Field Investigations of Cracking on Concrete Pavements

This paper presents the results of several investigations to identify the underlying causes of longitudinal cracking problems in Portland cement concrete (PCC) pavement. Longitudinal cracking is not intended and detrimental to the long-term performance of PCC pavement. Longitudinal cracking problems in five projects were thoroughly investigated and the findings indicate that longitudinal cracking was caused by: (1) late or shallow saw cutting of longitudinal joints; (2) inadequate base support under the concrete slab; and (3) the use of high coefficient of thermal expansion (CTE) aggregates. When the longitudinal cracks were caused by late or shallow saw cutting of longitudinal joints, cracks developed at a very early stage. However, when there was adequate base support, the longitudinal cracks remained relatively tight even after decades of truck trafficking. Another cause of longitudinal cracking was inadequate base support, and cracking due to this mechanism normally progressed to rather wide cracks. Some cracks were as wide as 57?mm. Evaluations of base support by dynamic cone penetrometer in areas where longitudinal cracks were observed indicate quite weak subbase in both full-depth repaired areas and surrounding areas. This implies that the current requirements for the subbase preparation for the full-depth repair are not adequate. Another cause of longitudinal cracking was due to the use of high CTE aggregate in concrete. Large volume changes in concrete when coarse aggregate with high CTE is used could cause excessive stresses in concrete and result in longitudinal cracking. To prevent longitudinal cracking, attention should be exercised to the selection of concrete materials (concrete with low CTE) and the quality of the construction (timely and sufficient saw cutting and proper selection and compaction of subbase material).     

Structural Evaluation of Cement Concrete Roads in Mumbai City

Plain jointed concrete pavements laid in Mumbai City (India) during the early 1990s were structurally evaluated using a falling weight deflectometer (FWD) and testing of concrete cores extracted from the pavement slabs. The ultrasonic pulse velocity (UPV) of the concrete in the cores was determined first and then the cores were crushed under compression. The pavement deflections were found to be within the limits as suggested in the Indian codes and the international literature. The joint conditions were also found to be satisfactory. The design strength of the concrete was back-calculated from the compressive strength of the cores and was found to conform to the design specifications. However, the construction quality was found wanting as the thickness of pavement slabs at a few locations was lower than that specified and it has resulted in cracking of the slabs. The dynamic modulus of elasticity of concrete as determined by the FWD was found to correspond well with that computed from the UPV of cores and from the compressive strength of concrete. A method is suggested to estimate the structural parameters of uncracked pavement slabs from the dynamic modulus of elasticity obtained through the indirect method of UPV testing which is less expensive compared to evaluation by the FWD.     

Long-Term Deflection and Cracking Behavior of Concrete Beams Prestressed with Carbon Fiber-Reinforced Polymer Tendons

This paper discusses the experimental result on the long-term deflection and cracking behavior of concrete beams prestressed with carbon fiber-reinforced polymer (CFRP) tendons, under sustained long-term service load, including cracked and uncracked sections. Six full-scale beams were cast and tested. The experimental parameters included the level of prestress, the level of sustained service loading, and concrete strengths. The experimental results showed that the performance of concrete beams prestressed with CFRP tendons meets the serviceability criteria in terms of deflection and cracking. The test results also showed that the long-term performance of concrete beams prestressed with CFRP tendons was comparable to those prestressed with steel tendons. Furthermore, the test results showed that with the increase of concrete strength, the serviceability performance also improved with concrete beams prestressed with CFRP tendons.     

Shanghai’s Experience on Utilizing the Rubblization for Jointed Concrete Pavement Rehabilitation

As agencies continue looking for cost-effective methods to rehabilitate deteriorated jointed concrete pavement (JCP), rubblization using a resonant breaker has been experimented by the Shanghai Municipal Roadway Authority (SMRA). It was demonstrated that rubblization using a resonant breaker offers a viable option for the SMRA because the rubblized pavement sections have been performing very well with no visible distress. Based on field observation for a typical hot mix asphalt concrete (HMAC) overlay on a nonrubblized JCP, it was found the treatment normally would have reflective cracking for the same overlay thickness in the first three years. Besides the cost advantage over the reconstruction, a resonant breaker also had yielded the minimum disturbance during the rubblization. It was observed that it was very effective to use water during compaction on a rubblized JCP surface to improve compaction efficiency and to control dust. Furthermore, there is no need to apply a prime coat before the HMAC overlay, as there was no detrimental effect that could be identified. The average rubblized JCP moduli were found to be 1,323?to?1,375?MPa, which are within the range reported in the literature. It was believed that there were high possibilities to increase rubblized JCP moduli without sacrificing the performance by increasing the particle size, because a reduction of 200?mm of HMAC was observed when rubblized JCP increased from 345?to?3,445?MPa at a subgrade modulus of 138?MPa and traffic of 30 million ESAL. However, further research is needed to optimize the rubblized JCP moduli in an attempt to reduce overlay thickness without creating reflective cracking.     

