Investigation of Settlement of a Jointed Concrete Pavement

A section of jointed concrete pavement on U.S. 75, which was built from 1982 to 1985, in the Paris District of the Texas Department of Transportation (TxDOT) experienced severe pumping and settlement, even though two types of treatment (full depth repair and polyurethane foam injection) were performed. An extensive field investigation was conducted using ground penetrating radar, falling weight deflectometer, dynamic cone penetrometer, and coring to identify the causes of the continued pumping and settlement problems, and develop an optimal repair strategy. The pavement evaluation included tie bar condition, load transfer efficiency (LTE) at transverse and longitudinal construction joints, and base support conditions. Some of the tie bars failed in shear due to corrosion, which resulted in substantially low LTEs (<40%) at longitudinal construction joints. Pumping and settlement problems were more pronounced where the tie bars failed; the resulting large deflections exacerbated the pumping and settlement problems. The results demonstrate the importance of adequate LTEs (>80%) provided by tie bars, base and subgrade support, in providing satisfactory JCP performance. Inadequate design or construction of any of these critical elements could lead to performance problems, potentially including severe settlement, which is quite difficult to repair. To repair this pavement section, the Paris District of TxDOT is planning to retrofit tie bars by the “slot stitching” method, along with filling the voids under the slab using grout, followed by thin overlay using latex modified concrete to correct the differential elevation problems at longitudinal construction joints. It is expected that this repair strategy will address the distress problems and extend the pavement life.     

Influence of Reinforcement on the Behavior of Concrete Bridge Deck Slabs Reinforced with FRP Bars

This paper presents the results of an experimental study to investigate the role of each layer of reinforcement on the behavior of concrete bridge deck slabs reinforced with fiber-reinforced polymer (FRP) bars. Four full-scale concrete deck slabs of 3,000?mm length by 2,500?mm width and 200?mm depth were constructed and tested in the laboratory. One deck slab was reinforced with top and bottom mats of glass FRP bars. Two deck slabs had only a bottom reinforcement mat with different reinforcement ratios in the longitudinal direction, while the remaining deck slab was constructed with plain concrete without any reinforcement. The deck slabs were supported on two steel girders spaced at 2,000?mm center to center and were tested to failure under a central concentrated load. The three reinforced concrete slabs had very similar behavior and failed in punching shear mode at relatively high load levels, whereas the unreinforced slab behaved differently and failed at a very low load level. The experimental punching capacities of the reinforced slabs were compared to the theoretical predictions provided by ACI 318-05, ACI 440.1R-06, and a model proposed by the writers. The tests on the four deck slabs showed that the bottom transverse reinforcement layer has the major influence on the behavior and capacity of the tested slabs. In addition, the ACI 318-05 design method slightly overestimated the punching shear strength of the tested slabs. The ACI 440.1R-06 design method yielded very conservative predictions whereas the proposed method provided reasonable yet conservative predictions.     

Finite Element Analysis of Concrete Pavements Over Culverts

Accelerated distress of Portland cement concrete pavements (PCCP) over structures such as culverts, pipes, and tunnels beneath roadways is a common occurrence. In this article, finite element analysis is employed to analyze the response of concrete pavements over such structures. The factors that influence the overlying pavement slabs include: (1) cover depth, (2) pavement slab thickness and length, (3) cement concrete elastic modulus, (4) foundation modulus, and (5) backfill soil modulus. The tensile stresses at the bottom and top of the slab induced by wheel loads are predicted. In the traditional pavement design only the tensile stress at the bottom of the slab is considered to be significant. However, this study shows that the tensile stress at the top surface of pavement slabs over culverts may also cause the concrete pavements to fail. A laboratory model was employed to study the mechanical characteristics of Portland cement concrete pavement slabs over culverts and to verify the theoretical analysis.     

