the use of plate dowels provides clearance
for the paver and allows for mechanical load
transfer. e performance of plate dowels
in transverse contraction joints is not well
understood in concrete overlay pavements 5
inches or less. ey have, however, been suc-
cessfully used in industrial parking lots. e
effects of exposure of epoxy or galvanized
coated plate dowels to deicing salts is also
limited. It is recommended that a proven and
tested corrosion-resistant surface be required.
Research on plate dowels in concrete overlays
is being conducted at the MnROAD facility
(Burnham and Izevbekhai 2012). See Chapter
4 for additional information on plate dowels.
e use of tiebars for unbonded overlays
should follow conventional use for pavements
5 in. (125 mm) thick or more. Using lane
tiebars may be appropriate in open-ditch (or
shoulder) sections of unbonded overlays if the
overlay is 5 in. (125 mm) or greater. In this
category, a no. 4 tiebar (0.50 in. [13 mm])
may be appropriate. e use of tiebars in
confined curb-and-gutter sections should be
considered if the overlay is 6 in. (150 mm) or
greater.
Typical joint sealing practices should be
followed.
Drainage
Stripping of the existing asphalt can lead
to nonuniform support of the unbonded
overlay. During evaluation and design of an
unbonded concrete overlay project, exist-
ing subgrade drainage should be evaluated,
as would be done with asphalt resurfacing.
If necessary, steps should be taken to ensure
adequate drainage in the future for the exist-
ing asphalt (i.e., retrofit edge drains, free
draining shoulder materials, geotextiles, etc.).
When underdrains are present, they should
be cleaned, video inspected, and repaired as
necessary.
Construction
Construction elements may include direct
placement, preoverlay repairs, milling, patch
preparation, surface cleaning, concrete place-
ment, curing, and joint sawing.
Direct Placement
Direct placement without milling is recom-
mended when rutting in the existing asphalt
pavement does not exceed 2 in. (50 mm). Any
ruts in the existing pavement are filled with
concrete, resulting in a thicker overlay above
the ruts.
Preoverlay Repairs
Unbonded overlays generally require only
minimal preoverlay repairs of the existing
asphalt; see Table 6. If significantly distressed
areas are not shifting or moving and the
subgrade/subbase is stable, costly repairs
typically are not needed, particularly with an
adequately designed overlay.
Table 6. Possible Preoverlay Repairs on Existing Asphalt Pavement in Preparation for
Unbonded Overlay
Existing Pavement Condition Possible Repairs to Consider
Area of subgrade/subbase failure Remove and replace with stable material; correct water
problems.
Severe distress that results in variation in
strength of asphalt
Remove and replace with stable material; correct water
problems.
Potholes Fill with asphalt.
Shoving Mill
Rutting ≥ 2 in. (50 mm) Mill
Rutting < 2 in. (50 mm) None or mill
Crack width ≥ maximum coarse aggregate
size used in the concrete overlay mixture Fill with asphalt or flowable fill.
Crack width < maximum coarse aggregate
size used in the concrete overlay mixture None
Milling
If surface distortions in the existing pavement
are 2 in. (50 mm) or greater, milling may
be considered prior to placing an unbonded
overlay. Milling can (1) reduce high spots to
help ensure minimum overlay depth, and (2)
remove significant surface distortions that
contain fractured asphalt material.
Spot milling only significant distortions, typi-
cally 1–2 in. (25–50 mm), is often adequate.
e objective of milling is not to obtain a
perfect cross section, and it is not necessary to
completely remove ruts. ere is no reason to
mill off good asphalt that can help carry traf-
fic loads. If a stripped (loose) layer of asphalt
is encountered, it should be completely
removed. Matching existing features or mini-
mizing the vertical change in profile grade will
often be the primary criteria for determining
the milling depth. When this is the case, a
thorough evaluation of the thickness and
condition of the existing asphalt pavement
must be performed to assure that the remain-
ing asphalt to be overlaid is sound and thick
enough to serve as a subbase and construction
platform.
An adequate layer of asphalt (3 in. [75 mm]
minimum) must remain to ensure that the
asphalt will function as a uniform subbase for
the unbonded overlay structure. Regardless of
whether the asphalt will be milled because of
vertical constraints or remain in its existing
condition, the minimum thickness of asphalt
to be overlaid must be adequate to provide
a stable working platform capable of with-
standing all anticipated construction traffic
(specifically, trucks loaded with concrete).
Patch Preparation
If any full-depth concrete patches exist in the
underlying pavement, each concrete patch
should be isolated to prevent its bonding to
41
Guide to Concrete Overlays 41
Guide to Concrete Overlays
Ch 3. OVERLAY OPTIONS
the concrete overlay. If bonding occurs, the
overlay over the patch will be restrained differ-
ently than the rest of the overlay over asphalt,
potentially resulting in cracking. To isolate
the patch, place a geotextile fabric or asphalt
slurry seal to the patch surface after milling.
Surface Cleaning
Before concrete placement, the asphalt surface
should simply be swept. Remaining small par-
ticles are not considered a problem.
Concrete Placement
When the surface temperature of the asphalt
is at or above 120°F (49°C), sprinkling the
surface with water can reduce the temperature
and minimize the chance of early-age crack-
ing. No standing water should remain on the
surface at the time of overlay placement.
Conventional concrete paving practices and
procedures are followed for placing, spreading,
consolidating, and finishing the unbonded
overlay. Because of the variation of the thick-
ness of concrete, the concrete material is bid
on a volume (cubic-yard) basis. Some states
also include a bid item for placement, mea-
sured on a square-yard basis.
Curing
Good curing practices are especially critical
to thin unbonded overlays because of their
high surface-area-to-volume ratio. is is
accomplished by applying a curing com-
pound immediately after surface texturing;
if the unbonded overlay is 6 in. (150 mm)
or thinner, use twice the usual rate of cur-
ing compound. e finished product should
appear as a uniformly painted solid white sur-
face, with the vertical faces along the edges of
the overlay also thoroughly coated.
Joint Sawing
Timely joint sawing is necessary to prevent
random cracking. Transverse and longitudinal
joints should be sawed to a depth of T/3.
When there is evidence of some wheel rut-
ting on the existing asphalt pavement, adjust
the saw-cut depth to account for distortions
in the underlying asphalt pavement, which
effectively increases the slab thickness; see
Figure 36.
Future Repairs
e recommended repair option for
unbonded overlays is the same as for standard
concrete pavements.
Key Resources
ACI Committee 325 (2006); ACPA (1998);
FHWA (2002a)
Figure 36. Consider asphalt rut depth when determining saw-cut depth (ACPA 1998)
Guide to Concrete Overlays
42
Ch 3. OVERLAY OPTIONS
Unbonded Concrete Overlay on Composite Pavements
Figure 37 illustrates a composite pavement
that may be a candidate for an unbonded
concrete overlay, along with the kinds of pre-
overlay repairs that may be appropriate.
Figure 37. Unbonded concrete overlay of poor-to-deteriorated condition composite pavement
Existing deteriorated
composite pavement
New unbonded overlay
Need for milling determined based
on degree of surface distortions
Application and Uses
• May be appropriate for composite pave-
ments with significant HMA deterioration
such as severe rutting, potholes, alligator
cracking, subgrade/subbase issues, shoving,
and pumping; see Figure 38
• Are generally 4–11 in. (100–280 mm) thick
(JPCP or CRCP)
• Are essentially designed as a new concrete
pavement on a stable base course
• Restore or increase the structural capacity
of existing pavement
• Eliminate surface defects such as asphalt
rutting, shoving, potholes, and concrete
with mild MRD or joint deterioration
• Improve surface characteristics (friction,
noise, and smoothness)
• Reduce urban heat island effect by increas-
ing pavement surface albedo Figure 38. Unbonded overlay of composite
43
Guide to Concrete Overlays 43
Guide to Concrete Overlays
Ch 3. OVERLAY OPTIONS
Performance
Unbonded overlays have the potential to
greatly extend the life of existing composite
pavements; see Figures 39 and 40. Uniform
base support from the existing asphalt and
concrete is an important factor affecting
performance. ough this overlay type does
not rely on bonding, some partial bonding
between the resurfacing and existing asphalt
pavement can contribute to enhanced perfor-
mance of the pavement. Unbonded overlays
of composite pavements do not require exten-
sive preoverlay repairs, but spot repairs may
be necessary to minimize localized failures.
Keys to Success
e following actions will help ensure a suc-
cessful project:
• Milling of existing asphalt may be required
to eliminate surface distortions of 2 in. (50
mm) or more.
• If the existing pavement profile indicates
isolated areas of vertical distortion in the
underlying concrete that could signal
movement from inadequate drainage or
MRDs, repairs may be necessary.
• Full-depth repairs should be considered
only at isolated spots where structural
integrity needs restoring.
• Concrete patches in the existing asphalt
pavement surface should be separated from
the overlay with a thin layer of geotextile
fabric or other bond breaker.
• Shorter joint spacing in the overlay can
help reduce curling and warping stress.
• Joints should be sawed in the overlay as
soon as possible because the sawing win-
dow may be shorter than it is typically for
full-depth pavements.
• e asphalt surface should be sprinkled
with water when the surface temperature is
greater than 120ºF (49ºC) during overlay
placement.
• No notable asphalt stripping should exist in
the asphalt after milling.
• If stripping is severe, the asphalt surface
may be milled off and a new interlayer
placed between the underlying concrete and
the new unbonded overlay (see unbonded
overlay over concrete, beginning on
page 46).
• Partial bonding between the overlay and
the asphalt layer of the existing composite
pavement is acceptable and may improve
load-carrying capacity.
Overlay Process
e overlay project consists of pavement
evaluation, design, construction, and future
repairs.
Pavement Evaluation
An evaluation of the existing pavement is
necessary to determine whether or not it can
provide a uniform platform for the unbonded
overlay and, if not, what actions are necessary
to obtain that uniformity. In addition, the
evaluation determines the existing pavement’s
structural contribution as a stable platform
and key inputs to the overlay design. For
general information on pavement evaluation,
including specific information about MRDs,
see page 13.
Composite pavements are good candidates for
unbonded overlays if the existing composite
section can provide, or can be cost-effectively
repaired to provide, a uniform and stable
platform for the overlay. Special consideration
should be given to (1) the condition of both
layers of the composite pavement; (2) deterio-
ration of the asphalt surface course (asphalt is
a good reflector of problems in the underlying
concrete); (3) existing profile grade line (pos-
sible evidence of active panel movements);
(4) panel tenting, which may indicate the
existence of a void under the panel, or joint
deterioration of the underlying concrete pave-
ment; and (5) foundation support value.
Overlay Design
Design elements include using the existing
pavement as a base, overlay thickness, mixture
design, joints, and drainage.
Existing Pavement as Base
In an unbonded overlay design, the existing
composite pavement is considered as a stable
base and the overlay is designed essentially as
a new concrete pavement. e design assumes
an unbonded condition between the layers.
ere are two approaches to assessing the
potential structural contribution of the exist-
ing composite pavement to the new pavement
system. e approach in the AASHTO
Design Guide (1993, 1998) considers the
k-value. e M-E PDG (AASHTO 2008)
considers both friction and k-value.
Overlay Thickness
Unbonded overlay thicknesses typically range
from 4 to 11 in. (100 to 280 mm). e
required overlay thickness is affected by the
desired load-carrying capacity and service
life, as well as the condition of the underlying
pavement.
Portions of a project with significantly differ-
ent existing pavement and subbase conditions
may be broken into separate sections and
designed to specifically address those given
conditions.
Figure 39. Composite pavement prior to unbonded concrete overlay Figure 40. Unbonded concrete overlay over composite pavement
(source: Todd Hanson, Iowa DOT)
Guide to Concrete Overlays
44
Ch 3. OVERLAY OPTIONS
e AASHTO Design Guide (1993, 1998)
and M-E PDG (AASHTO 2008) provide
design procedures. See basic highlights of and
differences among the various procedures in
Table 10 in Chapter 4.
Mixture Design
Conventional concrete mixtures are typically
used in unbonded overlays of deteriorated
composite pavements. When accelerated
opening is desired, conventional concrete
mixtures should be proportioned for rapid
strength gain without increasing shrink-
age properties. For additional information
on accelerated mixtures, see page 76. Early
opening can also be aided by use of maturity
measurements.
Joint Design
e load-transfer design is the same as for
new concrete pavements. Doweled joints are
used for unbonded overlays of pavements that
will experience significant truck traffic, typi-
cally pavements 7 in. (175 mm) and thicker.
For overlays less than or equal to 6 in. (150
mm) thick, the maximum spacing in feet is
1.5 times the slab thickness in inches.
For overlays greater than 6 in. (150 mm)
thick, a maximum joint spacing in feet of
2 times the slab thickness in inches is often
recommended for unbonded overlays. A
7-in. (175 mm) overlay would thus receive a
maximum 14-ft (4.3-m) joint spacing. e
maximum recommended spacing is typically
15 ft (4.6 m).
For situations where the design requires
mechanical load transfer across the joints and
the pavement is less than 7 inches in thick-
ness, conventional dowels cause slipform
paving clearance problems. Smaller diameter
dowels do not significantly help the clear-
ance issue and may not provide long-term
load transfer because of potential socketing in
concrete. One solution that should be con-
sidered is the use of structural fibers to help
hold cracks and joints together. Additionally,
the use of plate dowels provides clearance
for the paver and allows for mechanical load
transfer. e performance of plate dowels
in transverse contraction joints is not well
understood in concrete overlay pavements
of 5 inches or less. ey have, however, been
successfully used in industrial parking lots.
e effects of exposure of epoxy or galvanized
coated plate dowels to deicing salts is also
limited. It is recommended that a proven and
tested corrosion-resistant surface be required.
Research on plate dowels in concrete overlays
is being conducted at the MnROAD facility
(Burnham and Izevbekhai 2012). See Chapter
4 for additional information on plate dowels.
e use of tiebars for unbonded overlays
should follow conventional use for pavements
5 in. (125 mm) thick or more. Using lane
tiebars may be appropriate in open-ditch (or
shoulder) sections of unbonded overlays if the
overlay is 5 in. (125 mm) or greater. In this
category, a no. 4 tiebar (0.50 in. [13 mm])
may be appropriate. e use of tiebars in
confined curb-and-gutter sections should be
considered if the overlay is 6 in. (150 mm) or
greater.
Typical joint sealing practices should be
followed.
Drainage
During evaluation and design of an
unbonded concrete overlay project, exist-
ing subgrade drainage should be evaluated,
as would be done with asphalt resurfacing.
If necessary, steps should be taken to ensure
adequate drainage in the future (i.e., retrofit
edge drains, free draining shoulder materials,
geotextiles, etc.). When underdrains are pres-
ent, they should be cleaned, video inspected,
and repaired as necessary.
Construction
Construction elements may include direct
placement, preoverlay repairs, milling, patch
preparation, surface cleaning, concrete place-
ment, curing, and joint sawing.
Direct Placement
Direct placement without milling is recom-
mended when rutting in the existing asphalt
pavement does not exceed 2 in. (5.0 cm) and
there is no significant surface deterioration in
the asphalt. Any ruts in the existing pavement
are filled with concrete, resulting in a thicker
overlay above the ruts; saw-cut depths must
be adjusted to maintain a minimum of T/3
where thickness is increased over the ruts.
Table 7. Possible Preoverlay Repairs on Existing Composite Pavement in Preparation for
Unbonded Overlay
Existing Pavement Condition Possible Repairs to Consider
Area of subgrade/subbase failure Remove and replace with stable material (i.e., select
borrow, granular subbase, etc.); correct water problems.
Severe distress that results in variation in
strength of asphalt
Remove and replace with asphalt material or concrete
patch with slurry seal or geotextile separation layer;
correct water problems.
Reflective faulting or panel tenting Full-depth repair with concrete and use asphalt or
geotextile separation layer as bond breaker.
Potholes Fill with asphalt.
Shoving Mill
Rutting ≥ 2 in. (50 mm) Mill
Rutting < 2 in. (50 mm) None or mill
Crack width ≥ maximum coarse aggregate
size used in the overly mixture Fill with asphalt or flowable fill.
Preoverlay Repairs
Unbonded overlays generally require only
minimal preoverlay repairs of the exist-
ing composite pavement. If significantly
distressed areas are not shifting and the
subgrade/subbase is stable, costly repairs
typically are not needed, particularly with an
adequately designed overlay; see Table 7.
Note that concrete overlays will bond with
any concrete patches on the underlying pave-
ment. erefore, isolate concrete patches with
a geotextile fabric or other bond-breaking
material.
Panel tenting (early stages of blowups) may be
an indication that there is a void under exist-
ing panels. Sections with significant tenting
should be repaired to relieve the pressure and
provide uniform support before construction
of an unbonded overlay.
Milling
If surface distortions in the existing pavement
are 2 in. (50 mm) or greater, milling may
be considered prior to placing an unbonded
overlay. Milling can (1) reduce high spots to
help ensure minimum overlay depth, and (2)
remove significant surface distortions that
contain fractured asphalt material.
Spot milling only significant distortions, typi-
cally 1–2 in. (25–50 mm), is often adequate.
e objective of milling is not to obtain a
perfect cross section, and it is not neces-
sary to completely remove ruts. ere is no
reason to mill off good asphalt that can help
carry traffic loads. If a stripped (loose) layer
of asphalt is encountered, it should be com-
pletely removed. Matching existing features
or minimizing the vertical change in profile
grade will often be the primary criteria for
determining the milling depth. When this is
the case, a thorough evaluation of the thick-
45
Guide to Concrete Overlays 45
Guide to Concrete Overlays
Ch 3. OVERLAY OPTIONS
ness and condition of the existing asphalt
pavement must be performed to assure that
the remaining asphalt to be overlaid is sound
and thick enough to serve as a subbase and
construction platform. If the remaining old
asphalt is too brittle or broken up to provide
adequate separation, a new separation layer
should be constructed. Without an adequate
separation layer, working cracks from the
underlying concrete could cause reflective
cracking of the unbonded overlay.
An adequate layer of asphalt (3 in. [75 mm]
minimum) must remain to ensure that the
asphalt will function as a uniform subbase for
the unbonded overlay structure. Regardless
of whether the asphalt will be milled because
of vertical constraints or will remain in its
existing condition, the minimum thickness
of asphalt to be overlaid must be adequate to
provide a stable working platform capable of
withstanding all anticipated construction traf-
fic (specifically trucks loaded with concrete).
Patch Preparation
If any full-depth concrete patches exist or are
placed as part of the project in the underly-
ing pavement, each concrete patch should be
isolated to prevent its bonding to the concrete
overlay. If bonding occurs, the overlay over
the patch will be restrained differently than
the rest of the overlay over asphalt, potentially
resulting in cracking. To isolate the patch, a
geotextile fabric or other bond breaking mate-
rial, such as an asphalt slurry seal, should be
applied to its surface.
Surface Cleaning
Before concrete placement, the asphalt surface
should simply be swept. Remaining small par-
ticles are not typically considered a problem.
Concrete Placement
When the surface temperature of the asphalt
is at or above 120°F (49°C), sprinkling the
surface with water can reduce the temperature
and minimize the chance of early-age crack-
ing. No standing water should remain on the
surface at the time of overlay placement.
Conventional concrete paving practices and
procedures are followed for placing, spreading,
consolidating, and finishing the concrete over-
lay. Because of the variation of the thickness
of concrete, the concrete material is bid on a
volume (cubic-yard) basis. Some states also
include a bid item for placement, measured
on a square-yard basis.
Curing
Good curing practices are especially criti-
cal to thin unbonded overlays because of
their high surface-area-to-volume ratio. is
is accomplished by applying a curing com-
pound immediately after surface texturing;
if the unbonded overlay is 6 in. (150 mm)
or thinner, use twice the usual rate of cur-
ing compound. e finished product should
appear as a uniformly painted solid white sur-
Figure 41. Consider asphalt rut depth when determining saw-cut depth (ACPA 1998)
face, with the vertical faces along the edges of
the overlay also thoroughly coated.
Joint Sawing
Timely joint sawing is necessary to prevent
random cracking. Transverse joints can be
sawed with conventional saws to a depth of
between T/4 (minimum) and T/3 (maxi-
mum). When there is evidence of some wheel
rutting on the existing asphalt pavement,
saw-cut depth is of particular concern for
unbonded overlays because the distortions in
the underlying asphalt pavement can effec-
tively increase the slab thickness; see Figure
41.
Longitudinal joints should be sawed to a
depth of T/3.
Future Repairs
e recommended repair option for
unbonded overlays is the same as for standard
concrete pavements.
Key Resources
ACI Committee 325 (2006); ACPA (1998);
FHWA (2002a)
Guide to Concrete Overlays
46
Ch 3. OVERLAY OPTIONS
Unbonded Concrete Overlay on Concrete Pavements
Figure 42 illustrates a concrete pavement that
may be a candidate for an unbonded concrete
overlay, along with the kinds of preoverlay
repairs that may be appropriate.
Figure 42. Unbonded concrete overlay of poor condition concrete pavement
Existing concrete pavement
Possible preoverlay repairs
New unbonded overlay
Application and Uses
Unbonded concrete overlays on concrete
pavements
• May be appropriate for concrete pavements
in poor condition, including pavements
experiencing MRD, but should be stable
and provide uniform support; see Figure 43
• Are generally 4–11 in. (100–280 mm) thick
(JPCP or CRCP)
• Are designed essentially as a new concrete
pavement on a stable base course (with the
existing pavement acting as the stable base),
assuming an unbonded condition between
the layers
• Restore or enhance the pavement’s struc-
tural capacity
• Increase pavement life equivalent to full-
depth pavement
• Improve surface friction, noise, and
smoothness Figure 43. Unbonded concrete on concrete
47
Guide to Concrete Overlays 47
Guide to Concrete Overlays
Ch 3. OVERLAY OPTIONS
FAQ—Have thinner unbonded overlays actually been constructed?
Yes. in, 4 in. [100 mm] thick unbonded overlays are a viable solution for existing
concrete pavements that have top-down joint deterioration issues. Project specifics and
guidance for designing and constructing this type of unbonded overlays can be found at
www.intrans.iastate.edu/research/documents/research-reports/US_18_overlay_construc-
tion_web.pdf (Cable 2012).
Performance
Unbonded overlays of concrete pavements
have been successfully used in many states,
with more than 30 years of good-to-excellent
performance; see Figures 44 and 45. Critical
factors that affect the performance of
unbonded overlays include separation layer
design, overlay thickness, joint spacing layout,
and load transfer design. Uniform support
from the existing pavement is a key factor.
Keys to Success
e following actions will help ensure a suc-
cessful project:
• Full-depth repairs should be considered
only at isolated spots where structural
integrity needs restoring.
• A separation layer (typically 1 in. [25 mm]
asphalt or geotextile fabric) is required to
isolate the overlay from the existing con-
crete and eliminate reflective cracking.
• Provide a drainable asphalt separation
layer to prevent stripping or, in the case of
geotextile fabric, daylight the fabric to the
foreslope or a drainage conduit.
• e depth of joint faulting should be
checked and a determination made whether
or not the concrete overlay can elimi-
nate further faulting or other repairs are
necessary.
• Joints should be sawed in overlay as soon as
possible since the sawing window may be
shorter than it typically is.
• Shorter joint spacing in the unbonded over-
lay, as compared to full-depth pavement,
can help reduce curling and warping stress.
• It is not critical to mismatch overlay joints
to the underlying joints.
Overlay Process
e overlay project consists of pavement
evaluation, design, construction, and future
repairs.
Pavement Evaluation
An evaluation of the existing concrete pave-
ment is necessary to determine whether or not
the existing concrete and its subbase can pro-
vide uniform support and, if not, what actions
are necessary to obtain that uniformity if an
unbonded overlay is to be used. e evalua-
tion also determines the existing pavement’s
structural contribution as a stable base. For
general information on pavement evaluation,
including specific information about MRDs,
see page 13.
For faulted pavements, the cause can usually
be attributed to the combination of some loss
of load transfer between slabs and some loss
of subgrade/subbase support. If the subgrade/
subbase is stable, the increase in the carrying
capacity of the unbonded overlay has proven
to be adequate to overcome faulting. Faulting
of 3/8 in. (10 mm) or less in the existing
concrete pavement is generally not a concern
when the asphalt separation layer is 1 in. (25
mm) or more. When geotextile fabric is used
as an interlayer, faulting should not exceed
0.25 in. If geotextile is desired and faulting is
an issue, the pavement should be ground to
remove the faulting or an asphalt interlayer
should be used. Retrofitted edge drains have
been successfully used to reduce the progres-
sion of faulting.
Panel tenting (at the joint) may be an indica-
tion of bottom-up deterioration. Sections
with significant tenting should be repaired to
relieve the pressure and provide uniform sup-
port before unbonded overlay placement.
Overlay Design
Unbonded overlays are designed similarly to
new concrete pavements on a stabilized sub-
base, assuming a separated condition between
the layers.
Overlay Thickness
On heavily trafficked roads, unbonded overlay
thicknesses typically range from 6 to 11 in.
(150 to 280 mm); on lower-volume roads,
they can be as thin as 4 in. (100 mm). e
required overlay thickness is affected by the
desired load-carrying capacity and service
life, as well as the condition of the concrete
pavement.
Both the AASHTO Design Guide (1993,
1998) and the M-E PDG (AASHTO 2008)
consider the effects of the separation layer. See
basic highlights of and differences among the
various procedures in Table 10 in Chapter 4.
Figure 44. Route D35 existing pavement in poor condition (source:
Todd LaTorella, MO/KS Chapter, ACPA)
Figure 45. Route D35 5-inch unbonded overlay (source: Todd
LaTorella, MO/KS Chapter, ACPA)
Guide to Concrete Overlays
48
Ch 3. OVERLAY OPTIONS
Separation Layer Design
e separation layer design is one of the pri-
mary factors influencing the performance of
unbonded overlays on concrete pavements.
e separation layer provides a shear plane
that helps prevent cracks from reflecting up
from the existing pavement into the new
overlay. In addition, the separation layer pre-
vents bonding of the new pavement with the
existing pavement, so both are free to move
independently.
ere are three properties that should be
considered in the selection and design of the
separation layer:
1. Adequate isolation from the underlying
pavement to prevent reflective cracking
2. Bedding—the separation layer provides
a cushion for the unbonded overlay
pavement
3. Drainage—moisture should be able to
escape the separation layer
e most common and successful separa-
tion layer is a conventional 1 in. (25 mm)
well-drained asphalt surface mixture, which
provides adequate coverage over irregulari-
ties in the existing pavement. e thickness
can be slightly increased when irregularities
are large enough to impact placement opera-
tions. e separation layer does not provide
significant structural enhancement. us, the
placement of an excessively thick layer should
be avoided.
Stripping of a dense graded asphalt separa-
tion layer has led to premature failure of
some unbonded overlays. In locations where
water and heavy truck traffic will be present, a
drainable asphalt mixture should be used. is
can be achieved by reducing the sand content
and increasing the volume of 3/8 in. (10 mm)
aggregate in the asphalt mixture. See Table 18
on page 78 for information on gradation for
asphalt interlayers.
For the last five years, geotextile interlayers
have substantially increased in use and geo-
textiles have proven to be good separation
layers. For more information, see Chapter 4,
page 59.
Mixture Design
Conventional concrete mixtures are typically
used for unbonded overlays of concrete pave-
ments in poor condition. When accelerated
opening is desired, conventional concrete
mixtures should be proportioned for rapid
strength gain without increasing shrinkage
properties. For additional information on
accelerated mixtures, see page 76.
Joint Design
Load transfer can be better in unbonded over-
lays of concrete pavements than in new JPCPs
because of the load transfer provided by the
underlying pavement. Doweled joints are
typically used for unbonded overlays of pave-
ments that will experience significant truck
traffic, usually pavements 7 in. (175 mm) and
thicker. e load transfer design is the same as
for new concrete pavements.
Shorter joint spacing should be used to reduce
the risk of early cracking due to increased
curling caused by the stiff support provided
by the underlying pavement; see Table 8.
For situations where the design requires
mechanical load transfer across the joints and
the pavement is less than 7 inches in thick-
ness, conventional dowels cause slipform
paving clearance problems. Smaller diameter
dowels do not significantly help the clearance
issue and may not provide long-term load
transfer due to potential socketing in con-
crete. One solution that should be considered
is the use of structural fibers to help hold
cracks and joints together. Additionally, the
use of plate dowels provides clearance for the
paver and allows for mechanical load transfer.
e performance of plate dowels in transverse
contraction joints is not well understood in
concrete overlay pavements of 5 inches or less.
ey have, however, been used successfully in
industrial parking lots. e effects of exposure
of epoxy or galvanized coated plate dowels to
deicing salts is also limited. It is recommended
that a proven and tested corrosion-resistant
surface be required. Research on plate dowels
in concrete overlays is being conducted at the
Table 8. Typical Transverse Joint Spacing
Unbonded
Resurfacing
Thickness
Maximum Transverse
Joint Spacing
≤ 6 in. (125 mm)
6 x 6 ft (1.8 x 1.8 m) panels (not
to exceed 1.5 times thickness
in inches)
> 6 in.
Spacing in feet = 2 times
thickness in inches, not to
exceed 15-foot joint spacing
MnROAD facility (Burnham and Izevbakhai
2012). See Chapter 4 for additional informa-
tion on plate dowels.
e use of tiebars for unbonded overlays
should follow conventional use for pave-
ments 5 in. (125 mm) thick or more. Using
lane tiebars may be appropriate in open-ditch
(or shoulder) sections of unbonded overlays
if the overlay is 5 in. (125 mm) or greater.
In this category, a no. 4 tiebar (0.50 in. [13
mm]) may be appropriate. e use of tiebars
in curb-and-gutter (C/G) sections should be
considered if the overlay is 6 in. (150 mm) or
greater.
Many states do not intentionally mismatch
joints and have not experienced any adverse
effects. Some states, however, still intention-
ally mismatch joints, according to previous
guidance, to maximize the benefits of load
transfer.
Unbonded plain jointed concrete overlays
over continuously reinforced concrete pave-
ment (CRCP) are designed and constructed
the same as unbonded overlays on jointed
plain concrete pavements (JPCP). Texas has
completed many CRCP unbonded overlays
over existing CRCP and plain jointed pave-
ments, sometimes increasing the asphalt
separation layer thickness to greater than 1
inch.
Drainage
Without good drainage of the separation
layer, pore pressure builds up from heavy
truck traffic and can cause stripping of the
asphalt separation layer. Properly designed,
constructed, and maintained edge drains
may help reduce pumping, asphalt stripping,
faulting, and cracking. Deeper edge drains
(subdrains) are used to help stabilize sub-
grades/subbases. When geotextiles are used as
an interlayer, they need to also drain into sub-
drains or be daylighted at the shoulder.
During evaluation and design of an unbonded
concrete overlay project, existing subgrade
drainage should be evaluated, as would be
done with asphalt resurfacing. If necessary,
steps should be taken to ensure adequate
drainage in the future (i.e., retrofit edge
drains, daylighting free draining subbase
materials, geotextiles, etc.).
When underdrains are present, they should
be cleaned, video inspected, and repaired as
necessary.
49
Guide to Concrete Overlays 49
Guide to Concrete Overlays
Ch 3. OVERLAY OPTIONS
Construction
Construction elements may include preoverlay
repairs, separation layer, concrete placement,
curing, and joint sawing.
Preoverlay Repairs
Typically, only distresses that cause a major
loss of structural integrity require repair. If
significantly distressed areas are not shifting
or moving and the subgrade/subbase is stable,
costly repairs typically are not needed, partic-
ularly with an adequately designed overlay; see
Table 9. As an alternative to numerous repairs,
some states increase the unbonded overlay
thickness to provide additional load-carrying
capacity.
Separation Layer
Use of a sufficient separation layer can help
ensure good performance of the unbonded
overlay. Before separation layer placement,
the existing pavement surface should be
swept clean of any loose material either
with a mechanical sweeper or an air blower.
Conventional placement practices and pro-
cedures should be followed for placing the
separation layer (see Chapter 7, page 103).
Concrete Placement
When the surface temperature of the sepa-
ration layer is at or above 120°F (49°C),
sprinkling the surface with water can reduce
the temperature and minimize the chance of
early-age cracking.
When cooling a black-colored geotextile
interlayer, it should be damp and not satu-
rated with water. A simple test is to touch the
fabric and no water should show on the fin-
gers. No standing water should remain on the
surface at the time the overlay is placed.
Conventional concrete paving procedures are
followed for placing, spreading, consolidat-
ing, and finishing the unbonded overlay.
Adequately anchoring dowel baskets to the
underlying concrete pavement is important.
Alternatively, pavers equipped with dowel bar
inserters can be used. Because of the varia-
tion of the concrete thickness, the concrete
material is bid on a volume (cubic-yard) basis.
Some states include a bid item for placement,
measured on a square-yard basis.
Curing
Good curing practices are especially critical
to thin unbonded overlays because of their
high surface-area-to-volume ratio. is is
accomplished by applying a curing com-
pound immediately after surface texturing;
if the unbonded overlay is 6 in. (150 mm)
or thinner, use twice the usual rate of cur-
ing compound. e finished product should
appear as a uniformly painted solid white sur-
face, with the vertical faces along the edges of
the overlay also thoroughly coated.
Joint Sawing
Timely joint sawing is necessary to prevent
random cracking. Transverse and longitudinal
joints should be sawed with conventional saws
to a depth of T/3. Transverse joint saw-cut
depths for early-entry sawing should not be
less than 1.25 in. (31 mm). Saw longitudinal
joints to a depth of T/3.
Future Repairs
e recommended repair options for
unbonded overlays are the same as for stan-
dard concrete pavements.
Key Resources
ACI Committee 325 (2006); ACPA (1990b);
FHWA (2002b)
Table 9. Possible Preoverlay Repairs on Existing Concrete Pavement in Preparation for
Unbonded Overlay
Existing Pavement Condition Possible Repairs to Consider
Faulting; ≤ 0.25 in. for geotextile interlayer;
≤ 0.38 in. for 1-in. asphalt interlayer None
Faulting; > 0.25 in. for geotextile interlayer;
> 0.38 in. for 1-in. asphalt interlayer
Grind pavement to remove faulting for geotextile or
thicker asphalt separation layer.
Significant tenting Full-depth repair
Badly shattered slabs Full-depth repair
Significant pumping Full-depth spot repair and drainage improvements
Severe joint spalling Clean
CRCP with punchouts or other severe damage Full-depth repair
51
Guide to Concrete Overlays
Ch 4. DESIGN
Chapter 4.
CONCRETE OVERLAY DESIGN
With today’s limited highway funding and
aging highway network, and given the cost
effectiveness of concrete overlays for pavement
maintenance and rehabilitation, it is likely
that pavement engineers will be designing
concrete overlays more often and for a greater
variety of existing pavements and pavement
conditions. is section provides clear, reliable
guidance for designing high-quality con-
crete overlays and an outline of strategies and
resources necessary to implement concrete
overlay projects as part of an overall pavement
maintenance and rehabilitation program.
e information in this section has been
collected from several valuable resources pub-
lished by the American Concrete Institute
(ACI), AASHTO, FHWA, World Road
Association, NCHRP, ACPA, Portland
Cement Association (PCA), U.S. Army
Corps of Engineers, Federal Aviation
Administration, and various state depart-
ments of transportation. Existing procedures
are based on a variety of underlying assump-
tions and design strategies. It is important for
concrete overlay designers to understand the
interaction of design with both the selection
of mixture materials and the construction
process. Perhaps the most critical design
principle is that the concrete overlay and the
underlying pavement should be viewed as a
system.
Concrete Overlay
Design Variables
Regardless of the overlay system and design
procedure used, the analysis begins with
recognition of a number of common inputs
to the design process. It is important to first
define the scope of the planned project and
its intended structural performance require-
ments. Expected design life will affect both
the extent of repairs required on the existing
pavement and the design inputs. is in turn
influences the thickness, the amount of repair,
and thus the cost of the overlay; see Figure
46. e engineer is also required to character-
ize and understand the existing pavement
structure (see information about evaluating
the existing pavement in Chapter 2), the
anticipated traffic loading, and the materials
expected to be used. In most cases, climatic
influences play a role, particularly with a
bonded concrete overlay system.
Existing Pavement
Characterization
e design and performance of a concrete
overlay is affected by the condition of the
existing pavement structure. Although both
bonded and unbonded overlay systems ben-
efit from the load-transfer capabilities of
the existing pavement, bonded overlays are
influenced to a greater degree by the underly-
ing pavement condition. erefore, effective
characterization of the existing pavement
condition is important in selecting the proper
type of concrete overlay to build.
e first step in designing a concrete over-
lay project is a thorough characterization of
the existing pavement. At the very least, the
existing pavement section should be verified
with cores or historical records. Sometimes,
however, the historical records or plans do
not represent the actual in-place pavement, so
field verification of the records is important.
In addition, the existing pavement structure
FAQ – What if less than 3 inches of asphalt will remain after milling for a bonded
concrete overlay of asphalt?
ere are two issues to consider. First, the recommendation of having 3 inches of fair-
condition asphalt structure recognizes that pavement thicknesses found in the field have an
inherent variability—there are thicker sections and thinner sections; thus, the recommen-
dation is a nominal 3 inches. Second, if there is a quality base course or stabilized subgrade
below the asphalt, it may be acceptable to have less than the recommended nominal 3
inches of asphalt pavement remaining.
should be evaluated for its overall cur-
rent condition, which will influence both
the selection of overlay system (bonded or
unbonded) and the type, location, and extent
of any preoverlay repairs needed.
Surface Considerations
For a bonded overlay to be a practical solu-
tion on an existing asphalt surface, a nominal
3 in. (75 mm) minimum of fair-condition
existing asphalt pavement structure should
remain after any necessary preoverlay repairs
and milling. Failure to properly evaluate the
thickness and condition of an existing asphalt
pavement that will provide structural capac-
ity in a bonded overlay can lead to areas with
little or no asphalt remaining after milling.
is situation necessitates difficult field engi-
neering decisions, essentially thickening of
the concrete overlay to compensate for the
reduced structural contribution of the exist-
ing asphalt pavement. A thorough evaluation
of the existing pavement is necessary to avoid
time-consuming and costly delays.
Figure 46. Overlay design factors that affect one another
Desired service
life, load-carrying
capacity
Existing pavement
characterization
Analysis
Costs Design
(thickness, etc.)
Guide to Concrete Overlays
52
Ch 4. DESIGN
If the pavement evaluation finds the existing
pavement is in poor condition with many
localized failures, significant base failures may
be indicated. Depending on the potential
costs of repairing these failures, a bonded
overlay may not be advisable. An unbonded
overlay that is less sensitive to the underly-
ing pavement condition may be more cost
effective. Condition evaluation permits the
pavement engineer to determine the quantity
and location of preoverlay repair required.
It should be noted that random cracks in the
underlying pavement do not necessarily lead
to reduction in service life. Many miles of
unbonded concrete overlays have been built
that have performed very well with little
regard or consideration to repairing the crack-
ing in the underlying platform.
Structural Considerations
For bonded and unbonded overlays of exist-
ing asphalt or composite pavements, the layer
moduli can be determined through non-
destructive testing (see Chapter 2, page 16,
Deflection Testing). Cores are recommended
for all overlay projects.
When overlaying composite pavements, the
condition of the asphalt layer is a good indica-
tor of the existing base support. If the joints
and other discontinuities of the underlying
concrete are visible and extremely distressed
or exhibiting evidence of severe faulting, these
should be characterized. Excessive or visibly
large deflections under truck loading may
require full-depth repair prior to resurfacing.
Regardless of the design procedure used, the
designer should also define the degree of sup-
port directly beneath the structural layers. In
terms of what is defined as a “structural layer”
(as opposed to part of the support system),
departure from the AASHTO Design Guide
(1993, 1998) is becoming increasingly com-
mon, particularly in overlays. For example,
using the conventional AASHTO Design
Guide (1993, 1998) for new concrete pave-
ments, an asphalt layer is considered a support
layer. e property defining this support, the
k-value, describes the response of the material
immediately beneath the concrete pavement.
When using the design procedures, it is
important to understand at what location in
the pavement structure the k-value is being
considered. In other approaches to design,
principally with concrete overlay of asphalt,
the flexural capacity of the asphalt layer is
considered a structural component. e spe-
cific contribution of the asphalt layer depends
on the degree of bond with the concrete. In
this case, the k-value would describe the sup-
port provided by the materials beneath the
asphalt.
Designers are sometimes charged with mak-
ing decisions based on limited amounts
of information. is is particularly true in
rehabilitation project designs. Decisions on
the design selection should be logical and
defendable. e designer should be aware of
the impact that selecting the reliability level
can have on the final design thickness. In
the AASHTO Design Guide (1993, 1998),
the reliability level and the overall standard
deviation result in an increase in the effective
multiplier on the design traffic used in deter-
mining the thickness. Appropriate selection
of these parameters can build in a predictable
level of risk.
Traffic Characterization
To develop a proper pavement design, the
anticipated future traffic loading should be
known as accurately as reasonably possible.
Care must be taken not only to measure or
predict current traffic characteristics, but also
to assign reasonable growth characteristics.
A prediction of the number of trucks should
be made over the design life. Measures some-
times include a prediction of the number
of equivalent single-axle loads based on the
anticipated traffic distribution. In this case,
the designer should not approach traffic esti-
mates with conservative estimates. It is better
to make a reasonable estimate and adjust for
uncertainty later.
Alternative mechanistic-empirical pavement
design procedures use a distribution of traffic
loading. is loading describes the number,
weight, and geometries of the associated axle
loads. Sometimes this is further distributed by
the time of day and even the season. Highly
sophisticated models include the distribution
by lane and the wander of the wheel within
the lane. A number of typical distributions
available in the M-E PDG (AASHTO 2008)
may be adequate for most situations.
At a minimum, average annual daily traffic
and percentage of trucks is needed for thick-
ness design. Most of the design software
packages have default distribution models for
estimating total equivalent single axle loads
(ESALs).
Where special traffic generators are present for
portions of a concrete overlay project, it may
be advisable to adjust the thickness design for
discrete portions of the project that experi-
ence heavier traffic.
Material Properties
Certain properties of the overlay concrete
should be known or estimated prior to the
design process (see Chapter 5 for a full discus-
sion of materials used for concrete overlays).
is provides the designer additional flexibil-
ity to adjust the designs to available material
options that can be used to reduce costs with-
out compromising performance.
Strength of the concrete is one of the key
design inputs, but this is often misunder-
stood. e designer should use a strength
that is consistent with the assumptions of
the design method being used. For example,
all AASHTO methods require third-point
flexural strength in 28 days, yet it is not
uncommon for designers to erroneously use
the strength found in the construction speci-
fications. Since this value is often lower, it can
result in an unnecessarily thick overlay that
drives up cost.
Some methods require an estimate of the
modulus of elasticity of the materials. is is
often of secondary importance in unbonded
overlays and has negligible impact in terms of
thickness. is property, however, becomes
more important in bonded overlay designs.
Used in sufficient dosages, macro fibers
enhance the toughness and ductility of the
concrete and may result in reduced concrete
thickness for some bonded overlay design
procedures (see page 77 and Appendix C for a
full discussion of fiber-reinforced concrete).
In some mechanistic-based procedures, the
CTE of the concrete is also used. e CTE
is a measure of a material’s expansion or
contraction with temperature; for concrete
pavements this has an impact on internal
stresses, which may lead to cracks, unless
accounted for in the design of proper slab
dimensions.
e coefficient of thermal expansion can
have a much more significant effect on the
performance of bonded overlay designs. In
designing bonded concrete overlays for exist-
ing concrete pavements, it is important that
the CTE of aggregates specified for the con-
crete overlay mixture design have a similar or
lower CTE to that of the existing concrete
pavement. is helps ensure that both layers
experience similar thermal movements, thus
reducing stress on the bond between the two
layers. In most cases, using a coarse aggregate
FAQ – Do I really need to worry about CTE?
ough the effect of CTE is increasingly being considered in thicker overlays and even new
pavements, default values are adequate for the design of unbonded overlays.
53
Guide to Concrete Overlays
Ch 4. DESIGN
in the overlay concrete mixture with the same
mineralogy as that used in the underlying
concrete is sufficient.
Climatic Factors
Overlay system performance depends on
climatic factors, both during construction
and during the service life of the overlay.
Relatively thin bonded overlay sections are
more susceptible to adverse weather con-
ditions that may affect the ability of the
concrete to retain moisture, prevent excessive
heat buildup, or prevent freezing. Materials
should be selected that are compatible with
the anticipated climate and freeze/thaw condi-
tions. Joints and load-transfer systems should
be designed to accommodate the movements
of the joints due to seasonal changes in pave-
ment temperature. For example, shorter joint
spacing may be appropriate.
Curling and warping are also considerations
for pavement designers. Slab dimensions and
joint layout should be optimized to minimize
curling and warping stresses.
Distress Mode
Advancements in computing hardware
and the desire to better understand what is
occurring as pavements fail has led to newer
AASHTO and industry-developed methods
that, in essence, break apart the serviceabil-
ity model into its individual components.
Pavement designs are evaluated for “multi-
modal” deterioration modes that consider one
or more of the parameters. Multimodal deteri-
oration models carry a number of advantages.
ey may aid in forecasting potential mainte-
nance, and they may assist in developing more
effective and cost-efficient designs.
Thickness Design Selection
In most cases, the designer will have an idea
of the likely feasible alternatives based on the
initial survey of the project. In selecting the
final thickness design, however, it is important
for the engineer to anticipate the condition
of the existing section at the time of actual
construction of the new concrete surface. In
many cases, construction will not begin for
at least 2 or 3 years. Some degradation of the
existing structure should be anticipated and
considered in the analysis. Allowing for this
continued degradation in the surface condi-
tion, the designer can begin the process of
considering feasible design alternatives using
the procedures recommended in Table 10.
ere are several design procedures available
for determining the appropriate thickness
of bonded and unbonded concrete overlays.
Designers should consult the Guide to the
Design of Concrete Overlays Using Existing
Methodologies (Torres et al. 2012) pub-
lished by the National Concrete Pavement
Technology Center for current guidance
regarding comprehensive thickness design.
is document provides guidance for the fol-
lowing design procedures:
• Bonded Concrete Overlay on Asphalt (BCOA)
ickness Designer (ACPA 2012) (http://
apps.acpa.org/apps/bcoa.aspx)
• Guide for Design of Pavement Structures, 4th
edition (AASHTO 1993) (compatible soft-
ware at www.acpa.org/WinPAS/) (https://
www.google.com/#q=AASHTO.+1993.+G
uide+for+Design+of+Pavement+Structures)
• AASHTOWare Pavement ME Design
(AASHTO [no year]) (www.aashtoware.
org)
Background of Design
Methodologies
Designing either bonded or unbonded con-
crete overlays is a process that begins with
characterizing the existing pavement, defining
critical design variables, and then calculating
the required overlay thickness. is section
presents a general overview of the most com-
mon design methodologies:
• Bonded Concrete Overlay on Asphalt (BCOA)
ickness Designer (ACPA 2012) (http://
apps.acpa.org/apps/bcoa.aspx)
• BCOA ME (Vandenbossche 2013) (www.
engineering.pitt.edu/Vandenbossche/
BCOA-ME_DesignGuide/)
• Guide for Design of Pavement Structures. 4th
ed. (AASHTO 1993) (compatible software
at www.acpa.org/WinPAS/) (https://www.
google.com/#q=AASHTO.+1993.+Guide+
for+Design+of+Pavement+Structures)
• Mechanistic-Empirical Design Guide—A
Manual of Practice (AASHTO 2008)
(https://www.google.com/#q=4.%09AAS
HTO.+2008.+Mechanistic-Empirical+De
sign+Guide+%E2%80%93+A+Manual+of
+Practice)
• StreetPave (ACPA 2012) (http://acpa.org/
streetpave/)
• Optipave V2.0. (TCPavements 2010)
(www.tcpavements.com/index.
php?op=0&lang=en)
• Flowable Fibrous Concrete for in
Pavement Inlays (Bordelon and Roesler
2011) (http://ascelibrary.org/doi/
abs/10.1061/41167%28398%2984) (see
Appendix C)
• Illiniois DOT’s spreadsheet for bonded
concrete inlay/overlay of asphalt design
(Roesler et al. 2008) (www.dot.state.il.us/
desenv/pdp.html)
In addition, there is an ongoing effort to
develop a new methodology for unbonded
concrete overlay designs: Federal Highway
Administration Pooled Fund TPF 5-269
Development of an Improved Design Procedure
for Unbonded Concrete Overlays (under
development). Future developments and
refinements of concrete overlay thickness
design methodologies can be found at www.
cptechcenter.org/overlay.
