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Advances in Civil
Engineering Materials
S. T. Swarna,
1
K. S. Reddy,
2
M. A. Reddy,
2
and B. B. Pandey
2
DOI: 10.1520/ACEM20170028
Analysis of Stresses Due to Traffic
and Thermal Loads in Two-Lift
Bonded Concrete Pavements by
Finite Element Method
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S. T. Swarna,
1
K. S. Reddy,
2
M. A. Reddy,
2
and B. B. Pandey
2
Analysis of Stresses Due to Traffic and
Thermal Loads in Two-Lift Bonded
Concrete Pavements by Finite Element
Method
Reference
Swarna, S. T., Reddy, K. S., Reddy, M. A., and Pandey, B. B., “Analysis of Stresses Due to Traffic
and Thermal Loads in Two-Lift Bonded Concrete Pavements by Finite Element Method,”
Advances in Civil Engineering Materials https://doi.org/10.1520/
ACEM20170028. ISSN 2379-1357
ABSTRACT
The current practice in the construction of jointed plain concrete pavements in
India is to lay paving quality concrete (PQC) over roller-compacted concrete
designated as dry lean concrete (DLC). A 125-μm plastic sheet is placed as a
bond-breaking layer at the interface of the DLC and PQC. By placing the PQC layer
directly over fresh lean concrete (LC), the two layers will bond without any extra
bond-breaking layers, and there may be a considerable reduction in PQC thickness.
Reducing the PQC layer thickness decreases the amount of aggregates used,
which helps preserve quality aggregates that are rapidly depleting. Pavements in
which the PQC is laid directly over LC can be designated as a two-lift concrete
pavement (TLCP). Joints must be provided with deep saw cuts to avoid random
cracking. The LC can be made up of recycled concrete or marginal aggregates to
obtain a sustainable pavement. However, readymade analytical solutions are not
available for the computation of stresses in two-lift bonded concrete layers for
pavement design. This article presents a three-dimensional finite element solution
for stresses in bonded concrete pavements. Stresses in both layers are presented
in order to arrive at an optimum thickness combination so that both layers are safe
during the design life. Stress computation is done for the conditions of
simultaneous application of temperature gradients and axle loads. The cracking of
the LC layer because of high flexural stresses at the bottom is found to be the
critical factor in the design of TLCP.
Manuscript received March 15,
2017; accepted for publication
September 18, 2017; published
online April 16, 2018.
1
Department of Civil Engineering,
Indian Institute of Technology
Kharagpur, West Bengal 721302,
India (Corresponding author),
e-mail: ssurya.547@gmail.com,
https://orcid.org/0000-0003-
0406-6675
2
Department of Civil Engineering,
Indian Institute of Technology
Kharagpur, West Bengal 721302,
India, https://orcid.org/0000-
0002-2388-860X (K.S.R.)
Advances in Civil Engineering Materials
Copyright © 2018 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959
doi:10.1520/ACEM20170028 available online at www.astm.org
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Keywords
finite element analysis, two-lift concrete pavements, lean concrete, pavement quality concrete,
temperature gradient
Introduction
The conventional construction approach for concrete pavements in India is to lay high-
strength concrete in a single lift over a roller-compacted concrete (RCC) with a 0.125-mm-
thick plastic sheet at the interface to eliminate the possibility of any reflection cracking in
the pavement slab. The pavement slab and RCC require a lot of quality aggregates, which
are depleting at a rapid rate. The pavement design professionals can have an alternate
option of a two-lift construction, in which the pavement slab is bonded to the lean concrete
(LC) base. One great advantage of such construction is the use of recycled and low-
strength aggregates in LC.
A bonded concrete pavement, also known as two-lift concrete pavement (TLCP) in-
volves placing two lifts of concrete “wet-on-wet”rather than using the traditional method
of a single layer of quality concrete over RCC with a bond-breaking layer. TLCP consists of
an upper Plain Cement Concrete
(+)
(PCC) laid over a lower PCC
(−)
(LC). The PCC
(−)
is
generally thicker and may consist of recycled aggregates or local aggregates that are not
suitable for use in surface courses exposed to the abrasive action of traffic. The bottom
layer can also be “econocrete,”which is a concrete mix designed to use local aggregates that
do not necessarily confine to conventional standards. TLCP is more economical because
it makes use of marginal aggregates, recycled concrete aggregates (RCA), and reclaimed
asphalt pavement (RAP) and enables the TLCP to be a sustainable solution in road
infrastructure.
The construction of TLCP requires two batching plants (one is for preparing the
PCC
(+)
mix and the other for PCC
(−)
), and two pavers are needed to lay the PCC
(+)
and, subsequently, the PCC
(−)
, one after the other. TLCP can be constructed with or
without concrete or asphalt shoulders. A two-lift bonded concrete pavement was first built
in the year 1914 in San Antonio, Texas, as shown in Fig. 1. A core taken from the same
pavement with good quality aggregates in the upper lift over softer aggregates in the lower
portion is shown in Fig. 2. Unlike jointed and continuously reinforced cement concrete
pavements, an analytical study on TLCP is limited.