退化钢筋混凝土桥梁概率耐久性评估方法

提出了考虑时间、空间变异特性的退化钢筋混凝土桥梁耐久性概率评估的随机有限元方法.首先,通过考虑钢筋与混凝土之间时变的粘结滑移关系及腐蚀钢筋的应力应变关系,采用弥散裂纹方法对退化钢筋混凝土桥梁进行有限元分析.然后,提出了退化钢筋混凝土桥梁耐久性概率评估的随机有限元分析方法,基于文献及现场调查的数据,采用蒙特卡罗仿真方法对钢筋均匀及点锈蚀、混凝土保护层厚度、表面氯离子含量、氯离子扩散系数及腐蚀率等进行随机抽样,考虑这些时变及空间变异的因素对钢筋混凝土桥梁可靠度的影响.最后,以天津滨海新区的一座钢筋混凝土梁桥为例分析了所提方法的应用.     

Transverse Thermal Expansion of FRP Bars Embedded in Concrete

Fiber reinforced polymers (FRPs) have a thermal expansion in the transverse direction much higher than in the longitudinal direction and also higher than the thermal expansion of hardened concrete. The difference between the transverse coefficient of thermal expansion of FRP bars and concrete may cause splitting cracks within the concrete under temperature increase and, ultimately, failure of the concrete cover if the confining action of concrete is insufficient. This paper presents the results of an experimental investigation to analyze the effect of the ratio of concrete cover thickness to FRP bar diameter (c/db) on the strain distributions in concrete and FRP bars, using concrete cylindrical specimens reinforced with a glass FRP bar and subjected to thermal loading from ?30?to?+80°C. The experimental results show that the transverse coefficient of thermal expansion of the glass FRP bars tested in this study is found to be equal to 33 (×10?6?mm/mm/°C), on average and the ratio between the transverse and longitudinal coefficients of thermal expansion of these FRP bars is equal to 4. Also, the cracks induced by high temperature start to develop on the surface of concrete cylinders at a temperature varying between +50 and +60°C for specimens having a ratio of concrete cover thickness to bar diameter c/db less than or equal to 1.5. A ratio of concrete cover thickness to glass fiber reinforced polymers (GFRP) bar diameter c/db greater than or equal to 2.0 is sufficient to avoid cracking of concrete under high temperature up to +80°C. The analytical model, presented in this paper, is in good agreement with the experimental results, particularly for negative temperature variations.     

3D Finite Element Analysis of Temperature‐Induced Stresses in Dowel Jointed Concrete Pavements

A detailed 3D finite element (3DFE) model is developed to investigate the applicability of Westergaard’s curling stress equations to doweled jointed concrete pavements. The model does not rely on any of Westergaard’s assumptions and is capable of handling nonlinear and/or time‐dependent temperature profiles. However, only linear gradient is applied to facilitate the comparison with Westergaard’s results. The transverse stress calculated using Westergaard’s formula was found to be within 10% of that computed using 3DFE. Westergaard’s longitudinal stress equation required a correction. The 3DFE results confirm Westergaard’s finding that the slab curling stresses are independent of slab length. Thus, curling stress does not explain the field‐observed dependency of mid‐slab cracking on the slab length. Through the examination of the mechanism of dowel‐concrete interaction, it is shown that uniform temperature changes play the major role in mid‐slab transverse cracking of relatively long slabs. Due to built‐in slab curling as well as temperature or moisture curling, the dowel bars bend restricting the slab from free contraction due to uniform temperature drop. This gives rise to a large component of stress that has not been considered in previous investigations. Application of a combined temperature gradient and uniform temperature drop to slabs of different lengths revealed the dependency of mid‐slab transverse cracking on slab length.     

Influence of Reinforcing Bars on Shrinkage Stresses in Concrete Slabs

It is well known that cracking in concrete slabs significantly influences their service life. Concrete shrinkage may be the principle reason for the initial crack formation in the slabs. This paper presents an attempt to provide an analytical tool for the prediction of stress distribution in reinforced concrete slabs after undergoing matrix shrinking restrained by the reinforcing bars. The model incorporates the material parameters of the reinforcing bar and the concrete matrix, and it enables prediction of the stress development in concrete with time.     