Table 10 provides a summary of the cur-
rent design procedures, typical input values,
and pertinent information. Two of the most
important aspects in concrete overlay design
are (1) how each method handles the bond
between the existing pavement and the con-
crete overlay, and (2) whether the method
assumes the existing pavement will provide
significant structural capacity or, alternatively,
contribute to the quality of the pavement
foundation. With this type of information,
pavement designers are able to make an
informed decision about which method to
apply when designing a certain type of con-
crete overlay.
Note: Table 10 is to be used for general ref-
erence purposes only. For design purposes,
actual overlay thickness should be determined
based on specific design variables for the proj-
ect, using the appropriate design procedure.
ACPA BCOA Method
e American Concrete Pavement Association
(ACPA 1998) developed a mechanistic
procedure to design thinner (2 to 4 inch)
bonded concrete overlays of asphalt (BCOA)
pavements with smaller slab sizes, which are
not captured by the two AASHTO meth-
ods described earlier. is BCOA method
consists of an iterative design process, where
the designer evaluates the proposed overlay
thickness and joint spacing along with traf-
fic, concrete strength (modulus of rupture),
existing asphalt pavement thickness, and com-
posite subgrade/subbase stiffness (k-value).
e procedure determines the allowable
trucks for the trial design.
e ACPA procedure is based on calculating
the fatigue damage in the slab for a corner
loading condition, as well as limiting the
fatigue damage at the bottom of the exist-
ing asphalt pavement at the transverse joint
location (ACPA 1998). Temperature curling
stresses are also considered in the critical pave-
ment response. One limitation of this method
is that it is based on the PCA beam fatigue
model, which yields very conservative esti-
mates. As a result, Riley developed a modified
ACPA method in 2006 that incorporated a
new probabilistic concrete fatigue algorithm.
is modified method allows for inputting
the existing asphalt pavement properties,
accounts for the type and amount of struc-
tural fibers, and checks for a potential bond
plane failure.
Guide to Concrete Overlays
54
Ch 4. DESIGN
Table 10. Summary of Current Overlay Design Software (developed by Dr. Jeffery R. Roesler, University of Illinois at Urbana-Champaign)
Overlay
Type
Typical Design and Software Parameters
Traffic
(Millions
of ESALs)
Typical
Concrete
Slab
Thickness
Maximum Joint
Spacing (ft)
Range of
Condition
of Existing
Pavement
Macro-
fibers
Option (in
software)
Transverse
Joint
Dowel Bars
*Mainline
Longitudinal
Tie Bars
Recommended
Design
Procedure
Bonded
Concrete
Overlay of
Asphalt
Pavement
Up to 15 3–6 in. 1.5 times thickness (in.) Fair to Good Yes No No 1, 2, 8
Bonded
Concrete
Overlay of
Concrete
Pavement
Up to 15 3–6”
Match existing cracks
and joints and cut
intermediate joints
Fair to Good Yes No No 3, 4, 5
Bonded
Concrete
Overlay of
Composite
Pavement
Up to 15 3–6 in. 1.5 times thickness (in.) Fair to Good Yes No No 1, 2, 8
Thin Fibrous
Overlays
of Asphalt
Pavements
Up to 15 2–3 in. 4–6 ft Fair to Good Yes No No 7
Unbonded
Concrete
Overlay of
Asphalt
Pavement
Up to 100 4–11 in.
Slab < 6 in.—use 1.5
times thickness (in.)
Slab ≥ 6 in.—use 2.0
times thickness (in.)
Slab > 7 in.—use 15 ft
Deteriorated
to Fair Yes For slabs >
7 in.
T ≥ 6 in.—
use agency
standards
3, 4, 5
Unbonded
Concrete
Overlay of
Concrete
Pavement
Up to 100 4–11 in.
Slab < 5 in.—use
6 ft x 6 ft panels
Slab 5–7 in.— use 2.0
times thickness (in.)
Slab > 7 in.—use 15 ft
Deteriorated
to Fair Yes For slabs >
7 in.
T ≥ 6 in.—
use agency
standards
3, 4, 5
Unbonded
Concrete
Overlay of
Composite
Pavement
Up to 100 4–11 in.
Slab < 6 in.—use 1.5
times thickness (in.)
Slab ≥ 6 in.—use 2.0
times thickness (in.)
Slab > 7 in.—use 15 ft
Deteriorated
to Fair Yes For slabs >
7 in.
T ≥ 6 in.—
use agency
standards
3, 4, 5
Unbonded
Short-jointed
Concrete
Slabs
Up to 100 > 3 in. 4–8 ft Poor to Fair Yes For slabs >
7 in.
For ≥ 3.5 in.
slabs at tied
concrete
shoulders or for
T ≥ 6 in.—
use agency
standards
6
Bonded OverlaysUnbonded Overlays
*See additional guidance regarding tiebars for shoulders and widening section beginning on page 71.
Recommended Design Procedures (see previous page for links)
1. Bonded Concrete Overlay on Asphalt (BCOA) Thickness Designer (ACPA 2012)
2. BCOA ME (Vandenbossche 2013)
3. Guide for Design of Pavement Structures. 4th ed. (AASHTO 1993)
4. Mechanistic-Empirical Design Guide—A Manual of Practice (AASHTO 1993)
5. StreetPave (ACPA 2012)
6. Optipave V2.0. (TCPavements 2010)
7. Flowable Fibrous Concrete for Thin Pavement Inlays (Bordelon and Roesler 2011) (see Appendix C)
8. Illiniois DOT’s spreadsheet for bonded concrete inlay/overlay of asphalt design (Roesler et al. 2008)
55
Guide to Concrete Overlays
Ch 4. DESIGN
In January 2011, the ACPA released a BCOA
thickness design web application, Bonded
Concrete Overlay on Asphalt (BCOA) ickness
Designer (i.e., ACPA BCOA) that incorpo-
rates the work by Riley (2006). e ACPA
BCOA is valid for a slab thickness of 3 to 6
inches and a maximum panel size of 6 feet.
Shorter joint spacings (both transverse and
longitudinal) are typically used for bonded
overlays over asphalt pavements, such as 4
foot by 4 foot or 6 foot by 6 foot slabs for
a 12-foot wide lane. Note that the ACPA
BCOA web application does not allow designs
outside these ranges and provides warnings
to indicate that the trial design needs to be
modified or that a bonded overlay of asphalt
pavement may not be the appropriate solu-
tion. Furthermore, when BCOA designs are
approaching 6 inches thick and 6 feet wide,
the BCOA-ME procedure described below
should be considered.
Updates in 2012 improved the fiber reinforce-
ment input to the ACPA BCOA based on
work by Bordelon and Roesler (2012), which
used the residual strength ratio of the fiber-
reinforced concrete measured according to
ASTM C1609-10. In 2012, the ACPA BCOA
design tool was also upgraded to allow for
structural designs in any climate zone in the
United States by including site-specific effec-
tive temperature gradients (Vandenbossche et
al. 2012) for approximately 200 cities.
e input requirements for the ACPA BCOA
thickness design tool follow:
• ESALs
• Percentage of allowable cracked slabs
• Reliability
• Design location (to determine the site-
specific effective temperature gradient)
• Existing asphalt pavement
◦Remaining asphalt thickness and
modulus
• Composite subgrade/subbase k-value
• Concrete overlay
◦Strength, modulus, fiber residual strength
ratio, and CTE
• Proposed slab size and preoverlay surface
preparation
e recent implementation of the effective
temperature gradient for each city was deter-
mined as the equivalent negative temperature
gradient that gives the same cumulative dam-
age as the full distribution of temperature
differentials for that particular site and inputs
(slab thickness, slab length, asphalt thickness,
and concrete strength). For all site locations,
this effective temperature gradient occurs 100
percent of the time to give the same fatigue
damage as the full temperature differential
distribution.
BCOA-ME Method
In 2013, the University of Pittsburgh devel-
oped a new design procedure under the
FHWA Pooled Fund Study TPF-5(165)
(Vandenbossche 2013), the BCOA-ME. Since
a substantial number of bonded overlays
have been in service for an extended period
of time, the opportunity existed to reevaluate
the modes of failure for these overlays. is is
critical since the pioneering procedures that
have been traditionally used for the design
of bonded concrete overlays are based on the
limited amount of information available at
the time of their development. e perfor-
mance review revealed the failure mode is
dictated primarily by slab size and not overlay
thickness, as was previously assumed.
e BCOA-ME procedure incorporates the
ACPA BCOA performance prediction model
that addresses corner cracks for slab sizes
less than or equal to 4.5 feet by 4.5 feet, the
Colorado DOT performance prediction
model that addresses transverse cracking for
slabs with a 12-foot width (Sheehan et al.
2004), and a newly developed performance
prediction model that addresses longitu-
dinal cracking in 6-foot by 6-foot slabs. It
should be noted that at times diagonal cracks
develop in the 6-foot by 6-foot slabs, but
these diagonal cracks initiate at the intersec-
tion of the wheel path and the transverse joint
in the same manner that the longitudinal
cracks develop. Instead of propagating to the
adjacent transverse joint, as occurs with a
longitudinal crack, they veer off toward the
lane/shoulder joint and form a diagonal crack.
erefore, the initiation stress for both the
longitudinal and diagonal cracks are the same.
e design process also includes a check,
based on the work of Vandenbossche and
Barman (2010), to determine whether or not
there is a potential for reflective cracking. is
check does not influence the design thickness
but indicates whether or not preemptive mea-
sures should be taken prior to replacing the
overlay to prevent reflective cracking.
e six primary enhancements to current
methodologies provided by the BCOA-ME
procedure include the following:
1. e predominant failure modes are rede-
fined as a function of slab size and, unlike
in the other procedures, all modes are
addressed within this one procedure.
2. e variability of the asphalt stiffness with
temperature is considered.
3. e equivalent temperature gradient is
defined based on local conditions.
4. e prediction models have been cali-
brated with actual performance data.
5. e effects of fiber on the performance of
the overlay are more accurately quantified.
6. e effects of debonding are considered.
e BCOA-ME procedure provides an overlay
thickness after the following information is
entered into the design spreadsheet:
• Traffic
• Design location
◦Longitude, latitude, and elevation
◦Climatic zone
• Existing HMA pavements
◦Remaining asphalt thickness
◦Approximate percent fatigue cracking
◦Temperature cracking (yes/no)
• Composite subgrade/subbase k-value
• Concrete overlay strength, modulus, fiber
residual strength ratio, and CTE
• Proposed slab size
Enhancements (1) thru (4) have been
incorporated into the current version of the
procedure (Beta Version 1.3) and is available
at www.engineering.pitt.edu/Vandenbossche/
BCOA-ME/. e design procedure will be
finalized, including the incorporation of
enhancements 5 and 6, and available for use
at the same website.
1993 AASHTO Guide Method
e method found in the 1993 AASHTO
Design Guide is based on mathematical
models derived from empirical data collected
during the American Association of State
Highway Officials (AASHO) Road Test car-
ried out in the late 1950s. Even though no
overlay sections were evaluated during the
AASHO Road Test, experience has shown
that, when used properly, this procedure
provides suitable but conservative bonded
and unbonded concrete overlay designs. e
AASHTO computer software for implement-
ing the 1993 AASHTO Design Guide is
called DARWin. In addition, a number of
agencies and state DOTs have developed cus-
tom software and spreadsheets to apply this
procedure. e ACPA has also developed the
WinPAS software package, which implements
the procedure.
e 1993 AASHTO Design Guide uses the
concepts of structural deficiency and effective
structural capacity for evaluating and charac-
Guide to Concrete Overlays
56
Ch 4. DESIGN
terizing the existing pavement to be overlaid.
e structural capacity (SC) of a pavement
section decreases with traffic and time. In
this procedure, SC is expressed in terms of
the effective structural number for existing
asphalt pavements (SNeff), or the effective
slab thickness for concrete pavements (Deff).
Figure 47, which is an adaptation of Figure
5.1 in Part III of the 1993 AASHTO Design
Guide, illustrates this concept. is figure
shows how the structural capacity of an over-
lay (SCoverlay) restores the structural capacity of
the existing pavement (SCeffective) to meet the
requirements for carrying the predicted future
traffic (SCfuture traffic).
e 1993 AASHTO Design Guide presents
three evaluation methods for determining
the effective structural capacity of existing
pavements (SCeffective) when designing con-
crete overlays: Visual Survey and Materials
Testing (Condition Survey), Nondestructive
Deflection Testing (NDT), and Fatigue
Damage from Traffic (Remaining Life).
e designer should select the most feasible
method based on the available resources but
should recognize that each method yields dif-
ferent estimates.
Even though the Remaining Life method is
often used, it is important to note that the
1993 AASHTO Design Guide cites major
deficiencies associated with this method and
explains that the method is mostly applicable
when the existing pavement exhibits very
little deterioration. e 1993 AASHTO
Design Guide explains that the Remaining
Life procedure is based on the AASHO Road
Test equations, and estimating past traffic (in
ESALs) may be subjective and/or uncertain.
In addition, this method does not account
for preoverlay repairs. For these reasons, the
designer should use the Condition Survey
method or NDT when the structural capacity
estimates that result from the Remaining Life
method are inconsistent with the observed
existing pavement condition.
AASHTO Pavement ME Design
Guide Method
e AASHTO Pavement ME Design
Guide procedure was developed under
NCHRP Project 1-37A, Development of
the 2002 Guide for the Design of New and
Rehabilitated Pavement Structures: Phase
II (Transportation Research Board 2004),
and the original guide and accompanying
software were both called the Mechanistic-
Empirical Pavement Design Guide (M-E
PDG). e procedure is implemented in
an AASHTO professional software package
called AASHTOWare Pavement ME Design
(AASHTO [no year]) available at www.aash-
toware.org.
e AASHTO M-E PDG procedure com-
bines a mechanistic-based approach with field
performance data so that an engineer can
confidently predict the performance of pave-
ment systems not considered in the original
calibration. is method adopts an integrated
pavement design approach that allows the
designer to determine the overlay thickness
based on the interaction between the pave-
ment geometry (slab size, shoulder type, load
transfer, steel reinforcement), local climatic
factors, and concrete material and support
layer properties. e procedure is currently
under evaluation and implementation by a
number of state DOTs.
Chapter 7 in Part 3 of the M-E PDG
(NCHRP 2004), “PCC [Portland Cement
Concrete] Rehabilitation Design of Existing
Pavements,” contains detailed informa-
tion regarding the design of bonded and
unbonded concrete overlays. is procedure
is an iterative design process that involves
analyzing a trial overlay design not only in
terms of thickness but also in terms of other
relevant design features, such as joint dimen-
sions and load transfer, steel reinforcement (if
applicable), and concrete material properties.
e following list summarizes the AASHTO
M-E PDG inputs (NCHRP 2004):
• Rehabilitation type
• Design life
• Pavement failure criteria (cracking, fault-
ing, IRI)
• Reliability
• Traffic
• Local climate
• Pavement cross section and layer properties
• Pavement design features
◦Slab geometry
◦Joint and shoulder type
◦Concrete properties (strength, mixture
proportions, CTE, etc.)
◦Drainage and surface properties
ree input levels are available for pavement
design, depending on the quality of the input
data. Level 1 inputs are used if project-specific
traffic data are available and if certain pave-
ment layer material properties have been
measured. Level 2 inputs are used if correla-
tions with standard tests are necessary to
complete the design. Level 3 inputs assume
national default values in the design process.
is document emphasizes Levels 2 and 3
inputs as a recommended starting point for
using the AASHTO M-E PDG procedure.
e AASHTO M-E PDG method predicts
performance indicators, such as IRI, trans-
verse cracking, and mean joint faulting, over
the pavement’s design life for jointed plain
concrete overlays. For continuously reinforced
concrete overlays, the procedure predicts the
mean crack spacing as well as crack width,
IRI, and number of punch-outs over the
design life. For all of the distress predictions,
the AASHTO M-E PDG method calculates
incremental damage over the life of the pave-
ment by employing transfer functions for the
specific distresses, which are linked with the
corresponding maximum pavement response
(deflection or tensile stress).
ACPA StreetPave Method
In 2012, the ACPA released a new version
of StreetPave that includes bonded and
unbonded overlay designs for existing con-
crete, asphalt, and composite pavements. is
software utilizes new engineering analyses to
produce optimized designs for city, munici-
pal, county, and state roadways. For existing
concrete pavements and overlays, StreetPave
12 may be used to estimate service life and/or
failure criteria.
StreetPave 12 also offers an asphalt cross sec-
tion design process (based on the Asphalt
Institute method) to create an equivalent to
asphalt design for the load-carrying capacity
requirement. A “Life Cycle Cost Analysis”
module allows you to perform a detailed cost/
benefit analysis and make informed deci-
sions on your pavement design project. With
one pavement design tool, you can design
equivalent concrete and asphalt sections and
evaluate the best possible solution(s) for your
pavement needs.
Bonded concrete overlays on asphalt or
composite are designed using the same equa-
tions as the ACPA BCOA method. All other
concrete overlay design methods in StreetPave
use the same overlay design equations as the
1993 AASHTO Design Guide method. is
Figure 47. Illustration of structural capacity
loss over time and with traffic
57
Guide to Concrete Overlays
Ch 4. DESIGN
includes using the same equations and factors
for determining the Deff for existing concrete
pavements and the same overlay thickness
determination equations (e.g., DOL = Df – Deff
for a bonded concrete overlay on concrete).
e only differentiating factor between
StreetPave and the 1993 AASHTO Design
Guide overlay designs is that the required
composite thickness (Df) is calculated using
StreetPave’s core design equations, using
faulting and cracking as the failure criteria.
StreetPave also provides functionality to
include fibers in any design.
Slabs with Optimized Geometry
and OptiPave2™ Design
Software
A new methodology called TCP (thin con-
crete pavements) or short-jointed concrete
slabs has been developed to design the
concrete slab thickness by optimizing the
slab size given the geometry of the truck
axles (Covarrubias and Covarrubias 2008).
e key principle of the design method is
to select the slab size so that not more than
one set of wheels is on any given slab at one
time, thereby minimizing the critical top
tensile stress. Full-scale test sections were
constructed and tested at the University of
Illinois under accelerated pavement loading
conditions with a slab thickness of 3.5 to 8
inches on either aggregate or asphalt base
layer (Cervantes and Roesler 2009; Roesler
et al. 2013). e performance data from the
full-scale test were utilized in the development
of the mechanistic-empirical design software
called OptiPave2™ (Covarrubias et al. 2010;
Covarrubias 2011). OptiPave2™ software is
specifically tailored to design short-jointed
concrete pavements for any set of climate,
traffic, subgrade/subbase layer, and material
property inputs, including the addition of
macro fibers.
in concrete pavements designs include
unbonded concrete pavement over granular
or stabilized base layers. Typical slab sizes for
TCP are between 4.5 feet and 8 feet long by
6 feet wide with slab thickness ranging from
2.4 to 10 inches depending on traffic, climate,
and soil conditions. e OptiPave2™design
software predicts the level of cracking,
faulting, and IRI for a given set of inputs.
OptiPave2™ is currently the only pavement
design software that is able to optimize the
slab thickness requirements for slab sizes less
than 10 feet. Since 2006, multiple projects
have been constructed in Latin America,
including Chile, Peru, and Guatemala.
OptiPave™ software licenses are available in
North America from PNA Construction
Technologies, Inc. (www.pna-inc.com, tele-
phone number 800-542-0214).
Design Consider-
ations for Bonded
Overlay Systems
With bonded concrete overlays, the bond
between the overlay and the underlying pave-
ment assists the horizontal shear transfer at
the bond plain. is horizontal shear transfer
stresses into the underlying layers, thereby
decreasing tensile stresses in the bonded over-
lay. Somewhat different considerations are
required depending on whether the overlay
is bonded to existing concrete or to existing
asphalt. All bonded concrete overlay systems,
however, depend on the integrity of the
underlying pavement.
Bonded Overlays of
Asphalt and Composite
Pavements
A unique design consideration for bonded
overlays on asphalt or composite pavements
is the joint spacing to mitigate curling and
warping stresses in the bonded overlay. e
ACPA’s original 1998 design procedure for
this overlay type was based on a single mode
of failure—the corner break. e ACPA’s
2004 revised procedures incorporated proba-
bilistic methods into concrete fatigue models,
but the procedure for this overlay type con-
tinued to be based only on the corner break
mode of failure.
e corner break model has worked
adequately. In recent years, however, it has
been recognized that the two most common
precursors to failure for bonded concrete
overlays on asphalt or composite pavements
are delamination stemming from failure in
the bond plane or from failure in the underly-
ing asphalt layer. erefore, the most recent
revisions of the design procedure for this type
of overlay reflect a “weakest link” approach,
applying probabilistic techniques to all three
modes of failure.
First, design parameters are input into the
design model. en stresses are calculated
using the corner stress model. From that
information, strains in the bottom and top
of the asphalt layer, plus horizontal stresses
inferred at the bond plane, are calculated
based on the location of the composite neu-
tral axis.
Concrete corner stresses are then compared
against the ACPA’s 2004 fatigue model for
concrete. Strains in the asphalt are compared
to Asphalt Institute design fatigue models.
Bond plane stresses are evaluated using a
horizontal shear data model based on data
obtained from Iowa, Florida, and Colorado
projects. e calculated stresses and strains
for each mode are then compared against the
probabilistic models of each mode to deter-
mine which factor is the most likely mode of
failure, or the weakest link, driving failure in
the overall system.
e bottom line is that understanding the
interaction between bond plane stresses and
corner break stresses helps designers opti-
mize joint spacing and several other factors
in designs for bonded concrete overlays on
asphalt pavements.
In addition to the probabilistic adaptation
of the mechanistic procedures, new advance-
ments in materials were included, particularly
with regard to the inclusion of fibers. e
effect of fibers in the models is based on their
ability to enhance the fatigue resistance of
the concrete. e design procedure for fibers
is open ended in that as new fibers are devel-
oped and properties are established, these can
be incorporated accordingly.
Probably one of the more challenging aspects
in the design of bonded overlays of asphalt
and composite pavements is the consideration
of the supporting platform. For designs of
this type, the classic k-value described earlier
is based on the value at the bottom of the
asphalt layer rather than at the bottom of the
concrete layer.
e joint design of thin bonded overlays over
asphalt pavement is a distinguishing charac-
teristic when these projects are placed in the
field. e transverse and longitudinal joint
spacings are always 6 ft (1.8 m) or less in
length as determined by the design analysis.
It is important that joints in this type of over-
lay be cut as quickly as possible to minimize
the likelihood of curling stresses developing,
triggering delamination at the edge of the
pavement. Early-entry saws are often used.
ere are numerous examples of bonded over-
lays of asphalt and composite pavements that
are approaching 20 years of service. When
properly designed and constructed, these
concrete overlays can perform satisfactorily for
any desired design life.
FAQ – How is the thickness of an asphalt surface in a composite handled?
In this approach, the same failure model is used, but the assumption is made that the asphalt
layer has the maximum permitted thickness of 6 in. (150 mm), which corresponds to the
limits of the current design model. e elastic properties of the asphalt surface are used in
the model.
Guide to Concrete Overlays
58
Ch 4. DESIGN
Bonded Overlays of
Concrete Pavements
e AASHTO Design Guide (1993, 1998)
procedure for bonded overlays of concrete
pavements uses a “design deficiency” or
“remaining life” approach. e mode of fail-
ure most commonly used is serviceability.
is is largely due to the fact that most pave-
ment engineers today are comfortable with
the concept. e existing pavements in these
cases have not failed. It is assumed, however,
that some of the pavement life has been
consumed in either fatigue or serviceability,
depending on the design procedure being
used.
First, standard design methods (see existing
methodologies) are used to determine the
required thickness of a new pavement based
on the anticipated traffic, planned materials
to be used, and other parameters typically
considered in new pavement design. Having
determined the overall required pavement
thickness, the pavement thickness equivalent
after adjusting for the life consumed of the
existing section is estimated. is thickness
corresponds to the thickness required to carry
the number of loadings to failure as defined
by AASHTO. In the AASHTO Design Guide
(1993, 1998) and earlier terminology, this is
simply the change in serviceability and cor-
responds to the “remaining life.”
Additional minor adjustments may also be
made having to do with observations of
existing pavement condition, but these are
somewhat subjective. After the adjustments,
the resulting number represents how much
effective pavement thickness is still actually
available to be further “consumed” or used
in the new pavement system in addition to
the new overlay. e difference in the thick-
ness calculated for a new pavement and this
effective section is the “design deficiency” or
the required thickness of the new section that
should be bonded to the existing pavement.
For further information, see the AASHTO
Design Guide (1993, 1998).
Critical to the performance of this type of
overlay is the development of a bond between
the two layers. Existing design procedures for
bonded overlays do not specifically address
bond strength, treating it primarily as a
construction issue. If the section is cleaned
and constructed correctly and proper curing
procedures are used, bond strength is usually
not a problem. Extreme daytime to nighttime
temperature swings, however, can sometimes
trigger delamination failures. If ambient
temperature differentials in excess of 30˚F are
anticipated, from the time pavement is set
and for the next 12 to 18 hours the section
should be protected.
FAQ—What is serviceability?
Serviceability or present serviceability rating (PSR) was developed during the AASHO Road
Test. e PSR is defined as “the judgment of an observer as to the current ability of a pave-
ment to serve the traffic it is meant to serve” (AASHO 1962). e PSR scale ranges from 0
(very poor) to 5 (very good).
Maintaining the bond is especially critical
during the first few days when the overlay is
susceptible to curling and warping stresses,
especially at the pavement edges. erefore,
the bond must be protected through thor-
ough proper curing practices, particularly
of the pavement edge, minimizing relative
humidity and temperature differentials
between the two layers and keeping early
traffic away from the pavement edges until
adequate bond strength has been achieved
(usually when opening strength has been
achieved).
Joints in designs of this type must be matched
to the existing section. Transverse joints
should be cut full depth of the overlay plus
0.50 in. (13 mm) and must be as wide as or
greater than the crack below the joint in the
underlying pavement; see Figure 48. Note
that this is different from the width of the
existing joint reservoir. Longitudinal joints
should be cut at least T/2.
Designs for overlays of existing CRCPs are
also possible. In the case of CRCPs, however,
there is no need to match the transverse joints
since none exist, with the exception of termi-
nal joints and full-depth repairs.
e use of steel reinforcement or dowels is
not usually a consideration for bonded over-
lays on concrete pavements unless the overlay
is thicker than usual, new shoulders are being
tied, or there is also a desire to retrofit load
transfer.
Properly built, bonded overlays can reason-
ably be expected to provide a minimum
service life of 15 years before maintenance
is required. e first indication of problems
on these overlay projects is usually early
delamination at the bond plane, quickly fol-
lowed by classic fatigue failure at isolated joint
locations. ese can be repaired using partial-
depth repair techniques if the underlying slab
remains sound.
Design Consider-
ations for Unbonded
Overlay Systems
Unbonded overlay designs usually do not
consider bond, though in fact some bonding
usually occurs and is beneficial. ey are essen-
tially designed as new concrete pavements,
with the pavement being overlaid acting as a
base. Adaptation of existing design procedures
is relatively straightforward and construction
relatively easy. Unbonded overlays are usually
designed to serve 20 to 30 years.
e selection of the load transfer coefficient
in the AASHTO procedure should be made
with recognition of the character of the under-
lying layer in addition to the intended load
transfer system for the overlay. Consideration
should be given to the underlying structure
providing additional load transfer, which is not
necessarily true of new concrete pavements.
e designer should not arbitrarily pick a
“conservative” value, as this is not the intent
of the design procedure. e ACPA’s WinPAS
software program (based on AASHTO Design
Guide 1993) includes an entire section for use
in designing these types of systems.
Care must be exercised during construction
to ensure that the saw depth of the unbonded
overlay is adequate, particularly when the over-
lay thickness varies, such as in variable cross
slope, transitions, etc.
Figure 48. Width of overlay joint saw cut must be greater than the crack width in the existing
pavement
Note: Overlay joint width shall be equal to or
greater than crack in the existing slab.
If “X” is 0.50 in. (13 mm) or greater, the underlying
crack width in the existing slab should be
measured. If crack is 0.25 in. (6.4 mm) or greater,
and existing pavement does not have dowel bars,
the joints should be evaluated to determine if load
transfer rehabilitation is required to eliminate
faulting. If there are numerous joints of this type,
the existing pavement may not be a good
candidate for a bonded overlay.
Width of new
overlay
transverse joint
Concrete
overlay
Underlying crack
in existing slab
Saw cut in
existing slab (X)
Overlay joint
59
Guide to Concrete Overlays
Ch 4. DESIGN
FAQ—What happens if an unbonded
overlay bonds to the separation layer?
Beneficial bonding can occur when an
asphalt separation layer is used as part of
an unbonded overlay design. Although
not factored in the thickness design pro-
cedure, this beneficial bonding effectively
increases the load-carrying capacity of
the unbonded overlay system. is is one
reason that rubblization or crack and seat
methods are not recommended preoverlay
activities. Leaving the existing pavement
intact preserves the structural integrity
of the existing pavement and maximizes
the value of the investment placed in the
original pavement.
Unbonded Overlays of
Concrete Pavements
In many cases, an existing concrete pave-
ment—even one in poor condition—can
provide a cost-effective base for a new con-
crete overlay.
Suitability of Existing Pavement
as a Base
e existing pavement is suitable as a base
for an unbonded overlay if it can meet the
desired design life requirements for the base.
e existing pavement must be stable and
uniform; that is, it must not experience signif-
icant differential movement and there should
not be large areas lacking adequate structural
support.
When an entire concrete pavement has begun
to break up, it is a good indicator of serious
subgrade/subbase problems that need to be
addressed before other solutions are consid-
ered. If the subgrade is unstable, it may be
time to replace the pavement and correct the
subgrade/subbase.
Isolated areas of full-depth structural distress
are generally not a problem if they can be
repaired cost effectively before placing the
overlay. On the other hand, areas of MRD
that cause movement from expansion and/or
contraction in the existing pavement require
careful evaluation.
If MRD-related movement is limited primar-
ily to the joints (e.g., D-cracking movement),
and if full-depth joint repairs can be justified
from a cost perspective, a pavement may still
be a good candidate for an unbonded con-
crete overlay. Unbonded concrete overlays on
concrete pavements with full-depth structural
and/or joint repairs have proven performance
records as effective bases for unbonded con-
crete overlays. Some agencies have even had
success with infilling deteriorated joints with
stable material such as flowable mortar.
When an entire concrete pavement has
deteriorated severely along the length of the
pavement due to movement, it is probably
time to reconstruct the entire pavement. A
good option is to recycle the pavement in
place and use it as an unstabilized (granular)
subbase for a new, full-depth pavement if the
existing subgrade is adequate (see Appendix B
for a discussion of recycling options).
Interlayer
All unbonded concrete overlays on concrete
must be separated from the existing concrete
pavement by a stress-relief layer, or interlayer,
to prevent reflective cracking from movement
of the existing pavement. Interlayers serve
multiple purposes:
• e interlayer provides a shear plane that
relieves stress and helps prevent cracks from
reflecting up from the existing pavement
into the new overlay.
• e interlayer may prevent bonding of the
new pavement with the existing pavement,
so both are free to move independently.
• Drainage must channel infiltrating water
along the cross slope to the pavement edge
and then be outletted.
• Bedding is a cushion for the overlay to pre-
vent keying from existing faulting.
e design should consider the relative
importance of each purpose based on project-
specific conditions and the condition of the
existing pavement.
Over the years, many stress-relief methods
have been used successfully. e most com-
mon stress relief is a thin layer of asphalt
material. ickness is not critical, but 1 in.
(25 mm) is usually adequate to eliminate
potential problems with “keying” of faulted
slabs (see Figure 49), localized repairs, etc.
When constructing CRCP unbonded overlays
over both CRCP and plain jointed pave-
ments, Texas has sometimes increased the
asphalt separation layer thickness to greater
than 1 in. (25 mm).
It is important not to use the asphalt sepa-
ration layer as a leveling course. All grade
corrections, including leveling, should be
accomplished with the concrete overlay itself.
e geotextile should be either daylighted
past the edge of the shoulders or tied into a
longitudinal underdrain system to provide
positive drainage. Laps should be a minimum
of 8 inches, and the geotextile should be
anchored securely using nails and washers at 6
feet c/c each direction. e structural condi-
tion of the existing concrete pavement must
be carefully assessed before selecting a geotex-
tile instead of an asphalt interlayer.
ere has been one documented case where
noise from concrete slabs rocking against each
other was observed. is project was a 4-inch
thick unbonded overlay placed on a relatively
thick (3 mm+) geotextile. No formal studies
were performed on the project, but based on
informal observations, the general hypothesis
Figure 49. Upper sketch shows concrete
overlay locking up with old pavement
(keying), and lower sketch shows interlayer
separates overlay from existing pavement.
FAQ—Why is it better to use concrete as the material for making grade corrections?
ere are many reasons to use a nominal thickness asphalt separation layer while making
grade corrections with concrete:
• e cost of the two materials on a volume basis is very similar.
• When a cubic-yard pay item is used for the concrete overlay, the risk of yield loss to the
contractor is nil; thus, the agency pays only for the actual quantity of material used.
• It is very difficult to place variable thickness asphalt layers to true grade because of
variable roll down; there will still be significant thickness variation when this approach
is used.
• With cost being nearly equivalent, an increased thickness of concrete will add
significantly more life than a thicker asphalt separation layer.
• When dowel baskets are used in the concrete overlay, securely anchoring them into a
variable thickness asphalt separation layer has proven to be difficult.
Guide to Concrete Overlays
60
Ch 4. DESIGN
is that the compression of the fabric under
traffic loading allowed deflection of the slabs,
which caused the noise. e noise was less
prevalent during warmer temperatures when
the slabs were tight against each other and
eventually subsided completely. In 2013,
the Minnesota DOT started testing the dif-
ferent thicknesses of nonwoven geotextile
fabric under 3 -inch thick (fiber-reinforced)
unbonded concrete overlay over concrete.
e test sections were at Minnesota DOT’s
pavement test track, MnROAD, and the final
results will be available in 2014. Early obser-
vations indicate a difference in both physical
and audible behavior of the overlays for the
different fabric thicknesses.
Interlayer fabric is specified by weight and
thickness (mils) and color; see Figures 50
and 51. Table 11 provides a general rule of
thumb for weight and thickness. e weight
per square yard and thickness should be given
when specifying a geotextile separation layer.
See Chapter 5, Separation Layer Materials, for
additional details.
If joint faulting in excess of 3/8 inch for
asphalt interlayer and 0.25 inch for geotex-
tile interlayer is present, the joints should be
milled to eliminate the vertical offset or an
asphalt separation layer should be used.
Table 11. Typical Weight and Thickness for Geotextile Interlayer
Interlayer Fabric
≤ 4-in. overlay—consider
13 oz/ yd2 typical thickness,
130 mils
≥ 5-in. overlay—consider
15 oz/yd2 typical thickness,
170 mils
Weather resistance > 60%
2kPa—120–150 mils 2kPa—155–185 mils Test tensile strength after
500 hours of UV accelerator
20kPa—80–110 mils 20kPa—110–140 mils
Tensile strength after test
must be at least 60% of
initial strength
200kPa—20–50 mils 200kPa—40–70 mils
For unbonded overlays of concrete pavements,
some agencies note the underlying pavement
joint locations and intentionally place the joints
in the new overlay away from those joints such
that they are mismatched. e rationale for this
is that load transfer will be improved. Other
agencies discount this idea in favor of a more
construction-friendly approach. In this case,
joints are simply placed where they would nor-
mally be according to the type of design being
built. Both strategies have resulted in good
performance. An exception to this is existing
expansion joints, which must be matched in the
unbonded overlay; see Figure 52.
Drainage of Interlayer
e presence of water within the interlayer
system will often accelerate the development
of distress in the overlay. Water can enter a
pavement system from the top down or from
the bottom up due to any of the following
situations:
• Longitudinal joint trapping
• Tight, clay subgrade that does not drain
• Densely graded subbase that does not drain
• High water table capillary action
• No subdrains, or subdrains are not working
All else being equal, improvements to pave-
ment drainage can ultimately allow for a
thinner overlay design. Such improvements
have the additional benefit of facilitating the
egress of water from the pavement system,
which is often a key factor in the joint dete-
rioration being mitigated by the overlay.
For example, a change in profile and/or
cross slope can be designed in the overlay
so that water is more readily shed from
the pavement surface. Joints in the overlay
can be designed to resist excessive ingress
of water. is can be done by constructing
them with a narrow (single) saw cut and/
or filling or sealing them appropriately.
Subdrainage can also be improved if mea-
sures are taken to retrofit edge drains.
For an unbonded overlay, either a nonwoven
geotextile that meets certain transmissivity
requirements (see Table 11) or open-graded
hot-mix asphalt (HMA) can be used as an
interlayer that promotes drainage, provided
there is an outlet. Nonwoven geotextile
interlayers do promote drainage (wicks
water) but must also have a proper drainage
outlet. See miscellaneous details for drainage
outlets beginning on page 72.
Figure 50. Geotextile fabric separation layer (source: Missouri DOT) Figure 51. White geotextile fabric separation layer (source:
Larry Engbrecht, South Dakota ACPA)
Figure 52. Overlay blowup where expansion joint
should have been cut over existing concrete expansion
joint (source: Dan DeGraaf, Michigan Concrete Paving
Association)
61
Guide to Concrete Overlays
Ch 4. DESIGN
Asphalt interlayers have served as separation
layers on concrete for many years. Occasional
problems, however, have been noted with
asphalt stripping within the interlayer under
repetitive loading, causing a loss of support
for the unbonded overlay; see Figure 53. is
can occur occasionally with high truck-traffic
volumes in the presence of water in the inter-
layer. Usually, the stripping takes several years
to develop. e best preventive solutions are
the following:
• Provide positive drainage for the asphalt
layer. Under heavy truck-traffic loading,
consider using a drainable asphalt mixture
or the gradation used by the Michigan
DOT (see Chapter 5, page 78, Table 18).
e interlayer should be daylighted to the
edge of the shoulders or a subdrain system
installed.
• Incorporate antistrip additives such as lime
in the asphalt. Lime was found to be more
effective than liquid antistripping additives.
• Seal joints in the concrete overlay and at
the shoulders.
• Utilize a geotextile separation layer with
positive drainage.
Joint Design
Because of the high stiffness of the underlying
platform (the existing concrete pavement) in
unbonded overlays on concrete, it is neces-
sary to shorten joint spacing in the overlay
compared with normal designs. e shorter
joint spacing is necessary to reduce the risk
of early cracking due to temperature curling
and moisture warping stresses, combined with
loading stresses. Note that existing AASHTO
methods do not consider this in design.
Rule-of-thumb guidance for joint spacing
for unbonded overlays using these methods
is based largely on experience (see Table 21,
beginning on page 99, for information about
maximum joint spacings).
Transverse joints in the unbonded overlays
can be plain, doweled or, in a continuous
reinforced concrete overlay, totally eliminated.
Plain undoweled joints are the most common
for thicknesses less than 7 inches. ere are
conditions, however, when mechanical load
transfer is required to meet load criteria with
certain thickness restrictions due to costs or
vertical limits. Before dowels are used, con-
sideration should be given to shorter joint
spacing using synthetic fibers that help hold
the joints tight. If that is not possible, then
rounded or plate dowels can be considered.
in unbonded concrete overlays (less than
5 in. [125 mm] thick) have been built under
appropriate loading conditions using short
joint spacing, usually 6 ft (1.8 m) or less, and
do not have dowels.
e purpose of the dowels in transverse joints
is to help load transfer across the transverse
joint. Dowels are typically used when heavy
truck traffic is anticipated, which normally
drives the design thickness to 7 in. (175 mm)
or greater. e depth of the dowels is at T/2
except in super transition areas (see miscel-
laneous design details for further information
in supers). e transverse saw cut depth over
dowels is T/3 or T/4.
ere are constructibility issues (mainly
paving machine clearance to the rounded
dowel) when using load-transfer dowels in
thin overlays (< 7 inches) that necessitate
using smaller-diameter dowels (1 inch or less)
when dowels are needed. e use of smaller-
diameter dowels has a reduced bearing area
that increases the bearing stress on the smaller
concrete area under the dowel bar, sometimes
resulting in premature socketing (enlargement
of the area around the dowel), which defeats
the purpose of using dowels. In response to
the need to accommodate thinner pavements
and yet meet design loading for longer joint
spacings, the concrete paving industry is
beginning to utilize plate dowels, particularly
in industrial parking lots; see Figure 54. e
plate dowels solve paving machine clearance
problems and provide the load transfer across
the joint. Because of the larger horizontal sur-
face area of plate dowels versus round dowels,
the bearing pressure (psi) on the concrete is
reduced. e reduced restraint and stresses of
plate dowels also minimizes random cracking
in thinner sections. To date, there is a limited
number of plate dowels used in highway proj-
ects. In cases where thin unbonded overlays
are desired to meet vertical restrictions and
load demands, however, the use of synthetic
fibers for shorter contraction joints in com-
bination with plate dowels in construction
joints does have merit.
Manufacturers offer various plate dowel geo-
metrics and associated installation devices.
e shrinkage restraint is reduced by using
a tapered shape or formed void or by having
compressible materials on the vertical faces
with a thin bond breaker on the top and bot-
tom dowel surfaces, per ACI 360R-10. e
tapered shape, along with a thin bond breaker
on all sides, allows a void space to develop
along the vertical sides of the dowel, eliminat-
ing restraint as the slab shrinks from the joint;
see Figure 55. Compared to round dowels,
plate dowels allow adjacent panels to move
Figure 53. Asphalt stripping of interlayer
(source: Dan DeGraaf, Michigan Concrete
Paving Association)
Figure 54. Tapered plate dowel baskets in transverse
contraction joints and football-shaped plate dowels for
slipformed longitudinal construction joints
Figure 55. Higher shrinkage restraint in joint intersection with round
dowel (left) versus joint intersection with plate dowel (right)
Figure 56: Joint intersections - Compared to round dowels, plate
dowels allow for adjacent panels to shrink freely without restraint
and can therefore be placed within 6 in. of a joint intersection
where the curling / warping stresses are the greatest.
Guide to Concrete Overlays
62
Ch 4. DESIGN
freely without restraint and can therefore be
placed within 6 inches of a joint intersection
where curling and warping stresses are the
greatest. Similarly, a formed void or compress-
ible material can also eliminate restraint as the
slab shrinks from the joint.
Because of the various plate dowel geometries
and installation devices available, the indi-
vidual manufacturers’ published engineering
reports should be consulted to determine
optimum dowel size and spacing for a specific
project. Plate load-transfer devices are also
useful in other pavement applications where
joints should have load-transfer capability
while allowing two-directional doweling
and odd-shaped panels; see ACI 302-1R-04
(ACI 2010). e use of plate dowels exposed
to deicing salts is limited. It is recommended
that a proven and tested corrosion-resistant
surface be applied to these dowels when
exposed to deicing. See Miscellaneous Design
Details for further discussion on plate dowels.
Unbonded Overlays of
Asphalt Pavements
Unbonded overlays of asphalt pavements
can address existing sections that have crown
or ruts in the surface. Placing the concrete
directly on the surface positions the thickest
concrete at the points of highest load in the
pavement structure and is therefore one of the
more efficient designs. If rutting is extreme
(greater than 2 in. [50 mm]) or the change
in cross section due to crown is significant,
care should be taken to ensure that the design
plans call for adjusting the sawed joint depth
accordingly.
Due to the variability in thickness across the
section if placed directly on the asphalt, the
contract documents should include provi-
sions for payment for materials separately
from payment for placement. ese so called
“square-yard cubic-yard” provisions are rec-
ommended for all concrete overlay projects
and are important in reducing the contractors’
risk and owners’ cost in bidding the projects.
Unbonded Overlays of
Composite Pavements
Unbonded overlays of composite pavements
follow the same design guidelines as concrete
overlays of concrete pavements. e primary
difference is that the separation layer already
exists in the form of the asphalt layer of the
composite pavement. In some cases, the
existing asphalt may be unsuitable as a separa-
tion layer and must be milled off and a new
separation layer placed. is primarily occurs
when the asphalt is prone to lose stability
(resulting in a loss of support for the overlay)
due to stripping.
Plan Development
For DOTs that are inexperienced with the
design of concrete overlays, the approach
should be similar to that of designing an asphalt
overlay. ere is no need to add complexity to
the planning and engineering process simply
because the overlay type has changed. e loca-
tion, geometrics, and maintenance of traffic
requirements should dictate the level of design
detail that is required in the plans.
For decades, rural asphalt overlay projects have
been successfully designed and built from a
set of plans consisting of a title page, typical
section(s), pay quantities, notes, plan view
sheets, and standard drawings. is approach is
entirely acceptable for a concrete overlay under
the same conditions. at being said, for proj-
ects in urban or suburban locations, especially
where vertical (bridge clearance, drainage inlets,
etc.) and horizontal (barrier wall, curb, etc.)
constraints are present, the plans must include
the appropriate details and information to
communicate how the concrete overlay will be
treated to meet these conditions.
An example index of plans for a rural concrete
overlay on a state route or county road would
include the following:
• Title sheet with location map
• Typical sections—note limits of any correc-
tion of superelevation
• Estimated quantities and pay-item notes
• Summary of quantity estimates
◦Preoverlay repairs
◦Subdrain installation
◦Pavement removal
◦Separation layer (if used)
◦Concrete overlay—cubic yard and square
yard
◦Shoulders
◦Erosion control—temporary and
permanent
• Survey information in tabular format—con-
trol points, curve data, existing pavement
elevations, and proposed concrete overlay
elevations
• Sequence of construction, maintenance of
traffic, and traffic-control details
• Plan view sheets
• Design details
◦Overlay transitions at bridges, underpasses,
B.O.P., and E.O.P.
◦Jointing details
• Standard drawings
Engineering
Survey
e determination of whether or not a sur-
vey of existing conditions is needed during
the design phase of a project will primarily
depend upon the presence of vertical and/
or horizontal constraints at the construc-
tion site and the condition of the roadway.