Assessment of Retrofit Dowel Benefits in Cracked Portland Cement Concrete Pavements

A parametric study was conducted using the finite-element rigid pavement program ISLAB2000. For cracks that utilize aggregate interlock as the sole means of load transfer, the integrity of the cracks was initially modeled using the aggregate interlock factor. A subsequent analysis was then performed on the same cracks for the case where both dowel bars and aggregate interlock were available for load transfer purposes. The latter scenario represents the case where dowel bar retrofitting (DBR) has been performed on the cracks. In both cases, the deflection load transfer efficiency and critical slab tensile stresses were computed in order to examine the immediate theoretical benefits of the dowel bars. The validity of these theoretical benefits was tested using data from falling-weight deflectometer testing on DBR sites in both Michigan and Washington. It was found that installation of dowel bars did not increase the load transfer efficiency for cracks that had levels greater than 89–95%, depending on pavement parameters. When temperature gradients were not considered, little change in tensile stress due to a load at the crack was exhibited when DBR was performed on cracks that had load transfer efficiency levels less than 70–80%.     

Results from a Forensic Investigation of a Failed Cement Treated Base

After only 2 months in service, the frontage road of US 290 developed a series of depressions that caused a very poor ride. The main cause of the premature failure was attributed to disintegration of the cement treated base (CTB) layer. This was attributed to two primary factors: (1) a very coarse gradation of the aggregate used in the CTB layer which produced a mix that was prone to segregation during placement; and (2) the CTB layer was placed in two lifts, which were not well bonded together. Another contributing factor was the lack of bond between the CTB and the hot mix asphalt (HMA) surface layer. Secondary factors include high air voids in the HMA layer and low HMA layer thickness. The material, when prepared carefully in the lab at the design cement content, passed the strength requirement of 2.07?MPa. But this coarse mix appears to have been difficult to place correctly in the field. The coarsely graded aggregate used on this project appears to be prone to segregation, either during placement or compaction. The ground penetration radar results (with confirmation by core samples) indicated that most of the problems were at the bottom of the upper CTB lift. The CTB was placed in two lifts and very poor condition was found between the two CTB layers. This problem was coupled with a thin, porous, and poorly bonded HMA layer that permitted moisture to enter the CTB layer. Similar failures have also been reported recently on other CTB projects in Houston.     

Numerical Model for Time-Dependent Fracturing of Concrete

A finite-element formulation for the analysis of time-dependent failure of concrete is presented. The proposed formulation incorporates: (1) the viscoelastic behavior of uncracked concrete through a Maxwell chain model; and (2) the inelastic behavior of damaged concrete, characterized by a modified version of the microplane Model M4 which includes the rate dependence of fracturing. The proposed formulation is applied to the simulation of quasi-static concrete failure in the time domain. The different effects of creep and rate dependence of crack growth and their role in the lifetime of concrete structures are studied. The influence of different loading rates on the size effect is also analyzed with reference to single notched specimens, revealing the link between the size of the fracture process zone and the loading rate. The capability of the proposed numerical formulation is also verified for the case of sustained uniaxial compressive loads.     

Probabilistic Approach to Predict Cracking in Lightly Reinforced Microconcrete Panels

The ultimate strength of structures made of brittle materials—such as microconcrete—strongly depends on microstructural defects, the structure size, and the loading pattern. Probabilistic approaches allow one to take account of such dependencies. By using a Weibull model, cracking of ferrocement panels is analyzed. Provided the behavior of the reinforcement remains elastic, it is shown that the Weibull parameters identified on unreinforced microconcrete samples tested in flexure may be used to predict multiple cracking in ferrocement panels tested in tension. A key aspect of the analysis is related to the understanding and modeling of the stress heterogeneity effect on the local failure probability of unreinforced as well as reinforced microconcrete by the use of a so-called Weibull stress.     