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.     

R6.5／12—1200板坯纵裂原因分祈

针对R6．5／12—1200板坯连铸中出现的纵裂缺陷,采取降低和控制纵裂发生的措施。通过采取措施,使板坯纵裂大幅度降低。     

Experimental Study on the Performance of Approach Slabs under Deteriorating Soil Washout Conditions

In the U.S. bridge design practice, an approach slab is commonly provided to facilitate a smooth transition from the highway pavement to the bridge deck. Maintenance of bridge approaches often necessitates the repair or replacement of approach slabs owing to damage from heavy traffic loads, washout of fill materials, and settlement of the approach embankment. Approach slab damage because of embankment settlement is considered a more common problem and has been extensively investigated in the literature. In this paper, performance of the approach slab degraded by void formation underneath the slab is examined by load testing. Full-size approach-slab specimens were tested under increasing magnitude up to four times AASHTO HS20-44 design truck loads. The test matrix included four slab specimens with the following details: (1)?conventional steel reinforcement representative of current California design; (2)?steel reinforcement replaced by a double-layer pultruded fiber-reinforced polymer grating; (3)?steel reinforcement replaced by glass fiber-reinforced polymer rebars; and (4)?incorporation of steel and polyvinyl alcohol fibers in the concrete mix and removal of top longitudinal and transverse steel. Results indicated that the slabs show satisfactory performance under standard HS20-44 design truck load. Tests also revealed that these slabs exhibited similar performance in terms of stiffness, deformation, and crack pattern when fully supported, but registered noticeable difference in performance under deteriorating soil washout conditions. The fiber-reinforced concrete slab in general showed the best crack control and the smallest deflection and end rotation among the four slabs.     

连铸板坯纵裂原因浅析

根据宝钢连铸大生产实绩，调查了影响板坯纵裂的因素，分析了连铸板坯发生纵裂的原因，通过采取一定的措施，使连铸坯裂指数有一定的改善。     

Fatigue Life Evaluation of Concrete Bridge Deck Slabs Reinforced with Glass FRP Composite Bars

Since bridge deck slabs directly sustain repeated moving wheel loads, they are one of the most bridge elements susceptible to fatigue failure. Recently, glass fiber-reinforced polymer (FRP) composites have been widely used as internal reinforcement for concrete bridge deck slabs as they are less expensive compared to the other kinds of FRPs (carbon and aramid). However, there is still a lack of information on the performance of FRP–reinforced concrete elements subjected to cyclic fatigue loading. This research is designed to investigate the fatigue behavior and fatigue life of concrete bridge deck slabs reinforced with glass FRP bars. A total of five full-scale deck slabs were constructed and tested under concentrated cyclic loading until failure. Different reinforcement types (steel and glass FRP), ratios, and configurations were used. Different schemes of cyclic loading (accelerated variable amplitude fatigue loading) were applied. Results are presented in terms of deflections, strains in concrete and FRP bars, and crack widths at different levels of cyclic loading. The results showed the superior fatigue performance and longer fatigue life of concrete bridge deck slabs reinforced with glass FRP composite bars.     

Modeling Debonding Failure in FRP Flexurally Strengthened RC Members Using a Local Deformation Model

Reinforced concrete (RC) beams and slabs can be strengthened by bonding fiber-reinforced polymer (FRP) composites to their tension face. The performance of such flexurally strengthened members can be compromised by debonding of the FRP, with debonding initiating near an intermediate crack (IC) in the member away from the end of the FRP. Despite considerable research over the last decade, reliable IC debonding strength models still do not exist. The current paper attempts to correct this situation by presenting a local deformation model that can simulate IC debonding. The progressive formation of flexural cracks, and the associated crack spacings and crack widths are modelled from initial cracking to the onset of debonding. The bond characteristics between the longitudinal steel reinforcement and concrete, and the FRP and concrete, as well as the tension stiffening effect of the reinforcement and FRP to the concrete, are considered. The FRP-to-concrete bond-slip relation is used to determine the onset of debonding. The analytical predictions compare well with experimental results of FRP-strengthened RC cantilever slabs.     