When few constraints are present and
mirroring existing contours is acceptable,
a survey is not necessary. Plans need not
include a proposed profile grade for these
types of projects; the existing surface pro-
vides significant control information. Final
profile will be determined during construc-
tion through the combination of minimum
design thickness and design cross slope(s).
If, however, the existing roadway has
significant surface distresses, ride-quality
issues, drainage problems, or profile and
cross-slope corrections, an engineering
survey is recommended. is will allow the
development of an optimized profile and an
accurate estimate of the volume of concrete
required to construct the overlay. Complex
projects with multiple vertical and/or
horizontal constraints should be surveyed
during the design phase, and proposed fin-
ished elevations should be provided to the
contractor to assure that conflicts between
the overlay and existing conditions are
avoided. A vertical control system should be
established along the highway at 1,000-foot
intervals to assist in the development of the
plans and provide the construction forces
with a basis for profile development.
Survey Methods
Regardless of technologies used such as
GPS, total stations, differential leveling, or
laser scanning technology the principals of
survey and data collection apply. Horizontal
and vertical control must be established
throughout the project corridor so existing
and proposed elevation models are relative
to each other and can be verified at each
phase. e control points should be numer-
ous enough to facilitate the survey work as
well as well as be available for the construc-
tion of the project. Normally, horizontal
work is being performed with a total station
and/or GPS, whereas vertical control is
normally is completed with total stations
or component differential leveling. Total
stations do have limitations for vertical
control that needs to be understood by the
surveyor. erefore, component differential
leveling (digital level preferred) is suggested
to achieve the accuracy required. Physical
cross sections of the roadway should be per-
formed on 25 foot intervals or less for the
whole project.
63
Guide to Concrete Overlays
Ch 4. DESIGN
e decision of which technology to use is
up to the surveyor/engineer and the avail-
able technology. Conventional survey is more
labor intense when compared to LiDAR tech-
nologies of static and mobile laser scanning.
Laser Scanning
ere has been a steady if not rapid pro-
gression of improvements in the surveying
industry over the last decade. e efficiency
and accuracy of collecting elevation data has
been improved drastically over the tried and
true rod and level method. e simplest
method of control is to perform minor mill-
ing that is controlled with a traveling ski and
cross-slope system. e advent of laser scan-
ning has opened a new avenue for mapping of
pavement surfaces before overlay construction
to help eliminate excessive overruns. Laser
scanning (Figure 56) can offer reduction in
survey cost, savings in time, and less interfer-
ence to the traveling public.
is increased efficiency makes it cost effec-
tive to perform in-depth surveys. Based on
data obtained from a project constructed on
US-18 in Iowa in 2012 (Cable 2012), it was
found that performing a nine-line survey at
50-foot intervals provided the engineer with
the data necessary to confidently adjust the
profile of the concrete overlay and avoid a
potential 20 percent quantity overrun in the
cubic yards of concrete placed.
e latest development with laser scanning
is basically several existing technologies com-
bined into one unit or process. At the heart
of the unit is the light detection and ranging
(LIDAR) scanner, which measures the flight
time of a beam of light to calculate the range
to objects at predetermined angular incre-
ments, resulting in a very large-point data set
referred to as a “Point Cloud.” e LIDAR
or laser scanner conducts measurements to
targets and a 360-degree camera is used to
assist in identifying objects in the scan. e
unit also includes a global positioning system
(GPS) to record its position on the earth
surface at any time and the relative position
of the objects being scanned. An inertial mea-
surement unit (IMU) is used to account for
movement (pitch, roll, and yaw) in the survey
vehicle. A distance measuring instrument
(DMI) is used to compute wheel rotation
and measurements to aid the process. e
system is capable of repeatable 0.04- to 0.12-
inch accuracy in measurements. Appendix D
provides further information about static or
mobile scanning surveying.
Measurement and
Payment Items for
Concrete Overlays
It is strongly suggested that concrete over-
lays be measured and paid for by the square
yard for placement and by the cubic yard for
furnishing concrete material. is method
has been used successfully for many years by
DOTs that routinely design and construct
concrete overlays. e purpose of providing
a cubic-yard pay item for concrete overlays is
to minimize the risk to both the owner and
the contractor. e basis for using a cubic-
yard pay item is the fact that the underlying
surface is more irregular than a well-prepared
subgrade or subbase would be.
Recognizing that DOTs are acting on behalf
of the taxpayers and contractors are in the
business of taking calculated risks, it does not
seem inappropriate for DOTs to limit their
risk to some degree. Assuming that the vol-
ume of concrete has been correctly estimated
as recommended above, a cap on concrete
overruns of 102 to 106 percent may be con-
sidered reasonable. e agency should make
regular depth checks at the pavement edges,
mid-lane, and centerline of the concrete
overlay during construction to verify that the
thickness of the concrete overlay is equal to or
greater than the design thickness.
Establishing Plan Quantity
for Overlay Concrete
ere are two options to consider:
1. For minimal preliminary work and cost
• Do no preliminary survey other than
measuring wheel rut depth and pave-
ment cross slope at 500-foot intervals.
• Develop design profiles of centerline and
pavement edges.
• Estimate the quantity of concrete
required to meet the profiles and provide
minimum thickness at centerline and
edges of pavement.
• Add a reasonable percentage to the
concrete quantity to account for place-
ment tolerance, construction losses,
and surface/cross-section irregularities
and establish the “new theoretical”
plan quantity. Some states use 15 to 20
percent, depending on the thickness of
the overlay and the amount of pave-
ment cross-slope correction desired. e
thinner the overlay and the higher the
cross-slope correction, the higher the
percentage; see Table 12.
2. For optimization of concrete quantities
• Conduct nine-shot cross sections at
50-foot intervals to map the existing
surface.
• Develop a design centerline profile and
cross slope that optimizes pavement
smoothness, maintains minimum overlay
depth across the width of the pavement,
and optimizes concrete quantities.
• Limit the contractor to an additional
percent of the quantity identified by the
desired cross section and design profile.
Some states use 2 to 6 percent, depend-
ing on the thickness of the overlay.
Figure 56. Digital terrain model acquired through laser scanning
Table 12. Typical Adjustment Factors for Estimating Overlay Cubic Yard
Plan Quantities
Concrete
Overlay
Thickness
½ in. Placement
Tolerance As
a % of Design
Thickness
Additional %
Adjustment for Gross
Surface Irregularities
in the Existing Surface*
Total Adjustment
Factor to Be
Applied to
Theoretical Volume
4 inches 12.5 % 5 % 17.5 %
6 inches 8.3 % 5 % 13.3 %
8 inches 6.3 % 5 % 11.3 %
10 inches 5.0 % 5 % 10.0 %
12 inches 4.2 % 5 % 9.2 %
* Gross surface irregularities are not affected by the overlay thickness; this is a constant that is
entirely dependent on the existing surface condition and any other desired changes such as cross-
slope correction and profile adjustment to obtain a smooth pavement. Table 12 reflects 5 percent
as an example only. An appropriate percentage for gross irregularities should be developed from
the measurements of wheel rut depth and pavement cross slope at 500-foot intervals.
Guide to Concrete Overlays
64
Ch 4. DESIGN
Typical Costs of
Concrete Overlays
Since the onset of the Concrete Overlay
Field Application Program in 2009,
construction cost has been a common
question from state DOT personnel who
are inexperienced with concrete overlays.
To answer this question, bid tabulations
from six state DOTs that are currently
utilizing concrete overlays as an integral
part of their pavement rehabilitation
strategy were reviewed. Figure 57 shows
the cost data collected from 33 projects
with bid dates ranging from August 2008
through September 2009 (Fick 2010).
ese overlay costs include furnishing
concrete, placing the overlay, and all costs
associated with joints. Preoverlay repairs,
surface preparation, and separation layer
costs are not included, but note that the
amount of required preoverlay repairs for
a concrete overlay is significantly less than
that for a typical HMA overlay.
Miscellaneous
Design Details
Following are design details related to curb and
gutter (C/G), vertical grade changes, and other
special design considerations.
Curb and Gutter Details
Potential constraints such as surface drainage
should be considered in the design. Curb-
and-gutter sections may pose challenges with
respect to how to design a concrete overlay.
Projects might include removal and replace-
ment of the existing C/G, construction of an
inlay with the final pavement elevation match-
ing the existing C/G, or even an encasement of
the existing C/G with a new system.
Curb-and-gutter sections require additional
details since a decision needs to be made
about jointing. (Figures 58 through 60 show
three possible design options.) It is possible to
include an integral C/G, but this should be
balanced with the extent of this type of section
and the equipment that might be available to
construct it.
Leaving the Existing Curb in Place
To leave the existing curb in place, the milling
operation stops at the base of the curb, allow-
ing for the thickness of the concrete overlay; see
Figure 58.
ere is a cost savings associated with leaving
the existing curb in place, since driveways, side-
walks, and utility fixtures do not require raising.
e condition of the curb, however, should be
evaluated and, if the concrete is showing signs of
deterioration, it should be removed and replaced.
Also, when utility poles and other obstructions
are in close proximity to the back of the existing
curb, leaving the curb in place may prohibit the
use of conventional slipform paving equipment.
Removing Curb and Gutter
When obstructions behind the curb prohibit the
use of conventional slipform paving equipment,
it may be advantageous to completely remove the
curb and a portion of the gutter to allow place-
ment of the concrete overlay a few inches higher
than the existing curb; see Figure 59.
e full-depth section of C/G could be milled.
When there are obstructions behind the curb,
however, a full-depth saw cut and traditional
excavation methods are preferable to minimize
disturbance of materials on the edges of the road-
way. In this case, a new C/G section can then
be constructed after the overlay has been placed,
using a curb paving machine.
Overlay Curb
It is possible to place a concrete overlay that
encases the existing curb; see Figures 60 and 61.
Figure 61. Concrete curb overlay (source: Jim Amundsen, Grace
Construction Products)
Figure 58. Milling detail when leaving the existing curb in place (source:
Snyder & Associates, Inc.)
Figure 59. Milling detail when removing and replacing curb (source:
Snyder & Associates, Inc.)
Figure 60. Detail of curb overlay (source: Snyder & Associates, Inc.)
Figure 57. Concrete overlay cost by thickness (source: [Fick 2010])
65
Guide to Concrete Overlays
Ch 4. DESIGN
It should be noted, though, that this option
raises the profile grade of the existing curb
and may require adjustment of adjoining and
adjacent roadway features.
Vertical Grade Changes
Depending on the vertical change in profile
grade, there are numerous constraints that
need to be considered in the overlay design
process.
Overhead Clearance
Depending on the location of the project,
various regulations for minimum overhead
clearance may apply. e final pavement
elevation and thickness may need to be
limited or measures taken to raise overhead
obstacles. Alternatively, it may be preferred to
conduct full-depth reconstruction or build an
alternative section (i.e., mill down and place a
thinner but higher-strength concrete overlay)
at such locations.
Barriers and Rails
Safety barriers, guardrails, and cable barriers
may need to be raised/reconstructed depend-
ing on the change in profile grade and the
horizontal distance between the edge of pave-
ment and the safety feature.
Safety Edge
When the roadway is raised, it is necessary
to determine whether or not the new safety
slopes can fit to the existing ditches and
remain within the appropriate safety design
criteria. In some cases, it may be necessary
to regrade the ditches to meet safety slope
criteria. e safety edge is a beveled pavement
edge to help lessen the severity of roadway
departures; see Figure 62. When a driver
drifts off the paved surface, the safety edge
provides greater ease in reentering the road-
way and reduces the risk of oversteering and
loss of control of the vehicle.
Most likely, the projects that will need a safety
edge will be two-lane, rural highways without
paved shoulders. Most of these projects would
be resurfacing projects. e angle of the bevel
is important for the safety edge to function
properly. Measured from level, the bevel is 30°
with an equivalent run-to-rise ratio of 10.5
to 6.
Note the 30° angle does not account for sur-
face slope. Existing surface slopes range from
2 to 8 percent, which add an additional 1.1 to
4.6 degrees to the bevel angle when measured
from level. e resultant angle is within the
30- to 35-degree recommendation from the
FHWA. All safety edge requirements should
follow state agency requirements.
See Chapter 6 for temporary centerline fillets.
Cross Road Drainage Structures
When safety slopes are regraded to meet
appropriate design criteria, it may be neces-
sary to extend drainage structures to match
the new foreslopes.
Cross Slope and Superelevation
Changes to cross slope and superelevation can
lead to thicker concrete overlay sections. For
cost effectiveness, designers should consider
matching existing cross slopes whenever pos-
sible. When crown and/or superelevation
corrections are required, adequate informa-
tion on the depth of material to meet the final
grade is also required. e type of fill materi-
als to use (concrete, asphalt, flowable fill,
cement-treated base, etc.) should be selected
based on the depth of fill, installation and
construction issues, initial costs, and future
removal costs. Some projects combine over-
lays with full-depth reconstruction to address
extreme corrections in superelevation.
Typically, the desired results are not achieved
when an asphalt separation layer is utilized
for correcting cross slope and profile (smooth-
ness) deficiencies. is is because variable
asphalt thickness, when compacted, creates
variable roll down; the result is a nonuniform
surface that still must be corrected with addi-
tional concrete thickness. e most effective
and economical way to make corrections is to
make cross slope and smoothness adjustments
in the concrete overlay; see Figure 63. ere
are some considerations to make, however,
when correcting cross slope and profile fea-
tures through a variable thickness concrete
overlay:
• e depth of saw cut for contraction joints
must be adjusted through the thicker areas
of concrete placement.
• Dowels should be placed (baskets or
mechanical inserters) so that a minimum
cover of 2 inches is maintained around the
dowel bar (see Snyder 2011 for additional
information).
Figure 63. Dowel options in superelevation areas
Concrete overlay
Separation layer
Existing pavement
Inserted dowels (min. 2-in. cover)
or Dowel baskets (min. 2-in. cover)
Figure 62. Typical safety edge for concrete overlay without paved shoulder
30°
1 in. Min.
Concrete Overlay
Old Pavement
Subbase
New Graded
Material
Old Shoulder
30°
1 in. Min.
Concrete Overlay
Figure _: Typical Safety Edge for PCC Overlay Without Paved Shoulder
Note: To allow proper finishing with paver a minimum 1-inch vertical
face is required at the end of the safety edge.
Figure _: Typical Safety Edge Dimensions for PCC Overlay
Guide to Concrete Overlays
66
Ch 4. DESIGN
In-place Pavement
Structures
Existing manholes, inlets, and utility struc-
tures must be raised to match the new
pavement elevation. Figure 64 shows typical
details for raising a manhole.
Figure 64. Concrete overlay with standard manhole
(0.8–1.1 m)
Table 13. Size and Spacing of Plate Dowels for Construction Joints
Pavement Depth Plate Dowel Thickness
and Width at Joint
Plate Spacing for Heavy Traffic,
Wide Joint Openings, or Both
Plate Dowel Spacing for Light
Traffic or Narrow Joint Opening
125 to 174 mm 6 mm x 160 mm 450 mm 600 mm
175 to 224 mm 10 mm x 160 mm 450 mm 600 mm
225 mm+ 20 mm x 160 mm 450 mm 600 mm
Figure 65. Diamond-shaped plate dowels in fixed-formed construction joints (right side) and football-shaped
dowels by slipforms
Diamond shape
construction joint
(used fixed form)
Slipform
football shape
construction joint
(used slot cutter)
Table 14. Size and Spacing of Plate Dowels for Contraction Joints
Pavement Depth Plate Dowel Thickness and
Width at Center Line of Plate
Plate Spacing for Heavy Traffic,
Wide Joint Openings, or Both
Plate Dowel Spacing for Light
Traffic or Narrow Joint Opening
125 to 174 mm 10 mm x 50 mm 450 mm 600 mm
175 to 224 mm 13 mm x 65 mm 450 mm 600 mm
225 mm+ 20 mm x 65 mm 450 mm 600 mm
Plate Dowel Details
Unbonded concrete overlays can be con-
structed with different construction practices,
installation procedures, and joint types,
requiring different installation procedures and
plate geometries; see Figure 65.
See Table 13 for plate dowel size and spacing
for construction joints and Table 14 for dowel
size and spacing for contraction joints.
67
Guide to Concrete Overlays
Ch 4. DESIGN
Figure 66. Detail of construction joint plate dowel for fixed-form paving
Tapered shape with a thin bond
breaker on top and bottom
surfaces allows slab to shrink
without being restrained and joint
to activate
Taper-shaped plate dowel
installed when a construction
joint is formed with a hand form
Plate Dowel Construction Joint (by form)
Figure 68. Detail of construction joint plate dowel for slipform paving
Football-shaped plate dowel
installed in a cut in a previously
slip formed slab edge of existing
or new construction
Tapered shape with a thin bond
breaker on top and bottom surfaces
allows slab to shrink without being
restrained and joint to activate
Plate Dowel Construction Joint (by slot cutter)
Figure 67. Taper-shaped construction joint
plate dowel using fixed forms (source: Nigel
Parks, PNA Construction Technology)
Figure 69. Slots being cut to accept the
football-shaped plate dowels (source: Nigel
Parks, PNA Construction Technology)
Dowel installation devices that remain in the
pavement and transfer load to the concrete
by bearing should be made of thin, rigid
material to help minimize the vertical deflec-
tion. Dowel installation devices that are loose
fitting or made of soft material can result in
significant initial vertical deflection that may
cause early joint deterioration (Walker and
Holland 2007).
Plate Dowel Installation in
Slipform or Full-depth Saw Cut
(Butt-type) Construction Joints
In slipform or full-depth saw cut construction
joints (as would be encountered in a remove-
and-replacement area of topping), designers
Corrosion Resistance
Where corrosion resistance for plate dowels
is required, they are generally either galva-
nized or electroplated with zinc, but other
methods such as epoxy coating may also be
appropriate.
Plate Dowel Installation for
Construction Joints Formed
with a Bulkhead (Form)
Alignment or installation devices should be
incorporated into the bulkhead (forms) to
ensure that dowels are centered in the joint,
horizontal with the pavement’s surface, and
perpendicular to the joint; see Figures 66
and 67.
should recognize that when new concrete
topping, with an inherent tendency to shrink,
is tied to previously placed concrete topping
that has already gone through the shrinkage
process, stresses will develop that can cause
cracking; see Figures 68 and 69.
Load transfer between previously placed
sections and newly placed concrete can be
obtained through the use of football-shaped
plate dowels. In this application, slots can be
cut into the existing slab to receive the plate
dowels. An epoxy or similar material should
be used to rigidly grout the plate into the slot
to ensure a tight fit.
Guide to Concrete Overlays
68
Ch 4. DESIGN
Figure 71. Plan view of roadway with plate dowels
Transverse contraction joint
Football-shaped plate dowel
installed in a cut in a previously
formed slab edge of existing or
new construction
Alternating taper shape with a
factory-applied thin bond breaker
on top and bottom surfaces allows
slab to shrink without being
restrained and joint to activate
Longitudinal construction joint
Transverse construction joint
6 in.
Min.
6 in.
Min.
As
Specified
Figure 70. Detail of plate dowel for contraction joint
Alternating taper shape with a
factory-applied thin bond breaker
on top and bottom surfaces allows
slab to shrink without being
restrained and joint to activate
Dowel Installation for
Contraction Joints
Dowel baskets or mechanical dowel bar inser-
tion equipment should be used to maintain
alignment of tapered plate dowels in saw-cut
contraction joints. In this application, the
tapered plate dowels allow for horizontal
misalignment of the dowels without lock-
ing joints, inducing restraint or cracking in
the overlaid concrete topping; see Figures 70
and 71.
69
Guide to Concrete Overlays
Ch 4. DESIGN
Figure 72. Mill and fill transition for concrete
overlay of concrete pavement (adapted from
ACPA 1998)
(50 mm) min.
Figure 73. Mill and fill transition for concrete
overlay of asphalt or composite pavement
(adapted from ACPA 1998)
(75 mm)
Mill and Fill Transitions for Bonded Concrete Overlays
Transition Details for Bonded Concrete Overlays
Figure 74. New transition
tapers used to meet bridge
approach slabs or maintain
clearance under bridges with
bonded overlay of concrete
pavement (adapted from
ACPA 1990b)
Figure 75. New transition
tapers used to meet bridge
approach slabs or maintain
clearance under bridges with
bonded overlay of asphalt
pavement (adapted from
ACPA 1991)
8 in. (200 mm)
(75 mm)
Transitions
A concrete overlay design often requires tran-
sition details that link the concrete overlay
with the pavement structure adjacent to the
project length. Since these locations are often
subject to additional stress, , including thicker
concrete sections, conventional reinforcement
or wire mesh, and structural macro fibers.
Transitions must be designed and constructed
to connect the new overlay pavement with (1)
existing pavement, (2) existing structures, and
(3) driveways.
Figures 72 through 79 provide details for vari-
ous transitions used for overlay construction.
In general, transition length should be based
upon the design speed—40:1 for roadways
posted at 45 mph (miles per hour) or greater
and 25:1 for speeds less than 45 mph.
Guide to Concrete Overlays
70
Ch 4. DESIGN
Transition Details for Unbonded Concrete Overlays
Figure 76. New transition
tapers used to meet bridge
approach slabs or maintain
clearance under bridges
with unbonded overlay of
concrete pavement (adapted
from ACPA 1990b)
Separation
layer
Figure 77. New transition
tapers used to meet bridge
approach slabs or maintain
clearance under bridges with
unbonded overlay of asphalt
pavement (adapted from
ACPA 1991)
Figure 79. Asphalt wedge transition to existing side road/drivewayFigure 78. Temporary granular transition to existing side road/
driveway
Concrete Overlay
Existing Pavement Existing Side Road
or Driveway
Temporary Transition
Constructed with
Granular Material
Temporary Tr ansition
R.O.W.
Concrete Overlay
Existing Pavement Existing Side Road
or Driveway
Asphalt Transition
Asphalt Wedge Tr ansition
R.O.W.
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Guide to Concrete Overlays
Ch 4. DESIGN
Figure 81. Bonded overlay of asphalt or composite pavement with widening unit
of pavement
Keep joint out of
wheel path
where possible
3-6 ft (0.9-1.8 m)
concrete widening unit
Bonded
Overlay
Existing asphalt
Existing concrete
36-in. tiebars: staple, epoxy or insert;
if inserted, must have enough overlay
thickness to accomodate max.-sized
aggregate under the bar and min. 2-in.
cover above the bar
Figure 80. Bonded overlay of concrete pavement with widening unit
of pavement
Overlay
Bonded
Existing concrete
Keep joint out of
wheel path
where possible
3-6 ft (0.9-1.8 m)
concrete widening unit
36-in. tiebars: staple, epoxy or insert;
if inserted, must have enough overlay
thickness to accomodate max.-sized
aggregate under the bar and min. 2-in.
cover above the bar
Figure 82. View of tiebars for concrete overlay widening unit
Widening and Lane
Addition
Adding new lanes or shoulders can also
present issues unique to concrete pavement
design, especially if there is a change in
the underlying support of the overlay or if
the overlay is to join a full-depth concrete
pavement. Joint load transfer systems are
frequently used in these cases. Tiebars are
used to help ensure aggregate interlock.
Additional measures should be taken in the
design to minimize differential settlement or
water infiltration at these locations. For the
same reasons, intersections and blockouts for
utilities need to be understood, and joint pat-
terns need to be developed that will minimize
uncontrolled cracking.
Concrete overlay projects provide a good
opportunity for the widening of an old pave-
ment with narrow traffic lanes, the addition
of new travel lanes, or the extension of ramps.
Adequately designed and constructed widen-
ing can improve both faulting and cracking
performance of the pavement.
Widened slabs should be used with care with
concrete overlays on stiff foundations (such
as on concrete pavements) because of the
increased risk of longitudinal cracking.
ree- to six-foot (0.9- to 1-8-m) widening
units are illustrated in Figures 80 through 84.
e intent of the tiebars shown in Figures
80 to 82 is to tie the widening unit to the
existing pavement. In Figure 82, note that
care must be exercised not to loosen stapled
tiebars with truck tires; when horizontal lane
restrictions exist that require driving over the
stapled bars, a better option may be to use a
tiebar inserter.
Following are some rules of thumb for widen-
ing units:
• Where possible, keep joints out of wheel
paths, especially for bonded overlays on
asphalt or composite pavements.
• For concrete overlays 5 in. (125 mm) or
thicker at open-ditch (shoulder) sections,
tie longitudinal joints with no. 4 tiebars to
prevent pavement separation.
• e width of widening rather than depth
has more of a positive effect in reducing
stresses in the overlay section.
Not every detail shown will fit a specific
project. Apply the principles illustrated in the
details to address specific project issues.
Lane addition design details are illustrated in
Figure 85, on the following page. To prevent
cracking related to differential expansion and
contraction between a concrete overlay and a
full-depth adjacent concrete lane addition, use
a butt joint with no tiebars.
Guide to Concrete Overlays
72
Ch 4. DESIGN
Figure 83. Unbonded overlay of concrete,
asphalt, or composite pavement with
widening unit
Overlay
Unbonded
Existing asphalt or
separation layer
Existing concrete
of pavement Keep joint out of
wheel path
where possible
3-6 ft (0.9-1.8 m)
concrete widening unit
36-in. tiebars: staple, epoxy or insert;
if inserted, must have enough overlay
thickness to accomodate max.-sized
aggregate under the bar and min. 2-in.
cover above the bar
Figure 84. Bonded or unbonded overlay of
asphalt or composite pavement (previously
widened with asphalt or concrete, and to be
widened again with new concrete overlay)
New overlay
Existing concrete
of pavement
Keep joint out of wheel path
where possible
Saw cut joint
3-6 ft (0.9-1.8 m)
concrete widening unit
Previously widened with asphalt or concrete
Remove existing asphalt
widening to depth of existing
asphalt or to the depth of the
new concrete widening unit,
whichever is greater, and
replace with concrete
widening unit
36-in. tiebars: staple, epoxy or insert;
if inserted, must have enough overlay
thickness to accomodate max.-sized
aggregate under the bar and min. 2-in.
cover above the bar
Existing asphalt
(≥ 3 in. (7.62 cm) if bonded);
(≥ 1 in. (2.54 cm) if unbonded)
Figure 85. Unbonded overlay of
concrete, asphalt, or composite
pavement with full concrete lane
addition
Cold joint or
full-depth
saw cut
-no tie bar
Cold joint or
full-depth
saw cut
-no tie bar
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Guide to Concrete Overlays
Ch 4. DESIGN
Figure 87. HMA interlayer outlet for asphalt
shoulder
New paved HMA
shoulder
Travel lane(s)
Daylight HMA
shoulder
Place 4 to 6 in.- thick
permeable
HMA shoulder
New concrete overlay
Existing concrete pavement
HMA innerlayer
Figure 88. Geotextile interlayer outlet with
new paved shoulder (concrete or asphalt)
New paved
shoulder
Travel lane(s)
Daylight geotextile
fabric or install
vertical subdrain
New concrete overlay
Existing concrete pavement
Geotextile fabric innerlayer
Figure 86. Interlayer outlet for concrete
overlay shoulder
New concrete overlay
shoulder
Travel lane(s)
Daylight innerlayer/fabric
or install vertical subdrain
Existing concrete or
asphalt shoulder
New concrete overlay
Existing concrete pavement
HMA innerlayer or
Geotextile fabric
Typical Drainage Outlets
for Interlayers
Figures 86 through 90 illustrate various drain-
age outlets for separation layers.
Rural Conditions
Guide to Concrete Overlays
74
Ch 4. DESIGN
Figure 89. Drainage of separation layer (interlayer) into an existing underdrain system when existing curb is
removed and replaced (source: Dan DeGraaf, Michigan Concrete Association)
Existing Subgrade Underdrain
Existing Lane Tie Bars
Existing Granular Subbase
Existing Concrete Pavement
Interlayer
Thin Concrete Unbonded Overlay
Excavation
6 in. in a 1.0-ft x 1.0-ft Trench Backfilled with
CL-II Granular Material
Construct 12 in.- wide x 26 in.- deep Porous
Drainage Trench Adjacent to the Existing Subgrade
Underdrain Trench
Figure 90. Drainage of separation
layer fabric into intake when curb
is not removed (source: Snyder &
Associates, Inc.)
New Unbonded Concrete Overlay
Existing Pavement
Geotextile Wrapped and Pinned
Single Open-Throat
Curb Intake
Previous Pavement Height before Milling
Urban Conditions
Curbs Removed and Replaced
Water pressure in a geotextile fabric separation
layer can be reduced by draining the fabric
into storm sewer inlets. If the existing curb
is removed and replaced with the overlay, the
geotextile layer can be daylighted out to an
existing or new subdrainage system; see Figure
89.
Curb Remaining
If the curb is not removed for construction
of an unbonded overlay, the geotextile layer
that separates the underlying concrete pave-
ment from the overlay can be drained into an
intake. e fabric will need to be tied into the
wall of the intakes; see Figure 90.
75
Guide to Concrete Overlays
Ch 5. MATERIALS & MIXTURES
Chapter 5.
CONCRETE OVERLAY MATERIALS AND MIXTURES
A majority of concrete overlay mixtures are
designed and constructed using standard
materials. ese materials include cement,
supplementary cementitious materials
(SCMs), aggregates, water, and admixtures.
Concrete mixtures can be either conventional
or, in special circumstances, accelerated;
both types of concrete mixtures can be fiber
reinforced. Other materials associated with
concrete overlays include dowel bars, tiebars,
curing compound, joint sealant, and separator
layers.
is guide classifies concrete mixtures as
either conventional or accelerated. e pri-
mary difference is that accelerated mixtures
are designed for a faster rate of strength gain,
allowing earlier opening of the concrete
overlay to construction and/or public traffic
(see page 105 for comprehensive guidance
on accelerated construction techniques).
Producing a durable concrete mixture should
be the primary objective regardless of whether
the mix is conventional or accelerated. is
guide provides general recommendations for
developing durable concrete mixtures to be
used in concrete overlays. e design and
production of concrete mixtures for concrete
overlays should adhere to best practices for
local requirements (i.e., aggregate durability,
air entrainment, etc.).
Primary Concrete
Materials
e primary materials in concrete are
cementitious materials, water, aggregate, and
admixtures.
Cementitious Materials
Type I and Type II cements are commonly
used in concrete mixtures for concrete over-
lays. When high early strength is desired,
higher amounts of Type I can be used. Since
conventional Types I and II cements are nor-
mally adequate, the use of Type III cements
with overlays is not recommended because of
increased thermal shrinkage and potential for
thermal shock. As with conventional paving,
SCMs normally improve durability and can
enhance the ease of construction.
Replacement of some cement with SCMs
in well-cured concrete has multiple ben-
efits ranging from improved workability to
reduced permeability of the hardened con-
crete. Typical replacement rates with SCMs
are 15 to 35 percent, depending on the
chemistry of the system. Commonly used
SCMs include Class C fly ash, Class F fly
ash, and ground granulated blast furnace slag
(GGBFS).
Setting times for concrete may be retarded
when SCMs are used, especially in cool
weather conditions, which can cause difficulty
in sawing joints before random cracking
occurs. erefore, heating of the concrete
and/or the use of accelerating admixtures is
recommended during periods of extended
cool weather. Ensure that the strength gain
of the mixture is compatible with the sawing
plan (HIPERPAV can assist in assessing the
risk of random cracking). More information
is available in the Integrated Materials and
Construction Practices for Concrete Pavement
(Taylor 2006).
Since SCMs can retard set time in cold
weather, some agencies restrict their use in
colder seasons of the year. Supplementary
cementitious materials can, however, aid con-
struction during hot weather by extending
the placement time. ey typically improve
the workability of the mix and also increase
concrete durability; they also can increase the
long-term strength of the concrete, although
the short-term strength may be lower. In
addition, fly ash and GGBFS are effective
in reducing ASR (ASR mitigation should be
confirmed by ASTM 1567).
Aggregates
Aggregates used in concrete mixtures range
from crushed stones to river gravels and gla-
cial deposits. To help ensure the longevity of
the pavement, the aggregate should not only
possess adequate strength but also be stable
physically and chemically within the con-
crete mixture. Agencies generally require that
aggregates conform to ASTM C 33 for physi-
cal properties; a well graded mixture should
be specified. Extensive laboratory testing
or demonstrated field performance is often
required to ensure the selection of a durable
aggregate.
e use of well graded aggregates helps to
improve permeability in several ways; see
Table 15. First, mixtures made with well
graded systems tend to be more work-
able, which in turn means that less water
is required to achieve the same workability,
allowing use of a lower w/cm ratio. Second,
well graded systems allow use of higher aggre-
gate and lower paste contents. Because paste
is more permeable than aggregate, reducing
paste content while maintaining workability
will lead to reduced permeability (Yurdakul
2010). ird, better workability will lead
to better consolidation of the mixture, also
improving (reducing) permeability (Tayabji et
al. 2007) and reducing the risk of overvibra-
tion and the attendant problems. Finally, the
improved workability of well graded concrete
mixtures allows for more efficient placement,
especially in handwork, which means that the
pavement is able to be finished earlier while
the mix is still fresh.
e maximum coarse aggregate size used in
concrete mixtures for overlays is a function of
the overlay thickness. Some thinner concrete
overlays may require a reduction in size of the
standard aggregate used in concrete paving.
It is recommended that the largest practical
maximum coarse aggregate size be used in
order to minimize paste requirements, reduce
shrinkage, minimize costs, and improve
mechanical interlock properties at joints and
cracks.
Although maximum coarse aggregate sizes of
0.75–1 in. (19–25 mm) have been common
in the last two decades, smaller maximum
coarse aggregate sizes may be required for
Table 15. The Effect of Aggregate Gradation
on Mixture Properties
Well Graded Aggregates
Concrete mixtures produced with well graded,
dense aggregate matrix tend to
• Reduce the water demand
• Reduce the cementitious material demand
• Reduce the shrinkage potential
• Improve workability
• Require minimal finishing
• Consolidate without segregation
• Enhance strength and long-term performance
Gap-graded Aggregates
Concrete mixtures produced with a gap-graded
aggregate combination may
• Segregate easily
• Contain higher amounts of fines
• Require more water
• Require more cementitious material to meet
strength requirements
• Increase susceptibility to shrinkage
• Limit long-term performance
Guide to Concrete Overlays
76
Ch 5. MATERIALS & MIXTURES
concrete resurfacing. For nonreinforced
pavement structures, a maximum aggregate
size of one-third of the slab thickness is
recommended.
When selecting aggregate for a bonded
concrete overlay on an existing concrete
pavement, the CTE becomes a particularly
important parameter. Because aggregate
composes a majority of the concrete’s mass,
its CTE is a good indicator of concrete
movement due to thermal expansion and
contraction. Using an aggregate in the overlay
mixture with a CTE similar to that of the
existing pavement helps ensure that the two
layers move together, thus minimizing stress
at the bond line due to differential movement
and helping to maintain the bond between
the layers. e CTE can be determined using
AASHTO provisional test TP-60 (Coefficient
of ermal Expansion of Hydraulic Cement
Concrete).
If not similar to the CTE of the underlying
concrete pavement, the CTE of the overlay
should be less than that of the underlying
pavement. e overlay surface is exposed to
greater temperature swings than the under-
lying pavement. erefore, the lower the
overlay’s CTE, the less the differential move-
ment between the overlay and underlying
pavement.
Admixtures
Various admixtures and additives are com-
monly introduced into concrete mixtures.
ese include the following:
• Air entrainment protects the hardened con-
crete from freeze-thaw damage and deicer
scaling. Air entrainment, however, also
helps increase the workability of fresh con-
crete, significantly reducing segregation and
bleeding. e typical entrained air content
of concrete for overlays is in the range of 5
to 7 percent.
• Water reducers are added to concrete
mixtures in order to reduce the amount
of water required to produce concrete of a
given consistency. is allows for a lower-
ing of the w/cm (water-cementitious) ratio
while maintaining a desired slump and
thus has the beneficial effect of increasing
strength and reducing permeability.
Conventional
Concrete Mixtures
Conventional concrete paving mixtures are
typically used in the construction of concrete
overlays. As with conventional concrete pave-
ments, an effective mixture design is essential
to the performance of a concrete overlay. Each
of the components used in a concrete mixture
should be carefully selected so that the result-
ing mixture is dense, relatively impermeable,
and resistant to both environmental effects
and deleterious chemical reactions over the
length of its service life.
ere are numerous references for developing
durable concrete mixtures; the following sec-
tion is adapted from the Guide for Optimum
Joint Performance of Concrete Pavements
(Taylor et al. 2012), which provides recom-
mendations for designing and constructing
durable concrete pavements.
e permeability of a concrete mixture
determines how easily moisture can infiltrate
the paste structure of the concrete. A lower
permeability is desirable to slow the rate at
which concrete will become saturated. Recent
work led by the South Dakota DOT includes
recommendations to achieve durable, dense,
and impermeable concretes that withstand the
deleterious effects of deicing chemicals (Sutter
et al. 2008) and prevent or reduce joint dete-
rioration caused by water saturation at the
joints. Recommendations include designing
mixtures with low w/cm ratio, adequate air
void systems, appropriate use of SCMs, and
well graded aggregates.
Target permeability at 56 days should be less
than 1,500 coulombs when tested in accor-
dance with the rapid chloride permeability
test (ASTM C 1202) or 25 kΩ-cm when
tested using surface resistivity measured in
accordance with AASHTO TP 95.
Low w/cm Ratio
e permeability of a concrete mixture
is primarily governed by the amount of
water in the concrete at the time of mixing.
Permeability will decrease as less water is
used. e w/cm ratio should not exceed 0.45;
ideally, the w/cm ratio should be between
0.38 and 0.42 (especially for wet freeze-thaw
environments).
ere are a number of ways to achieve uni-
formly lower w/cm ratios while retaining
satisfactory workability, including combina-
tions of the following:
• Using SCMs in appropriate dosages
• Using water-reducing admixtures
• Using aggregate systems with combined
gradation, which promotes reduced paste
volume and improved workability
• Controlling concrete temperature
• Not adding water to a ready-mix truck at
the point of delivery, which exceeds the
design w/cm
Adequate Air Void System
Freeze-thaw durability is primarily affected
by the environment (wet freezing conditions)
and the air void system of the concrete. An air
void system consisting of many small, closely
spaced voids is a common means of providing
protection against freeze-thaw damage. An
adequate air void system in the as-placed con-
crete is vital. Air void systems can be affected
by varying the composition of concrete con-
stituents, placing techniques, and finishing
activities. For concrete that is exposed to deic-
ing chemicals or high water saturation (which
is considered “severe exposure”), a spacing
factor equal to or below 0.008 in. (0.2 mm)
is recommended, along with a specific sur-
face area of air voids equal to or greater than
600 in.²/in. (24 mm²/mm). PCA Bulletin
EB001.15 recommends a minimum of 5 per-
cent to 8 percent air content in the in-place
concrete to prevent damage (Kosmatka and
Wilson 2011). In addition, Sutter and Ley
have reported that these values are still appro-
priate based on recent laboratory work (Ley et
al. 2012).
Test procedures to determine air content in
fresh concrete include the pressure method
(ASTM C 231/AASHTO T 152), the volu-
metric method (ASTM C 173/AASHTO T
196), and the gravimetric method (ASTM
C 138/AASHTO T 121). e air content
should be checked in samples taken in front
of the paver, and periodically from behind the
paver, to quantify how much air content is
lost during placing. By periodically comparing
air content difference between samples taken
from the same hauling unit both before and
after the paver, the stability or quality of the
air system can be estimated. When the differ-
ence between the two test results is less than 2
percent, the hardened air-determined spacing
factor is usually acceptable. If the difference
is greater than 2 percent, then admixture dos-
age of the mixture should be adjusted and/or
the placement processes modified to ensure
adequate protection of the in-place system.
Concrete performance can be assessed in the
laboratory (during design stage) using ASTM
C 666/AASHTO T 161.
Accelerated
Mixtures
Although the use of accelerated mixtures and
expedited paving practices has become more
common in concrete overlay projects, there
has been some concern regarding potential
detrimental effects of faster-setting concrete
mixtures and reduced construction times on
the long-term durability of concrete due to
excessive shrinkage, heat generation, and poor
microstructure.
77
Guide to Concrete Overlays
Ch 5. MATERIALS & MIXTURES
FAQ—How do I determine the appro-
priate opening strength?
Opening strength should be determined
based on the anticipated early loading
traffic, concrete overlay thickness, and
ability to mitigate early edge loading
using traffic control devices. Table 16
provides general guidance regarding
opening strength and concrete thickness.
Table 16. Slab Thickness and Opening
Strength
Slab
Thickness (in.)
Strength for Opening
to Traffic (psi)
Comp Flex
6 3600 540
7 2700 410
8 2150 340
9 2000 300
10+ 2000 300
FAQ—What are the concerns when using accelerated mixtures?
Mixtures that gain strength quickly and generate high heat of hydration have had long-term
performance issues. ere is a trade-off between early opening and long-term durability
that needs to be evaluated when deciding whether or not to use an accelerated mixture.
Accelerated opening can often be achieved through good construction scheduling and
coordination, which negates the need for accelerated concrete mixtures. us, durability
and speed of construction are factors that should be considered together during the design
phase. In general, emphasis should be given to using conventional mixes whenever possible.
Some agencies use rapid-strength concrete
mixtures with a high cementitious material
content, low w/cm ratio, and smaller top size
aggregate (typically 0.75 in. [19 mm]).
ese mixtures can be used with accelerat-
ing admixtures to provide the early strength
required to place traffic on the overlay within
a short time period. A water-reducing admix-
ture is used to reduce the w/cm ratio and
provide the desired workability properties.
Other Materials
Other materials that may be introduced to
the mixture or used as part of the construc-
tion process include fibers, separation layers,
dowels and tiebars, joint sealant, and curing
compound.
Structural Fibers for
Concrete Overlays
In general, the use of fiber reinforcement is
not normally necessary for most concrete
overlays. In certain situations, however—
where, for example, vertical restrictions limit
the overlay thickness, heavier-weight traffic
loads are expected, increased joint spacing is
desirable, or conventional dowels cannot be
used—the use of fibers may be warranted.
During the last two decades, there has been
resurgence in the use of fiber reinforcement
in concrete; see Figure 91. e reason for this
is when properly used, newer fiber-reinforce-
ment technology can and does contribute to
the performance of thin concrete overlays.
Whether the use of macro fiber in concrete
overlays is warranted should be determined
based on the existing pavement base thickness
and condition, the owner’s desired finish, the
engineer’s expected design life, overlay thick-
ness, and cost. In appropriate dosages, fibers
can perform the following functions in a con-
crete mixture:
• Help increase concrete toughness (allowing
thinner concrete slabs)
• Help control differential slab movement
caused by curling/warping, heavy loads,
temperatures, etc. (allowing longer joint
spacing)
• Increase concrete’s resistance to plastic
shrinkage cracking (enhancing aesthetics
and concrete performance)
• Hold cracks tightly together (enhancing
aesthetics and concrete performance)
Although steel fibers have a long, successful
history in paving applications, in the last two
decades synthetic fibers have become pre-
dominant due to their ease of handling, better
dispersion characteristics (i.e., less “balling”),
Figure 91. Synthetic fibers (1.5 in. to 2.25 in.)
FAQ—Why do some accelerated mixtures have premature failures?
Accelerated mixtures typically have a higher potential for shrinkage and warping com-
pared to a conventional mixture due to their higher paste content. Increased shrinkage and
warping stresses at early ages can cause early cracking and can be detrimental to bond devel-
opment, which will result in premature overlay failures.
Guide to Concrete Overlays
78
Ch 5. MATERIALS & MIXTURES
and resistance to rust damage. Structural
macro synthetic fibers (ASTM C-116 Type
III, Section 4.1.3) are commonly used at 3 to
4 lb/yd3.
For current design technology, the dosage
of fiber, whether synthetic, steel, or some
blend, is specified to produce certain behav-
ior characteristics in the hardened concrete.
ese characteristics correlate with forecasts
of increased performance such as flexural
strength, and hence fatigue capacity is
enhanced. It should be noted that the actual
strength of the concrete given the current
technology increases only slightly, if at all.
Concrete will still crack if the load exceeds
that which can be borne mechanically at its
upper strength limit, given the geometric
properties of the section, but it will carry a
much greater number of lesser loads up to
that point and will continue to carry loads
beyond that point. A simple analogy is to
think of the concrete as being effectively
stronger than that measured in a beam test;
this effect varies as a function of dosage, not
on weight, but by volume of fibers in the con-
crete mixture.
Table 17 provides a summary of current
categories of fibers, with general descriptions
and application rates. For a more detailed
discussion of fibers, see Appendix C, Fiber
Reinforcement.
Separation Layer Materials
A separation layer (or interlayer) is an impor-
tant feature of unbonded concrete overlays on
existing concrete pavements. e performance
of these overlays depends largely upon using
a separation layer to isolate the two concrete
layers. All unbonded concrete overlays on
concrete must be separated from the existing
concrete pavement by a stress-relief layer, or
separation layer, to prevent reflective cracking
from movement of the existing pavement. e
separation layer provides a shear plane that
relieves stress and helps prevent cracks from
reflecting up from the existing pavement into
the new overlay.
Separation layers may serve three purposes:
1. Isolation from movement of the underly-
ing pavement—a shear plane that relieves
stress, mitigates reflective cracking, and
may prevent bonding with the existing
pavement
2. Drainage—the separation layer either must
be impervious so that it prevents water
from penetrating below the overlay or must
channel infiltrating water along the cross
slope to the pavement edge
3. Bedding—a cushion for the overlay to
reduce bearing stresses and the effects of
dynamic traffic loads and to prevent keying
from existing faulting
Asphalt Separation Layer
Until 2010, the most common and success-
ful separation layer used in the United States
was a conventional asphalt mixture. On most
projects, a nominal 1-in. (25-mm) thick layer
provides adequate coverage over irregularities
in the existing pavement. e thickness can
be slightly increased when irregularities are
large enough to impact placement operations.
Asphalt mixtures that contain higher percent-
ages of oil combined with smaller maximum
nominal aggregate size have contributed to
movement of dowel baskets during the paving
operation because of concrete sliding on top
of the asphalt separation layer. Typical base
mixtures with lower oil content that do not
seal up completely provide additional friction
during the concrete placement operation,
which may alleviate this condition.
e separation layer does not provide signifi-
cant structural enhancement; therefore, the
placement of an excessively thick layer should
be avoided.
When an unbonded concrete overlay pave-
ment is poorly drained and experiences heavy
truck traffic, scouring (stripping) of the
asphalt separation layer with a conventional
asphalt mix may occur. In an effort to reduce
the scour pore pressure and increase stability,
some states modify the asphalt mixture to
make it more porous. In particular, the sand
content is reduced and the volume of 0.38
in. (10 mm) chip aggregate is increased. is
modified mixture has a lower unit weight and
lower asphalt content, and it is comparable in
cost to typical surface mixtures. e Michigan
DOT has designed an asphalt mixture with
modified aggregate gradations to address strip-
ping of separation layers; see Table 18.
Other materials have been utilized for separa-
tion layers; however, the performance of these
materials has been inconsistent (for details on
other separation layers, see Smith et al. (2002)
and Rasmussen and Garber (2009).
