- Open Access
Investigation of Likelihood of Cracking in Reinforced Concrete Bridge Decks
© The Author(s) 2013
- Received: 30 December 2012
- Accepted: 15 January 2013
- Published: 29 March 2013
One of the biggest problems affecting bridges is the transverse cracking and deterioration of concrete bridge decks. The causes of early age cracking are primarily attributed to plastic shrinkage, temperature effects, autogenous shrinkage, and drying shrinkage. The cracks can be influenced by material characteristics, casting sequence, formwork, climate conditions, geometry, and time dependent factors. The cracking of bridge decks not only creates unsightly aesthetic condition but also greatly reduces durability. It leads to a loss of functionality, loss of stiffness, and ultimately loss of structural safety. This investigation consists of field, laboratory, and analytical phases. The experimental and field testing investigate the early age transverse cracking of bridge decks and evaluate the use of sealant materials. The research identifies suitable materials, for crack sealing, with an ability to span cracks of various widths and to achieve performance criteria such as penetration depth, bond strength, and elongation. This paper also analytically examines the effect of a wide range of parameters on the development of cracking such as the number of spans, the span length, girder spacing, deck thickness, concrete compressive strength, dead load, hydration, temperature, shrinkage, and creep. The importance of each parameter is identified and then evaluated. Also, the AASHTO Standard Specification limits live-load deflections to L/800 for ordinary bridges and L/1000 for bridges in urban areas that are subject to pedestrian use. The deflection is found to be an important parameter to affect cracking. A set of recommendations to limit the transverse deck cracks in bridge decks is also presented.
Although cracking can occur in hardened mature concrete, transverse deck cracking are more likely to occur in bridge decks in early ages. The cracking has been observed in reinforced concrete bridge decks in the State of Florida and in other bridges around the nation. Numerous factors can lead to transverse deck cracking in highway bridges including time dependent material properties, restraints, casting sequence, formwork, and environmental factors. Several studies investigated the issue of deck cracking (ACI 2001; Altoubat and Lange 2000; Cady et al. 1971; Eppers et al. 1998; Frosch et al. 2003; Krauss and Rogalla 1996; PCA 1970; Purvis et al. 1995; Saadeghvaziri and Hadidi 2002; Schmitt and Darwin 1995; Xi et al. 2003). Also, the development of cracking increases the effect of freeze and thaw cycles, which may lead to spalling of concrete and thus resulting in corrosion of steel reinforcement. Transverse deck cracking also increases carbonation and chloride penetration leading to accelerated corrosion. Also, a possible damage to underlying components may take place and the bridge may experience premature deterioration; therefore the bridge may experience loss of stiffness and eventually a loss of function. Transverse cracks can reduce the service life of structures and increase maintenance costs. Moreover, cracking will lead to undesirable aesthetic condition of the bridge. The developed cracks are full-depth cracks and are typically spaced at 92–305 cm apart. They are the most frequently observed cracks in concrete bridge decks.
There are several mechanisms contributing to cracking of hardened concrete of which three are important, namely, drying shrinkage, autogenous shrinkage, and thermal stresses. Restrained drying shrinkage occurs due to the volume change induced by a loss of moisture in the cement paste. The concrete would not crack if this shrinkage could occur without the restraint from structural elements, the subgrade, or the moist interior of the concrete itself. This volume change coupled with restraint cause tensile stresses in the concrete that can lead to cracking. These tensile stresses are influenced by the amount and rate of shrinkage, the degree of restraint, the modulus of elasticity, and the amount of creep. The amount of drying shrinkage is a function of the amount and type of aggregate and the cement paste content of the concrete. Methods to reduce shrinkage cracking include using contraction joints, careful detailing of reinforcement, shrinkage-compensating admixtures, and reducing the sub slab restraint. Autogenous shrinkage is a special type of drying shrinkage resulting from self-desiccation or internal drying that occurs in concrete with water-cementitious (w/c) materials below 0.42. This type of shrinkage differs from typical drying shrinkage since there is no loss of moisture from the bulk concrete. Autogenous shrinkage strain is typically about 40–100 microstrain, but has been measured as high as 2,300 microstrain in concrete with a w/cm ratio of 0.2. Autogenous shrinkage has been found to increase with increasing temperature, cement content, and cement fineness. Temperature differences in a concrete structure result in volume changes causing tensile stresses. The dissipation of the heat of hydration of cement and changes in ambient temperature can create temperature differentials that cause tensile stresses in concrete structures. These tensile stresses are proportional to the temperature differential, the coefficient of thermal expansion, the effective modulus of elasticity, and the degree of restraint. Methods of reducing thermal cracking include reducing maximum internal core temperature, delaying the onset of surface cooling, controlling the rate at which the concrete cools, and increasing the early age tensile strength of the concrete (PCA 1970).
