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Cost and Ecological Feasibility of Using UHPC in Bridge Piers

Authors:
Cost and Ecological Feasibility of Using UHPC in Bridge Piers
Joe and Moustafa 1
Cost and Ecological Feasibility of Using UHPC in
Bridge Piers
Christopher D. Joe
1
, Mohamed A. Moustafa
2
Abstract: There is a growing interest in expanding the use of Ultra-High Performance Concrete
(UHPC) from highway bridge deck joints for accelerated bridge construction to architectural
facades cast in unique and slender profiles. The high costs associated with the proprietary UHPC
mixes, besides the environmental concerns resulting from its high cement content and massive
energy consumption during its production, might limit the widespread use of UHPC in the built
environment. On the other hand, the higher strength and durability of UHPC should result in
more compact cross-sections, safer structures, and a longer service life compared to conventional
concrete. This study investigates several UHPC mix designs to design a multi-column bridge pier
and analyze its cost and ecological feasibility. The objective is to identify what would be the
optimal UHPC mix from an economic and eco-friendly perspective. Ultimately, the study lays
the foundation for future work to find the break-even costs of UHPC at which it would become
economically and environmentally feasible to design substantial bridge substructures entirely
with UHPC in lieu of regular concrete.
Keywords: UHPC, bridge piers, cost study, environmental impact
1. Introduction
Over the past few decades, ultra-high performance concrete (UHPC) has made major advances in
structural applications throughout highway and pedestrian bridges. UHPC has garnered increased
interests for its high strength, ductile behavior, long-term stability, and compactness. Its
particularly low porosity increases the uniformity of its mix and allows the concrete to attain its
extreme properties with a more uniform stress distribution (NPCA, 2014). Another advantage to
its low porosity is UHPC’s superior freeze-thaw durability. When water freezes, it experiences
an approximate 9% increase in volume. When water penetrates the voids of normal strength
concrete and freezes, the sudden increase in volume of water, once frozen, can rupture the voids
causing the concrete to crack. Water penetrating concrete can also become problematic as it can
corrode the reinforcing steel. This makes UHPC a very practical material for highway and
pedestrian bridge designs.
Quality control is a significant factor when it comes to mixing and curing UHPC. Unless a
qualified UHPC specialist is on site to inspect any field casts, most UHPC components
(structural or architectural) are cast under controlled environments by a qualified precast
concrete plant. Curing methods for UHPC vary for different circumstances and relies on two
components, temperature and moisture (FHWA, 2013). Curing UHPC in its early stages in room
temperature water leads to stronger formations of silicate hydrates. To continue this process, a
high temperature cure either through steam or another heat source is applied to accelerate the
silicate hydrate formation (Neville, 1995). Various methods of curing include steam curing at
1
Graduate Student, Department of Civil and Environmental Engineering, University of Nevada, Reno
2
Assistant Professor, Department of Civil and Environmental Engineering, University of Nevada, Reno
Cost and Ecological Feasibility of Using UHPC in Bridge Piers
Joe and Moustafa 2
140oF (60oC) or 194oF (90oC) for 48 hours, 24 hours post-casting, steam curing at 194oF (90oC)
15 days post-casting, and curing at standard, controlled temperatures in a laboratory until
satisfactory results are achieved. A study by Heinz et al. (2012) revealed that storage periods
have an additional contributing factor on top of temperature and time of curing methods.
Specimens immediately cured after setting for eight hours at 194oF (90oC), achieved
compressive strengths greater than 29 ksi (200 MPa) when tested 30 hours post-cure. Other
specimens that were 24 hours old were heat treated for eight hours in an autoclave at 300oF
(148.9oC), cooled down to room temperature within 11 hours, and stored at 68oF (90oC) and 65%
relative humidity until tested. These specimens achieved compressive strengths up to 38 ksi (262
MPa) (Heinz et al. 2012). The reason for elaborating on various curing methods is to emphasize
how UHPC may not be as practical for field casting for highway bridges if a higher compressive
strength is desired. Thus, this study utilizes UHPC mixes with respective mechanical properties
that can be achieved in normal curing conditions, i.e. up to 25 ksi compressive strength rather
than that 38 ksi so that it will be more suitable for field casting. However, it is worth noting that
controlled curing can be beneficial to consider for precast concrete members with increased
quality control and assurance.