Detailed Forensic Investigation and Rehabilitation Recommendation on Interstate Highway-30

The main objective of this study is to identify the cause of the punchouts observed on Interstate Highway 30 (IH-30), and to identify possible rehabilitation alternatives. Several nondestructive tests, as well as coring and trenching, were conducted in both distressed and nondistressed areas. Middepth horizontal cracks were found during routine repair and by the trenching performed in this study. It is believed that due to temperature variation at an early stage, horizontal cracks developed at the middepth interface between the steel and concrete. The truck traffic caused the horizontal cracks to deteriorate further. Repetitive truck traffic and thermal loading forced the concrete to crack vertically from the middepth where there were horizontal cracks. The closely spaced transverse and longitudinal cracks, along with the delamination, caused punchouts. Although the problem is not imminent, an immediate seal plus a 75 mm heavy-duty stone matrix asphalt (SMA) overlay will probably provide the most cost-effective remedy for this section of IH-30. Existing distressed areas should be repaired before the rehabilitation. To slow the deterioration, the district should use a latex modified chip seal or asphalt rubber seal (AC15-5TR) followed by a 75 mm heavy duty SMA. This is to provide bonding between the concrete and SMA overlay. If the district chooses to do nothing at this time, it will become costly in 2–3 years if current environmental and traffic conditions hold. The cost to repair a severely deteriorated continuously reinforced concrete pavement (CRCP) would be several times more than the 75 mm heavy duty SMA overlay.     

Modeling Cracking in Shell-Type Reinforced Concrete Structures

A three-dimensional (3D) hypoelastic material model for modeling material properties of cracked reinforced concrete is proposed. Material properties of multidirectionally cracked reinforced concrete are represented by the material properties of intact concrete and a number of uniaxially cracked concrete with their coupling solids. Cracking effects due to multiple nonorthogonal cracks are traced in each uniaxially cracked concrete. Tension softening and aggregate interlock occurring at the crack interface as well as tension stiffening and compression softening initiated in concrete between cracks due to multiple nonorthogonal cracks are all incorporated explicitly. RC panels under in-plane loading and RC slab under pure torsion have been analyzed. The developed 3D hypoelastic material model has been proved to be efficient and effective in modeling the material behaviors of cracked reinforced concrete in shell-type RC structures. The deformational response, the ultimate strength, and failure mode can be captured reasonably well.     

Microstructural Mechanisms of Early Age Cracking Behavior of Concrete: Fracture Energy Approach

This paper presents findings from a study directed at identifying key properties of ingredient materials that are influential on the early age cracking behavior of concrete, with an emphasis on the effects of aggregate size, aggregate morphologies, and water-cement ratio (w/c). Fracture energy (GF) was determined using a wedge-split test configuration for concrete samples at the age of 12?h. Based on image analysis, three signature morphologies of aggregate particles, i.e., the angularity, surface texture, and surface area, were quantitatively determined in terms of developed angularity index (AI), surface texture (ST) index, and surface area (SA) measurement, respectively. The high consistency between GF and aggregate SA of the concrete samples suggests that the interfacial transition zone (ITZ) at the cement paste-aggregate interface is the critical location that primarily accommodates the 12?h cracking of concrete. The critical role of ITZ in the early age cracking of concrete was further confirmed by its microstructural and chemical features under scanning electron microscopy/energy dispersive X-ray spectroscopy.     

Use of Material Interfaces in DEM to Simulate Soil Fracture Propagation in Mode I Cracking

Mode I fracture is common in geomechanics in desiccation cracking, hydraulic fracture, and pressuremeter testing. The cohesive crack model has been used extensively and successfully in numerical modeling of such fracture in concrete and steel but has not been applied in modeling of soil fracture to the same extent. It is argued that the cohesive crack model may be more appropriate than linear elastic fracture mechanics (LEFM) for soils because it takes into account finite tensile strength and any likely plasticity during fracture. With special reference to the Universal Distinct Element Code (UDEC) computer program, a methodology of using interfaces in the distinct element method (DEM) of analysis to model fracture has been validated herein, and this approach is considered to be useful in geomechanical modeling applications. The methodology is based on the cohesive crack approach and shows how softening laws could be back-calculated from load-displacement curves of test specimens. It has been validated using three geometries: a tension test with a rectangular cross section, a notched three-point bend beam, and a compact tension test. Approximate softening laws for St. Albans clay from Canada are proposed.     