The earliest noted study was conducted by the Portland Cement Association, the Bureau of Public Roads, and ten state highway departments. This study was released in 1970. The purpose of the study (PCA 1970) was to determine concrete bridge deck durability problems, causes of the types of deterioration, methods to improve durability, and methods to inhibit existing deterioration. In this study, transverse cracking was observed as the most common type of cracking. Older decks and longer spans showed more transverse cracking, whereas continuous span bridges and those with steel girders appeared to exacerbate transverse cracking.
In a study conducted for the Pennsylvania Department of Transportation, researchers surveyed 4 year old bridge decks in Pennsylvania to investigate the extent and causes of concrete bridge deck deterioration (Cady et al. 1971). The researchers found transverse cracks in 60 % of all spans and 71 % of all bridges. Also, bridges in Pennsylvania were assessed through 99 field surveys and 12 thorough surveys to determine the causes of transverse cracking. These surveys included crack mapping, crack width measurements, rebar location and depth surveys, concrete coring, and construction records. An important finding made by the researchers was that the transverse cracks intersected coarse aggregate particles; this indicates that transverse cracking occurs in hardened concrete rather than plastic concrete.
Schmitt and Darwin (1995) conducted a study on the effects of different variables on bridge deck cracking, classifying the variables into five categories: material properties, site conditions, construction procedures, design specifications, and traffic and age. The material properties considered included admixtures, slump, percent volume of water and cement, water content, cement content, water-cement ratio, air content, and compressive strength. Site condition factors considered in the study were average air temperature, low air temperature, high air temperature, daily temperature range, relative humidity, average wind velocity, and evaporation. The construction procedure factors considered, in the study, were placing sequence, length of placement, and curing. There were no observed relationships between length of placement or type of curing materials and cracking. There were not any correlation determined between cracking and placing sequence due to the lack of information. Design factors considered in the study included structure type, deck type, deck thickness, top cover, transverse reinforcing bar size, transverse reinforcing bar spacing, girder end conditions, span length, bridge length, span type, and skew. Regarding traffic and age, the researchers found that cracking increased with traffic volume and that bridges constructed, prior to 1988, exhibited less cracking than bridges constructed after 1988. The increase in cracking, in newer bridges, was attributed to changes in construction, material properties, and design specifications.
Krauss and Rogalla (1996) conducted, what is likely, the most comprehensive study to date. They surveyed 52 transportation agencies in the United States and Canada to evaluate early age transverse cracking. Over 100,000 bridges were found to have developed early transverse cracks. Analytical studies were also performed using both theoretical and finite element analysis to evaluate the influence of several parameters on transverse cracking. The researchers determined that span type, concrete strength, and girder type were the most important design factors influencing transverse cracking. Material properties such as cement content, cement composition, early-age elastic modulus, creep, aggregate type, heat of hydration, and drying shrinkage also influenced deck cracking. Researchers conducted a field investigation of 72 bridge decks in Minnesota. The researchers determined that the most related design factors to transverse cracking were longitudinal restraint, deck thickness, and top transverse bar size. The material factors that affect transverse cracking the most were cement content, aggregate type and quantity, and air content. Researchers in Minnesota performed a parametric study considering bridges with steel and prestressed concrete girders. Among variables considered for steel girder bridges were end conditions, girder stiffness, locations of cross frames, girder splices, supplemental reinforcing bars, shrinkage properties, concrete modulus of elasticity, and temperature differential due to heat of hydration. Variables considered for prestressed girder bridges were the times casting in relation to the times of both strand release and deck casting and shrinkage properties of the deck and girders.