On another note, cement production accounted for 9.5% of global carbon dioxide (CO2)
emissions in 2013 (Olivier and Muntean, 2014). These high emissions are caused by a
combination of carbonate oxidation during the cement clinker production process and fuel
combustion during the general cement production within the kiln. Limestone, a primary
component of cement production, is made up of calcium carbonate. When heated to
approximately 2,700oF (1,482 oC), the limestone breaks down into calcium oxide and CO2
contributing to roughly 50% of all CO2 emissions from cement production (Rubenstein, 2012).
Concrete is still the second most consumed substance on Earth next to water and will continually
contribute to the global CO2 emissions. In order to produce a ton of concrete, nearly 400 lb (181
kg) of coal (4.7 million BTU of energy) is required producing nearly one ton of CO2 (UNEP,
2010). According to a survey performed by the Portland Cement Association, nearly 2,044 lb
(927 kg) of CO2 is produced for every 2,205 lb (1,000 kg) of portland cement produced in the
United States (Marceau et al. 2006). This translates to 1 lb (0.45 kg) of CO2 produced for every
1.08 lb (0.49 kg) of portland cement produced. The easiest and simplest way to make an impact
on CO2 emissions within cement production is to follow the golden rule of global warming;
decrease the use of cement. By utilizing UHPC, smaller sections can be designed relative to
conventional concrete, which might require overall less cement, and furthermore decrease
cement demand and production.
The objective of this study is to investigate the monetary and ecological costs of using UHPC
in highway bridge piers in lieu of conventional concrete. Building bridge components entirely
using UHPC can significantly enhance the durability and service life of bridges. However, the
high costs might be a drawback. To help make a better engineering judgment, three different
UHPC mixes are used to redesign a typical California highway bridge pier. The required
concrete and associated cement along with reinforcing steel quantities are calculated and
compared to the conventional concrete case. These quantities are interpreted in terms of costs
and CO2 emissions to assess the feasibility of using UHPC. More details about the prototype
bridge, selected mix designs from literature, analysis, and results are presented in the following
sections.
Cost and Ecological Feasibility of Using UHPC in Bridge Piers
Joe and Moustafa 3
2. Prototype Bridge
This study focuses on redesigning a substructure of a three span highway bridge using UHPC.
The prototype bridge is a typical California reinforced concrete box-girder bridge that is used by
the Caltrans Bridge Academy. The substructure considered for this study is the bridge pier (bent)
that consists of two columns and integral bent cap beam. The UHPC bridge pier is designed in
accordance to the Caltrans Seismic Design Criteria (SDC, 2014) and AASHTO LRFD Bridge
Design Specifications (2012). A typical CA bridge was chosen for this study to involve both
vertical (gravity) and lateral (seismic) design, where UHPC can be beneficial for its exceptional
performance. A summary of the Caltrans Academy bridge specifications is shown in Table 1.
Note that this study considers only redesigning the bents and not the superstructure, i.e. values
such as the width and depth of the concrete box girder are the same, and the only changes are the
bent cap width, column diameter, and reinforcing steel. Thus, the column and bent cap demands
dictated by the superstructure dead and live loads are same as in original design. For the sake of
a simplified study, the analysis is performed on one of the bridge bents only, which is designated
as Bent 2.
To set the stage for the analytical framework adopted in this study, one of the two columns of
the original bent design is presented here as an example to calculate the concrete, cement, and
steel quantities and associated monetary and ecological costs. These quantities are summarized
in Table 2 based on conventional concrete use [f’c = 4.0 ksi (27.6 MPa)]. Note that only CO2
emissions associated with total amount of cement used is considered as environmental impact
(ecological) metric. For quantifying CO2 emissions, one pound of portland cement produces
0.926 lb (0.42 kg) of CO2, which is deduced from statistics by Marceau et al. (2006). There are
other metrics that can be used to assess environmental impact such as the energy consumed
during concrete production and pouring, but these are not included in this study. For the
monetary costs, A rate of $441 per metric ton of reinforcing steel (SteelBenchmarker, 2016) was
used to estimate the steel total cost. For estimating concrete costs, approximate rates reported by
the FHWA (2013) were used for both conventional and UHPC. A rate of $100/yd3 for
conventional concrete was used for estimating the original Caltrans design cost. A rate of
$2000/yd3, which is almost 20 times the cost of conventional concrete, is used for UHPC costs
for the later part of the study.
Table 1. Caltrans Highway Bridge Design Specifications
Superstructure Type
Continuous prestressed reinforced concrete box girder
Substructure Type
Two UHPC columns per bent
Span Lengths
126 ft. (38.4 m.) 168 ft. (51.2 m.) 118 ft. (36.0 m.)