Westergaard made a pioneering contribution [1–3] in the computation of the stresses
in concrete pavements due to load and temperature variation when considering the sub-
grade as a Winkler foundation. Teller and Sutherland [4] carried out extensive field tests in
Arlington, USA to experimentally determine the stresses in concrete pavements caused by
load, temperature, and moisture variation. The pioneering basic approach given by
Westergaard and Teller and Sutherland formed the basis of future development in the
analysis and design of concrete pavements.
The concept of equivalent flexural stiffness has been used by Huang [5] for the analy-
sis of stresses in a TLCP. If a polyethylene sheet is placed between PQC and LC layers, as
per the practice in India, the strain variation with depth will occur, as shown in Fig. 3. The
thickness of layers is so determined that stresses in each layer are below certain limits. This
approach requires a thicker layer for both materials. If bonding between the surface layer
and LC subbase is established, the monolithic action will result in reduced stress in the
pavement layers where the strain variation of monolithic pavements is shown in Fig. 4.
SWARNA ET AL. ON TWO-LIFT CONCRETE PAVEMENTS
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FIG. 2
Core taken from the TLCP.
FIG. 1
A view of a 102-year-old
bonded concrete pavement in
San Antonio, TX.
SWARNA ET AL. ON TWO-LIFT CONCRETE PAVEMENTS
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A three-dimensional (3-D) finite element (FE) model was developed by Mackiewicz
[6–8] for the analysis of concrete pavements with different dowel bar diameters, dowel
spacing, and temperature gradients. A relation was developed for the compressive stress
in concrete below the dowel that considers dowel diameter and load transfer efficiency to
determine the interaction between dowel and pavement. Detrimental tensile stresses
caused by small-diameter dowel bars in concrete slabs were also determined in the sides
of the dowels as a function of dowel diameter, spacing, and dowel length. Nishizawa et al.
[9] investigated the effects of transverse joint structure on the stresses in dowel bars and
concrete slabs using numerical simulations with PAVE3D (Fugro Roadware, Mississauga,
Ontario, Canada) and concluded that the geometry and spacing of dowel bars have a great
effect on the stress in dowel bars but also that the stresses are relatively lower. Increasing
the strength of subbase layers will decrease the stresses in both the dowel bars and concrete
slab. An ANSYS FEA model (SimuTech Group, Rochester, NY) of bonded concrete pave-
ments was analyzed by Surya Teja et al. [10], to find the interface stresses between PQC
and LC.
Greene, Nazef., and Choubane [11] built three test sections and evaluated the perfor-
mance of pavements with a lower layer of econocrete made of locally available aggregates,
RCA, and RAP. It was found that there was no significant difference among the subsections
with different econocrete. It is thus established that TLCP is a sustainable alternative with
high durability. The top lift concrete has to be of good quality because it is the factor that
is directly responsible for providing higher durability, better skid resistance, and bonding
between the layers. Bentsen et al. [12] concluded that the lower lift of econocrete can
encourage the reduction of pavement costs; thus, the TLCP has the potential for practical
application. The two major benefits of TLCP as observed by Taylor [13] are (i) lower
impact on the environment and (ii) much lower maintenance cost, even though initial
construction costs may be a little higher than those of conventional concrete pavements.
The large-scale slab capacity tests by Brand, Amirkhanian, and Roesler [14] demon-
strated that the recycled aggregate concretes had similar or slightly higher flexural load
FIG. 3
Strain variations in concrete
pavement over DLC with a
plastic sheet at the interface.
FIG. 4
Monolithic action of upper and
lower lift.
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capacities relative to those with virgin aggregate concrete. Rao et al. [15] carried out a field
performance study and reported that TLCP pavement was cheaper than single-lift conven-
tional concrete pavement for equal performance. Thus, it was found to be a significant
improvement in sustainability with respect to material and design practices.
Several full-scale demonstration projects (Cable, Frentress, and Williams [16]; and
Hu, Siddiqui, and David Whitney [17]) reported that two-lift construction can be very
cost effective and has similar performance values as conventional concrete pavements.
Review of work by different authors clearly indicates that TLCP can give an equally
good performance as that of single-lift concrete pavement at a reduced cost because of
lower thickness requirement. Flexural stresses both in the top and bottom layers should
be within certain limits so that pavement has good serviceability during the design period.