From a research sponsored by the Indiana Department of Transportation, researchers conducted a field study and constructed laboratory specimens to investigate the behavior of transverse cracks (Frosch et al. 2003). Using these specimens, the researchers evaluated the effect of differing bridge deck designs on the control of overall shrinkage and evaluated the contribution of stay-in-place (SIP) steel forms to the formation of transverse cracking.
1.1 Crack Sealers
The most commonly marketed sealers include; epoxies, reactive methyl methacrylates (MMA), methacrylates, high-molecular weight methacrylates (HMWM), and polyurethanes. All of these products have distinct characteristics that make them favorable for some uses and unfavorable for others. Properties of sealers include volatility, viscosity, initial shrinkage, tensile strength, and tensile elongation. From surveys of 40 states, 60 % indicated that they did not have a crack sealing program and 24 % use epoxies and methacrylates, however, none were asked about HMWMs, MMAs, or polyurethane resins (Soriano 2002; Tsiatas and Robinson 2002). Another survey stated that epoxy was the predominant sealer (Tsiatas and Robinson 2002). Only four of sixteen states that had a crack sealing program, claimed to use HMWM sealers.
This research concentrates on epoxies and methacrylates, both HMWM and MMA, as they possess the properties closest to the requirements in the qualified products list (QPL) of the Florida Department of Transportation. Also, an analytical investigation is conducted to identify major parameters affecting the likelihood of cracking and to provide recommendation to limit cracking of bridge decks.
The experimental phase of this study consisted of field and laboratory investigations to identify the most appropriate sealant materials suitable for crack sealing. Four milestone sealant materials are considered, MMA, HMWM, Polyurethane, and epoxy. The performance of the sealers is evaluated based on meeting a number of performance criteria. NCHRP indicated that crack sealers are measured in four primary ways including depth of penetration, bond strength, chloride content/resistance to corrosion, and seepage rate. It was decided to consider the elongation as well in this study when the performance is evaluated.
2.1 Depth of Penetration
The test for the depth of penetration for crack sealers is completely different from that of a concrete sealant. Sealers are used to cover or fill an already formed crack. It is presumed that the larger the depth a sealer can penetrate, the better the seal that it will create. Due to the variability of crack widths, it may be more useful to measure the percentage of penetration versus the actual penetration depth (Sprinkel 1998; Rodler et al. 1989; Eppers et al. 1998).
2.2 Bond Strength
The ability of a resin to repair the structural problem in a cracked deck is measured by its bond strength. Because there is no standard method to test for bond strength, engineers use a few different tests to determine bond strength. The most common test is the tensile splitting test—ASTM C496. Another method is the three-point bending flexural test—ASTM C293.
2.3 Chloride Ingress and Corrosion
Chloride ions can infiltrate the concrete and corrode the reinforcement if there exists any cracking on the bridge deck. Crack sealers act as a barrier to slow down this ingress of chloride ions into the concrete. This problem occurs mainly in the northern states where there is tendency of having freeze–thaw cycles and where the use of road salt for deicing is common.