Foundation
Piles
Seismic Design Category
D
Seismic Design Strategy
Type 1
Soil Profile
Type C
Magnitude
8.0 ± 0.25
Peak Rock Acceleration
0.5g
Design Spectral Acceleration (SD1)
0.97g
Latitude and Longitude
37.8800o, -122.522000 o
Cost and Ecological Feasibility of Using UHPC in Bridge Piers
Joe and Moustafa 4
Table 2. Summary of design, monetary and ecological costs of one bridge pier column
Column Diameter
6.0 ft. (1.83 m.)
Column Height
44.0 ft. (13.41 m.)
Compressive Strength (f’c)
4.0 ksi (27.6 MPa)
Modulus of Elasticity of Concrete (Ec)
4,372 ksi (30.0 GPa)
Longitudinal Reinforcement
26 #14 bars
Transverse Reinforcement
#8 hoop at 5 in. (12.7 cm.) c-c
Volume of Concrete
1,244 ft3 (35.2 m3)
Weight of Cement Consumed
12.53 tons (11,371 kg)
Weight of Steel Consumed
4.76 tons (4,323 kg)
Total Cost of Concrete
$4,607
Total Cost of Steel
$2,099
CO2 Produced
11.61 tons (10,529 kg)
3. UHPC Mix Design
Several previous studies developed and tested proprietary and non-proprietary UHPC mixes.
Many of the published mix designs with its respective mechanical properties, such as
compressive strength f’c, vary drastically based on different curing methods, admixtures, types
of silica fume, and steel fibers used. The goal of this study is to choose different UHPC mixes
and utilize them for redesigning the bridge pier based on their respective mechanical properties.
The optimization of the structural design along with the variation in the mix design and
constituents can be a first step towards identifying the most economical and eco-friendly mix
design to create the most efficient multi-column bridge pier. Three mix designs were considered
for this analysis with variable fc and E [Graybeal 2006, Graybeal 2007, Yu et al. 2014, Ritter
and Curbach 2015]. Based on each mix design, the total amount of concrete, cement, and
reinforcing steel utilized in each pier design will be used to calculate total cost per bent and total
CO2 produced. Tables 3 and 4 summarize the three mix designs in detail and their corresponding
mechanical properties, respectively.
Table 3. UHPC Mix Design Summary lb/yd3 (kg/m3)
Mix #2
Mix #3
Cement
1,180 (700)
1,402 (832)
Fine Sand
1,778 (1055)
-
Microsand
369 (219)
-
Ground Quartz
295 (175)
349 (207)
Quartz Sand
-
1,643 (975)
Silica Fume
74 (44)
228 (135)
High Range Water Reducer
77.4 (46)
50 (30)
Accelerator
-
-
Steel Fibers
82 (49)
324 (192)
Water
341 (202)
280 (166)
W/C
0.29
0.20
Source
Yu et al. 2014
Ritter & Curbach, 2015
Cost and Ecological Feasibility of Using UHPC in Bridge Piers
Joe and Moustafa 5
Table 4. UHPC Mechanical Properties Summary
Mix #1
Mix #2
Mix #3
Compressive Strength (f’c), psi (MPa)
17,200 (119)
21,611 (149)
25,240 (174)
Modulus of Elasticity (E), psi (MPa)
6.07E+6 (41851)
6.79E+6 (46815)
7.33E+06 (50,539)
Source
Graybeal, 2007
Yu et al. 2014
Ritter & Curbach, 2015
4. Pier Design
The analytical study presented in this paper involved design the Caltrans Academy bridge pier
(bent cap and 2 columns) using three different UHPC mixes. The new design considered the
actual mechanical properties (compressive strength, tensile strength, and modulus of elasticity)
of the selected UHPC mixes as discussed in previous section. The exceptional mechanical
properties of UHPC are expected to result in more compact cross-sections for the pier columns
and bent cap. Thus, the overall reduction in the required concrete volume can still result in a
substantial reduction in the associated cement and, in turns, CO2 content. The design procedure
is based on the bridge demands calculated and used in Caltrans LRFD Bridge Design (2006)
from the Caltrans Bridge Design Academy. The demands form the superstructure dead and live
loads along with the demands from seismic scenario were used to perform the column checks.
These checks included a demand analysis, displacement capacity using pushover analysis, shear
capacity design, and P-Δ checks. While there are no set design specifications for UHPC columns
in highway bridge design, this study assumed that current design equations are still valid for
UPHC. This exercise aims at demonstrating UHPC’s potential to reduce column cross-sectional
areas, cement consumption, and CO2 production.