Dowel bars may have to be provided even in two-lift construction where heavy traffic
conditions might occur. Readymade solutions for flexural stresses in different layers of
TLCP are not available. This article presents the results of the analysis of stresses in
TLCP considering both axle load and temperature gradient applied simultaneously to sim-
ulate field conditions. The effect of partial bonding of the two layers, as indicated by differ-
ent values of the coefficient of friction between the layers, is also presented.
Research Contribution
This article presents an analysis of stresses in TLCPs with various conditions of interface
bonding. It is clearly illustrated how stresses and strains vary in both the layers with change
in the coefficient of friction, which represents the degree of bonding from zero (smooth
surface) to 20 (partially bonded surface). It also illustrates the magnitude of stress in both
upper and lower layers of the bonded concrete pavements due to the simultaneous action
of axle load and temperature gradients for the varying values of the modulus of subgrade
reaction. No guidelines are available for TLCPs under these conditions.
Model Using the FE Method
An FE software package, ANSYS 15, was used for the analysis of TLCPs. In ANSYS 15, the
full-scale model consisted of TLCP layers that were 4.5 m in length, 3.5 m in width with
varying thicknesses of 0.15, 0.20, and 0.25 m. For this slab, meshing was done with an
element size of 0.08 by 0.08 by 0.05 m and defined by SOLID185 (an eight-node brick).
These elements are versatile in modeling simple linear and complex nonlinear analysis
involving contact and deformations. Mechanical properties of the material considered
for both PQC and LC are shown in Table 1. Linear discrete spring elements
COMBIN14 measuring 0.2 m deep were attached to PCC
(−)
at the nodes created in
TABLE 1
Input parameters considered for analysis.
Properties Upper Lift (PQC) Lower Lift (LC)
Modulus of Elasticity 30,000 MPa 15,000 MPa
Poisson’s ratio 0.15 0.25
Coefficient of thermal expansion 10
−5
/°C 10
−5
/°C
Reference Temperature 35°C 35°C
Density 2,400 kg/m
3
2,000 kg/m
3
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the mesh, which functioned as a Winkler foundation. To these springs, a stiffness con-
stant kwas assigned, which represented the modulus of subgrade reaction, as shown
in Fig. 5.
In a two-lift construction, the interfacial bonding may weaken during traffic load,
a difference in thermal expansions of the two layers, and curling due to temperature
gradient. So, the effect of the reduction in bond strength was also modeled by assigning
different coefficients of friction at the interface. CONTA174 was used to represent contact
and sliding between 3-D target surfaces and a deformable surface defined by this element.
The element is applicable to 3-D structural and coupled-field contact analyses. It can be
used for both pair-based contact and general contact. Between the bottom of the PCC
(+)
and top of the PCC
(−)
layers, a surface-to-surface contact element CONTA174 was
created.
The CONTA174 contact element was used to assign different coefficients of friction
to model the pavement for change in bonding strength. It was observed that by changing
the coefficient of friction between the two layers, the stress and strain throughout the depth
of the slab varies. A range of coefficients of friction from 0 to 20 was selected based on the
literature, as shown in Table 2.
FIG. 5
FE model of TLCP system.
TABLE 2
Theoretically computed coefficient of friction for different interface conditions.
Researcher Top Layer Bottom Layer Interface Layer Coefficient of Friction (μ)
[18] Concrete Slab Damp Sand Tar paper 1.30
Concrete Slab WBM Tar paper 2.40
Concrete Slab Dump Sand No interface 1.30
Concrete Slab Saturated WBM No interface 7.80
Concrete Slab Dry WBM No interface 10.40
[19] Concrete Slab DLC Plastic Sheet 1.20
Concrete Slab DLC No interface 20.00
[20] Concrete Slab WMM Smooth (Initial Cycles) 0.79–1.26
Concrete Slab WMM Smooth (Subsequent Cycle) 0.35–0.77
Concrete Slab WMM Rough (Initial Cycles) 3.16–3.56
Concrete Slab WMM Rough (Subsequent Cycle) 0.82–0.87
Concrete Slab DLC Smooth (Initial Cycles) 1.05–1.87
Concrete Slab DLC Smooth (Subsequent Cycle) 0.46–0.77
Concrete Slab DLC Rough (Initial Cycles) >20.00
Note: WBM =Water Bound Macadam; WMM =Wet Mix Macadam; DLC =Dry Lean Concrete.
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Two cases of loading conditions were considered for the analysis of two-lift bonded
concrete pavements. The first case considers day hours when the axle load and the temper-
ature gradients are applied across the upper and lower concrete layers at the same time, as
shown in Fig. 6. Another loading condition was in the night hours when the pavement
slab curls up because of the negative temperature gradient with axle load configuration, as
shown in Fig. 7.
NONLINEAR TEMPERATURE ANALYSIS
Temperature variations in a large number of concrete slabs were measured by
Subramanian [18], and one set of data for a 203.2-mm-thick concrete slab is shown
FIG. 6
Daytime loading condition.