Table 18. Michigan DOT Asphalt Separation
Layer Gradation
Sieve Size Percent Passing
½ inch 100
inch 85–100
No. 4 22–38
No. 8 19–32
No. 16 15–24
No. 30 11–18
No. 50 8–14
No. 100 5–10
No. 200 4–7
Table 17. Summary of Fiber Types
Fiber
Type
Size
(D = dia.)
(L = length)
Years
Used in
U.S.
Typical Fiber
Volume
(lb/yd3)
Comments
Micro
Synthetic
Fibers
D <
0.012 in. (0.3 mm)
L 0.50 to 2.25 in.
35 1.0 to 3.0
To reduce plastic shrinkage cracking and
settlement cracking; limited effect on
concrete overlay overall performance; more
workability issues when using higher rates
Macro
Synthetic
Fibers
D >
0.012 in.
(0.3 mm)
L 1.50 to 2.25 in.
15 3.0 to 7.5
Increases post-crack flexural performance,
fatigue-impact endurance; thinner concrete
thickness; longer joint spacing; tighter
joints, cracks; better handling properties,
dispersion characteristics than steel fibers;
not subject to corrosion
Macro
Steel Fibers
(carbon)
L 0.75 to 2.50 in. 40 33 to 100
Increases strain strength, impact
resistance, postcrack flexural performance,
fatigue endurance, crack width control per
ACI 544.4R
Blended 15 Varies
Blend of small dosage of micro synthetic
fibers and larger dosage of either macro
synthetic fibers or macro steel fibers
Synthetic (polymer) fiber materials
• Polypropylene
◦Monofilament (cylindrical)—Fibers of same length
◦Multifilament—Monofilament fibers of different lengths
◦Fibrillated (rectangular)—Net-shaped fiber collated in
interconnected clips
• Polyester
• Nylon
79
Guide to Concrete Overlays
Ch 5. MATERIALS & MIXTURES
Figure 92. Geotextile separation layer (The Transtec Group [no date]) Figure 93. Light-colored geotextile fabric used as a separation layer
for an unbonded overlay
Nonwoven Geotextile
Separation Layer
An alternative to an asphalt interlayer is a
nonwoven geotextile interlayer; see Figure 92
(see also design details in Figures 88–90 on
pages 73–74). e use of nonwoven geotex-
tile fabric as an interlayer has been on the
increase since 2010. e structural condition
of the existing concrete pavement must be
carefully assessed before selecting thin geo-
textile instead of a thicker asphalt interlayer,
particularly when heavy faulting exists in the
pavement to be overlaid.
According to Leykauf and Birmann (2006) of
the Munich University of Technology, geotex-
tiles have provided uniform, elastic support of
the concrete slabs, hence reducing stresses due
to temperature and moisture gradient. ey
also reduce pumping processes and prevent
origination of reflected cracks from bonded
base courses without notching them.
Leykauf and Birmann (2006) also state that
“concrete roads with a separation layer of
geotextiles are especially recommended for
concrete overlays on old concrete pavements,
in tunnels and on rigid base courses.”
In colder weather (spring and fall) black-
colored interlayer helps maintain a warmer
temperature for the placement of the overlays
because it has carbon molecules that absorb
ultraviolet energy. is is not, however, desir-
able in hot weather conditions, particularly
when the fabric reaches 110°F or greater.
Cooling the fabric with a water mist is then
required under this condition. To prevent
heat absorption, white-colored fabric has
been developed recently to help reflect ultra-
violet energy in hot and sunny weather; see
Figure 93. In the fall or spring, however,
white fabric is not the best choice to prevent
heat transfer from the concrete overlay to the
fabric.
Material specifications for a geotextile used
as a separation layer for unbonded overlays
are shown in Table 19. e weight/yd2 and
thickness should be given when specifying
a geotextile interlayer. Following are two
examples:
Table 19. Geotextile Separation Layer Material Properties (Modified from Material Specifications (The Transtec Group [no date]))
Property Requirements Test Procedure
Geotextile Type Nonwoven, needle-punched, no thermal treatment to
include calendaring† EN 13249, Annex F (Certification)
Color Uniform/nominally same color fibers (Visual Inspection)
Mass per unit area
≥ 450 g/m2 (13.3 oz/yd2)*
≥ 500 g/m2 (14.7 oz/yd2)
≤ 550 g/m2 (16.2 oz/yd2)
ISO 9864 (ASTM D 5261)
Thickness under load (pressure)
[a] At 2 kPa (0.29 psi): ≥ 3.0 mm (0.12 in.)
[b] At 20 kPa (2.9 psi): ≥ 2.5 mm (0.10 in.)
[c] At 200 kPa (29 psi): ≥ 0.10 mm (0.04 in.)
ISO 9863-1 (ASTM D 5199)
Wide-width tensile strength ≥ 10 kN/m (685 lb/ft) ISO 10319 (ASTM D 4595)
Wide-width maximum elongation ≤ 130 percent ISO 10319 (ASTM D 4595)
Water permeability in normal direction
under load (pressure) ≥ 1 x 10-4 m/s (3.3 x 10-4 ft/s) at 20 kPa (2.9 psi) DIN 60500-4 (modified ASTM D 5493)
In-plane water permeability
(transmissivity) under load (pressure)
[a] ≥ 5 x 10-4 m/s (1.6 x 10-3 ft/s) at 20 kPa (2.9 psi)
[b] ≥ 2 x 10-4 m/s (6.6 x 10-4 ft/s) at 200 kPa (2.9 psi)
ISO 12958 (ASTM D 6574)*
or
ISO 12958 (modified ASTM D 4716)
Weather resistance Retained strength ≥ 60 percent EN 12224 (ASTM D 4355 @ 500 hrs exposure for
grey, white, or black material only)
Alkali resistance ≥ 96 percent polyproplene/polyethylene EN 13249, Annex B (Certification)
*Added to Material Specifications (The Transtec Group [no date]) for overlays
†Calendering is a process that passes the geotextile through one or more heated rollers during the manufacturing process. The surface of the geotextile is modified during
this process. Calendering may reduce the absorption properties of the geotextile on the calendered side.
Guide to Concrete Overlays
80
Ch 5. MATERIALS & MIXTURES
• ≤ 4 in. overlay—13.0 oz/yd2 @ 130 mils
(3.3 mm)
• ≥ 5-in. overlay—15 oz/yd2 @ 170 mils (4.3
mm)
Each highway agency is encouraged to
develop their own weight and thickness cri-
teria for geotextile interlayer based on their
experiences and environmental conditions.
Dowel Bars and Tiebars
When needed for heavy traffic (typically pave-
ment thickness of 7 inches or greater), dowel
bars are usually billet steel, grade-60 bars
that conform to ASTM A615 or AASHTO
M31. e dowel bar size, layout, and coatings
should be selected for the specific project loca-
tion and traffic levels.
• Dowels should be nominally positioned
in the middle third of the depth of the
slab. Because of the variable thickness of
concrete overlays, dowel placement at
mid-depth is not always possible (guidance
provided by Snyder [2011] states that load
transfer efficiency is adequate with a mini-
mum of a 2-inch cover). Specify a single
height basket for each nominal overlay
thickness that will provide adequate cover.
• In some cases, because of the underlying
support of the old pavement, dowels are
not used in the overlay, or their size or
numbers are reduced.
• Tiebars are typically billet steel, grade-40
bars that meet ASTM A615 or AASHTO
M31 specifications. No. 4 or No. 5 (used
for slab thickness ≥ 10 inches) deformed
tiebars are typically spaced at 30 in. (76.20
cm) apart, but greater spacing may be used
in some cases.
Joint Sealant
Joint sealant materials, if used, are either hot-
poured rubberized materials conforming to
ASTM D6690, AASHTO M301, or per nor-
mal design; silicone materials conforming to
a governing state specification; or preformed
compression seals conforming to ASTM
D2628, AASHTO M220, or a governing
state specification. e need for seals depends
on whether or not the design allows water to
leave the pavement jointing system.
Curing Compound
White-pigmented liquid membrane-
forming curing compounds (ASTM C309
or AASHTO M148) are recommended.
Coverage should be at double the manu-
facturer’s recommendations for all concrete
overlays with a thickness of 6 in. or less.
Some agencies have implemented the use of
curing compounds containing poly-alpha-
methylstyrene (AMS) resin. eir use has
been based on studies that have shown better
moisture retention properties. Application
methods and coverage rates are similar to nor-
mal white-pigmented curing compounds. A
typical material specification for AMS curing
compound can be found at www.dot.state.
mn.us/products/concrete/pdf/curing_com-
pound_specifications_3753_3754_3755.pdf.
81
Guide to Concrete Overlays
Ch 6. WORK ZONES
Chapter 6.
CONCRETE OVERLAY STRATEGIES
IN WORK ZONES
is section discusses several issues related
to work zone management, including clear-
ances, traffic control, and staging. By their
nature, concrete overlays are accelerated
projects because demolition, excavation, and
base work are not necessary. In short, concrete
overlays can be executed in the same manner
Areas of Consideration Items to Consider
Traffic Management 1. Capacity analyses—lanes required, length of queues
anticipated
2. Time restrictions—peak hours, seasonal peaks
3. Limits to work areas
4. Capacity of detour routes
5. Work vehicle access and worker parking
6. Bicycle and pedestrian traffic
7. Warning sign locations—detours, long queues, intersecting
roads
8. Railroad crossings and train schedule
9. Nighttime delineation and illumination
10. Signals, turning lanes, bus stops
11. Traffic service—residential/business
12. Future rehabilitation
Concrete Pavement
Construction
Requirements
1. Accelerated construction—planning, concrete materials,
construction requirements, curing, jointing
2. Opening to traffic—maturity, pulse velocity, strength
requirements, cure time
3. Rehabilitation considerations
4. Off-peak traffic hours for increased production
5. Phasing of work—length of work zone, project limits
6. Special conditions such as dropoffs, sign bridge installation,
etc.
7. Prepaving and paving restrictions
8. Special contract provisions needed
9. Short-duration closures anticipated
10. Temporary drainage
11. Lights for night work
12. Temporary roadway lighting
Safety 1. Work zone crash rates
2. Traffic management strategies
3. Interstate system
4. Congestion
5. Nighttime
6. Large trucks
7. Workers on foot
8. Pedestrians
9. Local experience
Constructibility 1. Structural capacity of bridges, shoulders, and pavement
2. Timing of phases versus probable starting date
3. Strategy to allow contractor to finish project
4. Status of existing traffic control devices—signals, signs, railroad crossings, etc.
5. Wintertime restrictions—snow removal, etc.
Emergency Planning 1. Incident management plans
2. Emergency medical assistance
3. Accidents, breakdowns, tow trucks
4. Severe storms and storm-water runoff
5. Emergency closures
6. Utility interruptions
7. State police
8. Local law enforcement
Public Information
Coordination
1. Public information—public hearings, media, motorist service agencies, residents, local businesses, motor carriers
2. Local officials—police, fire, hospitals, schools, environmental agencies, utilities, toll facilities, ferries, railroads, airports
3. Special events
4. Intra-agency coordination—maintenance crews, permits section, adjacent project
5. Transit
Table 20. Concrete Overlay Work Zone Management Considerations
as other resurfacing projects have been for
decades. is section provides guidance on
specific details for optimizing constructibility
of the concrete overlay and maintaining traf-
fic. See Appendix E for more information
about constructing overlays under traffic.
Objectives of Work
Zone Management
A checklist of considerations in overlay work
zone management is provided in Table 20.
Guide to Concrete Overlays
82
Ch 6. WORK ZONES
Managing work zones for concrete overlay
projects is no more challenging than for any
other paving project under traffic, as long as
certain straightforward practices are followed.
Effective work zone management for all con-
crete pavement projects, including concrete
overlays for maintenance and rehabilitation,
involves designing a comprehensive plan of
action that balances several equally important
priorities; see Figure 94:
• Ensure safety of workers and motorists
• Minimize inconvenience to the traveling
public
• Maintain or enhance cost effectiveness of the
project
• Balance maintenance of traffic concerns
with long-term pavement performance
e basic elements of these priorities are dis-
cussed below. A checklist of considerations in
overlay work zone management is provided in
Table 20.
Safety
Promoting worker and traveler safety should
be an integral, high-priority element of every
project, from planning through construction.
Roadway users (vehicles, bicycles, pedestrians,
etc.) must be clearly guided by traffic control
devices and markings while approaching,
passing through, and leaving temporary traffic
control zones. Traffic control elements should
be regularly inspected. All people involved
in selecting, placing, and maintaining work
zones should be trained in safe traffic control
practices.
e exposure of highway workers and trav-
elers to traffic risks can be minimized by
reducing the frequency with which work
zones are established, reducing the length
of time work zones are in place, and, where
possible, reducing the volume of traffic
through the work zone. When compared
to reconstruction options, concrete overlays
have a significantly shorter construction dura-
tion, which reduces public and construction
worker exposure.
A detailed emergency response plan should
be in place to deal with any injury that might
occur in the work zone. e plan should
include protocols for emergency medical
services.
Traffic Flow
Minimizing disruption to traffic in work
zones requires a proactive, partnership
approach to work zone management. By
involving officials and the public during early
stages of project planning, the designer and
contractor can gain a better understanding of
traffic issues related to the project. As a result,
they can develop better, more coordinated
solutions. In addition, broadly publiciz-
ing the work zone well before construction
begins helps ensure that motorists have every
opportunity to plan travel routes and times
accordingly.
Cost Effectiveness
Strategies used to manage traffic in work
zones can significantly affect project costs.
erefore, it is important to carefully evalu-
ate road use demands and select the most
cost-effective strategies to accommodate the
demands. Traffic control costs and construc-
tion costs should be balanced against the
impact on the public, especially adjacent
businesses and residents. In many cases, a
short full-road closure has far less impact than
maintaining traffic through a construction
zone for extended durations.
Many urban intersections have been overlaid
with concrete utilizing only weekend work
hours, which has mitigated the impact on sur-
rounding businesses.
Partly or completely closing a work zone to
traffic can help minimize traffic management
costs. Informal project reviews that have been
performed on constructed concrete overlay
projects utilizing pilot car operations indicate
that there could have been an approximate
20 to 30 percent cost and time savings had
the roadway been closed to through traffic.
If closing the roadway to through traffic is a
viable option, the contract documents should
clearly state that the contractor is responsible
for maintaining local access for residents and
businesses. Putting the onus on the contrac-
tor, yet allowing flexibility in their methods
for providing local access, is a preferred
strategy rather than explicit details regarding
how and when the access shall be maintained.
When a roadway cannot be closed, higher
costs are probably justifiable. Potential ways
to manage costs include, where possible,
reducing traffic volume through work zones,
reducing the frequency and duration of work
zones, and minimizing detours and crossover
construction elements. For long (> 7 miles)
two-lane overlay projects, allowing for mul-
tiple work zones simultaneously can improve
construction operation efficiencies and cost
effectiveness.
Figure 94. Managing work zones effectively
involves balancing several priorities
Safety of the
traveling public and
highway workers
Minimal
disruption
to traffic
Cost-
effective
solutions
Superior
pavement
performance
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i
ma
lMi
n
i
ma
l
di
sru
p
t
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e
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s
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ut
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on
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afety of the
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afety of the
traveling public and traveling public and
high
wa
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Successful
work zone
management
83
Guide to Concrete Overlays
Ch 6. WORK ZONES
Figure 96. A three-track, zero-clearance paver placing concrete along
a median barrier (source: Kevin Klein, Gomaco)
Figure 97. A typical four-track paver modified to three tracks,
providing zero clearance in a C/G situation in Oklahoma (source:
Jim Duit, Duit Construction Co., Inc.)
Work Zone Space
Considerations
Constructing any overlay requires occupy-
ing some part of the traveled portion of the
roadway to accommodate work activities
and provide traffic control and other safety
provisions for workers and motorists. is
will affect traffic capacity through the work
zone for the duration of the work activities.
In some cases, safety considerations may
require partial or even complete closure of the
roadway.
When overlay projects are constructed under
traffic, space and traffic capacity consider-
ations impact three primary elements of a
work zone management strategy: construction
clearances, traffic control, and project staging.
Conventional Paving
Equipment Clearances
When work zones are set up under traf-
fic, adequate clearance must be provided to
accommodate the paving machine’s tracks
and frame, as well as the paving stringline.
For a standard concrete paver operation, the
typical paving equipment clearance is 4 ft
(1.2 m) on each side of the paving machine
(3 ft [0.9 m] for the paver track and 1 ft
[0.3 m] for the paver control stringline); see
Figure 95. Paving equipment clearances do
not include space for traffic control devices or
workers or space for highway users (vehicles,
pedestrians, bicycles, etc.). Additional clear-
ances needed should be determined on a
project-by-project basis.
Reducing Clearances
In some situations—narrow roadways,
minimum or no shoulders, traffic in adjacent
lanes, obstacles like retaining walls or safety
barriers—paving equipment clearances may
need to be reduced. ese situations are fairly
common with all maintenance and rehabilita-
tion projects. With adequate planning, zero
paving equipment clearance can be achieved
to accommodate specific project needs,
such as paving next to a median barrier; see
Figure 96. (As with asphalt paving, zero pav-
ing equipment clearance in concrete paving
does not include the 6–8 in. [150–200 mm]
for the paving machine edge form.)
Two-lane roads with wide (8–10 ft [2.4–3.1
m]) shoulders of granular or stabilized base
will allow room for pilot car traffic and
two lanes of construction traffic. e use of
stringless paving technology can reduce the
clearance required for paving equipment to
3 ft (0.9 m). It also allows the traffic cones to
be placed at the edge of the new lane directly
behind the texture/cure operations, which
maximizes the width of the existing lane for
pilot car operations.
Paving machine manufacturers have devel-
oped special paving machines designed to
execute minimum clearance projects. In
addition, many contractors around the
country have made various modifications to
standard pavers to achieve zero clearances; see
Figure 97.
Instead of specifying a certain manufacturer’s
machine, owner-agencies are advised to define
the maximum allowable clearance zone and
let the contractor select or modify the equip-
ment and operation to meet project needs.
Figure 95. Stringline paver
Guide to Concrete Overlays
84
Ch 6. WORK ZONES
Mechanical Methods
Alternative paving control options may be
used to reduce clearance as long as smooth-
ness criteria are met. For example, an average
profiler, a movable stringline, or a ski can
be used in tight areas, each relying on the
smoothness of an existing lane to ensure a
smooth profile on the new pavement; see
Figures 98 and 99.
Stringless Methods
Several companies have developed stringless
equipment control and guidance systems
using technologies such as GPS, robotic total
stations, and laser positioning. Stringless tech-
nology replaces the traditional stringlines with
an electronic tracking process that controls
the horizontal and vertical operation of the
slipform paver. e construction industry has
been using stringless technology for eleva-
tion and steering control of equipment for a
number of years. Stringless paving, however,
is now an emerging technology for concrete
paving because it can allow contractors and
owner/agencies to receive production benefits
(e.g., reduced survey costs, fewer construction
hours) while still meeting smoothness require-
ments. Details regarding various stringless
paving systems are provided in Appendix F.
Stringless paving is a technology that elimi-
nates the installation and maintenance of
stringlines and has the potential to decrease
the need for surveying and increase the
smoothness of the pavement profile; see
Figures 100 and 101. Any technology prob-
lems can arise, however, and lessons learned
can take time and may cause delays. Field
research on stringless paving was first started
in 2003 by the National Concrete Pavement
Technology Center at Iowa State University
(Cable et al. 2004).
e benefits that can result from stringless
paving include the following:
• Reduced construction costs. e stringless
systems eliminate the need for stringline
crews to place, maintain, and remove
stringlines. e stringless system requires
the survey crew to establish the project ref-
erence points but removes the need to place
paving reference hubs or pins at 12- to
50-foot intervals. Surface surveys are now
conducted by one- to two-person crews
versus three to four persons. Typically,
these persons are replaced by one surface
modeler and two persons to establish laser,
total station, or GPS base stations on the
project.
• Reduced time and manpower. Surface and
reference point surveys are now conducted
in much less time and with reduced man-
power. Many highway agencies do not have
the manpower or time to conduct string-
line operations, but they can prepare for
the stringless control operation.
• Construction access. Removal of the
stringlines opens up the site to both the
contractor and/or adjacent public. No
longer must the contractor worry about
damage to the stringline during construc-
tion or the workers tripping over the
stringline. Construction vehicles can enter
and leave the site at any location without
fear of stringline damage.
Figure 100. Stringless paver (source: Jim Cable, Iowa
State University)
Figure 101. Zero clearance stringless paver (source: GOMACO)
Figure 98. Controlling paving profile using a moveable stringline on the adjacent
lane (source; Kevin Klein, Gomaco)
Figure 99. Controlling paving profile using a paver ski on the
adjacent lane (source: Wouter Gulden, southeast chapter, ACPA)
85
Guide to Concrete Overlays
Ch 6. WORK ZONES
• Public access. ose living along the con-
struction site can enter and leave their
residence or business at all times except
during the actual pavement placement and
curing time without concern for stringline
interference.
• Urban and rural application. No longer
must the contractor and highway agency
be concerned about narrow roadway tops,
ground-level vegetation, or earthwork that
limits the location of the stringline or opera-
tion of both it and the paver.
Other Clearances
In addition to paving equipment clearances
on all construction operations, clearance must
be allowed for traffic control devices and con-
struction workers. e width of this clearance
zone varies depending on adjacent traffic vol-
ume, traffic speed, and agency requirements.
In addition, the location of workers with
long-handled floats should be restricted to the
nontraffic side of the pavement.
Construction Traffic
Control
All work zone traffic control, including
speed restrictions, should follow jurisdic-
tional requirements and the latest Manual on
Uniform Traffic Control Devices (FHWA 2009).
e fundamental principles of work zone traf-
fic control are given in Part 6. In addition,
the Traffic Management Handbook for Concrete
Pavements Reconstruction and Rehabilitation
(ACPA 2000) is a good reference on traffic
control strategies for common roadway reha-
bilitation categories, including overlays. See, in
particular, Chapter 4 on traffic control strate-
gies for concrete pavement.
e ACPA handbook explains that “as traffic
volumes increase, the ‘window’ of time where
the traffic demand is below the capacity of the
work zone will become smaller. When the time
is too short to allow for daytime work, the
work is usually moved to nighttime. In some
cases even the nighttime hours are restricted.”
For situations such as recreational routes,
the peak traffic hours may be on Friday and
Sunday afternoons. e allowable window of
time for road construction in this case may be
noon Monday to 6:00 p.m. ursday.
For roadways under high traffic demands, a
traffic analysis should be conducted to identify
which parts of the roadway can be occupied
by construction and public traffic at any point
during the construction time period. e goal
is to identify congestion points that could
affect traffic capacity and safety as well as con-
struction production levels.
Such an analysis answers specific questions:
• Is the capacity of the existing roadway
adequate for existing traffic levels?
• How will capacity be affected if some lanes
are shut down and other lanes kept open?
• Comparing existing traffic levels to the
under-construction capacity, are there any
capacity deficiencies?
e analysis should consider both the lat-
eral clearance (availability and need) and
the length of roadway needed to provide
efficient, cost-effective paving production. It
must also factor in peak and off-peak traffic
flows.
If deficiencies will occur, the work zone man-
agement plan must address them to prevent
congestion and increased project costs. For
example, the plan might include variable
work times (e.g., off-peak hours, nighttime)
or construction sequencing to meet produc-
tion and safety demands.
An increasingly popular alternative is to com-
pletely close the facility briefly to complete
the project or a critical phase of the project.
In some cases, this alternative has reduced
the overall project duration significantly.
Concrete Overlay
Staging
Many easy-to-use approaches exist for stag-
ing concrete overlay projects in almost any
situation. A system approach that considers
work zone safety, traffic requirements, and
key elements of construction should be used
in staging concrete overlay plans for fast,
cost-effective construction projects. When
construction acceleration is desired, it should
begin in the design phase with an analysis of
alternative maintenance of traffic schemes,
advance planning, and tailoring of project
details to facilitate shortened construction
durations. e plans and specifications
should provide the contractor with clear cri-
teria for maintenance of traffic requirements
(e.g., two lanes open in each direction at all
times, pilot car queues shall not exceed 10
minutes, etc.). Given the requirements for
maintenance of traffic, the contractor should
be given the responsibility to plan and pros-
ecute the project to meet the objectives for
accelerated construction and maintenance
of traffic. is approach of allowing the con-
tractor to innovate and plan the project to
meet their resources results in more efficient
workflow, shorter durations, and less impact
on the road users.
Some common staging scenarios are
described below.
Two-Lane Highway under
Traffic
When construction will be completed
under traffic and certain lanes need to carry
additional traffic, various options regarding
preoverlay spot repairs should be considered.
For example, if spot repairs can be made
quickly (and, if appropriate, a separation
layer can be placed immediately after the
repairs), then it is normally acceptable to
put temporary additional vehicle traffic on
the existing pavement until the overlay is
constructed. Another option is to wait and
make final spot repairs after the temporary
additional traffic is moved off the existing
pavement. is approach should be used only
when the extent of additional repairs needed,
the additional thickness of overlay required,
and related costs are clearly understood.
Alternatively, it is possible to temporarily
close the roadway (preferably during off-peak
hours), make the critical repairs and complete
the overlay at least on one lane, and open it
to traffic as soon as possible.
When staging a two-lane concrete overlay
project under traffic, the widths of the vehicle
lane and the construction lane must be con-
sidered. Typically, the minimum desirable
width for the vehicle lane is 11 ft (3.4 m).
Some jurisdictions may allow as little as 10
ft (3.1 m) under certain circumstances—for
example, in very short segments (less than
100 ft [30.5 m]).
e width of the construction lane depends
on several factors, including thickness of over-
lay, maximum allowable centerline dropoff
or edge fillet, slope of fillet, type of traffic
control device, type of paving machine, and
automobile and truck traffic.
Concrete overlays can be successfully con-
structed under traffic with conventional
paving machines; in some cases, where
minimum clearances are required, minor
adjustments may be necessary.
e length of the temporary traffic control
zone is another important factor. Typically,
when the length of traffic control zones is
less than 0.25 mi (0.40 km), a pilot car is not
used. In rural areas, however, it may be more
feasible to pave longer sections. In such situ-
ations, a pilot car and flaggers are often used
and the maximum length of the traffic con-
trol zone is established by the jurisdiction.
Other traffic control measures, including
flaggers and traffic control signals, may
be warranted according to jurisdictional
requirements.
When granular shoulders of adequate widths
are available to accommodate a conventional
paver, it is recommended that the shoulders
be treated with calcium chloride (3 ft [0.9 m]
Guide to Concrete Overlays
86
Ch 6. WORK ZONES
wide) before opening the road to vehicular
traffic. e calcium chloride treatment is a
successful way of stabilizing the shoulder in
case errant vehicles leave the pavement. Also,
vertical traffic control panels or a permanent
safety edge may be used to designate the pave-
ment edge; see Figure 102.
If shoulder paving is part of the project, the
trenching of paved shoulder base widening
should be completed in the first stage along
with surface preparation of the initial lane to
be overlaid. Once this is completed, this lane
can be opened to traffic and the adjacent lane
can be prepared for paving.
During the second stage, the second lane
is paved. A thickened edge may be paved if
pavement widening is part of the project.
Figure 103. Centerline safety edge fillets for overlays 3 in. (50 mm) or greater
Full-depth saw cut
or fabric or
formed gap of
1/4 in. or more Saw cut or fabric or
formed gap of 1/4 in.
or more
Unbonded separation layer
Traffic control device
Traffic control and slope of fillet depends on jurisdictional requirements.
Traffic control device
Overlay
Fillet T/2 or greater
Match existing centerline
for overlay on concrete
1 in. Min.
30°
1 in. Min.
2 in.
(50 mm)
Bonded and unbonded overlay 3 in.– 4 in.
(50–100 mm) thick
Unbonded overlay greater than 4 in. (100 mm)
T
T
e third stage includes opening the newly
placed overlay to traffic and shifting traffic
control for work on the opposite lane. e
final stage includes placing pavement mark-
ings, rumble strips if shoulders are paved, and
final shouldering.
Temporary Safety Fillet
If two-way traffic is desired on the roadway
after the first lane is cured, and agency-
established dropoff criteria require a dropoff
mitigation, construction of temporary cen-
terline and outside safety fillets may be an
option; see Figure 103. An outside safety edge
fillet should be considered if shouldering will
not be completed before opening the roadway
to traffic.
Pilot Cars for Continuous
Production
Pilot cars can be used to keep one lane of
traffic adjacent to the paving operation open
at all times. To minimize traveler delays,
many jurisdictions limit the length of such
work zones. Contractors must balance those
limitations with their need for continuous
production so that crews do not stand idle at
any time.
e following are some considerations
for staging a project using pilot cars cost
effectively:
• Typically, a contractor can prepare and pave
2,500 yd3 (1,911 cm) in one lane per work-
ing day. For thinner overlays, the rate of the
sawing operation may be the limiting factor
on production.
• Constructing an edge fillet may make it
possible to open the lane to traffic before
the shoulder backfill is completed.
• A new overlay can be opened in 24 hours
or less.
• Leaving gaps in or staggering construction
areas (that is, leapfrogging over a section of
pavement) can allow the contractor to stage
work in ways that use crews and machinery
more efficiently.
• Using multiple paving machines may make
it possible to stagger work zones more
efficiently.
• e direction of the initial pour is impor-
tant to make sure the paver ends each pour
in the optimum position to begin the next.
Examples of Staging
Sequences
Figures 104–108 on pages 88–97 illustrate a
variety of potential staging sequences. Note
that each half of a four-lane divided highway
is treated like a two-lane section.
Two-Lane Highway
Expanded to Three Lanes
under Traffic
When constructing a concrete overlay and
widening a pavement from two lanes to three
lanes, some states require that the remaining
shoulder after pavement widening be at least
4 ft (1.2 m) wide. erefore, using both exist-
ing shoulders for staging and widening has
distinct advantages.
First, base shoulder widening on one-half
of the road is accomplished. e overlay is
constructed in halves similar to the two-lane
Figure 102. Vertical traffic control panels may be used to mark pavement edge dropoff
(source: Dan DeGraaf, Michigan Concrete Paving Association)
Vertical traffic
control panel
Calcium chloride treatment
87
Guide to Concrete Overlays
Ch 6. WORK ZONES
staging example. e existing shoulder is
trimmed and properly compacted. e first
concrete overlay section is then placed with
a thickened edge. e other half of the over-
lay can be placed directly on top of the base
shoulder constructed first.
A possible staging sequence for this type
of construction management is shown in
Figure 107.
Four-Lane Divided Highway
without Crossovers and
under Traffic
Staging a concrete overlay on a four-lane
divided highway is similar to that on a two-
lane highway. Both two-lane sides may be
under construction at the same time, and
crossovers are eliminated. By eliminating
crossovers, project costs are reduced and safety
is increased. e existing shoulders usually
provide adequate room for the paver track,
stringline, and workers between the paver and
traffic.
A possible staging sequence for this type of
construction is shown in Figure 108. Because
each half of the four-lane divided highway is
treated like a two-lane section, any of the stag-
ing sequences from Figures 104–107 may be
used on either half of the section.
Guide to Concrete Overlays
88
Ch 6. WORK ZONES
Repair surface, prepare for overlay, and construct base shoulder
widening and separation layer
• Install traffic control and close the left lane. Follow
jurisdictional requirements for traffic control. Check
with jurisdiction regarding allowable lane closure
length. If surface repair and preparation for the
overlay are minimal, then slow-moving traffic control
may be appropriate. Closing the lane may require
additional traffic control (e.g., signals, flaggers, and/or
pilot cars).
• Repair the surface as appropriate. Prepare the surface
for the overlay (or, in the case of concrete overlay on
concrete, the separation layer) as described in the
contract document.
• Prepare for shoulder widening by trenching the
existing shoulder and trimming to the specified
width. The trench should be rolled and compacted
as necessary to obtain a firm and stable platform as
specified in the contract documents. A continuous
progression approach with the shoulder trencher
and placement of the base shoulder widening
material is encouraged.
• Construct separation layer (only for unbonded
overlay on concrete).
• Shift the traffic control to the left lane and close the
right lane to traffic. The length of the closure will
depend on the jurisdiction’s maximum closure length
with pilot car. Traffic controls and traffic control
signals will be based on jurisdictional requirements.
• Repair and prepare the surface for the overlay or the
separation layer and subsequent overlay as described
in the contract documents. Construct separation layer
(for unbonded overlay).
• Normal space for the paver stringline is 1–1.50 ft (0.30–
0.46 m) and the paver track is a minimum of 2.50–3 ft
(0.76–0.91 m). 1 ft (0.3 m) incremental encroachment
reduction (up to 2 ft (0.6 m) total) is common through
Construct right shoulder and concrete overlay
typical machine adjustment. Speeds should be
additionally restricted adjacent to paver when
clearance between the paver and vehicle traffic is
tight.
• Construct concrete overlay on the existing
pavement. Complete right PCC shoulder widening
with the overlay. Bull float work shall operate from
the outside shoulder only.
• The “X” dimension between the roadway centerline
and vertical panel is for the paving machine track
and stringline.
• Close the opposite lane to traffic and place the
concrete overlay according to contract documents,
using the same procedures as described in stage
2. Note that stringline may not be necessary for the
right edge of the paving when the paved overlay
constructed in stage 2 is used as the paver control in
this stage. If the right stringline is not used, the “X”
dimension could possibly be reduced to 3 ft (0.9 m).
Construct left lane concrete overlay
• If the outside edge dropoffs at the shoulder exceeds
the jurisdictional allowance for a 1:1 fillet, then
construct the granular shoulders in this stage.
• Complete shouldering. Install (mill) rumble strips
in the paved shoulders and complete pavement
marking and regulatory signing in accordance with
contract documents.
COMPLETED OVERLAY (Two-Lane Roadway with Paved Shoulders, Conventional Paver)
STAGE 1.
STAGE 2.
STAGE 3.
Bonded concrete overlay of concrete pavements Unbonded concrete overlay of concrete pavements
Bonded concrete overlay of asphalt pavements Unbonded concrete overlay of asphalt pavements
Bonded concrete overlay of composite pavements Unbonded concrete overlay of composite pavements
Applied to:
Typically
less than
0.25 mi
(0.40 km)
without
pilot car
Figure 104. Overlay of two-lane roadway with paved shoulders (conventional paver)
89
Guide to Concrete Overlays
Ch 6. WORK ZONES
Stage work area
Concrete
LEGEND
Base shoulder widening materials
(e.g., cement-treated base, porous
concrete, roller compacted con-
crete (RCC), asphalt, or concrete)
Granular material
Overlay of
Two-Lane Roadway
with Paved Shoulders
(Conventional Paver)
Construction area
Vehicle traffic
11 ft (3.4 m) lane
(Typical)
Varies Existing subbase
Existing pavement
Existing
shoulder
Separation layer (only for
unbonded overlay on concrete)
Existing
shoulder
Traffic
control
device
Surface repair
and overlay surface
preparation
Base shoulder
widening
material
Construction areaVehicle traffic
Shoulder
Traffic
control
device
Existing pavement
Concrete
overlay placement
Concrete thickened
paved shoulder
Concrete
fillet placed
with overlay
Surface repair
Varies
Varies
Varies
12 ft (3.7 m) lane
Separation layer
(only for unbonded overlay on concrete)
(Typical)
11 ft (3.4 m) lane
(Typical)
Varies
Construction area Vehicle traffic
Remaining
shoulder
Remaining
shoulder
Paved
shoulder
Varies
Existing pavement
Concrete
overlay
placement
Concrete
fillet placed
with
overlay
12 ft (3.7 m) lane
Separation layer
(only for unbonded
overlay on concrete)
8
9
8
9
(Typical)
Varies
11 ft (3.4 m) lane
(Typical)
COMPLETED OVERLAY
STAGE 1
STAGE 2
STAGE 3
NOTES:
1 Follow jurisdictional requirements
for traffic control devices.
2 Treat 3 ft (0.9 m) area outside of
proposed paved shoulder with
calcium chloride. If the existing
shoulder outside the proposed
paved shoulder is less than 3 ft
(0.9 m), it may be necessary to
adjust the slipform paver and/or
paver control to accommodate the
reduced space.
3 Minimum lane width next to the
paver may be reduced for short-
term, stationary work on low-
volume, low-speed roadways when
vehicular traffic does not include
longer and wider heavy commercial
vehicles.
4 If the overlay is opened to traffic
in this stage, and final shoulder
backfill is delayed, place fillet as
shown or (if overlay creates a
dropoff greater than jurisdictional
allowance) place granular shoulder.
5 See centerline fillet illustration and
subsequent removal on figure 103.
6 For “X” less than 4 ft (1.2 m),
adjustments to paver may be
necessary to accommodate paver
control and paver track.
7 The “X” dimension can be reduced
to 3 ft (0.9 m) minimum when the
right lane is used as paver control.
8 Mark edgelines and centerlines per
MUTCD (FHWA 2009) section 6F.77
(mark both lanes).
9 Construct longitudinal joint.
Remaining
shoulder
Paved
shoulder
Remaining
shoulder
Finished
shoulder
Paved
shoulder
Existing pavement
R
umble strip
Concrete overlay
Pavement
marking Pav
ement
marking
Saw joint
with tied steel
12 ft (3.7 m) lane 12 ft (3.7 m) lane
12 ft (3.7 m) existing lane
Separation layer
(only for unbonded overlay on concrete)
(Typical) (Typical)
Existing subbase
Guide to Concrete Overlays
90
Ch 6. WORK ZONES
COMPLETED OVERLAY (Two-Lane Roadway with Granular Shoulders, Conventional Paver)
STAGE 1.
STAGE 2.
STAGE 3.
Bonded concrete overlay of concrete pavements Unbonded concrete overlay of concrete pavements
Bonded concrete overlay of asphalt pavements Unbonded concrete overlay of asphalt pavements
Bonded concrete overlay of composite pavements Unbonded concrete overlay of composite pavements
Applied to:
Typically
less than
0.25 mi
(0.40 km)
without
pilot car
Repair surface, prepare for overlay, and construct left shoulder
and separation layer
• Install traffic control and close the left lane. Follow
jurisdictional requirements for traffic control. Check
with jurisdiction regarding allowable lane closure
length. If surface repair and preparation for the overlay
are minimal, then slow-moving traffic control may be
appropriate. Closing the lane may require additional
traffic control (e.g., signals, flaggers, and/or pilot cars).
• Repair the surface as appropriate. Prepare the surface
for the overlay (or, in the case of concrete overlay on
concrete, the separation layer) as described in the
contract document.
• Prepare shoulder widening by trenching the existing
shoulder and trimming to the specified width. The
trench should be rolled and compacted as
necessary to obtain a firm and stable platform.
Compact shoulder material as specified in the
contract documents. A continuous progression
approach with the shoulder trencher and
placement of the base shoulder widening is
encouraged.
• Construct calcium chloride treated granular
shoulder as outlined in contract documents. The
treated shoulder shall be firm and stable to support
vehicular traffic at low speeds.
• Construct separation layer (only for unbonded
overlay on concrete).
Construct right shoulder and concrete overlay
Construct left lane concrete overlay
• Shift the traffic control to the left lane and close the
right lane to traffic. The length of the closure will
depend on the jurisdiction’s maximum closure length
with pilot car. Traffic controls and traffic control
signals will be based on jurisdictional requirements.
• Repair and prepare the surface for the overlay or the
separation layer and subsequent overlay as described
in the contract documents. Construct separation layer
(for unbonded overlay on concrete).
• Normal space for the paver stringline is 1–1.5 ft (0.3–0.5
m) and the paver track is a minimum of 2.5–3 ft (0.8–0.9
m). 1 ft (0.3 m) incremental encroachment reduction (up
to 2 ft [0.6 m] total) is common through typical machine
adjustment. Speeds should be restricted adjacent to
paver when clearance between the paver and
vehicle traffic is limited.
• Construct concrete overlay on the existing
pavement. Construct right shoulder base with 6 in.
(150 mm) thick granular shoulder. Bull float work
shall operate from the outside shoulder only.
• Place 6 in. (150 mm) minimum thickness calcium
chloride treated granular shoulder to help stabilize
shoulder and minimize heavy dust that can impair
vision.
• The “X” dimension between the roadway centerline
and vertical panel is for the paving machine track
and stringline.
• Close the opposite lane to traffic and place the
concrete overlay according to contract documents,
using the same procedures as described in stage 2.
Stringline may not be necessary for the right edge of
the paving when the paved overlay constructed in
stage 2 is used as the paver control in this stage. If the
right stringline is not used, the “X” dimension could
possibly be reduced to 3 ft (0.9 m).
• If the outside edge dropoffs at the shoulder
exceeds the jurisdictional allowance for a 1:1 fillet,
then construct the granular shoulders in this stage.
• Complete shouldering. Complete pavement marking
and regulatory signing in accordance with contract
documents.
Figure 105. Overlay of two-lane roadway with granular shoulders (conventional paver)
91
Guide to Concrete Overlays
Ch 6. WORK ZONES
COMPLETED OVERLAY (Two-Lane Roadway with Granular Shoulders, Conventional Paver)
Construction area
Vehicle traffic
Varies
4 ft (1.2 m)
min.
Existing subbase
Existing pavement
Existing
shoulder
Existing
shoulder
Traffic
control
device
Surface repair
and overlay surface
preparation
Construct 6 in. (150 mm)
thick granular shoulder
treated with calcium
chloride
(10 ft [3 m] min.)
Separation layer
(only for unbonded overlay on concrete)
10
11 ft (3.4 m) lane
(Typical)
Construction areaVehicle traffic
Shoulder
Remaining
shoulder
Traffic
control
device
Existing pavement
Concrete
overlay placement Construct 6 in. (150 mm)
thick granular shoulder
base if needed
Surface repair
Varies
Varies
Varies
12 ft (3.7 m) lane
(Typical)
Separation layer
(only for unbonded overlay on concrete)
Base shoulder
widening
Varies
11 ft (3.4 m) lane
(Typical)
(10 ft [3 m] min.)
10
Construction area Vehicle traffic
Remaining
shoulder
Remaining
shoulderShoulder
Varies
Existing pavement
Concrete
overlay
placement
Temporary
concrete fillet
placed with
overlay
12 ft (3.7 m) lane
(Typical)
Separation layer
(only for unbonded overlay on concrete)
89
8
Varies
(10 ft [3 m] min.)
10
11 ft (3.4 m) lane
(Typical)
Overlay of Two-
Lane Roadway with
Granular Shoulders
(Conventional Paver)
Stage work area
Concrete
LEGEND
Granular material
COMPLETED OVERLAY
STAGE 1
STAGE 2
STAGE 3
Remaining
shoulder
Remaining
shoulder
Finished
shoulder
Granular
shoulder
Granular
shoulder
Existing pavement
Concrete overlay
Pavement
marking Pavement
marking
12 ft (3.7 m) lane
(Typical) (Typical)
12 ft (3.7 m) lane
Separation layer
(only for unbonded overlay on concrete)
12 ft (3.7 m) existing lane
Existing subbase
NOTES:
1 Follow jurisdictional requirements
for traffic control devices.
2 When the existing shoulder is less
than 4 ft (1.2 m), adjustment to the
slipform paver and/or paver control
may be necessary to accommodate
the reduced space for paver control
and paver track.
3 Minimum lane width next to the
paver may be reduced for short-
term, stationary work on low-
volume, low-speed roadways when
vehicular traffic does not include
longer and wider heavy commercial
vehicles.
4 If the completed overlay in this
stage opens to traffic and the final
shoulder backfill is delayed, place
fillet as shown. If overlay creates a
dropoff greater than jurisdictional
allowance, place granular shoulder
in lieu of concrete fillet.
5 See centerline fillet illustration and
subsequent removal on figure 103.
6 For “X” less than 4 ft (1.2 m),
adjustments to paver may be
necessary to accommodate paver
control and paver track.
7 The “X” dimension can be reduced
to 3 ft (0.9 m) minimum when the
right lane is used as paver control.
8 Mark edgelines and centerlines per
MUTCD (FHWA 2009) section 6F.77
(mark both lanes).
9 Use calcium chloride for dust
control.
For low-volume roads only
10
Guide to Concrete Overlays
92
Ch 6. WORK ZONES
COMPLETED OVERLAY (Two-Lane Roadway with Minimum Granular Shoulders, Zero-Clearance Paver)
STAGE 1.
STAGE 2.
STAGE 3.
Bonded concrete overlay of concrete pavements Unbonded concrete overlay of concrete pavements
Bonded concrete overlay of asphalt pavements Unbonded concrete overlay of asphalt pavements
Bonded concrete overlay of composite pavements Unbonded concrete overlay of composite pavements
Applied to:
Typically
less than
0.25 mi
(0.40 km)
without
pilot car
Repair surface, prepare for overlay, and construct left shoulder
Construct right shoulder and concrete overlay
Construct left lane concrete overlay
• In order to construct an overlay on a roadway with
a minimum of 2 ft (0.6 m) wide existing shoulders,
adjustments to typical slipform pavers are necessary
in order to meet existing clearances adjacent to the
paver. The width of the clearance zone is dependent
on traffic control, paver track, and paver control
(stringline). When there is not enough clearance for the
paver track, paving molds may be installed on typical
two-track pavers to provide zero clearances. The
outside edges of the mold are brought out behind the
rear tracks and then the material from the front of the
paver is moved to the back by an auger to be spread
and paved.
• Install traffic control and close the left lane. Follow
jurisdictional requirements for traffic control. Check
with jurisdiction regarding allowable lane closure
length. If surface repair and preparation for the
overlay are minimal, then slow-moving traffic
control may be appropriate. Closing the lane may
require additional traffic control (e.g., signals,
flaggers, and/or pilot cars).
• Repair the surface as appropriate. Prepare the
surface for the overlay (or, in the case of concrete
overlay on concrete, the separation layer) as
described in the contract document.
• Construct calcium chloride treated granular
shoulder as outlined in contract documents. The
treated shoulder shall be firm and stable to support
vehicular traffic at low speeds.
• Construct separation layer (only for unbonded
overlay on concrete).
• Shift the traffic control to the left lane and close the
right lane to traffic. The length of the closure will
depend on the jurisdiction’s maximum closure length
with pilot car. Traffic controls and traffic control signals
will be based on jurisdictional requirements.
• Repair and prepare the surface for the overlay or the
separation layer and subsequent overlay as described
in the contract documents. Construct separation layer
(for unbonded overlay).
• Normal space for the paver stringline is 1–1.5 ft (0.3–0.5
m) and the paver track is a minimum of 2.5–3 ft (0.8–0.9
m). 1 ft (0.3 m)incremental encroachment reduction (up
to 2 ft [0.6 m] total) is common through typical machine
adjustment. Modification to a conventional paver is
necessary to achieve these dimensions. Speeds
should be restricted adjacent to paver when
clearance between the paver and vehicle traffic is
limited.
• Construct concrete overlay on the existing
pavement. Bull float work shall operate from the
outside shoulder only.
• Place 6 in. (150 mm) minimum thickness calcium
chloride treated granular shoulder to help stabilize
shoulder and minimize heavy dust that can impair
vision.
• The 1.5 ft (0.5 m) dimension between the roadway
centerline and vertical panel is for the stringline
and fillet.
• Close the opposite lane to traffic and place the
concrete overlay according to contract documents,
using the same procedures as described in stage 2.