Efficient Strengthening Technique to Increase the Flexural Resistance of Existing RC Slabs

Composite materials are being used with notable effectiveness to increase and upgrade the flexural load carrying capacity of reinforced concrete (RC) members. Near-surface mounted (NSM) is one of the most promising strengthening techniques, based on the use of carbon fiber-reinforced polymer (CFRP) laminates. According to NSM, the laminates are fixed with epoxy based adhesive into slits opened into the concrete cover on the tension face of the elements to strength. Laboratory tests have shown that the NSM technique is an adequate strengthening strategy to increase the flexural resistance of RC slabs. However, in RC slabs of low concrete strength, the increase of the flexural resistance that NSM can provide is limited by the maximum allowable compressive strain in the compressed part of the slab, in order to avoid concrete crushing. This restriction reduces the effectiveness of the strengthening, thus limiting the use of the NSM technique. A new thin layer of concrete bonded to the existing concrete at the compressed region is suitable to overcome this limitation. Volumetric contraction due to shrinkage and thermal effects can induce uncontrolled cracking in the concrete of this thin layer. Adding steel fibers to concrete [steel fiber-reinforced concrete (SFRC)], the postcracking residual stress can be increased in order to prevent the formation of uncontrolled crack patterns. In the present work, the combined strengthening strategy, a SFRC overlay and NSM CFRP laminates, was applied to significantly increase the flexural resistance of existing RC slabs. Experimental results of four-point bending tests, carried out in unstrengthened and strengthened concrete slab strips, are presented and analyzed.     

Durability of GFRP Bars’ Bond to Concrete under Different Loading and Environmental Conditions

In the last decade, noncorrodible fiber-reinforced polymer (FRP) reinforcing bars have been increasingly used as the main reinforcement for concrete structures in harsh environments. Also, owing to their lower cost compared with other types of FRP bars, glass-FRP (GFRP) bars are more attractive to the construction industry, especially for implementation in bridge deck slabs. In North America, bridge deck slabs are exposed to severe environmental conditions, such as freeze-thaw action, in addition to traffic fatigue loads. Although the bond strength of GFRP bars has been proved to be satisfactory, their durability performance under the dual effects of fatigue-type loading and freeze-thaw action is still not well understood. Few experimental test data are available on the bond characteristics of FRP bars in concrete elements under different loading and environmental conditions. This research investigates the individual and combined effects of freeze-thaw cycles along with sustained axial load and fatigue loading on the bond characteristics of GFRP bars embedded in concrete. An FRP-reinforced concrete specimen was developed to apply axial-tension fatigue or sustained loads to GFRP bars within a concrete environment. A total of thirty-six test specimens was constructed and tested. The test parameters included bar diameter, concrete cover thickness, loading scheme, and environmental conditioning. After conditioning, each specimen was sectioned into two halves for pullout testing. Test results showed that fatigue load cycles resulted in approximately 50% loss in the bond strength of sand-coated GFRP bars to concrete, while freeze-thaw cycles enhanced their bond to concrete by approximately 40%. Larger concrete covers were found more important in cases of larger bar sizes simultaneously subjected to fatigue load and freeze-thaw cycles.     