The indication of how well the repaired specimen prevents chloride ion ingress, is called seepage. Seepage is measured by the volume of water that passes through the cracked concrete. It is suggested that the least amount of water that passes through the crack, the better the rebar of the deck is protected. Several tests are used to check for seepage. One test involves forming a barrier around the top of the concrete core sample, after the sides are waterproofed; water is poured into the barrier on top of the core sample. The water height is kept constant while the rate in which water passes through the core is recorded. The number of leaks before the cracks were sealed is compared to the number of leaks, after the cracks are sealed. This test is mainly used in the field to give an indication of the success of the repair.
There is a big variation for elongation of different sealers ranging between 3 and 60 %.
Crack pattern in the bridges inspected, in Fort Lauderdale, is consistent with that in the Jacksonville’s inspected bridges. Many transverse cracks have developed at mid span while a few have developed near the piers (negative moment region). There are evidences of some steel corrosion due to water leakage inside the steel box of one of the bridges in Fort Lauderdale. The location of corrosion is associated with the deck cracks identified at the top of the deck surface.
Sealant test results.
Test site #
Curing time (h)
Tensile strength ave. (kN)
2 part epoxy
3 part methacrylate
2 comp methacrylate
2 comp methacrylate
3 part methacrylate
3 part methacrylate
No sealer applied
Field test results.
Peak load (kN)
Concrete 44 mm core
Test section 1
Test section 2
Test section 3
Test section 5
Test section 6—first part
Test section 6—second part
Results of testing the sealant materials in the laboratory.
Lab test data (first attempt)
Lab test data (second attempt)
Foremost characteristics of bridge models.
Number of spans
Span length (m)
Number of girders
Deck thickness (mm)
Concrete compressive strength, 1c’ (MPa)
End conditions at abutment locations
Several load patterns are included in the study. Load patterns include dead load, increase in temperature due to hydration, temperature, shrinkage, creep, and truck loads. Only bridge deck was subjected to increase in temperature due to hydrations, which is assumed to be 20 °C. The temperature load was taken as a uniform increase in temperature of bridge deck and girders by 29.4 °C. The effect of shrinkage was considered through applying a strain due to shrinkage on bridge decks.
6.1 Truck Load
Summary of results.
SH + TR
(TE-increase) + TR
(TE-decrease) + TR
SHR + TR + (TE-increase)
SHR + TR + (TE-decrease)
Summary of results—incrementally increase of truck load and a decrease of temperature of 29.4 °C.
TE + 0.5TR
TE + 0.75TR
TE + TR
TE + 1.25TR
6.2 Effect of Secondary Loads
The secondary loads include hydration, temperature, shrinkage, and creep. As mentioned, hydration effect was considered by applying 20 °C of temperature load to all of decks of bridge models. Temperature effect was considered by applying an increase of temperature of 29.4 °C to bridge deck and girders. Shrinkage effect was considered by applying the proper value of strain due to shrinkage for the deck of each bridge model. Creep was accounted for also by applying the proper value of strain to bridge deck.
All of the tested sealers performed well. The sealed slabs performed very close to the control slab.
The three-part HMWM performed best for cracks <0.50 mm in width and the Epoxy was the best performer for cracks ≥0.50 mm in width.
The concrete compressive strength has an important contribution. Different conclusions can be drawn depending on the type of the applied load. It is recommended to use a moderate compressive strength concrete for bridge decks. It is recommended the use of a compressive strength of no more than 34.5 MPa as transverse cracking develops exponentially at higher compressive strengths.
Shrinkage or temperature tends to drive the initiation of cracking and hence cracks developed become working cracks. Application of live loads widens the induced cracks even further.
The stiffness of the bridge deck is also an important parameter and affects the behavior. The thicker the deck, the lower the stress developed, resulting in fewer cracks. Based on this study, it is recommended to use a deck thickness of more than 17.5 cm.
The deflection limit given by AASHTO affects the likelihood of cracking and should be revised to account for higher values of crack widths found in this research.
More research is needed in the area of crack behavior during the loading phase and the reaction of the sealer to crack opening and closing.
Open Access This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.
This article is published under license to BioMed Central Ltd.Open AccessThis article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.
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