FIG. 7
Nighttime loading condition.
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in Fig. 8.Table 3 shows temperature measurements made at the surface, the quarter
depth, the middepth, the three-quarter depth, and at the bottom of the 203.2-mm-thick
slab at different hours. The temperature variation across the depth of the pavement
slab was closer to a parabola, which was approximated by two straight lines across the
depth, as shown in Fig. 9, where Δis the temperature difference between the middepth
of the top layer and the bottom of the top layer. The difference in temperatures between
the top surface and the middepth was found to be about twice that of the difference
between the middepth and the bottom surface in most cases. The nighttime temperature
differential was almost half of the daytime temperature differential with linear variation
across the full depth. These thermal loads were applied on nodes of the FE model.
Preliminary analysis indicated that the stresses in the top fiber of the upper lift are
higher during nighttime because of a negative temperature gradient compared to the
stresses in the bottom fiber of the lower lift; the reverse is the case during the daytime,
indicating the correct trend of the analytical procedure.
-210
-180
-150
-120
-90
-60
-30
0
25 27 29 31 33 35 37 39 41 43 45 47
Depth of Slab (mm)
Temperature (°C)
12:00 AM 4:00 AM 8:00 AM 11:00 AM
*1 PM 4:00 PM 8:00 PM
FIG. 8
Temperature distribution in an
existing concrete pavement
from field data.
TABLE 3
Temperature distribution in an existing concrete pavement from field data.
Temperature (°C) at depth (mm)
Time 0 −50.8 −101.6 −152.4 −203.2
12:00 a.m. 28.5 30.2 31.9 33 33.5
4:00 a.m. 26.1 27.5 28.5 29.5 30.5
8:00 a.m. 29.2 27 26 26.3 27.5
11:00 a.m. 43 37 34 32.4 31
1:00 p.m. 47 42 39.2 37 34.2
4:00 p.m. 42 41 40.5 39 37.8
8:00 p.m. 32 33.5 35.3 36 35.9
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TIRE PRESSURE AND TIRE IMPRINTS
The contact pressure is considered equal to the tire pressure and is assumed to be uniform
over the tire imprint area. In one of the research studies conducted at IIT Kharagpur, it was
found that the tire imprint of commercial vehicles with tire pressure between 0.70 and
1.30 MPa is close to a rectangle. Hence, an equivalent rectangular contact area with di-
mensions of 240 by 160 mm was considered for each wheel and kept constant for all the
loads. The effect of tire pressure on flexural stresses is marginal in concrete pavements. The
relation between pressure and geometry of the imprint is as shown in Fig. 10.
High axle loads much greater than the legal limits are very common in India, and
loads of magnitudes 120, 160, and 200 kN are considered for the present stress analysis.
Temperature differentials of 0°C, 9°C, 15°C, and 21°C were used in the analysis to cover all
regions of India. Ranges of variables considered for daytime loading conditions are shown
in Table 4, and the ranges of input parameters for nighttime loading conditions are given
in Table 5.
The coefficient of friction between the pavement concrete slab and different types
of subbases indicated values in a range from about 0.5 to about 20 from the push-off
FIG. 9
Nonlinear temperature
distribution over depth of slab.
FIG. 10
Tire imprints and calculation of
tire contact area.
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tests [19,20]. By reducing the bonding from 20 to 0 between two lifts, which was indi-
cated by the coefficient of friction, there was an increase in stresses and strains at the
interface, as shown in Figs. 11 and 12. The rough interface between layers actuates the
monolithic action and the slab-foundation system experiences significantly lower
stresses.
Results and Analyses
A temperature differential of 21°C found in some parts of India caused the highest stresses.
A plot of flexural stress versus a modulus of subgrade reaction for lower-lift thicknesses of
150, 200, and 250 mm is very useful for the design of TLCP. A model was also developed in
TABLE 4
Range of parameters considered for daytime loading case.
Transverse Bottom-Up Cracking Daytime Nonlinear Temperature Gradient
Thickness for PCC
(+)
(mm) Thickness for PCC
(−)
(mm) Axle Load (kN) Temperature Differential (°C) Modulus of Subgrade Reaction (MPa/m)
150, 200, and 250 150, 200, and 250 120, 160, and 200 0, 9, 15, and 21 25, 50, 75, and 100
Total Number of Models =4by3by3by3=108 Models
TABLE 5
Range of parameters considered for night time loading case.
Transverse Top-Down Cracking Nighttime Linear Temperature Gradient
Thickness for PCC
(+)
(mm) Thickness for PCC
(−)
(mm) Axle Load (kN) Temperature Differential (°C) Modulus of Subgrade Reaction (MPa/m)
150, 200, and 250 150, 200, and 250 120, 160, and 200 0, 8, 12, and 15 25, 50, 75, and 100
Total Number of Models =4by3by3by3=108 Models
FIG. 11 Stress variation due to changes in coefficient of friction.