Improved Longitudinal Joint Details in Decked Bulb Tees for Accelerated Bridge Construction: Fatigue Evaluation

This companion paper focuses on an investigation of improved continuous longitudinal joint details for decked precast prestressed concrete girder bridge systems. Precast concrete girders with an integral deck, which are cast and prestressed with the girder, provide benefits of rapid construction along with improved structural performance and durability. Despite these advantages, the use of this type of construction has been limited to isolated regions of the United States. One of the issues limiting more widespread use is the perceived problem with durability of longitudinal joints used to connect adjacent girders. Four full-scale slabs connected by No. 16 (#5) headed reinforcement detail using a 152 mm (6 in.) lap length were fabricated and tested. An analytical parametric study was conducted to provide a database of maximum forces in the longitudinal joint. These maximum forces are then used to determine the loading demand necessary in the slab testing due to the service live load. Static and fatigue tests under four-point pure-flexural loading, as well as three-point flexural-shear loading, were conducted. Test results were evaluated based on flexural capacity, curvature behavior, cracking, deflection, and steel strain. Based on these test results, the improved longitudinal joint detail is a viable connection system that transfers the forces between the adjacent decked bulb tee girders.     

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.     

Effect of High-Performance Steel on the Tension Stiffening and Cracking Behavior of Reinforced Concrete (RC) Tension Ties

In construction industry, the application of high-performance reinforcement bar is required strongly. Unfortunately, not nearly enough research has been conducted on high-performance steel in comparison with high strength concrete. This paper describes the effect of high-performance steel as reinforcement steel bar on the tension response and cracking behavior of concrete and fiber-reinforced strain-hardening cement-based composite (SHCC) tension members. High-performance steel is characterized by higher strength in comparison to ASTM A615-06 Grade 60 steel. The tension stiffening effect on high-performance reinforcing bars embedded in cement-based composite prism is investigated experimentally. The variables in the study are types of cement-based composite (conventional concrete, synthetic fiber-reinforced cement composite), yielding strength of steel bars (400MPa and 600MPa), and types of loading (monotonic and repeated tension loading).     

Effect of Fiber-Reinforced Polymer Wraps on Corrosion Activity and Concrete Cracking in Chloride-Contaminated Concrete Cylinders

This paper presents the results of an experimental study designed to investigate the effect of fiber-reinforced polymer (FRP) wraps on corrosion activity and concrete cracking in chloride-contaminated concrete cylinders. Thirty-five concrete cylinders, each having 102?mm diameter and 204?mm height, concentrically reinforced with one steel reinforcing bar, were subjected to accelerated corrosion exposure for 80?days. Test parameters included level of applied potential, presence of FRP wraps, and bar diameter. The corresponding current and concrete expansion were continuously monitored throughout the corrosion exposure. At the end of the test, the steel bars were extracted, cleaned of rust, and weighed to determine the actual steel mass loss. The results showed that, for the same applied fixed potential, FRP wraps effectively reduced the corresponding current, the concrete expansion, and the steel mass loss. For the same applied potential, the current density increased as the bar diameter decreased. For the same corrosion depth, the circumferential expansion of the cylinder caused by corrosion decreased as the concrete cover-to-bar diameter ratio (c/d) increased.     

Investigation of Cracking in Concrete Bridge Decks at Early Ages

The loads, construction procedures, and material behavior influence the performance of the bridge deck as well as its structural integrity. This paper includes a thorough investigation to identify the probable causes of cracking in reinforced concrete bridge decks, particularly at early ages. The objectives of the study were addressed through a literature review process and a comprehensive nationwide survey. Experiments were performed to establish the magnitude of the modulus of elasticity of concrete at early ages as well as the curvature it can withstand without cracking. A computer program was developed to take into account the loads due to sequence of pours. A compendium was developed to categorize the various causes of cracking to identify appropriate procedures that may control this cracking. The parameters considered in the investigation were age of concrete, stage and sequence of pours, curing procedures, heat of hydration, strength gain, thermal changes, and construction type. Results of the literature review and survey indicated that in most cases, cracking of concrete may be attributed to the high evaporation rate and high magnitude of shrinkage. Other factors include the use of high slump concrete, excessive water in the concrete, insufficient top reinforcement cover, insufficient vibration of the concrete, inadequate reinforcing details of the joint between the new and old deck, sequence of pour, and weight and deflection of the forms. The calculated curvatures for the selected bridges were smaller than the curvatures needed to crack dynamically loaded fresh concrete in a laboratory environment.