• Complete shouldering. Complete pavement marking
and regulatory signing in accordance with contract
documents.
Figure 106. Overlay of two-lane roadway with minimum granular shoulders (zero-clearance paver)
93
Guide to Concrete Overlays
Ch 6. WORK ZONES
Construction area
Vehicle traffic
Varies
2 ft (0.6 m) min.
Existing
subbase
Existing pavement
Existing shoulder
Existing
shoulder
Surface repair
and overlay surface preparation
Traffic
control
device
(10 ft [3 m] min.)
Separation layer
(only for unbonded overlay on concrete)
8
11 ft (3.4 m) lane
(Typical)
Construction areaVehicle traffic
Granular
shoulder
Traffic
control
device
Traffic
control
device
Existing pavement
Concrete
overlay placement
Surface repair
Varies
1.5 ft (0.46 m) min.
12 ft (3.7 m) lane
(Typical)
Separation layer
(only for unbonded overlay on concrete)
11 ft (3.4 m) lane
(Typical)
8
(10 ft [3 m] min.)
Construction area Vehicle traffic
Traffic
control
device
Existing
pavement
Concrete
overlay
placement
6 in. (150 mm) plus
overlay thickness
granular shoulder
treated with
calcium chloride
1.5 ft (0.46 m) min.
12 ft (3.7 m) lane
(Typical)
Granular
shoulder
Separation layer
(only for unbonded
overlay on concrete)
7
7
(10 ft [3 m] min.)
8
11 ft (3.4 m) lane
(Typical)
Overlay of Two-
Lane Roadway with
Minimum Granular
Shoulders (Zero-
Clearance Paver)
Stage work area
Concrete
LEGEND
Granular material
COMPLETED OVERLAY
STAGE 1
STAGE 2
STAGE 3
NOTES:
1 Follow jurisdictional requirements
for traffic control devices. Outside
shoulder traffic control may depend
on width of shoulder.
2 Existing shoulder should have
minimum 6 in. (150 mm) of granular
material and should be treated with
calcium chloride.
3 Minimum lane width next to the
paver may be reduced for short-
term, stationary work on low-
volume, low-speed roadways when
vehicular traffic does not include
longer and wider heavy commercial
vehicles.
4 Place granular shoulder with
calcium chloride in two lifts. The
first lift is for the paver track. The
second lift is for final shoulder. If
the completed overlay in this stage
opens to traffic and the final lift
is delayed, place concrete fillet
as shown. If overlay creates a
dropoff greater than jurisdictional
allowance, place second lift before
opening overlay to traffic.
5 See centerline fillet illustration and
subsequent removal on figure 103.
6 Requires minimum to zero
clearance paver. 1.5 ft (0.5 m)
dimension is for the paver ski or
stringline.
7 Mark edgelines and centerlines per
MUTCD (FHWA 2009) section 6F.77
(mark both lanes).
8 For low-volume roads only
Finished
shoulder
Granular
shoulder
Granular
shoulder
24 ft (7.3 m)
12 ft (3.7 m) lane
(Typical) (Typical)
12 ft (3.7 m) lane
Pavement
marking Pavement
marking
Existing pavement
Concrete overlay
Separation layer
(only for unbonded overlay on concrete)
Existing subbase
Guide to Concrete Overlays
94
Ch 6. WORK ZONES
COMPLETED OVERLAY (Two-Lane Roadway Widened to Three Lanes with
Paved Shoulders, Conventional Paver)
STAGE 1.
STAGE 2.
STAGE 3.
Bonded concrete overlay of concrete pavements Unbonded concrete overlay of concrete pavements
Bonded concrete overlay of asphalt pavements Unbonded concrete overlay of asphalt pavements
Bonded concrete overlay of composite pavements Unbonded concrete overlay of composite pavements
Applied to:
Typically
less than
0.25 mi
(0.40 km)
without
pilot car
Repair surface, prepare for overlay, and construct base shoulder
widening and separation layer
Construct thickened shoulder and concrete overlay
Construct left lane concrete overlay
• Install traffic control and close the left lane. Follow
jurisdictional requirements for traffic control. Check
with jurisdiction regarding allowable lane closure
length. If surface repair and preparation for the overlay
are minimal, then slow-moving traffic control may be
appropriate. Closing the lane may require additional
traffic control (e.g., signals, flaggers, and/or pilot cars).
• Repair the surface as appropriate. Prepare the surface
for the overlay (or, in the case of concrete overlay on
concrete, the separation layer) as described in the
contract document.
• Prepare shoulder widening by trenching the existing
shoulder and trimming to the specified width. The
trench should be rolled and compacted as necessary
to obtain a firm and stable platform. Compact
shoulder material as specified in the contract
documents. A continuous progression
approach with the shoulder trencher and
placement of the base shoulder widening is
encouraged.
• Pave the existing shoulder a minimum of 6 ft
(1.8 m) with concrete.
• Use excavated granular material to widen
existing shoulder. Treat 3 ft (0.9 m) area of
shoulder with calcium chloride.
• Construct separation layer (only for unbonded
overlay on concrete).
• Shift the traffic control to the left lane and close the
right lane to traffic. The length of the closure will
depend on the jurisdiction’s maximum closure length
with pilot car. Traffic controls and traffic control signals
will be based on jurisdictional requirements.
• Repair and prepare the surface for the overlay or the
separation layer and subsequent overlay as described
in the contract documents. Construct separation layer
(for unbonded overlay).
• Construct concrete overlay on the existing
pavement. Complete right PCC shoulder
widening with the overlay.
• The “X” dimension between the roadway
centerline and vertical panel is for the paving
machine track and stringline.
• Close the opposite lane to traffic and place the
concrete overlay according to contract documents,
using the same procedures as described in stage 2.
Stringline may not be necessary for the right edge of
the paving when the paved overlay constructed in
stage 2 is used as the paver control in this stage.
• If the outside edge dropoffs at the shoulder
exceeds the jurisdictional allowance for a 1:1
fillet, then construct the granular shoulders in
this stage.
• Complete shoulders. Install (mill) rumble strips
in the paved shoulders and complete pavement
marking and regulatory signing in accordance
with contract documents.
Figure 107. Overlay of two-lane roadway widening to three lanes with paved shoulder (conventional paver)
95
Guide to Concrete Overlays
Ch 6. WORK ZONES
Construction area
Vehicle traffic
Existing subbase
Existing pavement
Existing shoulder
10 ft (3 m)
Existing shoulder
Traffic
control
device
Surface repair
and overlay surface
preparation
Subbase
widening
11 ft (3.4 m)
(Typical)
(Typical)
6 ft (1.8 m) min.
Separation layer
(only for unbonded overlay on concrete)
Construction area
Concrete
overlay placement
6 ft (1.8 m)
4 ft
(1.2 m)
4 ft
(1.2 m)
Existing pavement
4 ft (1.2 m)
shoulder
(Typical)
Traffic
control
device
Surface repair
Subbase
widening
Subbase
widening
11 ft (3.4 m)
(Typical) (Typical)
Separation layer
(only for unbonded overlay on concrete)
Vehicle traffic
11 ft (3.4 m)
(Typical) (Typical)(Typical)
Construction area
Remaining
shoulder
Remaining
shoulder
Concrete
overlay placement
6 ft
(1.8 m)
4 ft
(1.2 m)
4 ft
(1.2 m)
Existing pavement
Separation layer
(only for unbonded
overlay on concrete )
Paved shoulder
4 ft (1.2 m)
Traffic
control device
Surface repair
12 ft (3.7 m)
Subbase
widening
6
Vehicle traffic
11 ft (3.4 m)
(Typical)(Typical)
6
(Typical)(Typical)(Typical) Overlay of Two-
Lane Roadway
Widened to Three
Lanes with Paved
Shoulders
(Conventional
Paver)
Stage work area
Concrete
LEGEND
Base shoulder widening
materials
(e.g., cement-treated
base, porous concrete,
roller compacted con-
crete (RCC), asphalt, or
concrete)
Granular material
COMPLETED OVERLAY
STAGE 1
STAGE 2
STAGE 3
NOTES:
1 Follow jurisdictional
requirements for traffic
control devices.
2 Use excavated granular
material to widen existing
shoulder. Treat 3 ft (0.9
m) area of shoulder with
calcium chloride.
3 Minimum lane width
next to the paver may
be reduced for short-
term, stationary work on
low-volume, low-speed
roadways when vehicular
traffic does not include
longer and wider heavy
commercial vehicles.
4 If the completed overlay in
this stage opens to traffic
and the final shoulder
back fill is delayed,
place fillet as shown. If
overlay creates a dropoff
greater than jurisdictional
allowance, place second
lift before opening overlay
to traffic.
5 See centerline fillet
illustration and
subsequent removal on
figure 103.
6 Mark edgelines and
centerlines per MUTCD
(FHWA 2009) section 6F.77
(mark both lanes).
Remaining
shoulder
Finished shoulder
6 ft (1.8 m) min.
Pavement
marking Pavement
marking
Remaining
shoulder
Rumble
strip
Rumble
strip
4 ft (1.2 m)
(Typical)
4 ft (1.2 m)
(Typical)
Existing pavement
Overlay
placement
Surface repair
12 ft (3.7 m)
(Typical)(Ty pical)(Typical)
12 ft (3.7 m)12 ft (3.7 m)
Separation layer
(only for unbonded overlay on concrete)
Existing subbase
Tiebars optional
Guide to Concrete Overlays
96
Ch 6. WORK ZONES
COMPLETED OVERLAY (Four-Lane Roadway with Paved Shoulders, Conventional Paver)
STAGE 1.
STAGE 2.
STAGE 3.
Bonded concrete overlay of concrete pavements
Unbonded concrete overlay of concrete pavements
Bonded concrete overlay of asphalt pavements
Unbonded concrete overlay of asphalt pavements
Bonded concrete overlay of composite pavements
Unbonded concrete overlay of composite pavements
Applied to:
Typically
less than
0.25 mi
(0.40 km)
without
pilot car
Typically
less than
0.25 mi
(0.40 km)
without
pilot car
Repair surface and prepare for overlay
Construct concrete overlay on outside lane
Construct concrete overlay on inside lane
• Install traffic control and close the
inside lanes. Follow jurisdictional
requirements for traffic control. Check
with jurisdiction regarding allowable
lane closure length. If surface repair
and preparation for the overlay are
minimal, then slow-moving traffic
control may be appropriate. Closing
the lanes may require additional traffic
control (e.g., signals and flaggers).
• Repair the surface as appropriate.
Prepare the surface for the overlay
(or, in the case of concrete overlay
on concrete, the separation layer) as
described in the contract document.
• Evaluate the structural condition of
the existing shoulder. Mill existing
shoulder or reconstruct shoulder to
carry traffic load if necessary.
• Construct separation layer (only for
unbonded overlay on concrete).
• Shift the traffic control to the inside
lanes and close the outside lanes
to traffic. Traffic controls and traffic
control signals will be based on
jurisdictional requirements.
• Repair and prepare the surface for
the overlay or the separation layer
and subsequent overlay as described
in the contract documents. Construct
separation layer (for unbonded
overlay).
• Construct temporary shoulder for
paver track.
• Construct concrete overlay on the
existing pavement. Bull float work
shall operate from the outside
shoulder only.
• Shift the traffic control to the outside
lane and close the inside lane to
traffic. Place the concrete overlay
according to contract documents,
using the same procedures as
described in stage 2. Stringline may
not be necessary for the right edge
of the paving when the paved overlay
constructed in stage 2 is used as the
paver control in this stage.
If the right stringline is not used,
the “X” dimension could possibly
be reduced to 3 ft (0.9 m).
• Complete shoulder finish
grading. Install (mill) rumble
strips in the paved shoulders and
complete pavement marking and
regulatory signing in accordance
with contract documents.
Figure 108. Overlay of four-lane roadway with paved shoulders (conventional paver)
97
Guide to Concrete Overlays
Ch 6. WORK ZONES
Construction area
6 ft (1.8 m)
(Typical)
12 ft (3.7 m)
vehicle traffic
(Typical)
Existing subbase
Existing pavement
Separation layer
(for unbonded
overlay)
10 ft (3 m)
existing shoulder
(Typical)
Existing
shoulder
Traffic
control
device
Surface repair
and overlay surface
preparation
Construction areaVehicle traffic
Remaining
shoulder
Traffic
control
device
Existing pavement
Concrete
overlay
placement
Surface repair
Concrete shoulder
22 ft (6.7 m)
(Typical)
(Typical) (Typical)
12 ft (3.7 m) 10 ft (3 m)
11 ft (3.4 m)
(Typical)
Separation layer
(only for unbonded overlay on concrete)
Construction area Vehicle traffic
Remaining
shoulder
Temporary
concrete fillet
placed with
overlay
Concrete shoulder
Varies
Varies
Existing pavement
Concrete
overlay placement
12 ft (3.7 m)
(Typical)
Separation layer
(only for unbonded
overlay on concrete)
8
8
Varies
11 ft (3.4 m)
(Typical)
Overlay of Four-
Lane Roadway
with Paved
Shoulders
(Conventional
Paver)
Stage work area
Concrete
Existing shoulder
(Reconstructed
if necessary)
LEGEND
COMPLETED OVERLAY
STAGE 1
STAGE 2
STAGE 3
NOTES:
1 Follow jurisdictional
requirements for traffic
control devices.
2 Evaluate the structural
condition of the existing
shoulder. If necessary,
reconstruct shoulder with
PCC or asphalt to carry
the traffic load.
3 See centerline fillet and
subsequent removal
illustration on figure 103.
4 When the existing
shoulder outside of the
proposed paved shoulder
is less than 3 ft (0.9 m),
adjustment to the paver
may be necessary to
accommodate paver
control and paver track.
5 If the completed overlay
in this stage opens to
traffic and the final
shoulder backfill is
delayed, place fillet as
shown. If overlay creates
a dropoff greater than
jurisdictional allowance,
place second lift before
opening overlay to traffic.
6 For “X” less than 4 ft
(1.2 m), adjustments to
paver may be necessary
to accommodate paver
control and paver track.
7 The “X” dimension can
be reduced to 3 ft (0.9 m)
minimum when the right
lane is used as paver
control.
8 Mark edgelines and
centerlines per MUTCD
(FHWA 2009) section 6F.77
(mark both lanes).
Concrete
shoulder
Concrete shoulder
Rumble stripRumble
strip
10 ft (3 m)
paved shoulder
Concrete overlay
Existing pavement
Pav
ement
marking
Pavement marking
Paved
shoulder varies
12 ft (3.7 m) existing lane
12 ft (3.7 m) lane
(Typical) (Typical) (Typical)
12 ft (3.7 m) lane
Separation layer
(only for unbonded overlay on concrete) Existing subbase
99
Guide to Concrete Overlays 99
Guide to Concrete Overlays
Ch 7. CONSTRUCTION
Chapter 7.
CONSTRUCTION OF CONCRETE OVERLAYS
Concrete overlays are constructed using con-
ventional equipment and procedures. See
Appendix G for information about developing
project and supplemental specifications and
Appendix H for suggestions regarding owner-
contractor meetings.
Total construction time for concrete overlays
is significantly shorter than reconstruction
of a roadway because earthwork is limited
to minor quantities. Resurfaced streets and
highways can be opened to traffic within short
periods of time with adequate planning, expe-
dited staging, and efficient operations.
Key Points for
Concrete Overlay
Construction
Normal concrete paving construction prac-
tices can be used to complete concrete overlay
projects as quickly and efficiently as any
other paving method. Resurfaced streets and
highways can be opened to traffic within a
short period of time with adequate planning,
expedited staging, and efficient operations.
See Table 21.
FAQ – Is there anything different about constructing a concrete overlay?
Typically, no; the same methods and equipment are used as in new concrete pavement
construction. ere are, however, some considerations for placement during cooler periods
(spring and autumn). Under these conditions, the existing base and pavement will expand
and contract with the daily change in ambient temperature. Cracking may occur if the
concrete mixture has not gained enough strength to withstand the stresses caused by differ-
ential movement between the underlying pavement structure and the new concrete overlay.
Accelerating the rate of strength gain in the concrete mixture is the recommended way to
mitigate the effects of differential movement due to changes in ambient temperature. ere
are a number of methods that can be used to accomplish this; they may be used alone or, in
many cases, in combination:
• Heat the concrete to maintain a fresh concrete temperature of at least 75°F.
• Use a nonchloride accelerating admixture.
• Cover the new overlay pavement with insulating blankets, burlap, and/or polyethylene
sheeting.
• When possible, reduce the quantity of supplementary cementitious materials in the mixture.
HIPERPAV is a software tool available to
predict stresses in concrete. It is especially
useful when there is a need for more infor-
mation in less-than-desirable conditions,
such as inclement weather conditions, when
an overlay is particularly thin, or when a
project does not have much flexibility in
scheduling.
Payment is typically based on two items:
square yards and cubic yards. e surface
is measured to account for the square-yard
surface area, and batch tickets are collected to
account for the cubic-yard concrete volume,
including variable depths.
Construction Consideration
Bonded
Overlays of
Concrete
Bonded
Overlays of
Asphalt or
Composite
Unbonded
Overlays of
Concrete
Unbonded
Overlays of
Asphalt or
Composite
1. Mixture Design
Aggregate:
Physically and chemically stable and durable X X X X
Well-graded mix X X X X
Match aggregate thermal properties with existing pavement X
Maximum aggregate size should be D/2.5 in relation to the new overlay thickness X X X X
Use conventional mixtures with Type I or II cement. X X X X
Use fly ash and slag to reduce permeability with w/cm ratio not to exceed 0.42. X X X X
Use water reducer to help maintain w/cm ratio and desired slump, as well as to increase strength. X X X X
If accelerated construction is desired, accomplish this through careful scheduling and diligent
execution; accelerated concrete mixtures should only be used in limited areas where early opening
cannot be achieved through other means. X X X X
Fibers may be used to increase the “toughness” of concrete (measure of its energy-absorbing
capacity), improve resistance to deformation, hold concrete together in case of cracking, and serve as
an insurance policy that protects the surface from unseen base conditions.
X X
Verification testing in the laboratory of nonstandard mixes (trial batches) and specifications of testing at
temperatures representative of site conditions is encouraged to flag any mix problems. X X X X
Table 21. Concrete Paving Construction Practices for Overlays
Bonded Overlays Unbonded Overlays
Guide to Concrete Overlays
100
Ch 7. CONSTRUCTION
Construction Consideration
Bonded
Overlays of
Concrete
Bonded
Overlays of
Asphalt or
Composite
Unbonded
Overlays of
Concrete
Unbonded
Overlays of
Asphalt or
Composite
2. Grade Control
Centerline profile only (as-built) with uniform finished cross section X
Mill and
concrete
overlay
Three-line profile (edges and centerline) when cross slope varies or surface distortions exist XLittle or no
milling Inlays only Inlays only
Measure off existing pavement or top of milled surface to set stringline or form. Adjust individual points
up to produce a smooth line. X X X X
Survey 100–500 ft (30.5–152 m) cross sections when shouldering, foreslopes, and backslopes need
adjusting. If the existing profile grade is irregular, additional centerline elevations may be necessary for
grade corrections in certain locations for smoothness.
X X
Survey bridge tie-ins or bridge clearance conditions and extreme superelevations. X X X X
To prevent thicker asphalt separation layer and thus compaction, stability, and grade control issues, use
concrete to make up any 3 in. (75 mm) or greater variances in grade and a nominal 1 in. (25 mm) asphalt
separation layer.
X
3. Preoverlay Repairs for Uniform Support
Minimal minor repairs of surface defects. Remove deteriorated area and replace with overlay. X
An engineer should observe final condition of subbase pavement prior to overlay construction. For
minimal isolated distress that causes some loss of structural integrity that cannot be overcome with
milling, thicken the overlay in this area.
X
Replace isolated areas of subbase pavement when there is evidence of active movement. X X
Joint deterioration with little or no faulting can be bridged with the overlay. X
To widen the roadway, excavate the shoulder to allow for the widened thicker section to be placed with
the overlay. X X X X
Fill cracks in the HMA with sand or flowable mortar when the crack width exceeds the maximum coarse
aggregate size used in the concrete overlay mixture. X X
4. Surface Preparation
Surface roughness for bonding:
Shotblasting (even after milling) X
Milling to remove significant distortions or reduce high spots X X
Surface cleaning:
Sweeping followed by high-pressure airblasting
(waterblasting may be needed to remove dirt tracked onto surface) X X
Surface sweeping only X X
Maintain a clean and dry surface. X X
Sprinkle (mist) the existing pavement when the surface temperature exceeds 120°F; use
compressed air to remove any standing water directly ahead of the concrete-placing operation X X X X
Place nominal 1 in. (25 mm) asphalt layer to separate concrete layers and prevent bonding.
When heavy truck traffic is anticipated, it is advisable to consider a drainable asphalt layer and
drainage system.
X
If the existing asphalt surface of a composite pavement section remains intact, it can serve as a
separation layer. X
5. Concrete Placement
When the surface temperature of the asphalt is at or above 120°F (49°C), surface watering can be used
to reduce the temperature and minimize the potential for shrinkage cracking. No standing water should
remain at the time the overlay is placed.
X X X
The bonding of the overlay can be affected by the climatic conditions at the time of placement.
Significant stresses that develop due to rapid changes in temperature, humidity, and wind speed may
reduce the bond strength under severe conditions. HIPERPAV can predict interface bond stress based
on numerous factors.
X X
Feeding concrete consistently into the paver requires an adequate number of batch delivery trucks.
The number of trucks will often dictate the slipform or placement speed. The entire cycle of mixing,
discharging, traveling, and depositing concrete must be coordinated for the mixing plan capacity,
hauling distance, and spreader and paving machine capabilities. Extra trucks may be needed as the haul
time increases.
X X X X
Do not track paste or dirt onto the existing surface ahead of the paver because it can cause bond
failure. X X
Table 21. Concrete Paving Construction Practices for Overlays, continued
Bonded Overlays Unbonded Overlays
101
Guide to Concrete Overlays 101
Guide to Concrete Overlays
Ch 7. CONSTRUCTION
* Joint between overlay and curb and gutter should be sealed.
** Some states have experienced problems with asphalt stripping of the separation layer, particularly under heavy truck traffic and high speeds. Therefore, sealing is important
in these conditions. On lower speed roads without a heavy traffic loading, some states successfully do not seal.
Construction Consideration
Bonded
Overlays of
Concrete
Bonded
Overlays of
Asphalt or
Composite
Unbonded
Overlays of
Concrete
Unbonded
Overlays of
Asphalt or
Composite
The manner in which the crew deposits concrete in front of the paving operation is an important factor
for creating a smooth pavement surface in overlay projects. Placement in front of slipform paver should
be done in small overlapping piles so as to minimize lateral movements.
X X X X
Properly established, secure, and maintained stringline is very important for smoothness; constant and
continuous paving prevents interruptions that lead to bumps. X X X X
Tiebars may be appropriate in an open-ditch situation when constructing 3- to 6-ft (0.9- to 1.8-m)
widening units and overlay thickness is 5 in. (125 mm) or greater. Normally, tiebars are not used for lane
widening to prevent cracking from stresses due to differential expansion and contraction between lanes.
X X
Dowel bar use should follow full-depth pavement requirements. Pavements less than 7 inches thick
should not use load transfer dowels. When used for thicker pavements, they should be located
approximately in the mid-third of the overlay thickness. Isolated thicker sections should not dictate a
change in basket height or dowel bar insertion depth.
X X X
Texturing needs to be performed at the right time so as not to disturb setting of the concrete. Shallow
longitudinal tining or burlap/turf are two effective textures. Burlap/turf drag has shown adequate friction
with a quiet surface when hard sands are used in the mix.
X X X X
6. Curing to Prevent Rapid Loss of Water from Concrete
Proper curing of bonded and thin unbonded overlays is particularly important because they are thin
with a large surface compared with the volume of concrete. The curing rate may be increased from the
normal rate to provide additional protection. Standard curing compound rates may be used for thicker
unbonded overlays.
2 times normal 1.5–2 times
normal
1.5–2 times
normal
1.5–2 times
normal
During hot weather, steps should be taken to reduce the evaporation rate from the concrete. For
significant evaporation, provide a more effective curing application, such as fog spraying, or apply an
approved evaporation retarder.
X X X X
Adequate curing of overlays on a stiff support system (especially on underlying concrete pavement) is
important to minimize curling and warping stresses. X X X X
7. Joints
Joint spacing for concrete overlays requires special consideration for each type:
Joints are to be matched with underlying concrete to prevent reflective cracking. X
When feasible, it is a good policy to mismatch joints and/or cracks to maximize load transfer from
the underlying pavement. Some states that have not intentionally mismatched joints, however,
have not experienced any adverse effects.
X X
Slab dimensions match the underlying pavement. X
The recommended joint pattern for bonded overlays of asphalt should not exceed 1.5 times the
overlay thickness in inches. X
For overlays less than or equal to 6 inches thick, the slab dimensions (in feet) should not exceed
1.5 times the overlay thickness in inches (e.g., 4 in. x 1.5 ft/in. = 6 ft). X X
For overlays greater than 6 inches, the slab dimensions (in feet) should not exceed 2.0 times the
overlay thickness in inches, not to exceed 15 ft. X X
Because of the potential for higher curling and warping stress from a rigid underlying pavement,
shorter than normal spacing is typical (see pages 40, 44, and 48). X X
Joint sawing:
The timing of sawing is critical. Sawing joints too early can cause excess raveling. HIPERPAV
may be useful in helping to predict the appropriate time window for joint sawing, based on the
concrete mix design, construction times, and environmental conditions.
X X X X
Sawing must be completed before stresses exceed the strength developed. Sawing too late can
lead to uncontrolled cracking. X X X X
Transverse joint saw-cut depth for conventional saws Full depth +
0.50 in. (13 mm) T/3 T/4 min.-T/3 max.
Transverse joint saw-cut depth for early-entry saws Full depth +
0.50 in. (13 mm)
Not < 1.25 in.
(32 mm) Not < 1.25 in. (32 mm)
Longitudinal joint saw-cut depth T/2 (at least) T/4 – T/3 T/4 – T/3
Transverse joint width must be equal to or greater than the underlying crack width at the bottom of
the existing transverse joint. X
Sealing:
Seal joint using low-modulus hot-pour sealant with narrow joint. X* ** **
Table 21. Concrete Paving Construction Practices for Overlays, continued
Bonded Overlays Unbonded Overlays
Guide to Concrete Overlays
102
Ch 7. CONSTRUCTION
Bonded Overlays:
Ensuring Proper
Bond
When bonding a concrete overlay to an exist-
ing concrete surface, the necessity for a sound
bond cannot be overstated. Both theory and
practice show that without this bond, the
overlay will develop secondary distress quickly,
thus significantly compromising the life of
the pavement system. Research has attempted
to measure and characterize bond strength
during early ages of the concrete overlay. To
date, however, no simple and reliable test has
been developed. As a result, bond strength is
typically characterized using a surrogate test,
namely strength (compressive or flexural) of
the overlay. e strength of the bond between
the overlay and the existing concrete pave-
ment can be correlated with the flexural/
compressive strength of the overlay. If the
recommended construction procedures have
been performed correctly, and the early open-
ing strength criteria have been met, then the
bond strength should also be adequate to
allow the pavement to be open without bond
failure, provided that care has been taken to
prepare the existing pavement surface properly
and the overlay has been adequately cured.
Several elements (beyond those common to
a typical concrete pavement) are particularly
important in ensuring a good bond between
the concrete overlay and the underlying con-
crete pavement. ere are issues related to
the concrete mixture, joint spacing, surface
preparation and cleaning, curing, sawing,
and strength measurement. While several of
these factors are currently considered in con-
ventional concrete paving, specific emphasis
should be placed on certain key factors of
these elements, since bonded concrete over-
lays are particularly sensitive to volumetric
changes.
Concrete mixtures used in bonded concrete
overlays should shrink as little as possible and
have similar thermal properties, or CTE (see
page 52 for more information). is typi-
cally means optimizing the cement content
to minimize shrinkage while maintaining an
adequate strength. Another mixture-related
consideration is aggregate gradation (which
helps in reducing cement factors without
sacrificing strength), as well as aggregate
type. To help minimize the thermal strains
and stresses experienced at the bond line of
bonded overlays over concrete, the overlay
should have aggregate thermal properties simi-
lar to the aggregate in the underlying concrete
pavement. If local aggregate sources make
matching the thermal coefficient difficult, an
effort should be made to use only aggregates
with a thermal coefficient lower than that of
the aggregates in the existing pavement.
Surface preparation of the existing concrete
pavement is accomplished to produce a
roughened surface that will promote bond-
ing between the two layers; see Figure 109. A
variety of surface preparation procedures may
be used, including shotblasting and milling.
A bonding grout or epoxy is not required.
e most commonly used and most effective
surface preparation procedure is shotblasting.
Although milling will roughen the concrete
pavement surface, milling should not be used
solely for that purpose because of its poten-
tial for causing surface microcracking and
fracturing the exposed aggregate. If milling
is used to lower the pavement elevation, any
resulting microcracking should be removed
by shotblasting.
In some cases, a surface roughness or mean
texture depth is specified. e sand patch test
(ASTM C 965) is often used to measure and
verify the mean texture depth. Typically, a
mean texture depth in the range of 0.04–0.08
in. (0.9–2.0 mm) is deemed adequate for
proper bond development.
Following surface preparation, the surface
should be thoroughly cleaned to remove all
loose material to ensure adequate bonding.
Cleaning may be accomplished by sweeping
the concrete surface, followed by cleaning
in front of the paver with compressed air.
Airblasting and waterblasting should be used
only as supplementary cleaning procedures to
remove loose material from the surface after
shotblasting or milling. No visible moisture
should remain on the pavement surface when
the overlay is placed. Paving should com-
mence soon after cleaning to minimize the
chance of contamination.
Vehicles should be limited on the existing
surface after it is prepared. If it is absolutely
necessary to have vehicles on the existing
concrete, care should be taken that they do
not drip oil or other contaminants that could
compromise the bond. When the surface
temperature of the concrete is at or above
120°F (49°C), water misting can be used to
reduce the temperature and minimize the
chance of shrinkage cracking. Water stand-
ing on the surface should be blown off with
compressed air.
Curing also can have a pronounced impact
on concrete overlay bond. e diligent and
thorough application of a curing compound
(sometimes at twice the normal applica-
tion rate) is an effective method to control
FAQ—If the mean texture depth of the existing pavement is in the recommended
range or higher, do I have to shotblast or mill the pavement?
Yes; although the mean texture depth is a consideration, the shotblasting or milling is
necessary to remove laitance buildup from rubber, grease, and oil over many years of use.
Figure 109. Compare the surface texture of the nonshotblasted area (upper left half
of image) to the roughened surface texture on the shotblasted section of pavement
(under the pen) (source: Leif Wathne, ACPA)
103
Guide to Concrete Overlays 103
Guide to Concrete Overlays
Ch 7. CONSTRUCTION
moisture loss and thus lower shrinkage and
early-age cracking potentials. is is particu-
larly true for thin bonded overlays. More
“extreme” measures, such as wet or blanket
curing, can help to minimize the risks of poor
performance when proper curing compound
application is either difficult or doubtful.
ese types of more “extreme” curing regimes
are typically only applicable for short paving
sections such as intersection rehabilitation.
Good construction sawing practices can also
greatly reduce early pavement stresses and
help accommodate early opening to traffic.
As mentioned elsewhere in this document,
sawing the transverse joints in the new over-
lay full depth plus 0.5 inch, exactly over the
joints in the existing pavement, is absolutely
critical for proper bonding. ere have been
examples of early bonded concrete overlay
failures due to debonding as a result of not
sawing the joints completely through the
depth of the overlay or failing to match the
location of the underlying joint. e width
of the initial saw cut in the overlay should
be equal to or greater than the width of the
cracks under transverse joints in the existing
pavement; see Figure 48 on page 58.
When all of these factors have been properly
considered and executed during construction,
the overlay strength can be used to character-
ize the bond with some confidence. Strength
monitoring of the overlay concrete can be
done in a fashion similar to that of conven-
tional concrete paving. Maturity methods
for early-age strength prediction (ASTM C
1074) can be particularly helpful. If all recom-
mended construction procedures are followed,
and knowing that bond strength correlates
reasonably well with concrete strength, early
opening decisions can be made relatively reli-
ably, in-place, and in a timely fashion.
Unbonded Overlays:
Installation
of Geotextile
Interlayer Fabric
If an unbonded overlay is being constructed,
an asphalt or geotextile fabric separation layer
must be placed before the overlay is placed.
Geotextile separation layers require some spe-
cial installation practices.
Before placing the geotextile, the surface of
the existing pavement should be swept clean
of loose material with either a mechanical
sweeper or an air blower. en conventional
placement practices and procedures should be
followed for placing the separation layer.
Both pervious (geotextile fabric or open-
graded asphalt) and impervious (densely
graded HMA) types of separation layers must
drain at the pavement edges or risk trapping
water, which can be very damaging. e layer
can either be daylighted at the edges (allowing
the egress of water) or terminate in a subdrain
or other layer (allowing the water to flow
away from the pavement structure).
In general, the following construction prac-
tices have resulted in successful installations of
geotextile separation layers:
• Place the material as shortly before paving
as possible (ideally no longer than 2 to 3
days) to reduce the potential for it to be
damaged.
• Before placing the nonwoven geotextile
material, these actions should be taken:
◦Repair the existing pavement to correct
any significant cracking.
◦When faulting greater than 0.25 inch (or
as specified by the engineer) is present, it
may be reduced by milling.
◦Sweep the pavement surface clean.
Figure 110. Overlap
of nonwoven
geotextile material
section
Figure 111.
Fastening
nonwoven
geotextile fabric to
existing concrete
pavement
• Roll the material onto the base or other sur-
face, keeping the nonwoven geotextile tight
with no wrinkles or folds.
• Roll out sections of the material in a
sequence that will facilitate good over-
lapping, prevent folding or tearing by
construction traffic, and minimize the
potential that the material will be disturbed
by the paver.
• Overlap sections of the nonwoven geotex-
tile material a minimum of 6 inches and a
maximum of 10 inches, and ensure that no
more than three layers overlap at any point;
see Figure 110.
• Ensure that the edge of the material along
drainage areas extends at least 4 inches
beyond the pavement edge and terminates
above, within, or adjacent to the pavement
drainage system.
• Secure the material with pins (nails)
punched through 2.0- to 2.75-inch diam-
eter galvanized discs placed 6 feet apart or
less, depending on conditions; see Figure
111.
Guide to Concrete Overlays
104
Ch 7. CONSTRUCTION
• A limited number of projects have used an
adhesive for securing the geotextile to the
existing pavement; for more information,
see 3M (2013).
• Construction traffic on the geotextile
should be limited to only that necessary to
facilitate concrete paving; see Figures 112
and 113. If construction traffic is placed on
the geotextile, precautions should be taken
to mitigate tears and wrinkles in the fabric:
◦Leave temporary gaps in the geotextile
where trucks are crossing and making
sharp turns.
◦Minimize sharp turns and heavy braking,
which can cause tearing and wrinkling.
◦Reduce the travel speed of construction
traffic.
Figure 112. Paving on top of nonwoven
geotextile materials
Figure 113. Paving on top of white geotextile
fabric interlayer (source: Larry Engbrecht,
South Dakota chapter, ACPA)
Placing Dowel
Baskets
If dowel baskets are included in the overlay
design, good construction practices should be
followed. Anchoring dowel baskets securely to
the existing pavement is essential to provid-
ing the intended load transfer at contraction
joints. Movement of the dowel baskets has
been observed on some concrete overlay proj-
ects. is movement has been attributed to a
number of factors:
• Variable thickness asphalt separation layers
require different length nails and differ-
ent velocity shots as the asphalt thickness
changes across the pavement width.
• Newly placed, fine-graded asphalt mixtures
provide less friction than a milled surface
or existing concrete; reduced friction can
cause the dowel baskets to move as the con-
crete head in front of the paver slides along
the surface of the separation layer instead of
rolling as the paver moves forward.
• Excessive concrete head in front of the
paver can move the dowel baskets.
Figure 115. Manually verifying dowel placement
ere are several recommendations for
securely anchoring baskets and monitoring
their placement:
• Shipping wires should be left intact, unless
a MIT SCAN–2 is used for dowel place-
ment verification.
• Use six anchors per basket for existing con-
crete surfaces.
• Use eight anchors per basket for existing
asphalt and composite surfaces.
• Place an equal number of anchors on both
sides (paver side and downstream) of the
baskets; see Figure 113.
• Place the nails on the downstream side of
the basket; see Figure 114.
• Avoid excessive loading from the concrete
head in front of the paver.
Dowel placement should be periodically man-
ually verified after the paver has passed over
the baskets; see Figure 115. Suspend paving
if the baskets are moving during the paving
operation until a plan for securely anchoring
the baskets is approved. ere are numerous
Figure 114. Dowel basket anchor nails should be placed on the downstream side of the
basket relative to the direction of pavement
Paving Direction
105
Guide to Concrete Overlays 105
Guide to Concrete Overlays
Ch 7. CONSTRUCTION
methods available for checking the placement
of dowels once the concrete has hardened (MIT
SCAN-2, MIT SCAN–T2, ground-penetrating
radar, coring, etc.). Although the precision of
these methods varies, it is recommended that
dowel placement be verified through some
means.
Curing Concrete
Overlays
While curing is critical (yet often overlooked)
for all concrete pavements, it requires particular
attention for overlays less than 8 inches thick.
e ratio of surface area to volume is greater for
thinner overlays than that of typical concrete
pavements, thus the same rate of evaporation
will have greater detrimental effects on thinner
overlays if not properly cured. Excessive drying
shrinkage caused by late and/or inadequate cur-
ing can lead to reduced bond strengths due to
moisture warping within the concrete overlay.
ere are two primary issues to consider regard-
ing curing of concrete overlays:
1. Timing—e curing compound must be
applied before any surface evaporation
occurs.
2. Materials—A good quality curing
compound should be used; some state
DOTs have had good success with alpha-
methyl-styrene curing compounds, but at
additional material cost (see page 80 for
more information).
Evaporation retardant should be on hand and
available for use as emergency protection when
the curing operation is delayed. Evaporation
retardant should not be used as a finishing aid,
but applied when necessary after all finishing
operations are completed. A typical coverage
rate for thinner overlays (less than 7 inches) is
100 square feet per gallon, applied in two coats.
is heavier coverage of curing compound
can cause difficulty in sawing on steep hills,
especially when lighter early entry saws are uti-
lized, where there is a tendency for the saws to
slip on the curing compound. When this is an
issue, the second coat of curing compound can
be applied after the initial saw cuts have been
made.
Differential temperature and moisture values
throughout the slab can result in early-age curl-
ing and warping stress. When these stresses are
added under certain conditions to early-age
loading stress, cracking can occur. is can
be mitigated through proper curing and saw-
ing techniques. Large variations in ambient
temperature and relative humidity at the time
of overlay placement can contribute to these
stresses. When feasible, the overlay placement
should be scheduled around these conditions.
Sawing Joints
Particular attention should be paid to the
number of saws required to saw the joints
before cracking occurs. Most overlay projects
will require both earlier sawing and more
saws to accomplish this. Concrete overlay
placement rates can easily be limited by the
number of saws available; proper planning
is necessary to assure that production is not
adversely impacted by the capability to effec-
tively saw the joints before cracking can occur.
ere are a number of factors that contribute
to the need for earlier sawing and an increased
number of saws:
• Stiffer underlying layers increase internal
stresses in the early-age concrete.
• e ratio of lineal feet of joints to square
yards of paving is typically higher for con-
crete overlays; thinner overlays can have
significantly more (three to four times)
lineal feet of joint per square yard of paving
than conventional concrete paving.
• Paving production (square yards per hour)
is higher for thinner concrete overlays.
• inner overlay sections have a higher ratio
of surface area to volume. is can lead to
faster strength gain due to solar radiation
and also makes the sections more sensitive
to drops in ambient temperature, which
can increase the risk of random cracking
unless the joint sawing operation is timely.
Accelerated
Construction
Road improvements not only have direct
construction costs, but they also have indirect
time-related costs. Construction delays and
road closings are generally not well accepted
by the road users. One of the significant
benefits of accelerated concrete overlay con-
struction is decreasing total construction time,
which in turn reduces road user costs and
increases driver safety. In addition, concrete
overlays offer confidence that the improve-
ments will provide a long-life pavement.
One of the main goals during accelerated
overlay construction is to maintain successful
traffic management throughout the duration
of the project. Acceleration should begin in
the design phase with analysis of alterna-
tive maintenance of traffic schemes, advance
planning, and tailoring of project details to
facilitate shortened construction durations.
e plans and specifications should provide
the contractor with clear criteria for mainte-
nance of traffic requirements (e.g., two lanes
open in each direction at all times, pilot car
queues shall not exceed 10 minutes, etc.).
Given the requirements for maintenance of
traffic, the contractor should be given the
responsibility to stage and prosecute the
project to meet the objectives for accelerated
construction and maintenance of traffic.
Accelerated construction often uses con-
ventional concrete pavement materials
and procedures, but key changes can sig-
nificantly expedite projects; see Appendix
I. ese changes add flexibility for the
contractor. ey often involve contract
incentives, modifying pavement equipment
for minimum to zero clearance, materials
proportioning modifications, accelerated
curing methods, construction staging,
changes to pavement joint construction,
and revisions to opening criteria.
Road user costs should be evaluated when
determining the type of rehabilitation that is
to be implemented. When deciding if accel-
erated construction is to be implemented,
it is important that there is a benefit to be
gained such as reducing road user costs
and delays. e implementation of acceler-
ated construction techniques on concrete
overlays is based on project and user needs.
e techniques may be used on critical
parts of a project (such as intersections and
crossovers), the final segment, or the entire
project.
Typically, standard mixtures used in con-
junction with accelerated construction
techniques are capable of meeting project
accelerated opening requirements. In some
critical areas, accelerated concrete mixtures
are used for concrete overlays. Appendix I
outlines a variety of details for planning,
designing, and constructing concrete over-
lays in an accelerated process. Not all items
listed are needed for every accelerated over-
lay project. e following topics, however,
should be considered for most projects:
• Staging and maintenance of traffic
• Public relations—coordinating with adja-
cent businesses and residents to optimize
access and constructibility
• Implementing the use of time-related
incentives and disincentives to encour-
age concurrent scheduling and timely
completion
• Concrete mixture—using accelerated
mixtures only where critical
• Accelerated curing through the use of
insulating blankets
• Maturity methods for early opening
Guide to Concrete Overlays
106
Ch 7. CONSTRUCTION
Opening Overlay to
Traffic
Guidance on concrete strength require-
ments for opening concrete roadways to
traffic is readily available. For example,
the Flexural Strength Criteria for Opening
Concrete Roadways to Traffic, as published
by the Transportation Research Board (Cole
and Okamoto 1995), bases its opening flex-
ural strengths on thickness, k-values, and
estimated ESALs, whereas the FHWA and
ACPA’s Traffic Management Handbook (2000)
is based on thickness, foundation support,
and the number of ESALs between the time
of opening and the time concrete reaches
strength. Other methods are available (FHWA
1994) and depend on the type of traffic, early
loading locations on the slab, pavement thick-
ness, and subbase support.
Minimizing Early Loading
Fatigue Damage
e fatigue life of concrete pavement is
sensitive to early wheel loading. A fatigue-
consumption approach (Okamoto, et al.
1994) theorizes that concrete pavement has a
finite life and can withstand some maximum
number of load repetitions, N, of a given traf-
fic loading before fracture. Every individual
traffic loading applied decreases the life of the
pavement by an amount proportional to the
load. is damage value provides the percent-
age of life that is consumed by the actual
number of traffic loads up to a given point
in time. It is important to avoid decreases
in fatigue life caused by heavy early loadings
until the concrete has reached 3,000 psi.
Certain techniques can be employed to con-
trol early loading that reduces fatigue damage
until the concrete strength can accommodate
normal traffic loadings.
One of the most important techniques is
restricting wheel loads to no closer than 3–4
ft (0.9–1.2 m) from the edge of the pavement
(and ideally 6 ft [1.8 m]) to minimize stress.
Research has shown that allowing only inte-
rior early slab loadings greatly reduces fatigue
damage (FHWA 1994). Traffic cones are an
effective way of restricting construction traffic
along the pavement edges until the pavement
reaches the desired full opening strength. In
addition to restricting early edge loadings, the
use of higher modulus of subgrade reaction, k,
can help minimize early-age stress. With con-
crete unbonded overlays, this is a particular
plus, since the underlying pavement provides
a high level of base support.
Strength Conversions
e modulus of rupture, or flexural strength,
is an important parameter in the estimate
of fatigue damage. Many states use flexural
strength (modulus of rupture) for concrete
opening strength criteria, and others use
compressive strength. e following equation
is sometimes used to convert compressive
strength to third-point flexural strength,
although it is widely recognized that this rela-
tionship is mixture dependent:
MR = ( )0.667 psi
where
MR = flexural strength
(modulus of rupture), psi
f'c= concrete compressive strength, psi
Note: is empirical equation was developed
using data from four different studies, con-
ducted between 1928 and 1965 (Raphael
1984). Also, the equation is contained in
reports from ACI Committee 330 (2008).
Since early-age strength can change rapidly
in a short time, and since some agencies use
a variation of the above referenced equation,
it is recommended that each agency develop
its own relationship between the compressive
strength and flexural strength (modulus of
rupture) for the mixture they intend to use.
As described earlier, nondestructive tests such
as maturity can be used to determine opening
strength since it provides real-time results.
Strength Criteria for
Opening Bonded Overlay
Systems
Strength criteria for bonded overlay systems
depend on whether an overlay is placed on
concrete or on asphalt.
Bonded on Concrete
If proper surface treatment, curing, and
sawing are employed in the construction of
concrete overlays, the bond strength at the
time of opening should be adequate if 540 psi
(3.7 MPa) flexural or 3,600 psi (24.8 MPa)
compressive strength is achieved. As a rule
of thumb for bonded concrete overlays, the
bond tensile strength may be on the order of
2 to 10 percent of the compressive strength,
and the bond shear strength approximately 4
to 20 percent of the compressive strength.
FAQ—When can I open a bonded overlay to traffic so that the loading will not com-
promise the bond?
e answer is related to minimum concrete strength and not an arbitrarily selected time
from placement. Concrete opening strength (compressive or flexural) directly relates to
concrete’s load-carrying capacity and provides an indication of the bond strength.
Bonded on Asphalt
Bonded concrete overlays on asphalt have one
distinct advantage over bonded concrete over-
lays on concrete. e concrete panels can be
cut into small squares or rectangles in order
to reduce the curling and warping stresses and
the expansion and contraction of concrete at
the bond interface because there are no joints
that need to be matched in the underlying
pavement. e result is a reduction in shear
at the bond interface. is technique has
been successfully used for a number of years.
Overlays over asphalt, however, are typically
relatively thin and are therefore susceptible
to excessive temperature-related stresses,
particularly when the existing asphalt is hot
from solar heating. If accelerated methods are
used, extreme care must be taken to mini-
mize shrinkage cracking through diligent
and thorough curing (sometimes at double
the ordinary rate of curing compound, or,
in short sections, wet curing and/or blankets
may be necessary). Some states have incorpo-
rated fibers to increase the toughness of the
concrete as well as to improve its resistance to
cracking.