0
50
100
150
200
250
300
350
400
450
-4.0 -3.0 -2 .0 -1.0 0.0 1.0 2. 0 3.0 4.0
Depth of Slab (mm)
Flexural Stress (Mpa)
Depth of Slab vs Stress Variation
cof = 0.0
cof = 0.2
cof = 0.5
cof = 1.0
cof = 2.0
cof = 5.0
cof = 10.0
cof = 20.0
Bond ed
PCC (+)
PCC (-)
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FIG. 12 Strain variation due to changes in coefficient of friction.
0
50
100
150
200
250
300
350
400
450
-1.5 -1 .0 -0.5 0.0 0.5 1.0 1 .5
Depth of Slab (mm)
Elastic Strain x 10-4
Depth of slab vs Strain variation
cof = 0.0
cof = 0.2
cof = 0.5
cof = 1.0
cof = 2.0
cof = 5.0
cof = 10.0
cof = 20.0
Bonded
PCC (+)
PCC (-)
FIG. 13 k-value versus flexural stress in PCC
(+)
for 21°C temperature differential for (a) PCC
(+)
of 150 mm and PCC
(−)
of 150 mm,
(b) 200 mm, (c) and 250 mm.
1.3
1.4
1.5
1.6
1.7
1.8
1.9
0 20406080100120
Flexural Stress in PCC (+) (MPa)
Modulus of Subgrade Reaction, K (MPa/m)
PCC
(+)
= 150 mm/PCC
(-)
= 150 mm @ 21ºC
Temperature Differential
120 kN 160 kN 200 kN
(a)
1.05
1.1
1.15
1.2
1.25
1.3
1.35
0 20406080100120
Flexural Stress in PCC (+) (MPa)
Modulus of Subgrade Reaction, K (MPa/m)
PCC
(+)
= 150 mm/PCC
(-)
= 200 mm @ 21ºC
Temperature Differential
120 kN 160 kN 200 kN
(b)
1
1.02
1.04
1.06
1.08
1.1
1.12
1.14
1.16
0 20 40 60 80 100 120
Flexural Stress in PCC (+) (MPa)
Modulus of Subgrade Reaction, K (MPa/m)
PCC
(+)
= 150 mm/PCC
(-)
= 250 mm @ 21ºC
Temperature Differential
120 kN 160 kN 200 kN
(c)
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order to understand the behavior of TLCP in terms of the variation in flexural stress and
elastic strain within individual lifts.
Tensile flexural stresses at the bottom of the top layer and compressive flexural
stress at the top of the bottom layer in the vicinity of the interface are shown in
Fig. 11. These stresses are relatively lower than those cases of partially bonded to un-
bonded surfaces. A similar trend was observed for elastic strain in both PCC
(+)
and
PCC
(−)
in Fig. 12. It can also be seen that the strain at the top of PCC
(−)
and that
at the bottom of PCC
(+)
are nearly equal to a coefficient of friction value of 20, which
was not the case in the unbonded layers case. The slopes of the strain curves along the
depth are different in the two layers, which is caused by the difference in material prop-
erty of the TLCP.
Fig. 13a indicates that, with a constant temperature differential of 21°C applied to
the 150-mm-thick top concrete layer resting over 150 mm for the bottom layer, the
flexural stresses in the top layer will increase with the increase in the modulus of sub-
grade reaction. When the lower lift thickness is increased to 200 mm, there is negligible
effect on stresses for higher values of k,asshowninFig. 13b. The stresses decrease with
higher values of kwhen the thickness of the lower lift is further increased to 250 mm for
the same temperature gradient because of the lowering of neutral axis from the upper lift
to the lower lift.
FIG. 14 k-value versus flexural stress in PCC
(−)
at 21°C temperature differential for (a) PCC
(+)
of 150 mm and PCC
(−)
of 150 mm,
(b) 200 mm, and (c) 250 mm.