Longitudinal Cracking Distress on Continuously Reinforced Concrete Pavements in Illinois

The Illinois Department of Transportation (IDOT) initiated a failure investigation to determine the distress mechanisms causing premature longitudinal cracking on continuously reinforced concrete pavements (CRCP) on several Illinois interstates. The longitudinal cracking approximately followed the embedded reinforcement steel and occurred in both the driving and passing lanes. In this paper, the results from field visual surveys, coring, and petrographic analyses are reported along with a review of archival construction and material records of the distressed CRCP sections. A laboratory forensic study was also performed on several field extracted slabs. The results of the field and laboratory investigation show the cracking was not initiated by steel corrosion, deleterious reactions in the concrete materials, or an inadequate structural design. Rather, the cracking is related to settlement of the steel bars in the concrete. Settlement cracking is conventionally thought to occur only in concrete slabs and decks with plastic (high slump) concrete and small values of bar cover depth, while the studied CRCP sections have large values of cover depth and were cast with stiff (low slump) concrete. The settlement was likely caused by the relative settlement of heavy steel bars (22?mm diameter) within the lower density concrete during the original CRCP construction. The technique of placing the steel bars in the fresh concrete (called tube-feeding) further contributed to the development of this distress, and this practice is no longer employed by IDOT.     

Innovative ANN Technique for Predicting Failure/Cracking Load of Masonry Wall Panel under Lateral Load

This paper introduces an artificial intelligent technique for predicting the failure/cracking loads of laterally loaded masonry wall panels based on their corresponding failure/cracking patterns derived from the laboratory experiments. First, a lattice is made on a wall panel based on the dimension of the wall panel. Then, the numerical values, 0 or 1, are assigned to the cells in the lattice in order to describe the failure/cracking pattern. Thus, a numerical matrix is formed to show the failure/cracking pattern of the wall panel. Since the matrices for the wall panels with various sizes have different dimensions, the gray level cooccurrence matrix is innovatively used to transfer these matrices into the matrices whose dimensions are the same. Next, the numerical modes of failure/cracking patterns of experimental wall panels and the corresponding normalized failure/cracking loads can be used as the input and output of the artificial neural network (ANN) training data, respectively. Finally, three types of ANN models for predicting the failure/cracking load of the unseen wall panel are achieved by repeatedly training and adjusting so as to optimize its parameters. In a wide significance, this study opens a novel way to establish the relationship between the failure/cracking pattern and the failure/cracking load of the wall panel.     

Response Prediction of RC Beams Externally Bonded with Steel-Reinforced Polymers

This paper deals with an innovative technique for strengthening reinforced concrete (RC) structures using steel-reinforced polymer (SRP) materials. The results of an experimental campaign using RC beams strengthened in flexure with carbon fiber-reinforced polymer or SRP laminates are summarized, and the experimental outcomes are compared to the predictions provided by analytical models and code formulations in terms of flexural strength, curvature of the cross section, deflections, and crack widths. Under ultimate conditions, the ACI 440.2R-02 approach provided conservative flexural strength, and a modified expression for the bond coefficient km was proposed. Under serviceability conditions, good agreement was obtained between experimental results and a theoretical model developed by the writers. Comparisons of code models in terms of both crack width and deflections highlighted the need for a calibration of code formulas to account for effects due to externally bonded reinforcement.     

Stiffness Degradation and Time to Cracking of Cover Concrete in Reinforced Concrete Structures Subject to Corrosion

Corrosion-induced cracks in reinforced concrete (RC) structures degrade the stiffness of the cover concrete. The stiffness degradation is mainly caused by the softening in the stress-strain relation in the cracked concrete. Limited efforts have been made to model the cracking and the corresponding effects on the cover concrete, despite of its importance in assessing and modeling the behavior of RC structures. This paper proposes a stiffness degradation factor to model the stiffness degradation of the cover concrete subject to cracking. The proposed factor is computed in terms of the cracking strain corresponding to the maximum opening of the concrete cracks based on an energy principle applied to a fractured RC structure. The time to cracking of the cover concrete is then determined as the time from the corrosion initiation needed by the crack front to reach the outer surface of the cover concrete. The proposed stiffness degradation factor and the method to compute the time to cracking are illustrated through two numerical examples. The times to cracking of the cover concrete that are predicted using the proposed method are in agreement with the measured values from laboratory experiments.     