Determining a reasonable value for opening
bond strengths for these types of overlays may
prove difficult, as described above. Typically,
a value for opening strength of the concrete
of 420 psi (2.9 MPa) flexural (2,500 psi [17.2
MPa] compressive) to 480 psi (3.3 MPa) flex-
ural (3,000 psi [20.7 MPa] compressive) has
proven adequate. An additional consideration
for accelerated construction is to encour-
age bond via milling of the existing asphalt
surface. If shear failures do occur, they will
likely occur in the asphalt since concrete shear
strength is greater than asphalt shear strength.
Strength Criteria for
Opening Unbonded
Overlay Systems
Because unbonded overlays are essentially a
concrete pavement on a high-quality subbase,
it is appropriate and somewhat conserva-
tive to use opening strength criteria that are
commonly used for conventional paving. For
example, a minimum flexural strength (3rd
point) of approximately 340 psi (2.3 MPa) or
1,800 psi (12.4 MPa) compressive strength
can be used for noninterstate traffic. e state
of Georgia for example, uses a concrete open-
107
Guide to Concrete Overlays 107
Guide to Concrete Overlays
Ch 7. CONSTRUCTION
ing compressive strength criteria of 1,400 psi
(9.7 MPa) compressive strength, anticipating
that the approved mixture reaches 2,500 psi
(17.2 MPa) in 24 hours and 3,500 psi (24.1
MPa) in 3 days.
Repairs of Concrete
Overlays
Concrete overlays can be expected to provide
excellent performance and long life. eir per-
formance is directly related to the uniformity
and quality of the existing pavement base.
Isolated weak or thin spots in the existing
pavement may not be discovered during the
pavement evaluation, overlay design, or over-
lay construction phases, and, like all pavement
systems, some repairs may be necessary during
its service life. If a bonded or unbonded over-
lay panel becomes distressed, overlay repairs
are relatively straightforward and, in many
cases, easier to perform than repairs of con-
ventional concrete pavements.
Figure 116. Removing overlay panels (source: Randell Riley, Illinois
chapter, ACPA)
Figure 117. Finish and cure of concrete overlay repair (source: Dan
DeGraaf, Michigan Concrete Paving Association)
Figure 118. Typical concrete pavement milling operation (source:
Randell Riley, Illinois chapter, ACPA)
Figure 119. Typical concrete pavement milling operation (source: Dan
DeGraaf, Michigan Concrete Paving Association)
Repairs of Bonded or
Thin Unbonded Concrete
Overlays
Full-depth panel replacement rather than
partial-depth panel replacement is typical for
bonded and thin unbonded overlays, because
the panels are small and relatively thin. After
full-depth sawing of the panel perimeter, the
panel can be removed easily by jack hammers
or a backhoe; see Figure 116.
When the overlay has been removed, the
existing base should be examined. If the old
existing pavement is determined to be defi-
cient, it should be removed and replaced with
concrete; the pavement replacement may be
placed in a separate layer or poured mono-
lithically with the overlay. Asphalt should not
be used as a patching material because con-
crete does not bond well with new asphalt.
Replacing an overlay panel(s) is easily accom-
plished using typical overlay procedures and
materials; see Figure 117.
in concrete overlays at the end of their
service life can be milled and refilled easily;
see Figures 118 and 119. Removal by mill-
ing (also referred to as carbide milling, cold
planning, and rotomilling) is a good option
for concrete overlays, because they rely on
the existing pavement base for load transfer
and therefore do not typically require steel
reinforcement.
Guide to Concrete Overlays
108
Ch 7. CONSTRUCTION
Generally, the productivity of milling concrete
is very good, depending on aggregate hard-
ness, bit configuration, and removal depth. For
example, removal of a concrete overlay at a 2-in.
(50-mm) depth has been reported as high as
8,000 ft2/hr (720 m2/hr) and for a 4-in. (100-
mm) depth, as low as 2,700 ft2/hr (243 m2/hr).
e method of removal is similar to that used
for asphalt layers, particularly when there are no
steel tiebars in the overlay.
Figure 120. Typical concrete pavement millings from milling operation (source: Dan DeGraaf,
Michigan Concrete Paving Association)
Repairs of Full-Depth
Unbonded Concrete
Overlays
Full-depth unbonded overlays typically are
constructed with dowel basket and lane ties,
so common concrete pavement repair tech-
niques are used. ese include partial- or
full-depth repairs, diamond grinding, and
joint resealing. With thicker overlays (8 in.
[200 mm]) subject to heavy traffic, load trans-
fer restoration can also be applied to restore
load transfer and mitigate joint problems.
When a uniform separation course is used,
overlay thickness will likely vary, especially
where superelevation changes are encountered;
repairs made in these areas may require provi-
sions to account for additional saw-cut depth.
Standard full-depth concrete removal tech-
niques are used on thicker overlays. Eight- to
nine-inch (200- to 250-mm) concrete overlays
have been successfully removed by milling.
Milling can be performed under wet or dry
conditions. e milling depth can be feath-
ered into adjacent pavements. Milling can
be completed on specific selected sections.
e coarseness of the surface after milling
and the fineness of the millings can vary
based on the type and spacing of milling
teeth on the drum; see Figure 120.
109
Guide to Concrete Overlays
APPENDICES
APPENDIX A.
EVALUATION AND SELECTION TABLES
Tables 22 and 23 are tools for evaluating the conditions of concrete pavements and asphalt/composite pavements, respectively.
Table 22. Distress Types and Severity Levels Recommended for Assessing Concrete Pavement Structural Adequacy
Load-Related Distress Highway
Classification
Current Distress Level
Adequate Marginal Inadequate
Jointed plain concrete medium- and high-
severity transverse and longitudinal cracks and
corner breaks (% slabs)
Interstate/Freeway < 5 5 to 10 > 10
Primary < 8 8 to 15 > 15
Secondary < 10 10 to 20 > 20
Jointed reinforced concrete medium- and high-
severity transverse cracks and corner breaks (#/
lane-miles)
Interstate/Freeway < 15 15 to 40 > 40
Primary < 20 20 to 50 > 50
Secondary < 25 25 to 60 > 60
Jointed plain concrete mean transverse joint/
crack faulting (in.)
Interstate/Freeway < 0.10 (2.5 mm) 0.10–0.15 (2.5–3.8 mm) > 0.15 (3.8 mm)
Primary < 0.125 (3.2 mm) 0.13–0.20 (3.3–5.1 mm) > 0.20 (5.1 mm)
Secondary < 0.15 (3.8 mm) 0.15–0.30 (3.8–7.6 mm) > 0.30 (7.6 mm)
Jointed reinforced concrete mean transverse
joint/crack faulting (in.)
Interstate/Freeway < 0.15 (3.8 mm) 0.15–0.30 (3.8–7.6 mm) > 0.30 (7.6 mm)
Primary < 0.175 (4.5 mm) 0.18–0.35 (4.6–8.9 mm) > 0.35 (8.9 mm)
Secondary < 0.20 (5.1 mm) 0.20–0.40 (5.1–10.2 mm) > 0.40 (10.2 mm)
Continuously reinforced concrete
medium- and high-severity punchouts
(#/lane-miles)
Interstate/Freeway < 5 5 to 10 > 10
Primary < 8 8 to 15 > 15
Secondary < 10 10 to 20 > 20
Applicability of Bonded Concrete Overlays
Applicability of Unbonded Concrete Overlays
Guide to Concrete Overlays
110
APPENDICES
Table 23. Distress Types and Levels Recommended for Assessing Asphalt and Composite Pavement Structural Adequacy
Installation cost is on the order of $0.50 per yd2 (circa 2008)
Distress Type Highway
Classification
Distress Level
Adequate Marginal Inadequate
Fatigue cracking (% of wheel path area)
Interstate/Freeway < 5 5 to 20 > 20
Primary < 10 10 to 45 > 45
Secondary < 10 10 to 45 > 45
Longitudinal cracking in wheel path (ft/mi)
Interstate/Freeway < 265 (50.2 m/km) 265–1060 (50.2–200.8 m/km) > 1060 (200.8 m/km)
Primary < 530 (100.4 m/km) 530–2650 (100.4–501.9 m/km) > 2650 (501.9 m/km)
Secondary < 530 (100.4 m/km) 530–2650 (100.4–501.9 m/km) > 2650 (501.9 m/km)
Composite pavement reflection cracking crack
width (in.)
Interstate/Freeway < 0.50 (12.7 mm) 0.25–0.50 (6.4–12.7 mm) > 0.50 (12.7 mm)
Primary < 0.50 (12.7 mm) 0.50–0.75 (12.7–19.1 mm) > 0.75 (19.1 mm)
Secondary < 0.50 (12.7 mm) 0.50–0.75 (12.7–19.1 mm) > 0.75 (19.1 mm)
Transverse crack spacing (ft)
Interstate/Freeway > 200 (61.0 m) 100–200 (30.5–61.0 m) < 100 (30.5 m)
Primary > 120 (36.6 m) 60–120 (18.3–36.6 m) < 60 (18.3 m)
Secondary > 120 (36.6 m) 60–120 (18.3–36.6 m) < 60 (18.3 m)
Mean depth of rutting in both wheel paths (in.)
Interstate/Freeway < 0.25 (6.4 mm) 0.25–0.40 (6.4–10.2 mm) > 0.40 (10.2 mm)
Primary < 0.35 (8.9 mm) 0.35–0.60 (8.9–15.2 mm) > 0.60 (15.2 mm)
Secondary < 0.40 (10.2 mm) 0.40–0.80 (10.2–20.3 mm) > 0.80 (20.3 mm)
Shoving (% of wheel path area)
Interstate/Freeway None 1 to 10 > 10
Primary < 10 10 to 20 > 20
Secondary < 20 20 to 45 > 45
Applicability of Bonded Concrete Overlays
Applicability of Unbonded Concrete Overlays
111
Guide to Concrete Overlays
APPENDICES
APPENDIX B.
RECONSTRUCTION OPTIONS FOR CONCRETE
Should the existing asphalt or concrete of a
composite pavement section or plain concrete
pavement have major deficiencies that cannot
be overcome with preservation techniques
(i.e., concrete overlays), the existing pavement
can be recycled in place to serve as a granu-
lar base. e two acceptable methods are as
follows:
1. Recycled concrete aggregate (RCA) as base
material (preferred option)
2. Rubblization of concrete pavement (only
used under certain conditions if severe
MRD [ASR or D-cracking] exists or the
concrete pavement has failure due to unsta-
bilized open graded base)
In-place Recycled
Concrete as a
Processed Base
Material
Recycling concrete pavements into an RCA is
a viable alternative for unbound base course
construction. To be successfully utilized, recy-
cled concrete must be viewed as a source of
aggregate with characteristics and value equiv-
alent to the aggregate material it replaces ton
for ton; see Figure 121. e quality of RCA
concrete depends on the amount of mortar
that remains attached to the original aggre-
gate. If processing is such that little mortar
remains and no fines smaller than #4 sieve are
used, the properties of the RCA will be simi-
lar to the properties of the original aggregate.
An RCA, as a rule, is considered a high-
quality material for unbound or stabilized
applications such as bases when compared
to conventional new aggregate. An RCA has
rougher surface texture, higher shear strength,
higher rutting resistance, and higher resilient
modulus (Van Dam et al. 2012). ese excep-
tional qualities allow for unrestricted use of an
RCA as a base material up to and including
100 percent substitution of new aggregate.
It is generally accepted that after unbound
RCA base is compacted, its strength and
stiffness increase. A misinterpretation of this
phenomenon is that this is due to hydration
of unhydrated concrete contained within
the paste portion of the RCA. Instead, the
increased stiffness is credited to the carbon-
ation of very soluble calcium hydroxide
(CH) released by the RCA in the presence of
moisture, which is constantly available in the
subsurface base.
When using RCA as a drainable base, cer-
tain contained design conditions must be
considered. e mortar fraction of the RCA
contains CH as a by-product of concrete
hydration, which, when in the presence of
water, goes into solution. is solution can
react with atmospheric carbon dioxide and
form a solid material called tufa (leachate),
which, in the presence of fines, can reduce the
flow in improperly designed drainage systems
using RCA. Conditions that lead to this are
easily prevented in drainable bases (Wade et
al. 1995). A proper design places all RCA
above the water table, below the elevation of
the inlet of the drainage system, and, if geo-
textiles are used, the flow must be parallel to
the geotextile and not through it. Improper
design will result in the formation of tufa
from the fines and CH, clogging pipes, and
other elements of the drainage system.
Effluent from drainable bases containing RCA
can have pH values greater than 7.0 due to
the leaching of CH. is has not been found
to be problematic in ecosystems. Although
effluent from an RCA drainable base can have
increased pH, especially during the first flush-
ing cycle of water, it has no buffering capacity
and is equivalent to adding lime to stabilize
the effect of acid rain on a lawn. In stagnant
flow conditions, the leachate could reach a
pH as high as 12.4; however, this will quickly
dissipate as the leachate encounters soils and
organic materials commonly present in soils
(Van Dam et al. 2012).
Pavements with an MRD such as ASR,
D-cracking, or freeze-thaw distress have been
effectively used as unbound base material.
Before using these materials, however, it is
recommended that testing be performed
to determine the severity of the ASR in
accordance with the FHWA’s Report on
the Diagnosis, Prognosis, and Mitigation of
Alkali-Silica Reaction (ASR) in Transportation
Structures (FHWA 2010).
Rubblization of
Concrete Pavement
Rubblization is a technique that was devel-
oped to minimize reflective cracking in HMA
overlays. e intent of this technique is to
reduce the existing concrete pavement into
small sections to prevent reflecting into the
HMA overlay; see Figure 122.
Figure 121. Recycled concrete aggregate (source: Jonathan Gene Pitre,
University of New Hampshire)
Figure 122. Rubblized concrete pavement (source: Todd Hanson,
Iowa DOT)
Guide to Concrete Overlays
112
APPENDICES
Rubblization effectively destroys the existing
pavement structural condition and reduces
the support for the overlay to the least com-
mon denominator. It results in the loss of the
existing pavement’s structural carrying capac-
ity, and thus requires a thicker, more costly
overlay.
Rubblization may serve as a base for an
unbonded concrete overlay when the exist-
ing concrete slab exhibits fast-acting material
distress problems such as ASR, D-cracking, or
freeze-thaw damage. ese material problems
cause the concrete pavement to deteriorate
and lose structural integrity. Before these
pavements are rubblized, however, they
should be tested in accordance with the refer-
enced FHWA criteria.
e conditions for rubblization to be consid-
ered for a base for an unbonded overlay are
concrete pavements that have failed due to
unstabilized open graded bases. Many of these
pavements have migration of the subgrade
material into the open graded base layer,
creating voids and differential support condi-
tions. is differential settlement of the open
graded layer results in failed support condi-
tions and ultimately mid-panel cracks, corner
cracks, and significant faulting.
Rubblizing a concrete pavement successfully
is predicated on a number of conditions, and
there are several cautions to consider as well
when contemplating this technique:
• First and foremost, a complete and uniform
rubblization can only be accomplished
when the existing pavement is sitting on a
stable subgrade. e rubblization operation
must not be allowed to destroy the integrity
of the support layers below the pavement.
When base is soft, the rubblization process
under certain conditions can drive concrete
pieces into the subgrade, forcing water
upward and reducing subgrade stability.
Soft and yielding subgrade conditions result
in incomplete and nonuniform rubbliza-
tion. Moisture/water present under the
existing pavement may create a condition
that prevents the rubblized concrete par-
ticles from seating and locking together.
e ability of a particular pavement to
withstand rubblization and retain its drain-
age and support functions is typically
not known until the pavement is actually
rubblized.
• Prior to rubblization, all HMA surfacing
and joint filler material must be removed.
• Underdrains should be installed prior to
rubblizing the pavement.
• Care must be taken not to damage utilities
or underdrains with minimal cover.
• Rubblization must shatter the existing con-
crete for the full depth of the pavement. A
testing protocol should be established to
determine the quality and completeness of
the rubblization operation as well as actual
gradation.
• Steel reinforcement in the existing pave-
ment should be debonded from the
concrete. Some of the reinforcement may
surface during the rubblization opera-
tion, and steps should be taken to remove
exposed reinforcement.
• An aggregate choke stone layer is required
to fill voids and minimize the potential for
pavement quantity overruns.
Crack and Seat (Not
Recommended)
Crack and seat should be limited to isolated
locations like tented panels. It results in a
nonuniform support condition when applied
over large areas, and this can be problematic
for both HMA and concrete overlays.
Crack and seat concrete does not serve well
as a subbase for either concrete or asphalt
because it has no gradation or density con-
trol. During the crack and seat operation, the
wire mesh must be severed or the crack that
is tied by mesh may cause reflecting cracking
into the concrete overlay. e choke stone
and crack and seat material must be drained
to prevent trapped water. Subgrade support
influences the size of the cracked pieces.
Presence of water in the subgrade will cause
loss of subgrade support, which leads to rock-
ing of the slabs and subsequent distress in the
overlay. e quality of the subsurface materi-
als is highly suspect in the same areas that
the slabs in the concrete were in very poor
condition.
113
Guide to Concrete Overlays
APPENDICES
APPENDIX C.
FIBER REINFORCEMENT
Figure 123. Fibers in concrete mix (source: Randell Riley, Illinois chapter, ACPA)
Why Fibers?
Fiber reinforcement in concrete overlays
(FRC) can increase the concrete structural
integrity. It contains short, discrete fibers that
are to be uniformly distributed and randomly
oriented. e most common of these fibers
include synthetic and steel fibers. Synthetics
have played a predominant role for the last
two decades as the technology has improved.
Other fiber types such as glass, cellulose, and
natural fibers are occasionally used, but these
are relatively rare and are outside the scope of
this document; see Figure 123.
Characterization of the fibers with different
concrete is normally based on fiber materi-
als, geometries, distribution, and densities.
Used in sufficient dosages with uniform
distribution, fibers help increase, in engineer-
ing terms, the “toughness” and ductility of
concrete. Enhancing the toughness and duc-
tility provides some flexibility to the designer,
since longer joints and/or thinner sections
of concrete can be considered. A good
understanding of the several different fiber
technologies permits the designer to better
optimize designs for specific conditions.
Sufficient fibers provide an additional benefit
in controlling differential slab movement
because the fibers span the cracked portion
below the sawed joints. Plain concrete in
overlay applications occasionally exhibits dif-
ferential movement of the individual slabs as
a result of temperature, curling/warping, or
load-induced movement in the underlying
pavement. As a result, joints may open up
or not line up; this is principally an issue of
aesthetics, but it can affect performance when
materials and conditions exacerbate curling/
warping.
In extreme cases, joints may fault in high-
traffic-volume areas. Synthetic fibers have
been used successfully in helping to control
these problems for several years, although
long-term (greater than 15 years) duration
of the benefit is not yet well established, par-
ticularly for synthetic fibers. Steel fibers have
been around much longer and, provided cor-
rosion can be kept in check or is not found to
be objectionable on the surface, can be quite
effective as well, but they have other disadvan-
tages compared to synthetics.
Fibers have the ability to hold the inevitable
cracks tightly together. ese cracks can occur
from a variety of causes, but the fibers render
the cracks more an annoyance than an actual
problem. Such tight cracks will usually per-
form better than typical sawed joints. Good
performance across cracks has been observed
since fibers have been used in roadway appli-
cations. In the concrete plastic state, fibers
also offer the advantage of increased resistance
to “plastic shrinkage” cracking. is type of
cracking can occur in all concrete applications
when wind blows across the paved surface
and the rate of evaporation exceeds the rate of
bleed water coming to the surface of the con-
crete prior to set.
Types of Fibers
e type of fiber to be used and the recom-
mended dosages for specific types are evolving
fairly rapidly. Although steel fibers have a long
history in paving applications, their addi-
tion to the concrete using current technology
requires significant manpower, which raises
cost. Steel fibers also require more care to pre-
vent “balling” of the fibers as a result of their
tendency to sometimes clump together when
exposed to cement and water. e latter prob-
lem can be prevented with proper charging
of the mixers, which may vary with the other
materials in the concrete mixture. Steel fibers
are considerably heavier than synthetic fibers
and can settle near the bottom of the overlay
if not properly mixed.
Synthetic fibers are broadly classed as macro
fibers rather than micro fibers, which are also
common in the industry. Generally speaking,
synthetic fibers have been favored compared
to steel fibers in the last few years because of
the ease of handling and better dispersion
characteristics. e volume of fibers added to
a concrete mix is expressed as a percentage of
the total volume of the composite (concrete
and fibers), termed volume fraction (vf). e
vf typically ranges from 0.1 to 3.0 percent.
e aspect ratio (l/d) is calculated by dividing
fiber length (l) by its diameter (d). Fibers with
a noncircular cross section use an equivalent
diameter for the calculation of l/d.
Steel fibers with a much higher density
than synthetic fibers will weigh much more
than synthetic fibers at the same volume in
the concrete mixture. It may also, however,
take a higher volume of one fiber compared
to another to provide the same increase in
pavement performance. For this reason, it is
important to know the type of fiber being
used, the volume of the fiber needed in the
mixture to produce the desired properties,
and the fiber’s specific gravity. is informa-
tion is essential so that the concrete producer,
who batches concrete by weight rather
than volume, can produce a unit volume of
concrete having the appropriate behavior
characteristics upon setting.
Macro synthetic fibers starting at a minimum
dosage of 4 lb/yd3 have worked well on con-
crete overlays where they have been used.
For a typical concrete mix, this is about 0.26
percent volume. For comparison, the same
volume of steel fibers would weigh about 34
lb/yd3 but yield somewhat different char-
Guide to Concrete Overlays
114
APPENDICES
Figure 124. Fibers added at plant (left) and bags tossed into ready-mix truck (right)
(source: Randell Riley, Illinois chapter, ACPA)
acteristics in the concrete. Fiber producers
and suppliers can be of assistance in this area
since, as mentioned earlier, the technology
is undergoing a rapid evolutionary phase.
Various blends of fiber technologies are being
introduced that combine steel and synthetic
fibers. Also, higher modulus synthetics are
under development that may further advance
the technology in the next few years. A good
reference and some minimum recommended
dosages for a specific class of fiber based on
the current state of understanding can be
found at www.dot.state.il.us/materials/syn-
theticfibers.pdf (IDOT-BMPR 2013).
High-volume Macro
Synthetic Fiber
Mixtures
Certain types of macro synthetic fibers in
quantities greater than that mentioned earlier
can provide for reduction in overlay thickness,
enhance postcrack flexural performance, and,
in some cases under high doses, actually allow
the concrete to become yielding in nature
and to flex somewhat under loads. Work still
needs to be done to better define the optimal
amount of macro synthetic fibers to add or
the optimal performance volume, based on
current records of thin pavements with FRC.
e 4 lb/yd3 dosage mentioned earlier is
enough to impart the proper characteristics
in hardened concrete to improve postcracking
performance and increase the load-carrying
capacity of the entire slab. Higher dosages can
further improve this performance, but care
must be taken to avoid clumping of the fibers
in the mix. Mix adjustments such as chang-
ing aggregate gradation, cement content,
and admixture type and dosage are necessary
to accommodate the higher fiber contents.
Concrete mixtures with a high volume (5.0 to
7.5 lb/yd3) of macro synthetic fibers (typically
with lengths of 1.5 to 2.25 inches) ideally
should utilize well-graded aggregates. In addi-
tion, because of the fibers’ large surface area
compared to their volume, such mixtures may
require slightly more cementitious material
(20 to 50 lb/yd3) and slightly more water
to keep the same w/cm ratio; they also may
require adjustment to the amount of fine
aggregates.
Research on a concrete overlay wearing sur-
face using high fiber content was conducted
by Dr. Amanda Bordelon at the University of
Illinois, and published as Flowable Fibrous
Concrete for in Pavement Inlays (wearable
surface) (Bordelon 2011). A flowable fibrous
concrete (FFC) mixture with high workabil-
ity was developed, to be placed rapidly as a
2-inch (5-cm) thick concrete overlay or inlay.
To extend the service life of the thin overlay
(or inlay) through improved crack resistance
and improved residual load-carrying capac-
ity, the mixture contained higher macro-fiber
content (up to 0.5 percent by volume). To
retain workability at these higher fiber con-
tents, the mixture required a higher content
of cementitious material in order to coat the
fibers.
For example, a cementitious material content
of around 790 pounds/yd3 was utilized for
achieving twice the fracture toughness with
0.56 percent volume fraction of fiber content.
In addition, other material proportions were
found to enhance the mixture’s workability
and stability against segregation:
• Smaller maximum coarse aggregate size,
such as less than 3/8 inch (9.5 mm), in
order to be placed as a 2-inch (50-mm)
overlay or inlay
• Higher percentage of sand
• Use of micro-fiber
• Use of a high-range water reducer
A 325-foot long full-scale FFC inlay was
constructed in 2009 in Rantoul, Illinois,
to demonstrate and observe any challenges
related to the placement of the FFC material
and to monitor the cracking and bonding per-
formance of the hardened concrete pavement
inlay. e 2-inch FFC inlay sections were cast
on a milled asphalt pavement in good condi-
tion and demonstrated good bond strength
between layers. e residual strength ratio of
the mixture was measured between 40–50
percent, which was at least twice as high as
recommended in the standard BCOA calcula-
tor. Different size slab panels were attempted
at 4 feet, 5.5 feet, and 11 feet in the longitu-
dinal direction. e widest transverse joint
was around 0.05 inches (1.25 mm), and the
average joint crack remained tight at 0.016
inches (0.4 mm) for the 4-foot slab size.
Construction
Considerations
When Using Fibers
e fibers’ length and large volume will often
reduce slump from 4 inches to 2 inches in a
concrete mixture. With everything else being
equal, there is not a corresponding reduction
in workability. To a concrete finisher or ready-
mix concrete truck driver casually observing
the discharge of the first load of concrete, this
can trigger their natural instinct to add water
to the mixture to make it easier to place. In
reality, an appropriately designed and batched
concrete and suitable fiber will actually place
similarly to normal concrete and responds
especially well to mechanical vibration; if
needed, a moderate dose of a polycarboxylate
or other water reducer typically is used to off-
set any loss in workability, especially for fiber
dosages 5.0 lb/yd3 and greater. e admixture
supplier should be contacted for recommen-
dations. During construction, a few other
items may warrant attention when using
fibers, and these characteristics are further
exacerbated as the dosage of fibers increases:
• Fibers can be added at the batch plant or
placed in the ready-mix truck; see Figure
124.
• Fiber use may require slightly delayed
contraction joint sawing due to the fibers’
tendency to increase susceptibility to joint
raveling if not timed properly.
• e use of macro fibers adds costs to the
concrete mixture. For this reason, their use
must be weighed against other costs and
factors such as increasing the overlay thick-
ness without the fibers, possible reduced
number of sawed joints, better joint perfor-
mance, ability to minimize grade changes,
and benefits of increased design life. e
115
Guide to Concrete Overlays
APPENDICES
Figure 125. Finished concrete overlay with synthetic fibers Figure 126. Balling fibers
price of synthetic fibers can increase materi-
als costs +/- $0.08/ft2 ($0.70/yd2) per inch
based on a 4.0-lb dosage/yd3. e increase
in cost is, however, significantly driven by
the size of the project and the volume of
fibers being used; large projects can cost less
and small projects can be more than this
amount based on 2012 prices.
• Macro fibers can negatively affect the finish
appearance compared to concrete without
fibers, if care is not taken with the fiber
type, mix design, and texturing technique;
however, with proper care, the finish
appearance will be acceptable. Owners need
to be made aware up front that the concrete
surface will appear slightly different than
the clean smooth surface usually expected
of concrete paving. Some contractors will
pan finish the surface to embed the fibers
prior to texturing. is is not recom-
mended since the humidity, wind, sun,
shade, temperature, and rain can all affect
this operation; furthermore, if the panning
is not properly done, a significant amount
of the entrained air can be removed,
thereby reducing the concrete freeze-thaw
durability. e “hairy” surface can occur
with fiber volume rates near 0.5 percent or
more if the care noted above is not taken;
see Figure 125.
• Heavy doses of macro fiber can make the
surface more difficult to keep clean because
of the slight roughness created by each fiber
that manages to find its way up through
the surface. If this dosage rate is reduced
back down to maybe 0.2 to 0.4 percent,
the FRC can be easier to finish. Over time,
the fiber itself will wear away and disap-
pear, but the small roughness immediately
around the fiber may be evident. is is
not something that is noticed at highway
speeds, but for pedestrians walking across
commercial applications, it can be evident.
If it is objectionable, it can be removed
using a simple pan flame torch.
• Often skid-resistant or higher-friction sur-
faces are specified for paving applications.
Some fibers can create unsightly finishes
depending on which fiber and dosage
amount are chosen. With the addition
of fibers, it is more difficult to get a good
broom finish. Generally, an acceptable
broom finish can be achieved with a proper
mix design, suitable fiber, appropriate
broom kept relatively clean, one-directional
broom passes, and no “jiggling” of the
broom.
• Unless care is taken to prevent them, macro
fibers may occasionally ball up and create
a surface defect even if added to the ready-
mix discharge load under the utmost care;
see Figure 126.
• Some contractors drill out the “hair balls”
with a 4-inch core drill to a depth of an
inch or so. is allows for the hair ball to
be removed and replaced with a grout or
concrete mixture.
• Do not place or finish if rain is eminent
because surface water will make the fibers
more prominent.
• Limit the use of older types of high-range
water reducers (HRWRs) (naphthalenes
and melamines) to reduce the water-cement
ratio, as they tend to bleed and exacerbate
spotty concrete setting, thereby possibly
causing fibers to be more prominent. e
newer HRWR (polycarboxylates) are gener-
ally better and reduce segregation effects
in the mixture (both fiber and aggregate
related).
• Some solvent-based curing compounds will
make the fibers more prominent.
• Finally, know the product you are using.
e use of fibers is an excellent tool for
enhancing concrete overlays, but the
products are rapidly evolving and many
owners, contractors, and producers are still
learning how to best apply the technol-
ogy. When using macro synthetic fibers, a
trial mix should be batched and placed at
the ready-mix producer’s facility or placed
elsewhere using the ingredients and propor-
tions approved for the project so that all
know and understand what is expected.
Communication with the owner, general
contractor, and inspectors is important to
let them know what to expect during and
after construction. It is important to under-
stand the fiber product being used.
Guide to Concrete Overlays
116
APPENDICES
APPENDIX D.
LASER SCANNING SURVEY
Roadway Surface
3-D Laser Scanning
One of the problems experienced with
concrete overlays is minimizing quantity over-
runs due to the lack of survey of the existing
pavement. e advent of laser scanning has
opened a new avenue for mapping of pave-
ment surfaces before overlay construction to
help eliminate excessive overruns. To date,
pavement surface mapping has been done
with conventional survey equipment such
as a total station, rod and level, GPS rover
unit, or vertical (looking down) sonic units
that double as profile measuring devices.
ese methods are labor intensive and often
require traffic control to obtain the data. Laser
scanning can offer reduction in survey cost,
savings in time, and less interference to the
traveling public.
Scanning Applica-
tions to Pavements
Either static or mobile scanning will provide
a map of the surface of the roadway. Most
mobile units are developed to look at the
area ahead or behind the vehicle at a prede-
termined vertical angle. ese are designed
to gather large amounts of data from right-
of-way to right-of-way as well as high-quality
digital photo images so closely spaced that
it is similar to a video. ey are a step for-
ward from the traditional photolog van that
provides basic “relative” elevations on the
pavement, but they are not sufficient for con-
trolling concrete yield.
e type of laser from the traditional pho-
tolog van relevant to pavement overlays is
that contained in the units currently used to
measure finished pavement profile. ese are
downward-looking lasers (perpendicular to
the surface) and are used to measure pave-
ment surface texture or a very narrow profile
line. e type of laser (bandwidth) and the
height of the laser are used to measure a very
fine line or area of the surface.
Mobile lasers and those used for pavement
profiling are usually not found on the same
unit. Mobile lasers should be mounted
as high as possible on the unit to see over
obstructions, and the profiling type laser
units are mounted at bumper height or lower
to maximize accuracy and minimize light
interference.
Planning Items to
Be Considered
Preplanning of the GPS control-point mea-
surements along the roadway or the use of
known points throughout the project corridor
should be done with care to assure that the
amount of data is adequate for the accuracy
desired. e scan data is only as accurate as
the control-point data.
Traffic interference can be a problem with
static scans from the shoulder of the road.
is can be overcome with proper planning
and the fact that multiple scans will find the
gap in the traffic. e same goes with mobile
scanning; using additional vehicles for block-
ing and considerations to time of day for
off-peak traffic is beneficial.
Sun angles can impact the photo quality. is
item requires that the operators use the sun
angle to their advantage in determining what
to scan and when during the day.
Scan runs can be arranged in the planning
phase to collect all the mainline data in one
pass and the ramps or exits in a second or
separate pass if the distances from the main-
line become too great.
Start and stop areas need to be identified both
on paper and on the ground to assure that all
possible data is collected in one visit to the site.
117
Guide to Concrete Overlays
APPENDICES
Figure 129. Pavement cross section detail
Figure 127. Typical mobile scan project workflow
Control/
Target
Network
Layout
Trajectory
Post
Processing
QA/QC
Mobile
Data
Capture
Point
Cloud
Registration
Data
Extraction
CAD
Export
Figure 128. Pavement DTM/detail
Data Analysis
Figure 127 provides a step process of the
elements involved with 3-D scanning. e
larger portion of the scanning survey process,
regardless of static or mobile data collection,
is carried out in the office. e office process-
ing consists of establishing a digital terrain
model (DTM) at accuracies unachievable via
conventional survey methods. With scanning,
the transportation engineer or technician can
now see a grid of 0.5 to 1.0 foot, as shown
in Figure 128. is will allow detection of
various types of pavement failures that were
previously not visible and enable highly accu-
rate concrete quantity measurements. Data
filtering systems and other routines have been
developed to assist in the analysis and extrac-
tion of data from the point clouds for specific
purposes, such as pavement rehabilitation,
and still preserve the original data set for
future uses and historical documentation. An
example of this is shown in Figure 129 and
shows cross sections that provide data on rut-
ting across the slab and extent of deterioration
in the longitudinal direction, which can be
measured from the data. e edited data can
then be output in CAD or geographic infor-
mation systems (GIS) files to meet the need
of the user.
Guide to Concrete Overlays
118
APPENDICES
Figure 130. Static laser scanner
Figure 131. Mobile laser scanner
Figure 132. Mobile scanner onboard quality control operation area
Static Scanning
Operation
Scanning can be performed in a static mode
by placing a unit such as the one seen in
Figure 130 in a position so that it can refer-
ence itself to at least two or more known
points of X,Y,Z coordinates. Control is criti-
cal in the use of this device, just as in other
surveying techniques. Referencing to three or
more known points or setting a geometrically
sound control system along the project cor-
ridor is highly recommended to increase the
accuracy of the data. A network of control
points 250 to 300 feet apart should be used to
establish the control system.
With the inclusion of the laser and camera,
this device resembles a “Total Station on
Steroids.” is device operates in a 360°
radius to gather object and photo data. It
locates itself relative to the earth by sighting
two or more points of known location (X,Y)
and elevation (Z). In roadway scanning, these
points are part of a survey traverse. is type
of scan requires planning for a traverse of con-
trol points and locations of scans in order not
to be put in a position of missing key data in
a scan by shadows or objects.
e static system can be used to survey pave-
ments from the shoulder for a distance of up
to 250 to 300 feet in radius, depending on
conditions from the survey unit.
Mobile 3-D Laser
Scanning
Laser scanning is basically several exist-
ing technologies combined into one unit
or process. At the heart of the unit is the
light detection and ranging scanner, which
measures the flight time of a beam of light
to calculate the range to objects at predeter-
mined angular increments, resulting in a very
large point data set referred to as a “Point
Cloud.” e laser scanner conducts measure-
ments to targets, and a 360° camera is used to
assist in identifying objects in the scan. e
unit also includes a GPS to record its posi-
tion on the earth’s surface at any time and the
relative position of the objects being scanned.
An IMU is used to account for movement
(pitch, roll, and yaw) in the survey vehicle. A
DMI is used to compute wheel rotation and
measurements to aid the process. e system
is capable of repeatable 0.04- to 0.12-inch
accuracy in measurements.
Mobile Mapping
Operations
is system allows the surveyor to collect data
at highway speeds in a single pass without
being a traffic hazard. e equipment is syn-
chronized to allow multiple sensors to feed
data on the targeted road surface simultane-
ously. It does require the equipment used for
storage to handle terabytes of information in
short periods of time. is system also picks
up right-of-way hardware such as above-
ground utilities and other infrastructure
devices that can be problems in construc-
tion if not identified in the planning process
(anything you can see is collected). One such
device developed is shown in Figure 131.
is device can gather 600,000 to 1,000,000
points per second and capture photos at 3- to
10-foot intervals to give you a stereo view of
the front, sides, and downward-looking pho-
tos of the pavement at the back. e IMU,
GPS, and DMI units gather all the data about
the pavement and surrounding area in one
pass. is unit is controlled from the view
shown in Figure 132 and allows quality con-
trol of the data collection on the fly.
119
Guide to Concrete Overlays
APPENDICES
APPENDIX E.
FACTORS FOR CONSTRUCTING CONCRETE
OVERLAYS UNDER TRAFFIC
Table 24 provides information about various considerations when constructing concrete overlays under traffic.
Table 24. Considerations for Concrete Overlay Construction under Traffic
Factors to Consider Objectives / Expectations Considerations / Limitations
Incentives/Disincentives An effective way of managing successful accelerated
construction is to offer its incentives for the contractor. If the
schedule is very critical, the contractor may likely consider
innovative pavement techniques to complete the project on time
or even ahead of schedule. The use of incentives also allows for
a better competitive bidding environment for the owner.
Incentives and disincentives should be considered for the
project to encourage the contractor to perform within the
given schedule when a competitive bidding environment is
expected. Use of disincentives should not deter potential
bidders when the schedule is critical.
Grade Control Grade control for the project should be considered early. In
the planning of the project, the type of overlay and existing
pavement conditions will often dictate the level of survey
required for the design and stakeout of the project. Resurfacing
projects historically have required little in the way of surveying.
A vast number of them are even constructed without detailed
construction plans; they are referred to in many states as log
jobs. When concrete is used as the resurfacing material, there is
no need to increase the level of surveying required on a project.
With all resurfacing projects, it is advisable to visit the project
site during a rain event and verify that there is no drainage issue.
A drive through the project at the posted speed limit will alert
you to adverse cross-slope issues. For rural areas, surveying
is only required when you determine that there is some type
of a drainage, cross-slope, or profile issue that needs to be
corrected.
The elevation of the concrete paver can be controlled by either a
traveling ski or by a stringline that is referenced from the existing
pavement. When stringline control is used, establish grades
at each stringline pin by projecting the existing cross-slope,
sight the string longitudinally, and adjust individual grades up to
produce a smooth profile.
If payment is based on the plan area, then the contractor
may want a more detailed survey and additional cross
sections to ensure proper thickness and yield. If the
payment is based on the volume of concrete supplied and
the area paved, less survey is required.
When milling machines are used to remove existing
pavement, it is advisable to have them either follow the
same control as the concrete paver or wait to establish
the paving control until the milling has been completed.
One point of caution for multi-lane construction is that
on many pavements, the cross-slope of each existing
lane may differ, and the paver should have crowning
adjustment capability located at the intermediate lane
lines or actively remove any cross-slope differences
between the lanes with the milling operation.
Materials/Mixtures
Reliability of Material Supply All materials that are required on the project need to be available
or scheduled or properly stored for use prior to constructing the
overlay project.
Materials that are prone to delivery delays need to be
stockpiled.
Material Schedule Under an accelerated schedule, there is little time for deviation
from the intended plan. As such, representative samples from all
material supplies should be made with proper certification.
Contingency plans need to be developed to address
potential changes in critical material properties.
Concrete Mixture Normal concrete paving mixtures are typically used for concrete
overlay projects. Rapid strength gain to meet accelerated
construction schedules does not require special blended
cements or sophisticated material. It is possible to proportion
a mixture using locally available aggregates, type I and
type II cements, SCMs, and certain admixtures. Some initial
adjustments will probably be required by the paving crew as they
become accustomed to the mixture characteristics.
The mixture needs to match the opening requirements and
construction methods to obtain opening requirements.
However, the mixture should not be accelerated to a point
where there is a high probability of early-age cracking
from shrinkage and curling and warping. Each crew
member will have to be accustomed to the accelerated
duties that accompany expedited construction.
Guide to Concrete Overlays
120
APPENDICES
Factors to Consider Objectives / Expectations Considerations / Limitations
Cementitious Materials
Hydraulic cements include portland cement and blended
cements which contain SCMs. Other types of hydraulic cements
are rapid-setting calcium sulfo-alumina cements used for
repair materials or for pavements where fast turnaround times
are critical. Cements and SCMs play a major role in both heat
and strength development, and these properties depend on
the interaction of the individual compounds that constitute the
mixture.
The Integrated Materials and Construction Practices for
Concrete Pavement Manual (IMCP Manual) is a very good
reference in order to understand the importance of the
proper blend of cementitious materials.
Type I/II Cements Type I/II cements can reach opening strength without increasing
the risk of shrinkage cracks.
More cement does not necessarily mean higher strength
but it does increase shrinkage, as well as curling and
warping.
Slag Cement Slag cement can reduce ASR expansion, increase long-term
strength, reduce permeability, reduce concrete temperature, and
slow hydration.
Slag cement may reduce rate of strength gain and
hydration rate.
Fly ash Fly ash will increase long-term strength, reduce permeability,
and reduce set temperature. Some fly ash can slow hydration on
accelerated construction projects.
In the past, some states impose restrictions on the use
of fly ash in cold weather and may restrict the use of fly
ash to 10% on accelerated construction projects even in
warm weather months. Mixtures should be tested in the
lab to determine the appropriate replacement rates and
temperature restrictions.
Type C Type C fly ash will increase long-term strength and reduce water
demand and permeability. This may or may not slow hydration or
reduce ASR expansion.
Type C fly ash can affect strength gain. Mixtures must be
tested to determine how much class C fly ash is required
to reduce ASR-related expansion. Too high a dosage may
increase the risk of rapid stiffening and/or damage due to
salt scaling.
Type F Type F fly ash will increase long-term strength and reduce
permeability. It will also slow hydration and mitigate ASR
expansion.
Type F fly ash delays setting and reduces rate of strength
gain. High loss-on-ignition affects air entrainment. Type F
is generally effective at reducing ASR-related expansion.
Availability may be a limitation.
Chemical Admixtures Chemical admixtures are added to the concrete mixtures to
modify certain concrete properties such as strength. Adding
chemical admixtures can achieve these properties more
efficiently than adjusting other mixture ingredients such as the
type of cement. Admixtures that are combined and contain both
water reducers and accelerators are available.
The effects of set-modifying admixtures on other
properties of concrete, like shrinkage, may not be
predictable. Therefore, acceptance tests of set modifiers
should be made with job materials under anticipated job
conditions. Compatibility of the admixtures with other
ingredients should be tested as it relates to potential
constructibility problems.
Water reducers Water reducers can reduce water demand through reduced
paste content (lowers w/cm) to help minimize shrinkage,
temperature, and cracking without sacrificing workability. Water
reducing admixtures can also increase early strength gain by
lowering the quantity of water necessary for cement hydration
(by as much as 10% in 28 days). The w/cm ratio typically are at or
lower than 0.43 for accelerated construction.
Confirm that water reducers are compatible with other
chemical admixtures and cements, particularly under
harsh environmental conditions. Confirmed laboratory
testing is essential to determine if the admixtures will
develop the desirable properties. Type F and G water
reducers (superplasticizers) are not normally used in
pavements because of their high cost and because it is
difficult to control the slump range required for slipform
paving with their use. Overdoses of water reducers,
particularly normal-range products, may severely retard or
prevent setting.
Accelerators Accelerating admixtures are used to increase the rate of
strength development of concrete at an early age, including in
cold weather. It is important to test both fresh and hardened
concrete properties before using accelerators in overlays,
particularly bonded overlays.
Long-term strength may be lower. Excess acceleration
may result in cracking before finishing and/or saw cutting
can be completed. Care must be exercised in using
accelerators in thin overlays so as not to cause early
shrinkage, cracking, and high curling and warping.
Air entrainment Air entrainment will dramatically improve the durability of
concrete exposed to moisture during cycles of freezing and
thawing. It improves concrete resistance to surface scaling
caused by chemical deicers. It also tends to improve the
workability of concrete mixtures, reduce water demand, and
decrease mixture segregation and bleeding.
Need to check compatibility with other admixtures. For
about every 1% of air entrained, about 5% of concrete
compressive strength is lost. Loss of air through the
paver is acceptable up to 1.50% to 1.75%. However, when
the loss of air through the paver approaches 3%, the air
system (quantity and distribution) is not acceptable.
Table 24. Considerations for Concrete Overlay Construction under Traffic, continued
121
Guide to Concrete Overlays
APPENDICES
Factors to Consider Objectives / Expectations Considerations / Limitations
Retarders Retarders are useful in extending set times. They increase the
bleeding rate and capacity and may be accompanied by some
reduction in early-age strength gain (one to three days) but
higher later strengths.
Retarders delay early strength gain, but do not change
workability properties. Under certain conditions, retarders
can cause early stiffening and reduce workability.
Aggregates It is critical that aggregates be well graded (that is, there
should be a wide range of aggregate sizes). Well-graded
aggregates have less space between aggregate particles,
therefore reducing paste demand without loss of workability.
Reduced paste content reduces shrinkage and early-age
cracking, particularly with accelerated mixes. With all
construction, aggregate moisture content needs to be constantly
monitored since it can change significantly during the course
of construction. Physical properties of the aggregate such as
absorption may be one source of change.
An aggregate’s CTE is a measure of how much the
material changes in length (or volume) for a given change
in temperature. For bonded overlays over concrete,
use aggregates that as closely as possible matches
the underlying pavement CTE. The material is subject
to varying conditions in storage and handling. At the
very least, these changes should be anticipated, and
accommodations made to adjust the water content in the
mixture as necessary. Ideally, real-time monitoring of
the aggregate moisture content would allow for “on the
fly” changes. In most circumstances, a well-regulated
sampling program using rapid evaluation equipment will
improve this component of the process considerably.
Separation Layer A separation layer provides a necessary separation plane
between overlay and underlying pavement. For asphalt
separation layers under pavements carrying heavy truck traffic,
decrease sand content and increase 0.13 in. (3.3 mm) aggregate
in order to reduce stripping the asphalt due to pore pressure.
A separation layer does not provide structural support.
Heavy truck traffic may decrease stability and strip the
asphalt due to pore pressure. Consider drainable asphalt
layer and drainage system under heavy truck traffic.
Geotextiles may also be used as a separation layer.
Fibers Although not typically required for concrete overlays,
consideration needs to be given to the use of fibers for thinner
overlays (4” or less). Fibers improve the toughness of the
concrete overlay and resistance to plastic and dry shrinkage
cracking, particularly with bonded overlays. Fibers also can
increase the flexural strength of the concrete.
Placement of fibers in the mixture must be accomplished
so as to prevent balling of the fibers into clumps. In some
cases, water-soluble bags are added to the final batch.