0.65
0.85
1.05
1.25
1.45
1.65
1.85
0 20406080100120
Flexural Stress in PCC (-) (MPa)
Modulus of Subgrade Reaction, K (MPa/m)
PCC (+) = 150 mm/PCC (-) = 250 mm @ 21ºC
Temperature Differential
120 kN 160 kN 200 kN
(c)
1
1.2
1.4
1.6
1.8
2
2.2
2.4
0 20406080100120
Flexural Stress in PCC (-) (MPa)
Modulus of Subgrade Reaction, K (MPa/m)
PCC (+) =150 mm/PCC (-) = 200 mm @ 21ºC
Temperature Differential
120 kN 16 0 kN 200 kN
(b)
1.7
1.9
2.1
2.3
2.5
2.7
2.9
3.1
3.3
0 20 40 60 80 100 120
Flexural Stress in PCC (-) (MPa)
Modulus of Subgrade Reaction, K (MPa/m)
PCC (+) = 150 mm/PCC (-) = 150 mm @ 21ºC
Temperature Differential
120 kN 160 kN 200 kN
(a)
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For a fixed thickness of PCC
(+)
, flexural stresses in the lower lift increase with an
increase in kvalue for all thicknesses of PCC
(−)
for a temperature differential of 21°C, as
shown in Fig. 14a–c, indicating greater curling due to the temperature gradient, which
happens in cases of stiffer foundations
For the 0°C differential, the stresses in both the layers decrease with an increase in k-
values for all load cases, as shown in Fig. 15a. If the temperature differential for the top
layer is 21°C, the stress in both layers increases with an increase in k-values for all load
cases because the load as well as the self-weight of both the layers flatten the curvature, as
shown in Fig. 15d. If the temperature differential increases from 0°C to 21°C, computed
stresses increase with an increase in k-value for different types of loads, as shown in
Fig. 15b and 15c.
The flexural behavior of both the upper and lower layers is similar for different tem-
perature differentials, as shown in Figs. 15 and 16 because of monolithic action.
A computation was performed to estimate fatigue life for a pavement of a given
thickness of 200 and 150 mm of PQC and LC, respectively, considering a modulus
of subgrade reaction of 25 MPa/m. Stress ratios are computed for bonded conditions,
which are presented in this article, and the IRC: 58-2015 [21]methodwasusedforun-
bonded pavements in which the LC base is considered as the Winkler foundation.
Unbonded concrete pavements had a very short life as compared to bonded pavements,
FIG. 15 k-value versus flexural stress in PCC
(−)
at (a) 0°C, (b) 9°C, (c) 15°C, and (d) 21°C temperature differential for PCC
(+)
of 150 mm
and PCC
(−)
of 150 mm.
1.6
1.8
2
2.2
2.4
2.6
2.8
3
0 20 40 60 80 100 120
Flexural Stress in PCC (-) (MPa)
Modulus of Subgrade Reaction, K (MPa/m)
PCC
(+)
= 150 mm/PCC
(-)
= 150 mm @ 15ºC
Temperature Differential
120 kN 160 kN 200 kN
(c)
1.7
1.9
2.1
2.3
2.5
2.7
2.9
3.1
3.3
0 20406080100120
Flexural Stress in PCC (-) (MPa)
Modulus of Subgrade Reaction, K (MPa/m)
PCC
(+)
= 150 mm/PCC
(-)
= 150 mm @ 21ºC
Temperature Differential
120 kN 160 kN 200 kN
(d)
0.8
1
1.2
1.4
1.6
1.8
2
2.2
2.4
2.6
0 20 40 60 80 100 120
Flexural Stress in PCC (-) (MPa)
Modulus of Subgrade Reaction, K (MPa/m)
PCC
(+)
= 150 mm/PCC
(-)
= 150 mm @ 0ºC
Temperature Differential
120 kN 160 kN 200 kN
(a)
1.5
1.7
1.9
2.1
2.3
2.5
2.7
0 20 40 60 80 100 120
Flexural Stress in PCC (-) (MPa)
Modulus of Subgrade Reaction, K (MPa/m)
PCC
(+)
= 150 mm/PCC
(-)
= 150 mm @ 9ºC
Temperature Differential
120 kN 160 kN 200 kN
(b)
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and a much greater thickness of PQC is needed for the unbonded concrete pavements.
It was observed that, at higher temperatures, TLCP pavements perform better when
compared to that of conventional or single-lift concrete pavements as shown in
Tables 6 and 7.
FIG. 16 k-value versus flexural stress in PCC
(+)
at (a) 0°C, (b) 9°C, (c) 15°C, and (d) 21°C temperature differential for PCC
(+)
of 150 mm
and PCC
(−)
of 150 mm.
0.5
0.6
0.7
0.8
0.9
1
1.1
0 20 40 60 80 100 120
Flexural Stress in PCC
(+)
(MPa)
Modulus of Subgrade Reaction, K (MPa/m)
PCC
(+)
= 150 mm/PCC
(-)
= 150 mm @ 0ºC
Temperature Differential
120 kN 16 0 kN 200 kN
(a)
0.8
0.9
1
1.1
1.2
1.3
1.4
0 20 40 60 80 100 120
Flexural Stress in PCC
(+)
(MPa)
Modulus of Subgrade Reaction, K (MPa/m)
PCC
(+)
= 150 mm/PCC
(-)
= 150 mm @ 9ºC
Temperature Differential
120 kN 160 kN 200 kN
(b)
1.3
1.4
1.5
1.6
1.7
1.8
1.9
0 20 40 60 80 100 120
Flexural Stress in PCC
(+)
(MPa)
Modulus of Subgrade Reaction, K (MPa/m)
PCC
(+)
= 150 mm/PCC
(-)
= 150 mm @ 21ºC
Temperature Differential
120 kN 160 kN 200 kN
(d)
1
1.1
1.2
1.3
1.4
1.5
1.6
0 20406080100120
Flexural Stress in PCC
(+)
(MPa)
Modulus of Subgrade Reaction, K (MPa/m)
PCC
(+)
= 150 mm/PCC
(-)
= 150 mm @ 15ºC
Temperature Differential
120 kN 160 kN 200 kN
(c)
TABLE 6
Stress ratio comparison with IRC:58-2015 for PCC
(+)
=200 mm.