A simplified design framework was adopted here which involved: (1) select the column
diameter and reinforcement ratio; (2) perform design checks on column including sectional
analysis to calculate accurate moment capacity and ductility using UHPC properties; (3) compare
capacities versus the demands for the column to satisfy design checks; (4) optimize the design by
reducing the column diameter and/or reinforcement ratio if needed; (5) finalize the bent cap
beam dimensions by using same depth as original design but width equals to new column
diameter plus two feet as required by Caltrans SDC (2013); and (6) perform a capacity design
check for the bent cap beam using new dimensions to finalize required reinforcement if different
from original. This framework was repeated three times for each of the three UHPC mixes. To
perform the sectional analysis for capacity checks, the software XTRACT (Chadwell and
Imbsen, 2004) was used. In addition, SAP2000 was also utilized to perform a simple frame
analysis for the columns and the bent cap. The moment-curvature relationship obtained from
sectional analysis were applied to the pushover analysis for each column section. A sample
moment-curvature relationship as obtained from XTRACT for one of the columns designed
using UHPC mix #3 is shown in Figure 2. The final design and associated monetary and
ecological costs for one column is summarized in Table 5 for original and three UHPC cases. All
calculations are based on the rates previously described in Section 2 for steel and concrete costs
and CO2 emissions.
5. Discussion of Results
By utilizing UHPC in this column design, higher shear capacities can be immediately observed
along with much less axial load. By decreasing the column cross-sectional area, its own weight
decreases and the required bent cap width can decrease resulting in lower dead loads. Increased
Cost and Ecological Feasibility of Using UHPC in Bridge Piers
Joe and Moustafa 6
elastic modulus values for concrete also improved lateral bending stiffness significantly. From
the results summarized in Table 5, we can observe that UHPC can benefit in both cement and
steel consumption and CO2 emissions. Another way of interpreting the results is by estimating
the percentage of change in design parameters and costs with respect to the original design as
summarized in table 6. The designs demonstrate a reduction in cross-sectional area between
33.3% in Mix #1 up to 50% in Mix #3 along with a decrease of total reinforcing steel between
52.8% in Mix #1 up to 72.7% in Mix #3. Most importantly, between 3.5-36.6% of the cement
content was eliminated, effectively decreasing CO2 emissions as high as 36.6%. The main
drawback, which can be expected before hand, is the tremendous increase in concrete monetary
costs (up to 790% increase in cost/column in case of Mix #1 for instance). The objective of this
study was to identify the most feasible mix design for cost and ecological benefits. Mix #1
immediately broke-even with the original design in terms of cement and CO2 content. Mix #3
demonstrated the best properties with the lowest cement content, steel reinforcement, and CO2
emissions. From concrete cost perspective, all UHPC mixes and not feasible. However, the
reduction in the required concrete volume can be up to 75% as in case of Mix #3. Thus,
hypothetically, if UHPC cost is 5 times cheaper than the current $2000/yd3 FHWA estimate, a
cost-benefit can be observed as well. Further cost benefits can be observed if construction time
saving and overall extended service life as considered.
Figure 2. Moment Curvature for column design using UHPC Mix #3
Table 5. UHPC Column Design Summary
Design Per Column
Original Design
Mix #1
Mix #2
Mix #3
Column Diameter [ft (m)]
6.0 (1.83)
4.0 (1.22)
3.5 (1.07)
3.0 (0.91)
Longitudinal Reinforcement
26 #14 bars
22 #10 bars
18 #10 bars
16 #9 bars
Transverse Reinforcement
#8 hoop at 5 in.
#6 hoop at 5 in.
#5 hoop at 5 in.
#5 hoop at 5 in.