A staging area may be needed with adequate capacity
to avoid a queue. In other cases, individual (bulk) fibers
may be introduced into the mixture, where a blower
appropriate to the application should then be considered.
Batching Batching of concrete used in concrete overlays is usually no
different from conventional concrete paving, or even other
ready-mix applications.
Depending on the size of the job, a dedicated mobile
batch plant is a benefit to the project. In fact, this is
recommended when at all possible due to the potential for
increased concrete uniformity.
Capacity Having adequate batching capacity is a critical link in the
process of constructing concrete overlays. Both mixing time and
the availability of transport equipment should be balanced along
with cost.
Contingency plans should include preparation for rapid
responses (repairs) of the more common equipment
malfunctions
Consistency During batching, consistency and uniformity are critical.
Adequate mixing time should be balanced with the need for
increased production rates. If possible, a continuous type or
high-speed twin-shaft mixer could be used to accommodate both
objectives.
Overlays are particularly vulnerable to changes in material
properties due to their commonly thin sections.
Concrete Transportation
Traffic Separation In an ideal situation, a separation of the transit vehicles from
both the traveling public and other construction vehicles is
helpful.
In most situations, however, circumstances deviate from
the ideal, which warrants appropriate measures to ensure
continuous, uninterrupted delivery.
Transit Time Transit time is one variable that must be known. If a mobile
batch plant is used, transport of the concrete from the batch
plant to the paver may be quick. As a result, deviations from a
conventional concrete mixture (including the admixtures that are
used) may not be necessary. However, if there is a potential for
delay (e.g., due to traffic congestion), or if a ready-mix plant is
used for supply with a longer travel time,
a modified mixture may be necessary.
Caution must be exercised if a retarder is used as it may
also affect the strength gain of the mixture, thus affecting
the time of opening to traffic. Curing may also become
more critical in these situations as fresh concrete will be
exposed for longer.
Protection Protection of the mixture from environmental factors may also be
a consideration, particularly in long transit times
Dry and windy conditions can lead to rapid moisture loss
from any exposed concrete. Conditions that are marginal
for the risk of freezing or rain must also be addressed. In
each case, protection of the concrete in transit may be
warranted, and can often be done by use of tarps. If ready-
mix trucks are used, protection is often less critical as the
concrete is protected by the drum.
Table 24. Considerations for Concrete Overlay Construction under Traffic, continued
Guide to Concrete Overlays
122
APPENDICES
Factors to Consider Objectives / Expectations Considerations / Limitations
Haul Roads The condition of the haul roads is another consideration when
constructing concrete overlays.
Care must be taken to ensure that the repeated heavy
axles of the trucks will not excessively rut the haul road.
Evaluation of a haul road in questionable areas should be
done prior to the first batching.
Preoverlay Repairs Prior to the construction of overlays, there may be a need for a
variety of spot repairs on the existing pavement to be overlaid.
The timing of these repairs will affect the schedule of the overlay
construction.
If the preoverlay repairs dictate the accelerated overlay
schedule, the repairs should be considered under a
separate project or completed in off-peak hours.
Dowel Bar Retrofit Typically, dowel bar retrofit is not done in conjunction with
unbonded overlays since both can serve many of the same
functions. Dowel bars have been used in conjunction with
thin bonded overlays when you want to significantly increase
load-carrying capacity. Good candidate projects for dowel
bar retrofits have the following characteristics: pavements
with adequate slab thickness, but showing significant loss of
load transfer due to lack of dowels, poor aggregate interlock,
or subbase/subgrade erosion. Relatively young pavements,
because of insufficient slab thickness, excessive joint spacing,
inadequate steel reinforcement at transverse cracks, and/or
inadequate joint load transfer, are at risk of developing faulting,
working cracks, and corner cracks unless the load transfer is
improved. Typically, 3 to 5 smooth round steel dowel bars are
used in each wheel path.
Slots should be cut by special diamond slot cutters that
are capable of making multiple cuts at a time. Modified
milling machines are not recommended due to associated
spalling and variable cut widths that effect chair width
requirements. Slots should be cut parallel with the
direction of traffic. To properly prepare the slots, material
should be removed with a lightweight jackhammer, and
the slot should be sandblasted and cleaned. Re-establish
the working joint with a joint insert. When choosing
a repair material, select a material with the following
characteristics: little or no shrinkage, good ultimate
strength, thermal compatibility, freeze-thaw durability, and
good bond to existing concrete.
Drainage Drainage improvements are sometimes warranted to
complement the construction of a concrete overlay. These
improvements may include cleaning adjacent ditches, increasing
their capacity, or even retrofitting subdrains.
Since the equipment used for drainage improvements
often works on or near the pavement edge, their operation
before the overlay is complete would decrease the
likelihood of premature damage to the young concrete
but also results in less stable material under the track
line, thereby risking reduced smoothness. In addition, if
retrofit subdrains are to stabilize the subbase, they should
ideally be installed prior to the overlay in order to reduce
movement of the existing pavement. However, be careful
not to damage the subdrains during overlay construction.
Utilities Utility work is also sometimes done prior to overlay construction.
This may include relocation of utilities from beneath the
pavement to off of the pavement edge. If trenching or other
disturbance of the existing pavement is required, care should be
taken to ensure proper construction of patches.
New patches can be particularly troublesome as they may
not have adequate time to “settle” prior to the overlay
construction. As with drainage improvements, all utility
work should be completed prior to the overlay in order to
minimize interference or early-age damage.
Spot Repairs Some concrete overlays will require spot preoverlay repair to
the existing concrete or asphalt pavement structure. If there are
extensive repairs, the roadway may not be a good candidate for
an overlay.
In all cases, quality of the spot repairs will often be critical
to the success of the performance of the pavement.
Partial-depth repairs Good candidates are sections where slab deterioration is
contained to the upper one-third of the slab and where the
existing load transfer devices (if any) are still effective.
Poor candidates for partial depth repairs are those
with distress caused by compressive stress buildup
in long-jointed pavements, spalling caused by dowel
bar misalignment or lockup, transverse or longitudinal
cracking caused by improper joint construction
techniques, working transverse or longitudinal cracks,
and spalls caused by D-cracking or reactive aggregate.
It is important to verify that all delaminated concrete
is removed, and that no concrete around the repair
boundaries has been damaged during the process. For
bonded overlays, it may be possible to fill in the partial
depth repair areas as a part of the overlay paving
operation.
Full-depth repairs Full-depth repairs of existing concrete or asphalt pavements are
effective at correcting many different types of localized distress.
However, there are a few cases that limit the effectiveness of a
full-depth repair.
The effectiveness of a repair is dependent on the proper
sizing of the repair. Most agencies specify a repair with
a minimum length of 4 to 6 ft (1.2 to 1.8 m). Salvaging
the existing dowel system is not recommended. It is
also important to verify that all delaminated concrete
is removed, and that no concrete around the repair
boundaries has been damaged during the process.
Table 24. Considerations for Concrete Overlay Construction under Traffic, continued
123
Guide to Concrete Overlays
APPENDICES
Factors to Consider Objectives / Expectations Considerations / Limitations
Retrofitted edge drains A good candidate project for retrofitted edge drains is a
pavement that is showing early signs of moisture damage,
is relatively young (i.e., less than 10 years old), and is only
exhibiting a minimal amount of cracking (less than 5% cracked
slabs) (Mathis 1990; FHWA 1992). Many studies have concluded
that retrofitted edge drains are not effective at prolonging
the service life of pavements that have already experienced
significant moisture-related deterioration (Wells and Wiley 1987;
Young 1990; VDOT 1990).
Retrofitted edge drains are not recommended on
pavements where base contains more than 15% to 20%
fines. However, they may be used in these types of soils
to provide a drainage pathway for separation layers
used in unbonded overlays. When placing corrugated
polyethylene pipes, extra care is also required to prevent
overstretching of the pipes during installation. To avoid
damage to the pipes during compaction, a minimum of 6 in.
(150 mm) of cover over the drainage pipe is recommended
before compacting.
Slab stabilization Slab stabilization restores support beneath concrete slabs,
thereby reducing progression of support-related distresses such
as pumping, joint faulting, and corner breaks. Slab stabilization
is not intended to raise depressed or settled slabs to the desired
elevation. Cement grout mixtures and polyurethane are the most
commonly used materials.
Watch the maximum pressure to make sure it does not
exceed
100 psi (0.69 MPa). Monitor slab lift closely. Lift is typically
limited to <_ 0.13 in. (3.3 mm). Stop grout injection when
the grout is seen flowing from holes, cracks, or joints. Stop
injection if one minute has elapsed, regardless of pressure
or lift changes.
Surface Preparation/Cleaning Surface preparation and cleaning are required to prepare the
existing surface for the concrete overlay.
The techniques used will vary depending on the surface
type. The equipment used for repair should be sized to
provide not only adequate production rates but also to
minimize the disruption to the traveling public and to assist
with the accelerated schedule.
Traffic on Prepared Surface Phasing of the surface preparation operation can allow for
intermediate trafficking of the surface prior to the overlay
placement.
If trafficking is allowed on the prepared surface prior
to the paving of the overlay, subsequent cleaning of the
surface, particularly for bonded overlays, is required in
order to remove any potential contamination.
Bond on Concrete Existing pavement surface preparation typically consists of
shotblasting followed by sweeping the concrete surface.
Cleaning consists of compressed air.
Paving should commence soon after cleaning (i.e. minutes)
to minimize the chance of contamination of the surface.
Milling is used to lower the concrete elevation where
required and is not used as a concrete surface preparation
by itself since it can cause surface microcracking and
fracturing of the exposed aggregate.
Bond on Asphalt Existing pavement milling may be used where surface distortions
are 2 in. (50 mm) or greater to remove soft asphaltic material
that would result in inadequate bond surface or to roughen the
surface to enhance bond development. Cleaning consists of
sweeping the asphalt surface then cleaning with compressed air.
Water or moisture cannot be allowed to stand on the
asphalt surface prior to the bonding resurfacing. In order
to prevent contamination of the surface, it is important to
avoid a large lag time between the final surface cleaning
and paving.
Unbonded on Concrete Only the distresses that cause a major loss of structural capacity
require repair.
The existing pavement needs to be stable and not shifting
or moving, particularly at the subbase level.
Unbonded on Asphalt Milling may be used where surface distortions are 2 in. (50 mm)
or greater to remove distortions that contain soft or fractured
asphalt. Before concrete placement, the asphalt surface should
be swept. Remaining small particles are not considered a
problem.
Spot milling of only parts of the projects with significant
distortions or structural problems is often adequate.
Traffic Considerations
Vehicle Access Meet needs of user. May want to open pavement to cars earlier
and open to trucks later.
Use accelerated mixtures only when necessary. Opening
strengths are those typically specified.
Pedestrian Access in
Intersections/Urban Areas
Channel pedestrian movements around construction zone. In areas where heavy pedestrian traffic must be
accommodated, detouring the pedestrian path may be
necessary.
Traffic Control Devices Traffic can be accommodated during construction. Fit traffic
control to user needs and follow the MUTCD (FHWA 2003b).
Too many times concrete overlays are eliminated as
rehabilitation options when the project is to be built under
traffic. The limitation of clearance requirements for paver
tracks and stringline are no longer valid since many
options are now available.
Lighting Lighting allows night work. Lighting must be movable with
construction.
Number of lights and control of light patterns within work
zone must be considered.
Table 24. Considerations for Concrete Overlay Construction under Traffic, continued
Guide to Concrete Overlays
124
APPENDICES
Factors to Consider Objectives / Expectations Considerations / Limitations
Nighttime Construction Nighttime construction is increasing. It provides an off-peak
construction period that lessens disruption to the traffic.
Nighttime visual limits must be utilized. They include
shorter spacing of channelizing devices, longer transitions,
changing colors nearing off-ramps, , widening pavement
markings, using glare screens, using more truck-mounted
attenuators, using real-time information on signs and
changeable message signs, and covering signs when
work is not being done.
Lane Capacity Examine lane capacity of construction zone speed and not
design speed of roadway.
Must deal with existing traffic flows in a safe manner for
the driver and construction worker.
Large Trucks Limited data show that tractor-trailer crash involvement in work
zones is higher than the national average for these vehicles,
particularly on the interstate system.
Special attention should be given to accommodate
tractor-trailer combinations, both in work zones and
their transitions, especially where there are large truck
volumes. Items to consider are lane widths in curves with
runs of barrier on both sides and stopping distance where
congestion is expected.
Detours Must be conveniently located and have effective signage. May have negative impact on users. Always minimize the
out-of-distance travel where possible.
Events
School Coordinate schedule with bus routes and events. The schedule may be difficult to control because of limit
changes.
Commuters Plan project to minimize disruption. Normally limits can be relied upon.
Holiday Normally work stops during holidays. Holidays present an uncontrollable increase of traffic.
Visibility Provide adequate stopping distance, which increases overall
safety.
Equipment and traffic control must be considered in
regard to visibility.
Construction Staging
Staging Area The project limits should be evaluated to determine adequate
staging areas. The staging areas are necessary for ready
mix truck washouts, storage of equipment and materials,
construction trailers, and possibly a portable concrete mixing
plant.
A dedicated ready mixture plant or mobile batch plant
located near the project site will also cut down on the haul
times to the site, and the quality of the mixture will be more
easily controlled.
Incremental Lane Closure
(Leap Frog)
Allows for continuous single lane paving in one direction, leaving
opened areas for traffic recovery.
Requires multiple traffic control setups and pilot cars.
Mobilization It is important that the project is planned to minimize staging
operations. Every time a stage comes to an end, there are
mobilizations necessary to regroup and prepare for the next step
in the paving process.
Remobilizing of the paving crew on the project site takes
time, and time not paving increases costs. A preferred
approach is to minimize the staging operations and
mobilizations.
Work Production To keep paving crews busy and provide cost-effective work, it
is important to keep construction crews effectively utilized in
construction projects involving overlays. That requires the crews
to utilize effective work schedules that provide continuous and
uninterrupted results.
Length based on curing time and production rates and
acceptable traffic delays when under traffic.
Number and Type of Lane Closure Traffic control must meet acceptable standards. Methods and
materials used must meet project restriction.
Number and type of closures will depend on traffic
demands, lane capacity, adjacent access requirements,
and number of available traffic lanes.
Paver Encroachment All encroachment restrictions can be met. Normal stringline and track paver widths per side is
typically 4 ft (1.2 m). One foot incremental encroachment
reduction (up to 3 ft [0.9 m] reduction total) is common
through typical machine adjustment. These do not
require specialized pavers, but may require adjustment
or modifications to an existing paver. Stringless paving
minimizes this problem.
Construction Under Traffic Versus
Lane Closure
A thorough analysis comparing road user costs and construction
durations and construction costs should be performed for design
alternatives (full closure vs. maintaining traffic through the
construction zone).
Additional construction cost and delays to users when
construction is under traffic must be compared to travel
delay and out-of-distance travel for detours.
Table 24. Considerations for Concrete Overlay Construction under Traffic, continued
125
Guide to Concrete Overlays
APPENDICES
Factors to Consider Objectives / Expectations Considerations / Limitations
Overlay Construction
Thickness of Overlay Thinner overlays cure quicker, causing stresses to form earlier.
Therefore, early sawing is important.
Thin overlays are subject to higher risk of cracking
(shrinkage, curling, and warping stresses).
Weather
Cold weather (below 40°F
[4.4°C])
Consider covering pavement to help achieve opening strength. Develop a QC plan that addresses cold weather placement
issues. Specifically, insulation methods to assure that the
pavement will not freeze until it reaches opening strength.
Normal weather 40°F to 85°F
(4.4°C to 29°C)
Overlays have fast strength gain and high production rates with
reduced early-age cracking potential.
There should only be project restrictions and not normal
material or equipment limits.
Hot weather > 85°F (29°C) Faster strength gain exists during hot weather. There is a higher risk of surface cracking during hot
weather. Proper curing is important. Also, bottom up
cracking needs to be considered when the underlying
pavement is too hot.
Construction Equipment One of the most important aspects of accelerated construction
that is often overlooked is the availability and performance of
the equipment on the site. All equipment should be in working
condition and properly maintained. The contractor should
present a back up plan in the event of equipment failure during
construction. Proper parts, hydraulic fluids, oil, and fuel should
be readily available. Concrete saws should be abundant and
readily available on the job site.
In the event of failure to the concrete paver, a plan should
be available to continue operations. The plan could be
simple, such as keeping a mechanic on call, or it may
be more complex, such as having a backup paver in the
vicinity. A staging plan should be part of the back up
plan to properly rout traffic in the event of scheduling
disruptions. If the pavement is to be open in a matter of
hours after paving, the critical stage is often the sawing. It
is important to have the adequate manpower and saws on
the job site when constructing a concrete overlay on an
accelerated schedule.
Curing Curing is arguably more critical for overlays than for most other
paving. The relatively thin nature of concrete overlays increases
their surface area with respect to the volume of concrete. The
result is more susceptibility to excess moisture loss and the
distresses that can result from this. To avoid problems including
plastic shrinkage cracking, full-depth shrinkage cracking, wide
joints, and surface distresses, a rapid and effective curing
program should be adopted that includes using twice the
recommended compound rate for thin overlays.
While cost should be a consideration, the incremental
quality improvements, such as high production curing from
an effective curing program, will often far outweigh the
additional cost.
Special curing For overlays that require a very short opening to traffic and are
relatively short in length, special curing in addition to curing
compound is used. It normally consist of insulating blankets that
provide a uniform temperature environment for the concrete.
Special curing is normally not required in summer months
for accelerated construction, but it does have an effect
on strength gain when air temperatures are less than 65°F
(19°C), and it has a pronounced effect when temperatures
are less than 55°F (13°C) in colder months.
Sawing Sawing concrete overlays is also typically a more critical
operation as compared to more conventional concrete paving.
The thin section will often gain stresses rapidly, and thus require
accelerated sawing. Sometimes the need for accelerated
sawing is underestimated and the sawing operations fall too far
behind the paver. To respond to this, the contractor should be
prepared with the proper type and number of saws. In the case
of sawing, redundancy in equipment is also important.
The timing of the saw cutting should be done to balance
the potential for uncontrolled cracking with the potential
for excessive joint spalling during sawing. Bonded
concrete overlays over concrete require the most effective
sawing operations to prevent overlay failures. Not only
does the transverse joint require full depth saw cut plus
0.50 in. (13 mm) over the existing joint, the width of the
cut should not be less than the existing transverse crack
below the existing saw cut. This allows the two monolithic
pavements (overlay and existing pavement) to contract the
same way. For overlays on asphalt, particularly when there
is wheel rutting in the asphalt, the depth of the saw should
be increased to account for the extra depth in the wheel
rut areas.
Fillets Provide fillets for a level of safety precaution at dropoffs. Placement of form fillets may require sawing.
Table 24. Considerations for Concrete Overlay Construction under Traffic, continued
Guide to Concrete Overlays
126
APPENDICES
Factors to Consider Objectives / Expectations Considerations / Limitations
Opening Pavement Considerations
Public Relations Where construction will affect adjacent homeowners and
businesses along with the traveling public, an effective public
relations campaign should be implemented. Flyers, media
coverage, and public meetings regarding the project schedule
and the reason for the schedule timeline need to be developed
and implemented. Preconstruction meetings between the
government and the citizens, with the contractor in attendance,
help keep the public well informed and allow the contractor to
understand any concerns.
Construction needs to follow the schedule and, during
construction, signing to business access is very important,
along with daily communication between the contractor
and the impacted business. Informed local drivers can
avoid the area when possible, thus reducing delays.
Schedule The project schedule must be reachable and realistic. The
schedule affects public acceptance, contractor’s methods,
payment and incentives, quality of work, and safety. Most
accelerated construction projects are moving more to calendar
days and days when work is not usually done in order to address
critical completion dates where a large volume of traffic is
affected. It also allows for the counting of weekends when
necessary and eliminates working day issues of whether a
contractor could or could not work.
Proper equipment and staffing, mixture, construction
methods, curing, and sawing are all considerations. There
is a need to understand the impact of traffic controls and
openings, staging, material requirements, and isolated
restricted spot locations on the construction schedule.
Maturity Method Utilizing maturity testing for concrete paving provides a reliable
technique for estimating in-place strength and thus the time
of opening. Maturity testing provides a reliable technique
for continuous monitoring of concrete strength gain. Most
importantly, maturity testing enables any pavement to be opened
to traffic as soon as it meets strength criteria. Concrete maturity
concepts are being applied by 32 states.
Development of a maturity curve is an important element
of maturity testing. As construction proceeds on a project,
validation of the maturity curve may be necessary when
changes occur in mixture constituents, material sources,
mixture operations, and the water–cementitious materials
ratios. Also some states set an automatic validation
criterion based on a time period. Most states that use a
maturity curve have validation criteria established which
allows some flexibility in mixture changes without the
development of a new maturity curve.
Opening Strength See “Early Opening of Overlays to Traffic” section. See “Early Opening of Overlays to Traffic” section..
Table 24. Considerations for Concrete Overlay Construction under Traffic, continued
127
Guide to Concrete Overlays
APPENDICES
APPENDIX F.
STRINGLESS PAVING OPERATION
Figure 133. Paving machine control
In the stringline operation, the paving
equipment gets horizontal and verti-
cal guidance through the locations and
elevations of the stringline relative to a set
centerline profile and pavement cross sec-
tion. e stringless operation compares
the elevation and position of the paving
machine to a predetermined computer
surface model or electronic set of cross sec-
tions of the required final pavement surface
at any given time and location. e paving
machine computer processes its exact X,
Y, and Z location and position in relation
to a computer model of the new pavement
surface. e onboard computer first adjusts
the alignment of the slipform paver relative
to the existing roadway. It then adjusts the
elevation of the machine on each of the four
corners of the paver to achieve the correct
pavement thickness, crossfall, and mainfall;
see Figure 133. e stringless system directs
the paver to make necessary changes to
meet these values.
Just as with stringline paving, the field staff
can make adjustments in the operation of
the stringless system to improve the final
surface profile or adjust for local situations.
Stringlines can be adjusted up or down or
moved horizontally by the paving crew to
meet local needs. ey can also manually
adjust the paving surface up or down on
the paving machine. e paving hubs or
reference points at predetermined distances
(usually 12 to 25 feet) along the route
become the reference for any disputes over
the final product. Changes in stringless paver
operations are all made from a touchscreen
on the paver to raise or lower any of the four
corners of the machine. Reference points at
250–500 feet to 2 miles (dependent on the
system) along the route become the reference
for the stringless operation.
Base and concrete surface elevation checks
for the stringline operations are usually done
through the use of a string being pulled
between the two stringlines and vertical
measurements being obtained between the
string and the surface in question. In the
case of the stringless system, a rover unit
(GPS locator and hand-held computer) is
used to check any location on any surface
within the model area, in front of or behind
the paving equipment. e rover must be
in contact with a total station, laser, or GPS
positioning unit.
Horizontal and
Vertical Control
Requirements and
System Limitations
Tight vertical and horizontal control is essential
in either stringline or stringless paving. e ver-
tical control must be within 0.03-foot accuracy
to provide the acceptable ride for incentive pay
in most states. Minimum vertical curve lengths
of 150 feet and desirable curve lengths of greater
than 350 feet are suggested to meet profile
criteria.
Coordination of sensor sensitivity in the paver
hydraulic system and in the response of the
paver to an electrical impulse both must be
coordinated to achieve the desired profile results.
Retrofits of the hydraulic systems on older slip-
form pavers may be necessary to provide smooth
vertical movements in the paving operation.
In the case of any system that relies on GPS
horizontal control, it is important to have
constant communication between the ground
receivers and the satellites. Loss of signal may
stop the machine or put it into a constant direc-
tion and profile slope to allow it to pass under a
bridge, tree, or other item blocking the satellite
reception.
e operation of total stations can be affected by
the following environmental conditions:
• Heavy surface wind vibration of the
instrument
• Spring and fall low-sun-level interference with
line of sight
• Paver exhaust system location relative to
prisms
• Location of nighttime lighting systems relative
to the paver and instrument
• Fog limiting or halting paving until clear
communication between prisms and instru-
ment is established
Each of the systems has the ability to be used on
each of the items in the paving train from the
bulldozer, grader, and trimmer on the construc-
tion of the subgrade and base to the spreader/
belt placer and slipform paver. e number of
control units required varies with the length of
this portion of the paving train. Texture/cure
equipment behind the paver is usually controlled
mechanically with sensors on the side and top of
the finished product.
Guide to Concrete Overlays
128
APPENDICES
Center line
Wheel line
Edge
1/4 point
Wheel line
ATV with GPS unit
25 ft +/- Spacing or shorter
Ref point #3
Ref point #2
Ref point #1
(4 ft rod with plate (TYP))
250’ +/-
4 ft
Figure 134. Survey existing surface to develop and build database
Figure 135. ATV with GPS and laser profile
Three-step Process
for Stringless
Paving
Utilizing stringless paving technology involves
a three-step process. e first step is col-
lecting survey data of the existing surface to
develop and build a roadway surface map; see
Figure 134. Step two is to design the road-
way and create the proposed 3-D computer
model using the existing surface and proposed
profile and cross sections. e third and final
step is to construct the proposed pavement by
transferring the computer model to the pav-
ing machine and utilizing a noncontact X,Y,Z
guidance system.
In order to map the existing roadway surface,
an all-terrain vehicle (ATV) can be used,
equipped with a laser profiler (Z coordinates)
or GPS receiver and GPS (X,Y coordinates);
see Figure 135. e utility vehicle is driven
along the pavement at 5 to 15 mph, record-
ing the existing pavement profile at 25- to
50-foot intervals along the pavement edges,
wheel paths, lane quarter points, and center-
line. It needs to be noted that GPS accuracy
is good vertically to only 1 inch, so to obtain
the proper accuracy in the Z coordinate, the
ATV had to be augmented with a laser system
or software correction. An alternate to the
ATV is to survey the existing pavement with a
total station.
e data collected are used to produce a 3-D
plot of the pavement surface utilizing read-
ily available CADD (computer-aided design
and drafting) software. Data is streamed from
both units to a central computer for storage.
e ground reference system should contain
reference points with known X,Y,Z values,
spaced on alternating sides or one side of the
roadway depending on the system used. e
Z value should be obtained through elec-
tronic three-wire leveling just in advance of
the construction to verify the overlay design
assumptions and assure that the final prod-
uct will meet the designer and contractor
requirements. e data management method
involves translating data to a project coordi-
nate system.
129
Guide to Concrete Overlays
APPENDICES
Slope sensor
Other Reference Points
and Total Stations
Robotic total station (TS)
Ref point #3
(x,y,z)
Ref Point #1
(x,y,z)
Ref point #2
(x,y,z)
Robotic total station (TS)
Single lane under trac
with pilot car control
.
Single lane under
construction.
360° Prism (front)
360° Prism (back)
Concrete overlay
Electronic stingline
Figure 137. System 1—Stringless paving operation using total stations and reference points
Figure 136. Total robotic station
Figure 138. Computer controls on paving
machine
Existing Stringless
Control Systems
Currently there are three systems in use to
partially or fully utilize stringless paving
technology. Field training and support are
required for each of the systems and should
be requested in any agreement with the
contractor.
System No. 1
e first such system, shown in Figures 136–
138, utilizes surveying total stations, lasers,
and radio communications to provide
machine control. Two total stations are shown
in Figure 136. Prisms on the two masts shown
on the paver in Figure 137 form the receiv-
ing ends of transmissions from the two total
stations on the backslope of the roadway in
the same figure. e screen in Figure 138
represents the controls the contractor has
to monitor the operation or make manual
changes. It relies on an initial reference system
established by the highway agency at 1,000-
foot intervals with X,Y,Z coordinates; see
Figure 137. X and Y may be established with
GPS survey equipment, but Z must be estab-
lished through the use of digital or three-wire
level circuit operations to provide an accuracy
of 0.01 to 0.03 foot. Contractor surveys are
required to provide intermediate control
points, map the existing pavement surface,
establish a final surface with profiles of the
centerline and pavement edges, and calculate
concrete quantities and pavement depths to
meet highway owner requirements.
e paving equipment in this operation is
controlled by two total stations that may be
set on one or opposite sides of the road to
communicate with the paving train equip-
ment. Each total station locates itself through
sighting three known and previously estab-
lished reference points (approximately 250
feet apart) inside the primary control or
1,000 foot points of the highway department.
Lasers on the total stations locate a prism on
the paving equipment, and a specific radio
frequency for each total station communicates
the relative position of each to the computer
model in a computer on the paving machine.
e paver onboard computer contains the
pavement surface model and instructs the
paving device on changes in direction and
elevation for the paver. Similar equipment can
be installed on a spreader/belt placer for hori-
zontal control only or in conjunction with
vertical control. Other paving train equip-
ment such as the cure/texture carts are usually
controlled by mechanical means.
Guide to Concrete Overlays
130
APPENDICES
Slope sensor
Rotating laser unit
Single lane under trac with pilot car control
.
Single lane under construction.
360° Prism (front)
360° Prism (back)
Concrete overlay
Figure 141. System 2—Stringless paving operation using GPS, a rotating laser, and reference
points
Figure 139. Rotating laser over reference
points
Figure 140. System 2 paving machine
System No. 2
A second stringless system, shown in
Figures 139–141, utilizes GPS and laser
communications to achieve horizontal and
vertical guidance of the paving equipment. It
relies on an initial reference system inside the
primary control or 1,000 foot points of the
highway department with X,Y,Z coordinates.
Coordinates X and Y may be established
with GPS survey equipment, but Z must be
established through the use of digital or three-
wire level circuit operations to provide an
accuracy of 0.01 to 0.03 foot. Contractor or
owner surveys are required to map the exist-
ing pavement surface, establish a final surface
with profiles of the centerline and pavement
edges, and calculate concrete quantities and
pavement depths to meet highway owner
requirements.
e paving equipment in this operation is con-
trolled by a rotating laser unit that may be set
on either side of the road to communicate with
the paving train equipment; see Figure 139. e
equipment locates itself over one known and
previously established reference point (approxi-
mately 500–600 feet apart) inside the primary
control or 1,000 foot points of the highway
department. Elevation of the laser (Z coordi-
nates) is established through the use of a vertical
pole, of set vertical length, under the laser and
over the point. e laser is self-leveling and legs
are adjusted vertically to allow the tip of the ver-
tical pole to touch the point and the laser frame.
e rotating laser emits a 10-degree vertical band
to the units on the paver.
Paver receivers consist of two devices as shown
on the paver masts in Figure 141. e top part
of the mast is a GPS receiver (X,Y coordinates)
that is used to communicate horizontal guid-
ance information to the paver onboard computer
and surface model. Below the GPS receiver is a
1 mm correction receiver that relates paver and
reference point locations to the computer. e
paver onboard computer contains the pavement
surface model and instructs the paving device on
changes in direction and elevation for the paver;
see Figure 141. e same rotating laser can be
used to guide the spreader/belt placer with only
the GPS receiver and an onboard computer with
surface program installed. Other paving train
equipment such as the cure/texture carts are usu-
ally controlled by mechanical means.
System No. 3
e third system, shown in Figures
142–144, is a new emergence of stringless
paving technology and is a blend of the ele-
ments currently being used in the first two
systems and the additions of items that can
reduce the time of survey prior to and dur-
ing paving. It is based on the use of GPS
to guide the paving train and a computer
program that can react quickly enough
to give real-time corrections from the
elevation portion of the GPS signal to the
slipform paver or belt placer, in order to
provide accurate elevation data to 0.01 foot
for development of profile information
necessary to meet highway agency needs.
e GPS system requires a base station on
site with a 2+ mile radius of influence and
known X,Y,Z coordinates at the begin-
ning, ending, and third points of a typical
5-mile project. e base station location
can also be tied to other known survey
points outside the pavement corridor. e
slipform paver or spreader is equipped with
one GPS mast and two-way slope sensors
to adjust the paver movement. e opera-
tor can manually observe the action of the
paver from an onboard computer screen
and make manual adjustments.
One of the advantages of this system is the
use of the four-wheel ATV equipped with
a GPS base station receiver and software
131
Guide to Concrete Overlays
APPENDICES
Figure 142. GPS base station mobile or fixed
Figure 143. GPS paver control system
Figure 144. System 3—Stringless paving operation using GPS
Slope sensor
Single lane under trac with pilot car control
.
Single lane under construction.
360° Prism (back)
Concrete overlay
GPS base station
(within a 2-mile range)
360° Prism (front)
that contains the design centerline profile and
cross section; see Figure 142. By driving the
ATV along a known and set location on the
roadway (5–15 mph), the GPS on the ATV
determines the existing surface elevations.
Using the vehicle’s software, the surface eleva-
tions are then compared to the design profile
at given points to create a 3-D model. is
model is then provided to the stringless paver.
is particular view of the vehicle contains
both the data collection equipment on the
machine and the separate GPS base station
that acts as the reference point for data col-
lection and communication with the paving
train. e information from the existing sur-
face profile, a design overlay centerline profile,
and a typical pavement surface cross section
is fed to a program that cuts cross sections at
specified stations along the route.
e output is a set of pavement surface cross
sections by station rather than a surface
model as in the first two systems. It interpo-
lates changes between stations as the other
systems do between points in the model. e
software is built on the concepts used by the
early geodimeters and total stations, but it
relies heavily on the manipulation of the GPS
signal through mathematical models to gain
the vertical accuracy of 0.01 foot. e control
equipment on the paver shown (Figure 143)
is similar to that used on the other systems.
Keep in mind this system does not require
any laser or radio communications between
reference points and the paving equipment—
only GPS communications.
Stringless System
Equipment
Selection Criteria
e decision regarding the type of stringless
paving system to be used should be made by
the contractor. is decision should be based
on several factors, such as the following:
• Site control provided by the owner. e
highway agency may not have the resources
or desire to set paving hubs. It may request
the contractor to develop the horizontal
and vertical control for paving.
• Construction site accessibility. e highway
agency may not allow stringlines along the
centerline or outside edges because of traf-
fic control requirements. Tight working
areas can limit the access by the public and
construction equipment when stringlines
are used.
• Accuracy and repeatability specification on
equipment. e contractor must weigh the
ability of the stringless system to meet the
agency profile, accuracy, and repeatability
specifications for the quality product the
agency requires.
• Agency goals in profile and concrete yield.
Can the system under consideration pro-
vide the agency and contractor with profiles
that meet or exceed agency goals and pro-
vide accurate information on yield of the
concrete?
• Contractor options to meet owner goals.
Can the system provide information for
machine control that allows for staged con-
struction of pavement sections and meet
the overall goals of the finished product in
terms of construction and profile?
• Research, test, and demonstrate perfor-
mance. e contractor should test the
equipment on the paving train for some
500 to 1,000 feet or more without the
inclusion of concrete. Paving hubs and
stringline should also be in place to assure
all parties that the system is working
properly.
• Level of training and support available. e
contractor should understand the amount
of training required to operate the system
and the amount that will be given prior to
paving.
e contractor should retain access to a ready
response system during the paving season that
minimizes work stoppage due to an unfore-
seen system problem.
Guide to Concrete Overlays
132
APPENDICES
APPENDIX G.
CONSIDERATIONS FOR DEVELOPING PROJECT
AND SUPPLEMENTAL SPECIFICATIONS
Every jurisdiction has its own project devel-
opment process and concrete pavement
specifications. e following guidelines can
be used in overlay project development and
in developing supplemental specifications
or special provisions. ey apply to bonded
and unbonded concrete overlay projects on
existing concrete, asphalt, and composite
pavements.
e guidelines are specific only to concrete
overlay projects and do not represent every
item that needs to be considered in a concrete
paving project.
General
Contractor Submittal
Considerations
• Maturity method for strength determina-
tion prior to opening to traffic.
• Paving mixture design for each source
of aggregate to be used for review and
approval by the engineer.
• Provide material certifications to the
engineer.
• Where required, submit a plan for con-
struction sequence and schedule prior to
commencing construction. If the plans
show a specific sequence/schedule, the con-
tractor may need to verify compliance with
the schedule or submit an alternate plan to
the engineer for approval. A detailed stag-
ing and sequencing plan is recommended
for concrete overlay projects when using an
expedited construction process and sched-
ule of opening.
Scheduling and Conflicts
• Construction sequence: A preconstruction
meeting is recommended to discuss critical
items such as staging, opening strengths,
time of placement, and overall schedule.
• Typically, a concrete overlay schedule is
much shorter than a standard concrete pav-
ing project.
• Conflict avoidance: Expose possible con-
flicts in advance of construction. Verify
elevations and locations of each and verify
clearance for proposed construction.
• Complete elements of the work that can
affect line and grade in advance of con-
struction unless noted on plans.
• Traffic control plan: e contractor
should develop a traffic control plan where
required based on the MUTCD (FHWA
2003b) and approved by the engineer.
Limitations of Operations
In addition to the limitations of operations
for the placement of standard concrete pave-
ment, the following limitations for concrete
overlays apply:
• At air temperatures below 55°F (13°C),
the opening of the pavement should be
established using in-place strength mea-
surement devices, such as the maturity
method (ASTM C-1074). In order to place
concrete in cold weather, air temperature
requirements for the jurisdiction should
apply.
• e engineer may impose a restriction on
edge loading of construction equipment on
the finished slab until opening strength is
reached.
• Bonded concrete overlays should be placed
according to the local jurisdiction’s sched-
ule, based on seasonal temperatures.
• Unbonded overlays should not be placed
when the asphalt or concrete pavement
surface temperature exceeds the maximum
temperature allowed by the engineer.
Typically, this temperature is around 120°F
(49°C). Water may be added to cool the
pavement ahead of the paver. e surface
should be dry and free of standing water
prior to paving.
Method of Measurement
and Basis of Payment
e quantity of the various items of work
involved in the construction of concrete
overlay will be measured by the engineer in
accordance with the following provisions:
• Surface preparation may include milling,
air, water, and sand- or shotblasting; these
should be measured and paid in square
yards. Sweeping and cleaning with com-
pressed air is a surface preparation task but
is most often incidental to paving.
• Concrete overlay, furnish only: e quan-
tity of concrete furnished will be measured
in cubic yards. is quantity should include
concrete placed in widening sections and
partial depth patches. e contractor can
be paid the contract unit price per cubic
yards. is payment should be full com-
pensation for furnishing all raw materials,
and for proportioning, mixing, and delivery
of concrete to the paving machine.
• Concrete overlay, placement only: e
quantity of concrete overlay, placement
only, should be measured and paid for
in square yards. is will be the quantity
shown in the contract documents. e
area of concrete overlay placement can
be determined from the length and pave-
ment width, including widening sections.
Payment should be full compensation for
labor and equipment necessary to place,
finish, texture, protect and cure the pave-
ment, including sawing and sealing (if
required) joints, furnishing, and installing
reinforcement (if required).
• Separation layer: Hot mix asphalt or other
approved separation layer material should
be measured and paid by area or weight.
• If the contract documents require accelerat-
ing curing, such as wet or blanket curing,
the curing area should be measured and the
contractor should be paid per square yard.
Materials
• e CTE of the bonded overlays over
concrete need to be similar to that of
the existing concrete pavement. is is
typically accomplished by using similar
aggregates in the concrete mixture. If it is
not possible, a coarse aggregate should be
used in the overlay that has a lower CTE
than in the existing pavement.
• e largest particle size of the coarse
aggregate should be less than or equal to
one-third of the overlay thickness.
• Refer to contract requirements for concrete
mixture parameters.
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Guide to Concrete Overlays
APPENDICES
Separation Layer for
Unbonded Overlays
• If asphalt is used as the separation layer
material, it should be designed with the
intention of preventing asphalt stripping
from the build up of pore pressure from
heavy traffic. Special consideration should
be given to pavements where high speeds
and heavy trucks are expected. ese vari-
ables are known to contribute to stripping.
• Fabric: Technology is evolving rapidly on
the use of geotextile fabric for the separa-
tion layer. Care should be exercised in
selecting geotextile fabric, however, because
not all products perform equally well for
this application.
Construction
Preoverlay Repairs
• Preoverlay repairs include: slab stabiliza-
tion and slab jacking, partial depth repairs,
full-depth repairs, retrofitted edge drains,
load transfer restoration, and milling. If
milling is part of the repairs, it should be
completed prior to other repairs.
• Materials removed in the preparation
operation may be temporarily placed in
the shoulder area unless otherwise specified
in the contract documents. e removal
of materials must take place prior to the
removal of approved construction signage.
• Surface preparation equipment used
should be subject to approval of the engi-
neer. Milling, air, water, sandblasting, and
shotblasting equipment should be power
operated and capable of preparing and
cleaning of the existing surface in accor-
dance with the contract documents.
Bonded Concrete Overlays Over
Concrete
• e surface of the existing pavement should
be prepared by shotblasting, sandblasting
and/or milling. Milling, if used, should
be followed by shotblasting or high pres-
sure water blasting to remove concrete
damaged during milling (evidenced by
microcracking).
• Preparation should be adequate to remove
all dirt, oil, and other foreign materials, as
well as any laitance or loose material from
the surface and edges against which new
concrete is to be placed.
• Airblast surface to remove loose debris and
prevent resettlement of debris into cleaned
area. e surface should be free of oil or
other automobile fluids. e pavement
surface should not be moist or damp or
have standing water prior to placement of
the overlay.
Bonded Concrete Overlays Over
Asphalt
• A guideline to determine whether milling
is required is if asphalt surface distortions
are 2 in. (5.08 cm) or greater. If milling
is specified, it is important that there is
at least 3 to 4 in. (7.62 to 10.16 cm) of
asphalt remaining prior to the overlay.
Milling should remove the asphalt to the
nearest tack line.
• After milling, the surface should be
inspected for further preoverlay repairs.
e milling operation may expose wide
thermal cracks. If the cracks are wider than
the maximum overlay aggregate size, they
may be filled with fly ash slurry, sand, or
other appropriate material.
• Following any milling, partial or full depth
repairs should be completed with concrete
to ensure bonding with the overlay.
• All concrete patches plus the overlay should
be isolated from the rest of the overlay
using normal joint patterns.
Unbonded Overlays Over
Concrete
• For uniform support of the overlay, all
partial and full-depth repairs should be
completed with concrete.
• e concrete surface should be cleaned
prior to the placement of the separation
layer. If a leveling course is required, it
should be completed with the concrete
overlay and not with the asphalt separation
layer.
Unbonded Concrete Overlays
Over Asphalt
All partial and full-depth patching should be
completed with asphalt. Existing concrete
patches in the existing asphalt pavement
should be isolated to prevent bonding to the
concrete overlay. A debonding agent, fabric,
or other bond-breaking material should be
applied to the patch before the overlay is
placed.
Surface Cleaning
Bonded Concrete Overlays Over
Concrete or Asphalt
• e surface of the existing pavement should
be cleaned by sweeping and followed
by compressed air in front of the paver.
Paving should commence soon after clean-
ing to minimize contamination.
• Pressure washing should only be consid-
ered when surface contaminants are hard
to remove or when mud or other debris is
tracked on the surface. If pressure washed,
no standing water should be allowed prior
to paving. Paving should commence soon
after cleaning to minimize contamination.
Unbonded Concrete Overlays
Over Concrete or Asphalt
Surface cleaning is provided by sweeping of
the existing asphalt surface with a mechani-
cal sweeper or air blower. Paving should
commence soon after cleaning to minimize
contamination.
Concrete Placement
Grade Control
• e engineer will review and approve the
control system. Information detailing the
pavement thickness at the various survey
points and material quantities should also
be provided.
• Concrete paver should place in single lane
width or be capable of adjusting the crown
at each plan lane line when placing mul-
tiple lanes.
• When appropriate, grade control for the
paving operation should be referenced
off the milled surface, unless the milling
machine is controlled by a previously estab-
lished paver control line.
Overlay Placement
• Surface watering may be allowed by the
engineer to help cool the pavement in
extremely warm conditions and when the
existing pavement surface condition is at
or exceeds 120°F (48.89°C). e pavement
surface should not be moist or wet prior to
placement of the overlay.
• Conventional concrete paving procedures
should be followed for placing, spreading,
consolidating, and finishing the unbonded
overlay when required. When dowels
are specified, anchoring dowel baskets to
the underlying pavement must be done
according to the jurisdictions requirements.
Alternatively, paving machines equipped
with dowel bar inserters can be used.
• A quality control plan should dictate the
time of placement with consideration
given to air and pavement temperatures.
For bonded overlays on concrete, it is not
desirable to have the overlay pavement
contracting, due to shrinkage, at the same
time as the existing underlying concrete is
expanding due to the heat of the day. e
best time to place a bonded overlay over
concrete is when the temperature differen-
tial between the existing pavement and new
overlay is minimal.
Guide to Concrete Overlays
134
APPENDICES
Liquid Membrane Curing
• Apply curing compound immediately
after surface moisture has disappeared but
typically no later than 30 minutes after
finishing/texturing. Apply liquid curing
compound in a fine spray to form a con-
tinuous, uniform film on the horizontal
surface and vertical edges of pavement,
curbs, and back of curbs.
• Use a white pigment liquid curing com-
pound for concrete.
• For overlays with a thickness of 6 in. (150
mm) or less, apply curing compound at
2 times the manufacturer’s recommended
application rate for a standard concrete
pavement. Do not dilute the compound.
• For overlays with a thickness greater than
6 in. (150 mm), curing compound should
be applied at 1.5 times the manufacturer’s
recommended rate for a standard concrete
pavement.
• When white pigment curing compound is
employed correctly, the surface of the con-
crete pavement should be solid white with
no visible grey.
• If forms are used, apply to pavement edges
and back of curbs within 30 minutes after
forms are removed.
• Protect concrete pavement during cold
weather for at least 5 days, or protect for
a minimum of 24 hours and until flexural
strength of 340 psi (2.3 MPa) is achieved
for unbonded concrete overlays, 420 to 480
psi (2.9 to 3.3 MPa) for bonded concrete
overlays over asphalt, and 540 psi (3.7
MPa) for bonded concrete overlays over
concrete.
Joint Sawing
General
• e contractor should provide a joint saw-
ing plan that demonstrates how all saw cuts
will be accomplished within a shortened
sawing window. Details should include
the number of saws and anticipated sawing
production rates, as well as estimated start-
ing and finishing times. All sawing must
be completed within the first one-half of
the sawing window.
e contractor should exercise care in
placing, consolidating, and finishing the
concrete at and around all joints.
• Wet sawing should be used when required
by the contract documents for dust control.
Joint Width
• All conventional sawing widths are nor-
mally 0.19 in. (4.8 mm) +/- 0.06 in. (1.5
mm).
• All early entry sawing are normally 0.13 in.
(3.3 mm) +/- 0.06 in. (1.5 mm) in width
and a minimum T/4 inches in depth.
Joint Seal
• Joint sealing should follow the jurisdic-
tional requirements. When narrow (.13 in.
[3.3 mm]) saw cuts are used and sealing is
required, follow jurisdictional requirements
for low modules hot-pour sealant.
Timing
• Timely sawing is necessary to prevent ran-
dom cracking due to shrinkage. is is
particularly important for overlays less than
6 in. (150 mm).
Bonded Overlays Over Concrete
• Prior to construction of a concrete bonded
overlay, the exact location of each contrac-
tion and expansion joint in the existing
pavement, including joints created by full-
depth patches, should be identified and
marked on both sides of the pavement by a
reliable method.
• Transverse joints should be placed in the
overlay pavement directly over existing
transverse joints.