Evaluating and Proposing Models of Predicting IC Debonding Failure

Debonding failure due to intermediate crack-induced (IC) fracture is one of the most dominant failure modes associated with the fiber-reinforced polymer (FRP) bonding technique. To date, extensive efforts have been paid by many researchers worldwide to study the debonding phenomenon for effective applications of FRP composites and rational design of FRP-strengthened structures. Based on these efforts and various relevant field applications, different models and code provisions have been proposed to predict IC debonding failure. Out of all the existing code provisions and models, five typical ones are investigated in the current paper. A comprehensive comparison among these code provisions and models is carried out in order to evaluate their performance and accuracy. Test results of 200 flexural specimens with IC debonding failures collected from the existing literature are used in the current comparison. The effectiveness and accuracy of each model have been evaluated based on these experimental results. Finally, based on a statistical analysis, a simple and more effective model for predicting the load-carrying capacity of FRP-strengthened flexural members due to IC debonding failure is proposed.     

Evaluation of Flexural Behavior and Serviceability Performance of Concrete Beams Reinforced with FRP Bars

Flexural behavior and serviceability performance of 24 full-scale concrete beams reinforced with carbon-, glass-, and aramid-fiber-reinforced-polymer (FRP) bars are investigated. The beams were 3,300?mm long with a rectangular cross section of 200?mm in width and 300?mm in depth. Sixteen beams were reinforced with carbon-FRP bars, four beams were reinforced with glass-FRP bars, two beams were reinforced with aramid-FRP bars, and two were reinforced with steel, serving as control specimens. Two types of FRP bars with different surface textures were considered: sand-coated bars and ribbed-deformed bars. The beams were tested to failure in four-point bending over a clear span of 2,750?mm. The test results are reported in terms of deflection, crack-width, strains in concrete and reinforcement, flexural capacity, and mode of failure. The experimental results were compared to the available design codes.     

Cracking and Reinforcement Corrosion in Short-Span Precast Concrete Bridges

A nationwide survey revealed 14 states having bridges comprised of precast, nonprestressed, concrete channel beams. Currently, the Arkansas State Highway and Transportation Department (AHTD) bridge inventory includes approximately 389 in-service bridges using 5.79?m precast channel beams that were constructed using 1952 AHTD bridge details. Results from a statewide inspection of these bridges conducted by the writers revealed bridges with extensive concrete longitudinal cracking at the flexural reinforcing steel level and exposed reinforcing steel. Approximately 2,000 beams in 95 precast concrete channel beam bridges were inspected during a statewide investigation; longitudinal cracking at the reinforcing steel level was observed in 60.4% of the beams and exposed flexural reinforcement in 21.2%. A combination of flexure cracking from the live-load overloads and the presence of moisture has led to this high level of beam deterioration. The source of this moisture is humidity and water seepage at joints between adjacent beams. This paper examines the causes of longitudinal cracking deterioration by examining the influences of water permeation and humidity on the corrosion of flexural reinforcement in precast concrete channel beams.     

New Approach for Estimating the Deflection of Beams Reinforced with FRP Reinforcement

Due to concerns with corrosion, the use of fiber-reinforced polymer (FRP) as a replacement to conventional steel reinforcement has greatly increased over the last decade. Researchers have identified the distinctive mechanical and bond properties of FRP reinforcement that prevent the use of existing relationships to establish serviceability of concrete structures reinforced with such products. Although studies have modified these empirical relationships to describe the behavior of structures reinforced with FRP reinforcement, this paper will provide a new approach to estimate deflection of concrete beams by considering material properties of the reinforcement and incorporating the effects of tension stiffening. Accuracy and precision of the approach was established by performing a statistical analysis on a database containing 171 FRP-reinforced concrete beams. Results were compared to those from existing proposed relationships and indicate the potential of the method to estimate deflection at various service conditions.