Volume of Concrete [ft3 (m3)]
1,244 (35.2)
552.9 (15.7)
423.3 (12.0)
311.0 (8.8)
Weight of Cement [ton (kg)]
12.53 (11,371)
12.09 (10,969)
9.09 (8,250)
7.94 (7,207)
Weight of Steel [ton (kg)]
4.76 (4,323)
2.24 (2,037)
1.82 (1,653)
1.30 (1,181)
Total Cost of Concrete
$4,607
$40,955
$31,355
$23,037
Total Cost of Steel
$1,003
$990
$803
$574
CO2 Produced [ton (kg)]
11.61 (10,529)
11.20 (10,156)
8.42 (7,639)
7.36 (6,673)
Cost and Ecological Feasibility of Using UHPC in Bridge Piers
Joe and Moustafa 7
Table 6. Percentage of change in UHPC design parameter and costs with respect to the original conventional
concrete design
Design Per Column
Mix #1
Mix #2
Mix #3
Column Diameter
33.3%
41.7%
50%
Longitudinal Reinforcement
52.2%
60.9%
72.6%
Transverse Reinforcement
87.3%
92.3%
93.5%
Volume of Concrete
55.5%
65.9%
75%
Weight of Cement Consumed
3.5%
27.4%
36.6%
Weight of Steel Consumed
52.9%
61.8%
72.7%
Total Cost of Concrete
-790%*
-578%*
-400%*
Total Cost of Steel
52.9%
61.8%
72.7%
CO2 Produced
3.5%
27.4%
36.6%
*minus sign indicates an increase not a reduction, i.e. unfavorable change with respect to original design
6. Conclusions
While UHPC is garnering much more interest across North America, advances in research and
applications can accelerate UHPC deployment. Two aspects that are strongly tied to UHPC vast
deployment are the costs, which stem from the use of steel fibers and stringent quality control on
materials and production, and environmental impacts due to higher cement content and
production energy consumption. This preliminary study focused on assessing the cost and
environmental aspects of using UHPC in highway bridge piers. The benefit associated with
introducing UHPC to bridge piers is reducing cross-sections, which in turns, result in overall less
material and cement quantities, and reduced CO2 emissions. Additional benefits include higher
durability and longer service life. However, the high monetary costs remain the main drawback
that slow the widespread use of UHPC.
This study showed that up to 75% less materials can be used in bridge piers if UHPC is used
in lieu of conventional concrete. This translates to faster construction and smaller footprints for
bridge columns which allow for better traffic flow. Moreover, the use of UHPC of compressive
strength in the 25 ksi range can result in reducing bridge piers’ carbon footprint by up to 35%.
This means that the high cement content in typical UHPC mixes is outweighed by overall
reduction in the required concrete quantities, i.e. utilize UHPC for more structural applications
can be sough as one solution towards green construction.
Finally, cost benefit of using UHPC can be achieved if associated material costs are reduced
by four to five times than the current $2000/yd3 FHWA estimate. Cost benefits can be
maximized with respect to inspection and maintenance costs given UHPC’s durability and
superior service life. Thus, it is recommended for future work to consider full life cycle
assessment of using UHPC in bridges to accurately identify break-even UHPC costs. Developing
non-proprietary UHPC with local materials and comparable quality to commercial proprietary
ones should be the focus of more studies as well to alleviate UHPC costs.
7. References
American Association of State Highway and Transportation Officials (ASSHTO), “AASHTO
LRFD Bridge Design Specifications, 6th Edition” (2012).
American Concrete Institute Committee 211, “Standard Practice for Selecting Proportions for
Normal, Heavyweight, and Mass Concrete (ACI 211.1-91).” (2002).
Cost and Ecological Feasibility of Using UHPC in Bridge Piers
Joe and Moustafa 8
Caltrans, “Seismic Design Criteria Version 1.7.Caltrans, Sacramento, CA (2013).
Caltrans Bridge Design Academy, “LRFD Design Example B.” Caltrans, Sacramento, CA
(2006).
Erlin, B., Hime, W., and Pistilli, M., “The Cost of Doing Business with Concrete.” Concrete
Construction. Web. (2005).
FHWA, Development of Non-Proprietary Ultra-High Performance Concrete for Use in the
Highway Bridge Sector, Federal Highway Administration, FHWA-HRT-13-10 (2013).
Graybeal, B., “Material Property Characterization of Ultra-High Performance Concrete.”
FHWA, U.S. Department of Transportation, Report No. FHWA-HRT-06-103 (2006)
Hanson, K., “UHPC Offers Endless Possibilities.” NPCA (2014).
Heinz, D., Urbonas, L., and Gerlicher, T., “Effect of Heat Treatment Method on the Properties of
UHPC.” 3rd International Symposium on UHPC and Nanotechnology for High Performance
Construction Materials. (2012).
Marceau, M.L., Nisbet, M.A., and VanGeem, M.G., “Life Cycle Inventory of Portland Cement
Manufacture.” Portland Cement Association (2006).
Neville, A.M., “Properties of Concrete, 4th Edition.” (1995).