• Transverse joint width must be equal to or
greater than the underlying crack width at
the bottom of the existing transverse joint
to prevent debonding due to movement.
• Saw all transverse joints to full depth of
overlay plus 0.50 in. (13 mm).
• Saw longitudinal joints to T/2.
Bonded Overlays Over Asphalt
• Saw transverse joints to a minimum depth
of T/4.
• Saw longitudinal joints to a depth of T/3.
• Early entry saws may be required unless
otherwise specified in contract documents.
• When 0.13 in. (3.3 mm) wide saw cuts
are used and sealing is required, follow the
jurisdictional requirement for low modulus
hot-pour sealant.
Unbonded Overlays
• Saw transverse joints to a depth of T/4
(minimum) or T/3 (maximum). For early
entry, saw depth will be 1.25 in. (31 mm)
or greater.
• Saw all longitudinal joints to a depth of
T/3.
• Sealing will follow jurisdictional
requirements.
• For unbonded overlays over asphalt, the
saw cut depth may need adjustment over
rutted asphalt location in order to maintain
a depth of T/4 to T/3 requirements.
• When 0.13 in. (3.3 mm) saw cuts are used
and sealing is required, follow jurisdictional
requirement for low modulus hot-pour
sealant.
135
Guide to Concrete Overlays
APPENDICES
APPENDIX H.
SUGGESTED OWNER-CONTRACTOR MEETINGS
TO ENSURE A QUALITY PRODUCT
e following information is provided as a
starting point or guide for ensuring quality
concrete performance in concrete overlays.
Key elements are identified that are required
of the pavement owner and contractor for
each project. is is an outline for success but
is not detailed in nature so that items can be
added or deleted according to common prac-
tice in a given state or local government.
To accomplish the construction objectives
in concrete overlay projects, it is necessary
to have meetings during the design (prebid)
and construction (prepour/preconstruction)
period between the contracting agency and
the contractor(s) to work out the details. e
purpose of the prebid, prepour, and precon-
struction conferences and the key elements
(checklists) of each are shown below.
Prebid Meeting
Check List
Prebid meetings provide an opportunity for
the owner to review project requirements
and receive input from contractors who may
have an interest in bidding for the project.
Although prebid meetings tend to be primar-
ily a review of administrative and contractual
matters, it is important to use them to high-
light modifications implemented in the plans
and specifications.
e prebid meeting gives the contracting
agency an opportunity to identify new and
different items in the areas of specifications,
materials, and construction processes that
are expected in the construction project.
It is also a good time to receive input from
the contractors on important design and
construction items such as jointing, surface
preparation of the existing pavement, paving
exceptions, schedules, and staging. It is also
an opportunity to discuss the intent of the
work changes. Critical material supply/avail-
ability issues and specific acceptance testing
requirements also need to be addressed.
Minutes of the meeting should be distrib-
uted to all potential bidders (those who have
requested bid documents) whether they are
in attendance or not. Paving-related items for
discussion are listed below.
Prebid Meeting
I. Overlay Project Items of Special
Attention
1. Construction differences between con-
ventional paving and overlays
2. Phasing and staging plan
3. Scheduling criteria, including which
areas are accessible, restrictions on site
access, and working hours
4. Scheduling milestones with incentives/
disincentives
5. Allowable mixes and special condi-
tions such as fibers
6. Strength requirements and strength-
testing measurement methods
7. Traffic control, clearances, stag-
ing requirements, and edge-drop
restrictions
8. Expected and unexpected delay
resolution
9. Plant and staging area locations
10. Paving sequence, paver clearance, and
pavement dropoff limitations
11. Haul road locations
12. QA acceptance testing and QC
requirements
13. Issuance of design and specification
changes
14. Pre-overlay repairs and surface
preparation
15. Special conditions such as tie bar loca-
tions, widening details, etc.
16. Saw cut depths as well as timing and
importance of early joint development
17. Curing, particularly curing for thin
pavement sections
18. Incentives and disincentives applied to
overlay construction
19. Pavement ride requirements on the
finished product
20. Importance of reducing the length of
time for job completion
II. Alternative Bid Provisions
1. Materials selection
2. Management method (conventional,
A+B, etc.)
III. Discussion of Questions from the
Prospective Contractors
IV. Issuance of Addenda to Clarify Questions
Raised at the Prebid Conference
1. Minutes of the meeting to all who
attended and those who call for plans
on the project
Prepour/
Preconstruction
Review Checklist
Prepour or preconstruction meetings can
be very productive when the contractor is
tasked with addressing the pertinent items.
ey may be conducted as one combined
meeting or two separate meetings, depending
on the level of detail the contractor is able
to provide at the preconstruction meeting.
e contractor should be able to present the
plan for addressing each of the items on the
review checklist for review and comment at
this meeting. Forcing the contractor to think
about the project and build it on paper before
the prework meeting will pay big dividends.
e overlay team should be involved in the
prework so they can receive guidance and
answers to unresolved issues and/or identify
potential problems with the contractor’s
approach.
I. General Items
1. Identify the chain of command in the
decision-making process
2. Identify roles and responsibilities of
key staff for all involved parties
3. Review of all design and construction
changes issued since bid
4. Certification of materials sources
5. Mix design submittals
6. QMP/CQC laboratory and personnel
certifications
7. Batch plant certification and mixer
Guide to Concrete Overlays
136
APPENDICES
efficiency tests
8. Construction schedule
9. Payment schedules
10. Subcontractor activities
11. Construction survey
12. Haul roads and access points
13. Traffic control plan for each phase of
the work
14. Working days allowed and method of
counting
15. Expected start date
16. Phone numbers and email addresses of
key personnel such as contractor and
agency representatives, traffic control
manager, material suppliers, and util-
ity location representatives
17. Liquidated damages
18. EEO/AA requirements
19. Public information notification pro-
cess to be used during construction
20. Pollution control plans
21. Safety inspections
22. Change order process
23. Conduct of a half-day overlay
workshop
II. Contractor Project Plan
1. Identify the chain of command in the
decision-making and construction
process
2. Work schedule breakdown by major
task, starting date, and expected
duration
3. Field lab location
4. Field office location
5. Subcontract documentation
6. Material source and quality
certifications
7. Material testing lab and technician
certifications
8. Submittal of concrete mix design
9. Water sources and testing
10. Traffic control plan for each phase of
the work
11. Haul road and access point location
and duration identification
12. Construction survey
a. Method—contract or owner
b. Type and amount of available
information
c. Stringline or stringless construction
d. Development of the profile grade
and concrete quantity by whom
and when (Is there an approval pro-
cess and timeline before
construction?)
e. Reestablishment of land corners
and centerline control points
13. Public information notification pro-
cess to be used during construction
III. Utility Concerns: Locations in the proj-
ect limits, key personnel for location
contact, and expected plans for relocation
where necessary
IV. Local Jurisdiction Concerns:
Coordination with local road projects
or city/county special activities (e.g.,
festivals)
V. Concrete Placement Activities (is can
be part of the preconstruction conference
or a separate prepour conference.)
1. Batching activities
a. Identification of central mix or
ready-mix supply source
b. Stockpile management to eliminate
segregation
c. Batch plant certification and mixer
efficiency testing
d. Anticipated plant production rates
e. Concrete haul route identification
and estimated truck number
needed for existing traffic along
the route
f. Consideration of alternative mixes
to meet weather changes
g. Aggregate stockpile moisture
h. Identify washout areas for trucks
2. Concrete paving (placement, finishing,
texturing, and curing)
a. Overlay temperature planning and
management (on-site weather con-
dition monitoring and who and
how it entered into the decision to
pave and cover or not to pave)
b. Placement and filler lane scheduling
c. Base preparation (patching, milling,
recycling)
d. Equipment breakdown procedures
e. Maximum allowable concrete haul
times
f. Placement procedures (equipment
and methods)
g. Estimated mix temperature at the
time of placement
h. ickness verification during
placement
i. Estimated time from placement to
time that allows for joint sawing
j. Hot/cold weather specifications and
precautions
1) Changes in mix for weather or
material changes
2) Identification of method and
materials to be used to protect
the concrete in case of changes
in weather (rain, snow, or hot/
cold)
k. Temperature control of existing
asphalt surfaces
l. Vibrator testing/consolidation
issues
m. Curing and texturing equipment,
rates, and construction procedures
n. Tie bar/dowel location, inser-
tion, alignment, spacing, offset
verification
o. Straight edge and edge slump
tolerances
p. Plastic shrinkage cracking, edge
slump, joint spalling, and full-depth
cracking treatments
3. Joint development (longitudinal and
transverse)
a. Review of contractor saw cut-
ting QC plan (number, type, and
method of sawing)
b. Consideration of employing early
entry saws
c. Backup saw availability (number,
personnel, and location to project)
d. Rain conditions and skip-sawing
procedures
e. Joint reservoir size, shape, and
depth-cut dimension tolerances and
dimensions
f. Joint sealing installation and accep-
tance procedures
g. Saw-cutting sequence and accept-
able degree of saw-cut raveling
137
Guide to Concrete Overlays
APPENDICES
h. Joint sealant and backer-rod mate-
rial certification submittals
i. Requirements on removal and
flushing of joint-sawing residue
j. Joint beveling procedures (if
required)
k. Joint sealant and concrete curing
time requirements and methods
l. Joint sandblasting, reservoir clean-
liness, and moisture condition
requirements before sealing
m. Joint sealant surface depth toler-
ances, sealant pump, water truck,
and saw-cutting equipment
n. Allowable ambient temperatures
during sealing operations and com-
pression seal reservoir requirements
o. Joint inspection procedures
4. QA/QC activities
a. Delineation of owner and contrac-
tor responsibilities in testing and
sampling
b. Review of contractor’s QC plan
c. Aggregate durability, soundness,
abrasion, and gradation test data
and requirements
d. Reinforcing steel and dowel bar
submittals
e. Materials sampling and testing
procedures
f. Development and use of control
charts
g. Concrete mixture designs and
water-cementitious ratio effects on
strength
h. Concrete sampling, fabrication,
curing, and testing procedures
i. Sampling and pay factor computa-
tion overview
j. Documentation of test results and
deviations
k. Verification of failing acceptance
tests, retesting, and referee testing
l. Actions to be taken if specification
requirements are not met
m. Pavement smoothness (ride) test-
ing and timing
n. Treatment of premature cracking
and spalling
o. Resolution procedures for expected
and unexpected delay
Guide to Concrete Overlays
138
APPENDICES
APPENDIX I.
INNOVATIVE METHODS FOR ACCELERATED
CONCRETE OVERLAY CONSTRUCTION
Table 25 provides a summary of innovative accelerated construction methods (adapted from Simon et al. 2003).
Table 25. Applicability, Pros, and Cons of Various Accelerated Construction Methods
Method Applicability/Limitations Pros(+)/Cons(–)
Formal partnering with design
consultants, contractors, local
authorities, and regulatory agencies
• This method has not been used very much
with designers or other agencies.
• Little training has been done and much
skepticism is in place regarding this method.
+ Provides a faster and cheaper construction process due to reduction of
conflicts, litigation, and claims (win-win situation)
+ Brings about continuous improvement in the quality of services and
products
+ Utilizes resources more effectively
+ Implements easily because already being used on an informal basis
+ Improves communications
– Limits completive market strategy
– Creates strong dependency on the partners
Methods for expediting utility
relocation work
• In highway construction, the need for the
relocation of utilities often arises, particularly
in urban areas.
• Relocation is handled primarily by utility
companies.
• Currently, there is little recourse that can be
taken against utilities for delays.
• Utilities have to pay for relocations.
+ Encourages project managers to develop more economical means and
methods
+ Shortens project execution by using less formal documentation and
improving communication
+ Reduces executive personnel
+ Produces more continuity during the project
– Brings about need for independent engineers to check PMs’ work
– Encourages overcoming the “specialist mindset” of the organization
Intelligent transportation systems and
work zone traffic control
• Applicable areas include but are not limited
to traffic control, route guidance, automated
highway systems, collision avoidance,
en-route driver information, transportation
demand management, etc.
+ Increases safety
+ Reduces congestion
+ Enhances mobility
+ Minimizes environmental impact
+ Increases energy efficiency
+ Promotes economic productivity for healthier economy
– Requires additional training of employees
– Includes costs to implement
Public input on phasing of
construction
• This method is applicable on construction
projects where there is a significant impact
on the public.
+ Allows for more expeditious construction methods to be employed
– Requires more public relations effort earlier
Multiple approaches to traffic control
plans (TCPs)
• TCP solutions for small simple jobs are
often apparent, but otherwise they should
be thoroughly investigated earlier in the
process.
+ Reduces both construction costs and user costs through optimal TCPs
– Requires larger consultant fees for development because of more
thorough TCP analysis
Descriptive catalog of construction
technologies
• Applicability of new technologies could
be widespread, but specifications may be
affected.
+ Provides an online catalog that could easily be accessed and
supported by FHWA and other states
– Requires effort for maintenance and upkeep of the catalog
Contractor preparation of the TCP
based on minimum requirements
• This approach will encourage contractor
innovation but may be possible only on
smaller, simpler projects.
+ Reduces efforts
+ Provides incentive for construction innovation
– Increases costs
– Excludes impact on local businesses
– Means that contractor compliance with safety standards may be
challenging
139
Guide to Concrete Overlays
APPENDICES
Method Applicability/Limitations Pros(+)/Cons(–)
Linear scheduling method (LSM) and
accurate productivity to rate data and
establish project target duration
• This method can be used for repetitive
projects in which there are no strict
dependencies/constraints between project
activities.
• Resurfacing overlays and shoulder
improvement are good types of projects for
the LSM.
+ Provides a better understanding of the project
+ Enables the planner to determine when and where a change in
resources must take place to satisfy the goals set by the project
+ Helps identify existing relationships and encourages the project team
to try different alternatives
+ Shortens schedule by overlapping activities instead of sequencing
– Scheduling projects involving large cuts and fills might be more difficult
to schedule with LSM
A+B contracting (costs plus time) • A+B bidding can be used to motivate the
contractor to minimize the delivery time for
high-priority and highly trafficked roadways.
• There must be a balance between the
benefits of early completion and any
increased cost of construction.
• This approach requires incentives and
disincentives to be effective.
+ Includes consideration of the time component of a construction
contract
+ Includes favorable treatment of contractors with the most available
resources to complete the project
+ Involves incentives for contractors to compress the construction
schedule
+ Includes greater potential for early project completion
– Requires that incentives and disincentives are carefully managed
– Means that costs are defined whereas benefits are distributed to the
public
Contractor milestone incentives • Incentives must be relevant.
• Goals must be reachable.
• Incentives cannot be conflicting.
+ Encourages contractors to finish on time
– Causes impacts to contractors to be highly scrutinized
– Causes disagreements over compensable delays that may be
problematic
Packaged multiprimes contracting • This method can be used when a specific
highway project is composed of several
major segments or is very large.
+ Increases competition among construction bidders
+ Reduces pyramiding of costs, particularly overhead and profit
+ Reduces project time through overlap of design and construction or
from multiple work forces
+ Requires more direct control by the project owner
– Presents interface management challenges for the agency
– Leads to physical interferences between contractors
Prequalified bidders based on past
schedule performance
• Bidders qualify based on several key items,
including specific project type experience,
individual experience, past performance,
capacity of the firm, and primary firm
location.
+ Provides a shorter and easier selection process
+ Provides possibly better contractors
– Reduces the competition
– Requires that schedule performance data are well kept
– Requires that agency and other noncontractual schedule impacts are
recognized and equitably settled
Incentives for TCP development with a
contractor who values an engineering
cost-savings sharing provision
• To use this method, seek involvement of local
municipalities in funding the incentive (e.g.,
5 percent of estimated user cost savings).
• This method requires close scrutiny to
determine actual time savings.
+ Leads to innovative ideas for successful TCPs
– Means that savings are difficult to estimate
Incentives for contractor work
progress with a lane-rental approach
• Incentives must be explicitly described in the
bid package.
• Rental rates have to be significant and should
address high-impact lanes.
+ Leads to innovative ideas for successful TCPs
+ Minimizes contractor impact on the traffic
– Causes administration to be difficult
Increased amount of liquidated
damages and routine enforcement
• Just as important as the damages happening
in the contract are the claims made for
damages. The time and effort involved
in pursuing these claims is, however, a
limitation. This should be weighed against
potential benefits.
• Possibly provide incentives to finish projects
ahead of time.
+ Motivates better contractor performance
– Requires rigorous documentation and quick request for information
response to enforce
“No excuse” incentives • These incentives preclude delay claims by
contractors, give contractors incentives to
finish early, and require a realistic schedule.
+ Results in considerable improvements in schedule performance
– Transfers risk to contractor and therefore may increase costs on the
average over time
Table 25. Applicability, Pros, and Cons of Various Accelerated Construction Methods, continued
Guide to Concrete Overlays
140
APPENDICES
Method Applicability/Limitations Pros(+)/Cons(–)
Tools and best practices for
implementing multiple work shift and/
or night work
• New technologies (such as intrusion
alarms), modified traffic control plans, and
new methods to monitor traffic provide
improvements in night work zone safety.
• These improvements will lead to high
nighttime productivity.
+ Increases safety for road users and workers
+ Reduces user costs
+ Provides faster completion time
– Requires research and design costs
Exploitation of web-based team
collaboration system
• To be efficient, access to information is
needed quickly and without hassle. A web-
based system can be used to track project
deliverables, track project tasks online,
receive email alerts as items become due,
share documents, and reduce administrative
document production and delivery cost by
uploading documents. This is handy for CAD
drawings or anything else that needs to be
shared with the project team.
+ Enhances project communication
+ Eases collaboration with project managers, designers, contractors,
vendors, and the public
+ Keeps everyone in the loop
+ Allows tracking of project online, which minimizes time taken and
enhances performance
– Requires high installation and learning costs
– Lacks standards
Encouragement of the use of
automated construction technologies
• Numerous research and implementation
efforts are currently under way to automate
conventional infrastructure construction,
condition assessment, and maintenance
actives such as earth moving, compaction,
road construction, and maintenance.
• Commercial systems are available.
+ Results in possible savings
+ Presents opportunity for significant schedule compression
– Requires some training
– Requires contractor implementation
Employment of methods for
continuous work zones
• These methods can be used where road
geometry and weekend or night scheduling
permit.
+ Decreases duration and unit costs
+ Increases safety
– Results in possible higher user costs and traffic congestion
Use of windowed milestone • This method can be used where milestone
dates are not based on hard constraints.
Milestones should be related to allow the
contractor maximum flexibility in efficiently
allocating project resources.
+ Lowers project costs
+ Lowers user costs
– Reduces ability to “hold contractors’ feet to the fire”
Schedule of calendar day projects • Scheduling calendar day projects is
applicable to projects where the completion
is critical and a large volume of traffic is
affected.
+ Produces better weather management
+ Provides a direct method of expediting
– Requires strict adherence to the schedule for credibility with the
public, even with breakdowns or weather problems
Construction time shortened by full
closure of the roadway instead of
partial closure
• Full closure could be used in areas where
there is at least one alternative route for
drivers and where volume is limited.
+ Shortens construction time
– Causes possible traffic congestion on alternative routes
Duration and productivity effects
tracked and associated with different
technologies
• Data collected can be very useful in cost and
time estimation for optimal plans.
• Technology choices may be limited, however,
by project conditions and logical equipment
spreads.
+ Produces quicker and more dependable exploitation of new
technologies
– Requires personnel to devote time to properly monitor and record data
– Can be perceived as costly
Optimal approaches to crew shifts
and scheduling to eliminate long work
hours
• The schedule can be shortened through use
of additional crews on regular shift, multiple
shifting, or selective overtime.
• Scheduled overtime can be used where
appropriate, but effects should be evaluated
carefully.
+ Provides possible cost savings
+ Increases productivity
+ Reduces cycle time of tasks, which improves the schedule
– Creates possible negative results if planning is done carelessly
– Creates a necessity for contractor to implement
Selected field personnel trained in
scheduling methods and claims
• Schedule flexibility may be minimal in
practice, but for complex jobs a broad
understanding of scheduling issues should
help expedite progress.
+ Creates a flexible and quick-to-adapt project team
+ Leads to faster project completion
– Leads to possibly too many people trying to manage
Lessons-learned database on ways to
expedite schedules
• This database would be broadly applicable
but limited by legal and policy constraints.
+ Requires quick reference for implementation of expediting measures
– Creates a need for the database to be maintained
Table 25. Applicability, Pros, and Cons of Various Accelerated Construction Methods, continued
141
Guide to Concrete Overlays
SOURCES
SOURCES
REFERENCES
3M. 2013. Geotextile Seaming Cylinder
Spray Adhesive. Tech Data Sheet. Industrial
Adhesives and Tapes Division.
American Association of State Highway
Officials (AASHO). 1962. e AASHO Road
Test. Report 5 Pavement Research. Washington,
DC: Highway Research Board.
———. 1993. Guide for Design of Pavement
Structures. 4th ed. Washington, DC:
American Association of State Highway and
Transportation Officials.
———. 1998. Supplement to the AASHTO
Guide for Design of Pavement Structures.
Washington, DC: American Association of
State Highway and Transportation Officials.
———. 2007. Transportation—Invest in Our
Future: A New Vision for the 21st Century.
Washington, DC: AASHTO.
———. (no year). AASHTOWare Pavement
ME Design. www.aashtoware.org [accessed
March 9, 2014)
ACI Committee 302. 2010. Guide for
Concrete Floor and Slab Construction.
Publication ACI 302-1R-04. Farmington
Hills, MI: American Concrete Institute.
ACI Committee 325. 2006. Concrete Overlays
for Pavement Rehabilitation. Publication ACI
325.13R-06. Farmington Hills, MI: American
Concrete Institute.
ACI Committed 330. 2008. Guide for the
Design and Construction of Concrete Parking
Lots. Publication ACI 330R-08. Farmington
Hills, MI: American Concrete Institute.
American Concrete Pavement Association
(ACPA). 1990a. Guidelines for Bonded
Concrete Overlays. Technical Bulletin
TB-007P. Skokie, IL: American Concrete
Pavement Association.
———. 1990b. Guidelines for Unbonded
Concrete Overlays. Technical Bulletin
TB-005P. Skokie, IL: American Concrete
Pavement Association.
———. 1991. Guidelines for Concrete
Overlays of Existing Asphalt Pavements
(Whitetopping). Technical Bulletin TB-009P.
Skokie, IL: American Concrete Pavement
Association.
———. 1998. Whitetopping—State of the
Practice. Engineering Bulletin EB210.02P.
Skokie, IL: American Concrete Pavement
Association.
———. 1999. Construction Specification
Guideline for Ultra-in Whitetopping.
Information Series IS120P. Skokie, IL:
American Concrete Pavement Association.
———. 2000. Traffic Management Handbook
for Concrete Pavement Reconstruction and
Rehabilitation. Publication EB213P. Skokie,
IL: American Concrete Pavement Association.
———. 2012. Bonded Concrete Overlay on
Asphalt (BCOA) ickness Designer. (http://
apps.acpa.org/apps/bcoa.aspx, accessed
March 9, 2014)
———. 2012. StreetPave. (http://acpa.org/
streetpave, accessed March 9, 2014)
———. 2013. National Concrete Overlay
Explorer. (www.overlays.acpa.org/webapps/
overlayexplorer/index.html, accessed March 9,
2014)
Applied Pavement Technology, Inc. 2002a.
Conventional Whitetopping Overlays.
Technical Brief. Publication FHWA IF-03-
008. Washington, DC: Federal Highway
Administration. (http://isddc.dot.gov/
OLPFiles/FHWA/010933.pdf, accessed
March 10, 2014)
Applied Pavement Technology, Inc. 2002b.
Unbonded Portland Cement Concrete
Overlays. Technical Brief. Publication
FHWA-IF-03-006. Washington, DC: Federal
Highway Administration. (http://isddc.dot.
gov/OLPFiles/FHWA/010935.pdf, accessed
March 10, 2014)
Bordelon, A. C. 2011. Flowable Fibrous
Concrete for in Concrete Inlays. PhD diss.,
Department of Civil and Environmental
Engineering, University of Illinois at Urbana-
Champaign. (https://www.ideals.illinois.edu/
handle/2142/29805, accessed March 10,
2014)
Bordelon, A. and J. Roesler. 2011. “Flowable
Fibrous Concrete for in Concrete Inlays.”
1st Transportation and Development Institute
Congress 2011. Ed. I. Al-Qadi and S. Murrell.
Chicago, Illinois: American Society of Civil
Engineers. pp. 874-883.
Burnham, T. R. and B. I. Izevbekhai. 2012.
Performance of in Jointed Concrete
Pavements Subjected to Accelerated Traffic
Loading at the MnROAD Facility, in
Advances in Pavement Design through Full-scale
Accelerated Pavement Testing, ed. David Jones,
John Harvey, Angel Mateos, Imad Al-Qadi,
289–297. Monograph of 4th International
Conference on Accelerated Pavement Testing.
Boca Raton, FL. CRC Press.
Cable, J. K. 2012. Concrete Overlay Field
Application Program, Iowa Task Report: US 18
Concrete Overlay Construction under Traffic.
Ames, IA: National Concrete Pavement
Technology Center, Iowa State University.
(www.intrans.iastate.edu/research/documents/
research-reports/US_18_overlay_construc-
tion_web.pdf, accessed March 9, 2014)
Cable, J. K., C. Bauer, E. J. Jaselskis, and L.
Li. 2004. Stringless Portland Cement Concrete
Paving. Iowa Department of Transportation/
Iowa Highway Research Board Project
TR-490. Center for Portland Cement
Concrete Pavement Technology.
Cervantes, V., and J. R. Roesler. 2009.
Performance of Concrete Pavements with
Optimized Slab Geometry. Final Report,
FHWA ICT-09-053. Urbana, IL: Illinois
Center for Transportation, University of
Illinois.
Christopher, B. R. 2000. Maintenance of
Highway Edgedrains. NCHRP Synthesis of
Highway Practice 285. Washington, DC:
Transportation Research Board. (http://
ntl.bts.gov/lib/17000/17600/17652/
PB2001102763.pdf, accessed March 10,
2014)
Cole, L. W., and P. A. Okamoto. 1995.
Flexural Strength Criteria for Opening
Concrete Roadways to Traffic. Transportation
Research Record 1478:53–61.
Covarrubias T and Covarrubias V. 2008.
TCP Design for in Concrete Pavements.
9th International Conference on Concrete
Pavements, San Francisco, CA.
Covarrubias V, J. P. 2011. Optipave2
v 1.0. (www.tcpavements.com/index.
php?op=4_1&lang=en, accessed March 14,
2014)
Guide to Concrete Overlays
142
SOURCES
Covarrubias V, J. P., Covarrubias, and T.
Roesler. 2010. Design of Concrete Slabs
with Optimized Geometry. 11th International
Symposium on Concrete Roads, October
20–22, Sevilla, Spain.
Daleiden, J. 1998. Video Inspection of
Highway Edgedrain Systems. Publication
FHWA SA-98-044. Washington, DC: Federal
Highway Administration.
Federal Highway Administration (FHWA).
1994. Guidelines for Timing Construction
Joint Sawing and Earliest Loading for Concrete
Pavements. Volume 1. FHWA-RD-91-079.
Washington, DC: FHWA.
——— 2003a. Distress Identification Manual
for the Long-Term Pavement Performance
Program. 4th revised ed. Publication FHWA
RD-03-031. Washington, DC: Federal
Highway Administration.
———. 2009. Manual on Uniform Traffic
Control Devices. 2003 ed. with revisions 1 and
2 incorporated. Washington, DC: Federal
Highway Administration.
Fick, G. 2010. Concrete Overlay Cost:
Frequently Asked Questions. Concrete Overlay
Field Application Program. Ames, IA:
National Concrete Pavement Technology
Center, Iowa State University.
Fournier, B., M-A Berube, K. J. Folliard, and
M. omas. 2010. Report on the Diagnosis,
Prognosis and Mitigation of Alka-silica Reaction
(ASR) in Transportation Structures. FHWA-
HIF-09-004. Washington, DC: Federal
Highway Administration. (www.fhwa.dot.
gov/pavement/concrete/pubs/hif09004/
hif09004.pdf, accessed March 10, 2014)
Hall, K. T., C. E. Correa, S. H. Carpenter,
and R. P. Elliott. 2001. Rehabilitation
Strategies for Highway Pavements. NCHRP
Project C1-38. Washington, DC:
Transportation Research Board.
Harrington, D. 2008. Guide to Concrete
Overlays: Sustainable Solutions for Resurfacing
and Rehabilitating Existing Pavements. 2nd
ed. Ames, IA: National Concrete Pavement
Technology Center, Iowa State University.
Harrington, D, D. DeGraaf, R. Riley, R. O.
Rasmussen, J. Grove, and J. Mack. 2007.
Guide to Concrete Overlay Solutions. Ames,
IA: National Concrete Pavement Technology
Center, Iowa State University.
Harrington, D., G. Fick, and P. Taylor. 2014
(tentative). Preservation and Rehabilitation of
Urban Concrete Pavements Using in Concrete
Overlays: Solutions for Joint Deterioration
in Cold Weather States. Ames, IA: National
Concrete Pavement Technology Center, Iowa
State University.
Hoerner, T. E., K. D. Smith, H. T. Yu, D.
G. Peshkin, and M. J. Wade. 2001. PCC
Pavement Evaluation and Rehabilitation:
Reference Manual. NHI Course 131062.
Arlington, VA: National Highway Institute.
Illinois Department of Transportation–Bureau
of Materials and Physical Research (IDOT–
BMPR). 2013. Approved/Qualified Product
List of Synthetic Fibers. Springfield, IL: Illinois
DOT. (www.dot.state.il.us/materials/synthet-
icfibers.pdf, accessed March 10, 2014)
Kosmatka, S.H., and M. L. Wilson. 2011.
Design and Control of Concrete Mixtures, 15th
Edition. PCA Bulletin EB001.15. Skokie, IL:
Portland Cement Association.
Ley, M.T., R. Felice, and J. M. Freeman.
2012. Assessment of Air Void System
Requirements for Durable Concrete. Ames, IA:
National Concrete Pavement Technology
Center, Iowa State University (www.intrans.
iastate.edu/research/documents/research-
reports/mda_air_void_w_cvr.pdf, accessed
March 17, 2014)
Leykauf, G., and D. Birmann. 2006.
Concrete Pavements with Geotextile
Interlayer in Germany: Measurements
and Long-term Behavior. Proceedings,
10th International Symposium on Concrete
Roads. Brussels, Belgium: European Cement
Organisation (CEMBUREAU), World Road
Association (PIARC). CD-ROM.
Mallela, J., G. Larson, T. Wyatt, J. Hall,
and W. Barker. 2002. User’s Guide for
Drainage Requirements in Pavements: DRIP
2.0 Microcomputer Program. DTFH61-
00-F-00199. Champaign, IL: ERES
Consultants. (http://isddc.dot.gov/OLPFiles/
FHWA/010942.pdf, accessed March 10,
2014)
Minnesota Department of Transportation
(MnDOT). 2013. e Effect of Joint Sealing
on the Performance of in Whitetopping
Sections at MnROAD. MnROAD [Safer,
Smarter, Sustainable Pavements through
Innovative Research]. (www.dot.state.mn.us/
mnroad/reports/PDF%27s/jointsealing.pdf,
accessed March 10, 2014)
National Cooperative Highway Research
Program (NCHRP). 2004. Development of
the 2002 Guide for the Design of New and
Rehabilitated Pavement Structures: Phase
II. NCHRP 01-37A. Washington, DC:
Transportation Research Board. (http:/apps.
trb.org/cmsfeed/TRBNetProjectDisplay.
asp?ProjectID=218, accessed March 10, 2014
———. 1982. Resurfacing with Portland
Cement Concrete. Synthesis 99 (discontinued).
———. 1994. Portland Cement
Resurfacing—A Synthesis of Highway Practice.
Synthesis 204 (discontinued).
———. 2007. AASHTO Mechanistic-
Empirical Design Guide. Version 1.0
NCHRP Project 1-37a. Washington, DC:
Transportation Research Board.
Okamoto, P.A., P. J. Nussbaum, K. D.
Smith, M. I. Darter, T. P. Wilson, C. L. Wu,
S. D. Tayabji. 1994. Guidelines for Timing
Contraction Joint Sawing and Earliest Loading
for Concrete Pavements, Volume 1: Final
Report. FHWA RD-91-079. Washington,
DC: Federal Highway Administration.
Portland Cement Association. 1984. ickness
Design for Concrete Highway and Street
Pavements. Skokie, IL: Portland Cement
Association.
Raphael, J. M. 1984. Tensile Strength of
Concrete. ACI Journal 163:158–165.
Rasmussen, R. O., and S. I. Garber. 2009.
Nonwoven Geotextile Interlayers for Separating
Cementitious Pavement Layers: German
Practice and U.S. Field Trials. International
Technology Scanning Program. Washington,
DC: Federal Highway Administration.
Rasmussen, R. O., and D. K. Rozycki.
2004. in and Ultra-in Whitetopping.
NCHRP Synthesis of Highway Practice 338.
Washington, DC: Transportation Research
Board.
Riley, R. 2006. Modified ACPA Ultra-in
Whitetopping Design Software.
Roesler, J., A. Bordelon, A. Ioannides, M.
Beyer, and D. Wang. 2008. Design and
Concrete Materials Requirements for Ultra-
in Whitetopping. Urbana, IL: University of
Illinois at Urbana-Champaign.
Roesler, J. R., V. G. Cervantes, and A. N.
Amirkhanian. 2013. Accelerated Performance
Testing of Concrete Pavement with Short
Slabs. International Journal of Pavement
Engineering, doi:10.1080/10298436.2011.5
75134.
Simon, E., G. E. Gibson, C. T. Haas, J. T.
O’Connor, B. Somali, and Z. Zhang. 2003.
Development of a Tool for Expediting Highway
Construction While Retaining Quality. FHWA/
TX-03/4386-1. Austin, TX: Center for
Transportation Research, University of Texas
at Austin.
Smith, K. D., H. T. Yu, and D. G. Peshkin.
2002. Portland Cement Concrete Overlays:
State of the Technology Synthesis. Publication
FHWA IF-02-045. Washington, DC: Federal
Highway Administration.
Smith, K. D., T. E. Hoerner, and D. G.
Peshkin. 2008 (draft). Concrete Pavement
Preservation Reference Manual. Ames, IA:
National Concrete Pavement Technology
Center, Iowa State University.
143
Guide to Concrete Overlays
SOURCES
Snyder, M. B. 2011. Guide to Dowel Load
Transfer Systems for Jointed Concrete Roadway
Pavements. Ames, IA: National Concrete
Pavement Technology Center, Iowa State
University.
Sutter, l., K. Peterson, G. Julio-Betancourt,
D. Hooton, T. Van Dam, and K. Smith.
2008. e Deleterious Chemical Effects of
Concentrated Deicing Solutions on Portland
Cement Concrete, Final Report. Publication
SD2002-01-F. Pierre, SD: South Dakota
Department of Transportation.
Tayabji, S., J. Anderson, H. Barzegar, G.
Fick, E. Gowder, J. Shilstone, P. C. Taylor,
and M. Torres. 2007. Supplemental Report
for Proposed Specification for Construction of
Concrete Airfield Pavement. Report IPRF-01-
G-002-04-1A. Washington, DC: Innovative
Pavement Research Foundation.
Taylor, P. C., ed. 2006. Integrated Materials
and Construction Practices for Concrete
Pavement: A State-of-the-Practice Manual.
Publication FHWA HIF-07-004. Ames,
IA: Center for Transportation Research and
Education, Iowa State University.
Taylor, P., R. O. Rasmussen, H. Torres, G.
Fick, D. Harrington, and T. Cackler. 2012.
Guide for Optimum Joint Performance of
Concrete Pavements. Ames, IA: National
Concrete Pavement Technology Center, Iowa
State University.
TCPavements. 2010. Optipave V2.0. (www.
tcpavements.com/index.php?op=0&lang=en,
accessed March 10, 2014)
e Transtec Group. No date. Material
Specifications. (www.transtecgroup.com/
nonwoven-geotextile-interlayers-concrete-
pavements/ [search www.concreteontop.com],
accessed February 25, 2014)
omas, M. D. A., B. Fournier, K. J. Folliard,
and Y. A. Resendez. 2011. Alkali-Silica
Reactivity Field Identification Handbook.
FHWA HIF-12-022. Washington, D.C.:
Federal Highway Administration.
Torres, H. N., J. Roesler, R. O. Rasmussen,
and D. Harrington. 2012. Guide to the
Design of Concrete Overlays Using Existing
Methodologies. FHWA Project DTFH61-
06-H-00011 (Work Plan 13). Ames, IA:
National Concrete Pavement Technology
Center, Iowa State University.
Trevino, M., B. F. McCullough, and D. W.
Fowler. 2004. Techniques and Procedures
for Bonded Concrete Overlays. FHWA/
TX-05/0-4398-2. Austin, TX: Center for
Transportation Research, University of Texas
at Austin.
Van Dam, T., P. Taylor, G. Fick, D. Gress, M.
Van Geem, and E. Lorenz. 2012. Sustainable
Concrete Pavements: A Manual of Practice.
Ames, IA: National Concrete Pavement
Technology Center, Iowa State University.
(www.cptechcenter.org/technical-library/
documents/Sustainable_Concrete_
Pavement_508.pdf, accessed March 10, 2014)
Vandenbossche, J. M. and M. Barman. 2010.
Whitetopping Overlay Design Considerations
for the Development of Reflective Cracks
and Joint Sealing. In Transportation Research
Record: Journal of the Transportation Research
Board.
Vandenbossche, J., N. Dufalla, and Z. Li.
2012. A Revised in and Ultra-in Bonded
Whitetopping Design Procedure. Presented at
2013 TRB Annual Meeting.
Vandenbossche, J. 2013. BCOA ME.
Swanson School of Engineering, University
of Pittsburgh. (www.engineering.pitt.edu/
Vandenbossche/BCOA-ME_DesignGuide/,
accessed March 10, 2014)
Wade, M. J., G. D. Cuttell, J. M.
Vandenbossche, K. D. Smith, M. B. Snyder,
and H. T. Yu. 1995. Performance of Concrete
Pavements Containing Recycled Concrete
Aggregate. Report No. DTFH61-93-C-
000133-Task B. Interim Report. Washington,
DC: Federal Highway Administration.
Walker, W. W. and J. A. Holland. 2007.
Performance-Based Dowel Design: Lift-truck
design changes require a new look at joint
durability. In Concrete Construction Jan. 2007.
Yurdakul, E. 2010. Optimizing concrete
mixtures with minimum cement content for per-
formance and sustainability. MS esis. Ames,
IA: Iowa State University.
Guide to Concrete Overlays
144
SOURCES
SOURCES
BIBLIOGRAPHY
AASHTO. 1993. Guide Specifications for
Highway Construction. Washington, DC:
American Association of State Highway and
Transportation Officials.
———. 2002. Guide for Design of New and
Established Pavement Structures. Washington,
DC: Transportation Research Board.
American Concrete Pavement Association
(ACPA). 2000. Repair of Ultra-in
Whitetopping: Roadways and Airfields.
Publication PA397P. Skokie, IL: American
Concrete Pavement Association.
———. 2006. Concrete Pavement Field
Reference: Preservation and Repair. Publication
EB 239 P. Skokie, IL: American Concrete
Pavement Association.
———. 2007. Subgrades and Subbases for
Concrete Pavements. EB204P. Skokie, IL:
American Concrete Pavement Association.
———. 1999. Ultra-in Whitetopping.
Information Series IS100.02P. Skokie, IL:
American Concrete Pavement Association.
———. 2007. Concrete Intersections: A Guide
for Design and Construction. TB019P. Skokie,
IL: American Concrete Pavement Association.
———. 2008. Concrete Pavement Field
Reference: Pre-Paving. EB237P. Skokie, IL:
American Concrete Pavement Association.
Altoubat, S. A., J. R. Roesler, D. A. Lange,
and K.-A. Rieder. 2008. Simplified Method
for Concrete Pavement Design with Discrete
Structural Fibers. Construction and Building
Materials 22 (3): 384–393.
Anderson, S. D., G. L. Ullman, and B.
C. Blaschke. 2002. A Process for Selecting
Strategies for Rehabilitation of Rigid Pavements.
NCHRP Project 10-50A. Washington, DC:
Transportation Research Board.
Cable, J. K., M. L. Anthony, F. S. Fanous, and
B. M. Phares. 2006. Evaluation of Composite
Pavement Unbonded Overlays. IHRB Project
TR-478. Ames, IA: Iowa State University.
Cable, J. K., L. E. Edgar, and D. R.
Anderson. 2005. Ultra-in Portland Cement
Concrete Overlay Extended Evaluation. IHRB
Project TR-432. Ames, IA: Iowa State
University.
Cable, J. K., F. S. Fanous, H. Ceylan, D.
Wood, D. Frentress, T. Tabbert, S.-Y. Oh,
and K. Gopalakrishnan. 2005. Design and
Construction Procedures for Concrete Overlay
and Widening of Existing Pavements. IHRB
Project TR-511. Ames, IA: Iowa State
University.
Cable, J. K., J. M. Hart, and T. J. Ciha.
2001. in Bonded Overlay Evaluation.
IHRB Project HR-559. Ames, IA: Iowa State
University.
Delatte, N., S. Chen, J. Davidson, A.
Sehdev, N. Amer, and M. Endfinger. 2001.
Design and Quality Control of Concrete
Overlays. UTCA Report 01220. Tuscaloosa,
AL: University Transportation Center for
Alabama.
ERES Consultants. 1999. Evaluation of
Unbonded Portland Cement Concrete Overlays.
NCHRP Report 415. Washington, DC:
Transportation Research Board.
Federal Highway Administration (FHWA).
1992. Drainable Pavement Systems, Participant
Notebook. FHWA-SA-92-008. Washington,
DC: Federal Highway Administration.
———. 1999. Pavement Preventive
Maintenance Reference Manual. Washington,
DC: Federal Highway Administration.
———. 2000. Insights into Pavement
Preservation: A Compendium. Washington,
DC: Federal Highway Administration.
———. 2001a. Pavement Preservation:
Selecting Pavements for Preventive Maintenance.
NHI Course 131058. Washington, DC:
Federal Highway Administration.
———. 2001b. PCC Pavement Evaluation
and Rehabilitation. NHI Course 131062.
Washington, DC: Federal Highway
Administration.
———. 2004. Pavement Preservation:
Integrating Pavement Preservation Practices
and Pavement Management. NHI Course
131104. Washington, DC: Federal Highway
Administration.
———. 2007. in Whitetopping—e
Colorado Experience. FHWA-HIF-07-025.
Washington, DC: Federal Highway
Administration.
———. 2012. Alkali-Silica Reactivity Field
Identification Handbook. FHWA-HIF-12-022.
Washington, DC: Federal Highway
Administration.
Mack, J. W., L. D. Hawbaker, and L. W.
Cole. 1998. Ultrathin Whitetopping: State-
of-the-Practice for in Concrete Overlays
of Asphalt. Transportation Research Record
1610:39–43.
Mathis, D. M. 1990. Pavement Drainage
Rehabilitation. Proceedings, Virginia Pavement
Drainage Workshop. Williamsburg, VA:
Virginia Department of Transportation.
McGhee, K. H. 1994. Portland Cement
Concrete Resurfacing. NCHRP Synthesis of
Highway Practice 204. Washington, DC:
Transportation Research Board.
National Cooperative Highway Research
Program (NCHRP). 2005. Versions
0.900 and 1.0 of the M-E Pavement
Design Software. NCHRP Project 1-40A.
Washington, DC: Transportation Research
Board.
———. 2006. Technical Assistance to
NCHRP and NCHRP Project 1-40a.
NCHRP Project 1-40d. Washington, DC:
Transportation Research Board.
———. 2007. AASHTO Mechanistic-
Empirical Design Guide. Version 1.0.
NCHRP Project 1-37a. Washington, DC:
Transportation Research Board.
Rasmussen, R. O. 2008. Geotextile Interlayers
for Separating Cementitious Pavement
Layers: European Practice and U.S. Field
Trials. Washington, DC: Federal Highway
Administration and Transtec Group, Inc.
Riley, R. C., A. Gotlif, and J. Mallela. 2005a.
Whitetopping: Atypical is Typical. Proceedings
of the International Conference on Best Practices
for Ultrathin and in Whitetoppings. Denver,
CO, April 12–15.
Riley, R. C., L. Titus-Glover, J. Mallela,
S. Waalkes, and M. Darter. 2005b.
Incorporation of Probabilistic Concepts into
Fatigue Analysis of Ultrathin Whitetopping
as Developed for the American Concrete
Pavement Association. Proceedings of the
International Conference on Best Practices for
Ultrathin and in Whitetoppings. Denver,
CO, April 12–15.
145
Guide to Concrete Overlays
SOURCES
Roesler, J. R. 2004. Fracture of Plain and
Fiber-reinforced Concrete Slabs under
Monotonic Loading. Journal of Materials in
Civil Engineering 16 (5): 452–460.
Roesler, J. R. 2007. Design and Specification
of Concrete Pavements with Structural
Fibers. Paper presented at the International
Workshop on Best Practices for Concrete
Pavements, Recife, Brazil.
Sheehan, M. J., S. M. Tarr, and S. D. Tayabji.
2004. Instrumentation and Field Testing of
in Whitetopping Pavements in Colorado
and Revision of the Existing Colorado in
Whitetopping Procedure. Report CDOT-
DTD-R-2004-12. Denver, CO: Colorado
Department of Transportation.
Tarr, S. M., M. J. Sheehan, and P. A.
Okamoto. 1998. Guidelines for the ickness
Design of Bonded Whitetopping Pavements
in the State of Colorado. Report CDOT-
DTD-R-98-10. Denver, CO: Colorado
Department of Transportation.
Titus-Glover, L., J. Mallela, M. I. Darter,
G. Voigt, and S. Waalkes. 2005. Enhanced
Portland Cement Concrete Fatigue Model
for StreetPave: Rigid and Flexible Pavement
Design 2005. Transportation Research Record
1919:29–37.
Vandenbossche, J. M., and A. J. Fagerness.
2002. Performance, Analysis, and Repair
of Ultrathin and in Whitetopping
at Minnesota Road Research Facility.
Transportation Research Record 1809:191–198.
VDOT. 1990. Guidelines for Providing
Improved Drainage Systems for VDOT
Pavement Structures. Charlottesville, VA:
Virginia Department of Transportation.
Winkelman, T. J. 2002. Bonded Concrete
Overlay Performance in Illinois. Report
FHWA/IL/PRR 143. Springfield, IL: Illinois
Department of Transportation.
Wu, C.-L., S. M. Tarr, T. M. Refai, M. A.
Nagi, and M. J. Sheehan. 1999. Development
of Ultra-in Whitetopping Design Procedure.
PCA R&D Serial 2124. Skokie, IL: Portland
Cement Association.
Wells, G. K., and S. M. Wiley. 1987. e
Effectiveness of Portland Cement Concrete
Pavement Rehabilitation Techniques. FHWA/
CA/TL-87/10. Washington, DC: Federal
Highway Administration.
Young, B. 1990. Evaluation of the
Performance of Fin Drains in Georgia.
FHWA-GA-90-8709. Atlanta, GA: Georgia
Department of Transportation.
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