Concrete bridges play an important role in the efficiency and reliability of transportation civil infrastructure. Significant advancements have been made over the last decades to enhance the performance and durability of bridge elements at affordable costs. From an application perspective, novel analysis techniques and construction methods are particularly notable, which have led to the realization of more sustainable built-environments. As far as the evaluation and rehabilitation of constructed bridges are concerned, new nondestructive testing approaches provide accurate diagnosis and advanced composites, such as carbon fiber reinforced polymer (CFRP), have become an alternative to conventional materials. This Special Publication (SP) contains nine papers selected from two technical sessions held at The ACI Concrete Convention and Exposition – Spring 2018, in Salt Lake City, UT. The objective of the SP is to present technical contributions aimed to understand the state of the art of concrete bridges, identify and discuss challenges, and suggest effective solutions for both practitioners and government engineers. All manuscripts were reviewed in accordance with the ACI publication policy. The Editors wish to thank all contributing authors and reviewers for their rigorous efforts. The Editors also gratefully acknowledge Ms. Barbara Coleman at ACI for her knowledgeable guidance in the development of the SP.

This research focused on concrete beams with voids simulating beams with fully corroded steel that were repaired with CFRP laminates. The experimental program included testing five, approximately one-third-scaled simply supported rectangular concrete beams. In three beams, the oiled steel rebars for flexure and shear were safely pulled out of the formwork after the concrete had cured for six hours, leaving voids. This technique was used to represent an extreme case of corrosion, albeit non-realistic, that is even worse than being exposed to the most corrosive environment. The aim was to investigate the extent of improvement by CFRP to flexural and shear capacity of beams that contain fully corroded steel bars, simulated by voids. The first specimen was with voids representing completely deteriorated steel. The second was a plain concrete beam without voids. The third beam was a typical code-designed reinforced concrete (RC) beam, that represented the “original undeteriorated” beam. The two remaining deteriorated beams were repaired by externally bonding one and two layers of CFRP. Load carrying capacity, deflection, and ductility were measured and compared. The novel results of this investigation were that test results showed that one layer of CFRP increased the load capacity to slightly higher than the RC beam, and two layers of CFRP increased it by a factor of two. Finally, a computer model was created to estimate the performance of the tested beams and to carry out a parametric study to investigate the effects of CFRP longitudinal reinforcement ratio and CFRP transverse confinement ratio on the flexural performance of CFRP-repaired concrete beams. The predicted contribution of CFRP to flexure and shear capacities was in good agreement with test results.

Basalt-Fiber Reinforced Polymer (BFRP) bars have been recently proposed to be used to prestress precast concrete elements. Mechanical properties, potential low production cost, low carbon footprint, and enhanced durability make the application of BFRP to prestressed concrete promising. Nevertheless, some issues related to anchorage and sustained stress still need to be fully addressed. Applications are so far limited to few laboratory tests. This paper discusses how the Serviceability Limit State (SLS) and Ultimate Limit State (ULS) checks of prestressed elements employing this technology vary with respect to elements pre-stressed with steel tendons. Furthermore, an attempt is made to investigate the potential application into the precast concrete industry, by analyzing several typical roof and floor slab elements with different cross-sections. This investigation highlights which type of element could be more advantageously switched to the use of pre-stressed BFRP bars, and at which cost in terms of structural performance.

Two severely damaged concrete column-to-cap beam specimens were successfully repaired, using a carbon fiber-reinforced polymer (CFRP) cylindrical shell, non-shrink repair concrete, and headed steel bars. The first cast-in-place specimen experienced concrete crushing and longitudinal bars fracture/buckling; for the second precast specimen, the column was completely separated from the cap beam. In this paper, two analytical models, Model Fiber and Model Rotational Spring (RS), simulating the seismic performance of the repaired specimens are proposed. In Model Fiber, plasticity considering bond-slip effects was distributed over the defined plastic hinge length of the nonlinear beam-column element. In Model RS, a non-linear rotational spring was used to consider the concentrated plasticity located at the repaired cross-section. Low-cycle fatigue of the damaged column longitudinal steel bars was included in the analytical models. Simulations show that the analytical results, in terms of hysteretic response and moment-rotation, are in very good agreement with the experimental results. Model fiber performed better for predicting the pinching effect in the hysteretic response of the repaired cast-in-place specimen; Model RS performed better for matching the hysteresis curves of the repaired precast concrete specimen. In addition, Model Fiber was able to predict the local response of the columns including the fracture of longitudinal bars due to low-cycle fatigue.

This paper investigates the effects of material constituents on fresh and hardened properties of Self-Consolidating Concrete (SCC) mixture necessary for efficient prestressed bridge girder fabrication using a surrogate modeling technique. Response surface methodology (RSM)-based surrogate models consisting of input parameterssuch as density of coarse and fine aggregate were created based upon the past laboratory testing results for differentSCC mixture trials. These models were used to estimate various SCC material characteristics, including slump flow, J-ring flow, passing ability, filling capacity, Visual Stability Index (VSI), T50 (concrete spread time to reach the 50.8 cm [20 in] mark), column segregation, 16-hour compressive strength, and 28-days compressive strength, while examining the correlation between the input parameters on each material characteristic. To observe the effect of core input parameters in an efficient manner, 2D contour plot and 3D surface plot for material characteristics were also created. Then, statistical analyses with the testing results were performed to determine the accuracy of the surrogate models in terms of coefficient of regression (R2). Most of the R2 values are higher than 90%, indicating a higher degree of correlation among the testing and surrogate data. Average predicted-to-measure ratios of the surrogate models were almost equal to or slightly greater than 1.00, showing good agreement with the testing results, and specifically, the surrogate and testing values for J-ring flow and 28-days compressive strength were nearly identical. Key findings indicate that the coarse aggregate content significantly affected the characteristics of the SCC mixtures.