Olivier, J.G.J. and Muntean, M., “Trends in Global CO2 Emissions, 2014 Report.” PBL
Netherlands Environmental Assessment Agency (2014).
Ritter, R. and Curbach, M., “Material Behavior of Ultra-High Strength Concrete under
Multiaxial Stress States” ACI Materials Journal, Sept-Oct (2015).
UNEP Global Environmental Alert Service, “Greening Cement Production has a Big Role to
Play in Reducing Greenhouse Gas Emissions.” (2010).
Rubenstein, M., “Emissions from the Cement Industry.” State of the Planet, Earth Institute |
Columbia University. Web. (2012).
Russell, H.G. and Graybeal, B.A., “Ultra-High Performance Concrete: A State-of-the-Art Report
for the Bridge Community.” FHWA, U.S. Department of Transportation, Report No. FHWA-
HRT-13-060 (2013).
Steel Benchmaker ™, “Price History – Tables and Charts Global HRB Prices.” (2016)
Yu, R., Spiesz, P., and Brouwers, H.J.H., “Mix Design and Properties Assessment of Ultra-High
Performance Fibre Reinforced Concrete (UHPFRC).” Elsevier, Cement and Concrete Research
(2013)
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... UHPC columns are likely more compact and lighter in weight and easier-to-handle and transport when considered for accelerated precast construction techniques. Preliminary analytical studies led by one of the authors [2][3][4], that was later supported by experimental work by same authors [5,6], showed that seismic UHPC columns with proper reinforcement design can result in about 40% reduction in cross-sections when compared to conventional RC columns while maintaining a comparable ductile performance. Such results motivates the need to investigate the stability and behavior of slender UHPC columns and assess whether current analysis and design provisions are valid for future slender UHPC columns, which is the main focus of this study. ...
Article
Ultra-high performance concrete (UHPC) is a relatively new class of concrete and cementitious materials with much higher strength and durability than conventional concretes. The use of UHPC is currently expanding worldwide from bridge deck joints and connections to full components and larger applications. With the superior mechanical properties of UHPC, future UHPC columns in buildings and bridges will have compact cross-sections and smaller footprint. The main goal of this study is to provide experimental demonstration and reliable datasets of slender UHPC columns to validate current analytical procedures and inform future designs. This paper presents results and discussions from five full-scale UHPC columns (largest set of axially-tested UHPC columns to-date) at a 4 million-lb [∼18,000 kN] testing facility. The specific objectives are to investigate the structural and buckling behavior of slender UHPC columns under concentric axial loading, and assess the current ACI procedure for slenderness effects using the moment magnification method. When the actual material properties of UHPC and longitudinal bars are used for assessment, the ACI equations were found to overestimate the axial load capacity of slender columns by approximately 9%, on average. The study is concluded by design guidance and several recommendations for applying the moment magnification method for slender UHPC columns, which can be readily incorporated into future design codes.
... Thus, UHPC columns could be of great benefit for reducing the columns cross-sections because of UHPC higher compressive strengths. Several exploratory analytical studies [6][7][8], supported by recent experimental work [9,10], demonstrated that both axial and seismic UHPC columns with proper reinforcement design can be reduced by about 40% in cross-sections when compared to conventional RC columns while exhibiting a better ductile response. These results motivated the need to investigate the behavior and strength of UHPC columns with varied reinforcement details and assess whether the current ACI 318 [11] design provisions are valid for future UHPC columns, which is the main focus of this study. ...
Article
Ultra-high performance concrete (UHPC) applications are currently expanding worldwide from bridge deck joints and connections to full components and larger applications. UHPC has superior structural properties relative to other cementitious materials with multiple times the compressive and tensile strength, durability, and ductility. These outstanding mechanical properties of UHPC make it a strong candidate for full structural columns. The goal of this study is to provide experimental demonstration and reliable datasets of UHPC columns to validate current analytical procedures and inform future designs. This paper presents results and discussions from five full-scale UHPC columns tested at a 4 million-lb machine. The first objective is to analyze the experimental behavior of long UHPC columns with negligible slenderness effects and varying reinforcement details, i.e. different longitudinal, transverse, and fiber reinforcement ratios, under concentric axial loading. The second objective is to inspect the validity of ACI 318 equations for estimating the UHPC columns axial compressive strength. The results indicated that using the actual material properties of UHPC and longitudinal bars for ACI 318 equations overestimates the axial load capacity of columns with different reinforcement details by approximately 13% on average. Furthermore, a new strength reduction factor of 0.75 is suggested (instead of 0.85) for estimating axial capacity of UHPC columns with slenderness limit less than 30.