Wheel Load, kN
Temperature
Differential, °C
Stresses in TLCP, MPa Critical Stress
Ratio, TLCP
Stresses in Concrete Slab
as per IRC:58, MPa
Critical Stress Ratio
as per IRC:58LC PQC
120 9 1.21 0.91 0.55 2.55 0.58
15 1.27 1.06 0.57 2.75 0.62
21 1.35 1.21 0.61 3.15 0.71
160 9 1.55 1.13 0.70 3.05 0.69
15 1.63 1.28 0.74 3.30 0.75
21 1.71 1.43 0.77 3.75 0.85
200 9 1.91 1.36 0.86 3.65 0.83
15 1.99 1.51 0.90 4.15 0.94
21 2.07 1.66 0.94 4.40 1.00
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Conclusions
•Two-lift constructions can offer an ecofriendly solution for a concrete pavement at a
lower life cycle cost because it provides longer life compared to unbonded concrete
pavements.
•For a fixed thickness of 150 mm of the upper lift with a constant temperature differ-
ential of 21°C, the flexural stresses in the upper lift increase with increment in k
values of the foundation. When the lower lift thickness is increased to 200 mm,
there is no effect on stresses in the upper layer for higher values of kbecause of
the lowered neutral axis. The stresses decrease with higher values of kwhen the
thickness of the lower lift is further increased to 250 mm for the same temperature
gradient because of further lowering of the neutral axis.
•For the lesser thickness of the bottom lift, the stresses are less for the lower modulus of
subgrade reaction (k) because of the higher temperature differential, which increases with
the increase in modulus of the subgrade reaction for similar temperature conditions.
•With an increase in the temperature differential, stresses increased with an incre-
ment in k-value for different loads at lower thickness of PCC
(−)
and vice versa.
•Stresses increase in the top layer with the reduction in bond condition, as indicated
by the coefficient of friction at the interface.
•The analysis presented in this paper can be used for the design of TLCPs.
References
[1] Westergaard, H. M., “Computation of Stresses in Concrete Roads,”Highway Research
Board Proceedings, Highway Research Board, Washington, DC, Vol. 5, Part I, 1926,
pp. 90–112.
[2] Westergaard, H. M., “Stresses in Concrete Pavements Computed by Theoretical
Analysis,”Public Roads, Federal Highway Administration, Washington, DC,
Vol. 7, No. 2, 1926, pp. 25–35.
[3] Westergaard, H. M., “Analysis of Stresses in Concrete Pavement Due to Variations of
Temperature,”Highway Research Board Proceedings, Highway Research Board,
Washington, DC, Vol. 6, 1927, pp. 201–215.
[4] Teller, L. W. and Sutherland, E. C., “The Structure Design of Concrete Pavements,
Part 2: Observed Effects of Variations in Temperature and Moisture on the Size,
Shape, and Stress Resistance of Concrete Pavement Slabs,”Public Roads, Federal
Highway Administration, Washington, DC, Vol. 16, No. 9, 1935, pp. 169–197.
TABLE 7
Stress ratio comparison with IRC 58-2015 for PCC
(+)
=250 mm.
Wheel Loads, kN
Temperature
Differential, °C
Stresses in TLCP, MPa Critical Stress
Ratio, TLCP
Stresses in Concrete Slab
as per IRC 58, MPa
Critical Stress Ratio
as per IRC 58LC PQC
120 9 0.92 0.78 0.42 1.85 0.42
15 0.99 0.88 0.45 2.15 0.49
21 1.06 0.98 0.48 2.35 0.53
160 9 1.19 0.99 0.54 2.45 0.55
15 1.26 1.09 0.57 2.60 0.59
21 1.33 1.19 0.60 2.85 0.64
200 9 1.46 1.20 0.66 2.90 0.66
15 1.53 1.30 0.69 3.15 0.71
21 1.60 1.66 0.72 3.35 0.76
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[5] Huang, Y. H., Pavement Analysis and Design, 2nd ed., Pearson, London, UK, 1993,
791p.