... Este concreto especial proporciona una más que competitiva relación entre la resistencia y el peso, así como una baja porosidad y facilidad de construcción [4]. Sin embargo, y pese a que hay desarrollos de concretos con resistencias superiores a los 200 MPa desde los años 70 [5] y aplicaciones in crescendo a nivel mundial [4,[6][7][8][9][10][11], el UHPC es material relativamente nuevo. Todavía presenta un gran desconocimiento en muchos mercados, existiendo una ausencia de normativa que avale su empleo en elementos estructurales [12,13], por lo que se debe recurrir a recomendaciones como las de la AFGC [14] o la JSCE-08 [15]. ...
Article
Full-text available
Las aplicaciones de los concretos de ultra altas prestaciones (UHPC por sus siglas en inglés) han tenido una gran proliferación a nivel mundial, específicamente en el desarrollo y rehabilitación de infraestructuras, debido a sus superiores propiedades mecánicas y de durabilidad en comparación con los concretos convencionales. Dentro de estas aplicaciones se podrían destacar la contribución del UHPC a la ingeniería de puentes, el desarrollo de estructuras singulares, el mobiliario urbano y las fachadas de elevado valor estético, entre otras. Sin embargo, entre los aspectos más desfavorables de este con-creto especial encontramos sus elevados huella de carbono y costos, a consecuencia de su alto contenido en cemento, por un lado, y otros insumos como la microsílice, el polvo de cuarzo o las fibras, por otro. El presente artículo de revisión tiene por objetivo evidenciar y analizar los aportes de las investigaciones desarrolladas en Colombia en los últimos dos años sobre la optimización de dosificaciones de UHPC, buscando un concreto de menores costos y huella de carbono. Los resultados de esta revisión demostraron que es posible la sustitución parcial de cemento y humo de sílice por diversas adiciones minerales disponibles en el mercado colombiano, así como la obtención de excelentes parámetros de ductilidad con un contenido de fibras inferior al 2% en volumen.
... El análisis de este caso, primera aplicación del UHPFRC a la ingeniería de puentes, nos brindará la posibilidad de analizar las características y las ventajas del uso del UHPFRC que han permitido a la construcción moderna diseñar y producir formas complejas de gran resistencia, muy ligeras y esbeltas [57]. Estas propiedades muy apreciadas en la construcción de puentes peatonales se complementan por las excelentes propiedades del UHPFRC: elevada resistencia a la compresión, flexión y al desgaste, además de una gran durabilidad [16,17,58]. ...
Article
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Esta investigación tiene como objetivo el analizar y comparar la información recolectada sobre la aplicación de UHPFRC en puentes en los casos encontrados, pasando a la discusión sobre las ventajas y aportes de la implementación de este material, además de sus limitaciones u obstáculos que se tienen antes del escogerlo. Es importante también reflejar qué tan efectivo es el UHPFRC frente a los materiales convencionales (acero y concreto) a nivel económico, ambiental e ingenieril. Se destacaron las características más relevantes en los casos expuestos.
... The slight increase in cost of construction is offset by safer structure, longer service life, and low maintenance cost [25]. The reliability of girders poured using ultra-high-performance concrete mixes are investigated and reliability indexes for bridge girders are calibrated to ensure their compliance to current AASHTO LRFD design equations [26]. A relevant study showed that reliability of NU I-girders, fabricated using UHPC, in shear and flexure is compliant to current AASHTO LRFD provisions [27]. ...
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Ultra-high-performance concrete (UHPC) is a new class of concrete developed in France in the 1990s with superior characteristics including high workability, high compressive strength, increased ductility, and high resistance to environmental attacks. UHPC is increasingly used in local and international construction markets in the construction of high rise structures, long-span precast/prestressed bridge girders, marine, aviation, and defense construction applications due to its superior mechanical properties, and favorable long-term performance. This study presents recent research findings regarding the UHPC mix designs, fresh and hardened concrete properties, and current UHPC applications in the construction industry including specific bridge applications. Despite of UHPC advantages, multiple impediments are present that delays the widespread of UHPC application in the construction industry including lack of design codes and specifications for estimating UHPC performance, the need for special batching, mixing, and curing. This study assists different construction stakeholders in understanding the unique characteristics, advantages, and impediments to the widespread of UHPC applications. The deciphering of UHPC will help increase its overall market share in local and global construction markets.
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In designing a concrete structure under a severe chloride environment by applying a new material and mixture proportion without enough previous data, it is required to determine the chloride-ion diffusion coefficient of concrete to predict the chloride-ion concentration at the reinforcing bar position during its service life. The diffusion coefficient can be evaluated by test methods such as the immersion test or electrophoretic migration test. The electrophoretic migration test, such as NT BUILD 492, is helpful from the point of view of reducing the test period and cost. This research focused on the non-steady-state electrophoretic migration test (NSSM), which improves some problems of NT BUILD 492 proposed by the Public Works Research Institute in Japan, and conducted a round-robin test to verify the reliability of the NSSM. The test results confirmed the reliability of the NSSM and some minor issues to standardize the NSSM.
Article
Accelerated bridge construction (ABC) field joints, e.g. precast deck panels joints, are among the common structural applications of ultra-high performance concrete (UHPC). The higher cost and limited availability of commercial UHPC products have motivated researchers to develop non-proprietary UHPC (NP-UHPC) using locally available materials. One of these efforts is the recent work by the ABC University Transportation Center (ABC-UTC) in the United States to develop NP-UHPC mixes for use in ABC field joints. This paper documents the ABC-UTC mix design and proportions and has two main objectives. First, provide a full material characterization of such mix to allow for future replication and use of this material for different bridge applications as well as modeling purposes. Second, investigate the effect of material sourcing and variability, such as fine aggregate types and particle gradation, on the main mechanical properties of the material. The material characterization tests included flowability, compression, flexure, and direct tensile tests of the NP-UHPC mixes. The results from these tests are then compared with various proposed equations from the literature to verify their validity for use with the considered NP-UHPC mixes.
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The term Ultra-High Performance Concrete (UHPC) refers to a relatively new class of advanced cementitious composite materials whose mechanical and durability properties far surpass those of conventional concrete. This class of concrete has been demonstrated to facilitate solutions that address specific problems in the U.S. highway bridge infrastructure. Initial material development research on UHPC began more than two decades ago. First structural deployments began in the late 1990s. First field deployments in the U.S. highway transportation infrastructure began in 2006. For this study, UHPC-class materials are defined as cementitious-based composite materials with discontinuous fiber reinforcement that exhibit compressive strength above 21.7 ksi (150 MPa), pre- and post-cracking tensile strength above 0.72 ksi (5 MPa), and enhanced durability via a discontinuous pore structure. The report documents the state of the art with regard to the research, development, and deployment of UHPC components within the U.S. highway transportation infrastructure. More than 600 technical articles and reports covering research and applications using UHPC have been published in English in the last 20 years, with many more published in other languages. The report includes information about materials and production, mechanical properties, structural design and structural testing, durability and durability testing, and actual and potential applications. The report concludes with recommendations for the future direction for UHPC applications in the United States.
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In the past decade significant advances have been made in the field of high performance concretes. The next generation of concrete, Ultra-High Performance Concrete (UHPC), exhibits exceptional strength and durability characteristics that make it well suited for use in highway bridge structures. This material can exhibit compressive strength of 28 ksi, tensile strength of 1.3 ksi, significant tensile toughness, elastic modulus of 7600 ksi, and minimal long-term creep or shrinkage. It can also resist freeze-thaw and scaling conditions with virtually no damage and is nearly impermeable to chloride ions. Prestressed highway bridge girders were cast from this material and tested under flexure and shear loadings. The testing of these AASHTO Type II girders containing no mild steel reinforcement indicated that UHPC, with its internal passive fiber reinforcement, could effectively be used in highway bridge girders. A large suite of material characterization tests was also completed. Based on this research, a basic structural design philosophy for bridge girder design is proposed.
Article
To evaluate new fields of application of concrete structures in any processes where complex stress states occur, and to optimize concrete structure geometries regarding such applications, the material behavior of concrete under multiaxial loading has to be known. With the aim of determining the material behavior of an ultra-high-strength concrete (UHSC), 35 multiaxial stress states with primarily one tensile stress component are examined and the measured stress-strain curves are shown. Using the test results, the arbitrary parameters of a damage-based material law concerning the single-stress ratios are determined. To describe the material behavior for load-induced isotropic and orthotropic damage, an approximation of the calculated arbitrary parameters is deduced. These enable determining the material behavior of the investigated UHSC for any stress ratios. The prediction of the described material law is compared and discussed regarding the measured stress-strain curves and the maximum strength values from the tests.
Seismic Design Criteria Version 1.7
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