[6] Mackiewicz, P., “Thermal Stress Analysis of Jointed Plane in Concrete Pavements,”
Appl. Therm. Eng., Vol. 73, No. 1, 2014, pp. 1169–1176, https://doi.org/10.1016/
j.applthermaleng.2014.09.006
[7] Mackiewicz, P., “Analysis of Stresses in Concrete Pavement under a Dowel According
to its Diameter and Load Transfer Efficiency,”Can. J. Civ. Eng., Vol. 42, No. 11, 2015,
pp. 845–853, https://doi.org/10.1139/cjce-2014-0110
[8] Mackiewicz, P., “Finite-Element Analysis of Stress Concentration around Dowel
Bars in Jointed Plain Concrete Pavement,”J. Transp. Eng., Vol. 141, No. 6, 2015,
06015001, https://doi.org/10.1061/(ASCE)TE.1943-5436.0000768
[9] Nishizawa, T., Koyanagawa, M., Takeuchi, Y., and Kimura, M., “Study on Mechanical
Behavior of Dowel Bar in Transverse Joint of Concrete Pavement,”presented at the
Seventh International Conference on Concrete Pavements, Orlando, FL, Sept. 9–13,
2001, International Society for Concrete Pavements, East Lansing, MI, Vol. 2,
pp. 571–587.
[10] Surya Teja, S., Reddy, K. S., Reddy, M. A., and Pandey, B. B., “Analysis of Bonded
Concrete Pavements Using 3D FEM,”presented at the Transportation Planning and
Implementation Methodologies for Developing Countries (TPMDC), Mumbai, India,
Dec. 19–21, 2016, Indian Institute of Technology, Bombay, Mumbai, India.
[11] Greene, J., Nazef, A., and Choubane, B., “A 30 Year Performance Evaluation of a
Two-Layer Concrete Pavement System,”Technical Report FL/DOT/SMO/10-540,
Florida Department of Transportation, Gainesville, FL, 2011, pp. 21–29.
[12] Bentsen, R. A., Vavrik, W. A., Roesler, J. R., and Gillen, S. L., “Ternary Blend Concrete
with Reclaimed Asphalt Pavement as an Aggregate in Two-Lift Concrete Pavement,”
presented at the 2013 International Concrete Sustainability Conference, San Francisco,
CA, May 6–8, 2013, Tilt-Up Concrete Association, Mount Vernon, IA, pp. 6–8.
[13] Taylor, P., “Two Lift Paving: An Overview,”Two-Lift Concrete Paving Workshop,
University of Austin, Austin, TX, May 23, 2013.
[14] Brand, A., Amirkhanian, A., and Roesler, J., “Flexural Capacity of Full-Depth and
Two-Lift Concrete Slabs with Recycled Aggregates,”Transp. Res. Rec., Vol. 2456,
2014, pp. 64–72, https://doi.org/10.3141/2456-07
[15] Rao, S. P., Darter, M., Tompkins, D., Vancura, M., Khazanovich, L., Signore, J., Coleri,
E., Wu, R., Harvey, J., and Vandenbossche, J., Composite Pavement Systems, Volume
1: HMA/PCC Composite Pavements, SHRP Report S2-R21-RR-2, Transportation
Research Board, Washington, DC, 2013, 130p.
[16] Cable, J. K., Frentress, D. P., and Williams, J. A., “Two-Lift Portland Cement Concrete
Pavements to Meet Public Needs,”Final Report DTF61-01-X-00042 (Project 8),
Federal Highway Administration, Washington, DC, 2004, pp. 1–14.
[17] Hu, J., Siddiqui, M. S., and David Whitney, P. E., “Two-Lift Concrete Paving—Case
Studies and Reviews from Sustainability, Cost Effectiveness and Construction
Perspectives,”presented at the Transportation Research Board 93rd Annual Meeting,
Washington, DC, Jan. 12–16, 2014, Transportation Research Board, Washington,
DC, pp. 1065–1078.
[18] Subramanian, V. V., 1964, “Investigation on Temperature and Friction Stresses in
Bonded Cement Concrete Pavement,”Ph.D. thesis, Indian Institute of Technology,
Kharagpur, India.
[19] Suh, Y. C., Lee, S. W., and Kang, M. S., “Evaluation of Subbase Friction for Typical
Korean Concrete Pavement,”Transp. Res. Rec., Vol. 1809, 2002, pp. 66–73.
[20] Maitra, S. R., Reddy, K. S., and Ramachandra, L. S., “Experimental Evaluation
of Interface Friction and Study of its Influence on Concrete Pavement Response,”
J. Transp. Eng., Vol. 135, No. 8, 2009, pp. 563–571, https://doi.org/10.1061/
(ASCE)0733-947X(2009)135:8(563)
[21] IRC:58-2015, Guidelines for the Design of Plain Jointed Rigid Pavements for Highways,
Fourth Edition, Indian Road Congress, New Delhi, India, 2015.
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