GFRP bars are considered an alternative to steel for concrete reinforcement. This project investigated the fatigue behavior of GFRP bars embedded in concrete, studying bond behavior at material and structural scales. GFRP bars (12 mm [0.47 in.] nominal diameter) were embedded in concrete cylinders leaving a 50 mm [2 in.] protrusion at the free end and featuring different bonded lengths. Two types of GFRP bars with different surface treatment (lacquered and unlacquered) were used. Static tests were used to determine the bonded length required for cyclic pull-out tests, Cyclic tests at 1.5 Hz showed GFRP bar failure was possible at just 20% of their reduced tensile strength (0.8ffu) as prescribed in ACI 440.1R-15. Two full-scale slabs internally reinforced with unlacquered GFRP bars were tested using a four-point bending configuration. A quasi-static test was used as a control to determine the fatigue amplitude, considering the fatigue loading provided by the ACI 440.1R-15 document and the pull-out test results with cyclic loading presented in this work. Cyclic load between 10 kN [2.25 kips] and 40 kN [9 kips] at a 1.5 Hz frequency was applied up to 5 million cycles before a subsequent quasi-static test was conducted. The load range was determined using cross-section analysis to cycle the bars between 5% and 20% of their reduced tensile strength (0.8ffu). Both slabs ultimately failed due to shear failure, with cyclic loading having little impact on the slab compliance. Displacements of the load points and supports were measured using linear variable displacement transformers (LVDTs), while digital image correlation (DIC) was utilized to obtain the full-field displacement and strain in the central region of the slab. The strain and displacement fields from DIC were used to determine the opening of flexural cracks and relate it to the stress level in the GFRP bars. A comparison between the static pull-out tests and the four-point bending tests of slabs indicated that the pull-out test could be used to describe the flexural behavior of the slab at low stress level. However, in terms of fatigue behavior, the comparison between the small- and large-scale tests indicated that the fatigue phenomenon in the slab was quite complex and could not be directly described by the results of pull-out tests.

While reinforced concrete is one of the most used construction materials, traditional reinforcement steel may cause undesirable side effects, as corrosion and the associated volume changes can lead to damages in the concrete matrix and can cause spalling, which may significantly reduce the load-bearing capacity and service life of structures. Alternative reinforcement methods, such as glass or basalt fiber reinforced polymer rebars, can serve as a viable alter-native to reduce or eliminate some of the disadvantages associated with steel reinforcement. In addition to an increased tensile strength and a reduction in weight, fiber reinforced polymer rebars also offer a high corrosion resistance among other beneficial properties. Because these materials are not fully regulated yet and the durability properties have not been conclusively determined, further research is needed to evaluate the material durability properties of FRP rebars. To determine the durability properties of GFRP and BFRP rebars in cold climates, the freeze-thaw resistance of these materials was evaluated throughout this study. Specifically, two types of materials (basalt and glass reinforced polymers) and two common rebar sizes (8 mm (#2) and 16 mm (#5) diameters) were tested. To quantify the freeze-thaw-durability, tensile tests according to ASTM D7205, transverse shear strength tests in line with ASTM D7617, and horizontal shear strength tests as specified in ASTM D4475 were conducted on numerous virgin fiber rebars and on fiber rebars that were subjected to 80 and 160 freeze-thaw cycles. While the results from the virgin materials served as benchmark values, the measurements and analysis from the aged (by freeze-thaw cycles) materials were used to quantify and determine the strength retention capacity of these bars. The results showed that a higher number of freeze-thaw cycles lead to lower strength retention for some rebar types. In addition, it was seen that rebar products respond differently to the aging process; while some material properties notably deteriorated, other material properties were insignificantly affected.

This paper presents experimental and theoretical investigations on the residual tensile and bond response of polypara-phenylene-benzo-bisthiazole (PBO) fabric reinforced cementitious matrix (FRCM) composites after the exposure to elevated temperatures ranging between 20 °C [68 ºF] and 300 °C [572 ºF]. Experimental results obtained from direct tensile (DT) and single-lap direct shear (DS) tests carried out respectively on PBO FRCM specimens and PBO FRCM-concrete elements were reported and discussed. Overall, specimens exposed to temperatures up to 200 °C [392 ºF] did not present significant reductions of both bond and tensile properties. This result can be attributed to the thermal shrinkage underwent by the inorganic matrix, which may enhance the bond between the fibers and the matrix. On the other hand, when the specimens were heated at 300 °C [572 ºF], marked reductions were observed, primarily stemming from the degradation of both mechanical properties of the FRCM constituent materials and the fiber-to-matrix bond. Subsequently, the experimental results were used for the following purposes: (i) to assess whether the Aveston–Cooper–Kelly (ACK) theory is able to describe the tensile behavior of FRCM materials at elevated temperatures; (ii) to define temperature-dependent local bond stress vs. slip law and (iii) to evaluate the ability of degradation models to simulate the variation with temperature of the FRCM tensile and bond properties. The results obtained from the theoretical analyses showed that, for all the tested temperature, the relative differences between predicted and experimental results are very low, confirming the accuracy of the proposed approaches.

Deterioration of concrete bridges has resulted in reduction of their service lives and increase in required maintenance which is associated with cost and inconvenience to the public. A prevalent cause of concrete bridge deterioration is corrosion which initiates by chloride ions penetration past the protecting layers and by corroding the steel reinforcement. Because corrosion in prestressed concrete members has more serious consequences than in non-prestressed reinforced concrete, it is important that bridge designers and inspectors be aware of the potential problems and environments that may cause the issue and address them as soon as they are detected. This paper discusses a case study of a highway bridge (Hyndman Bridge, Ontario) including its deterioration, causes, mitigation measures, structural evaluation and the selected repair method. The rehabilitation design is based on guidelines of the latest editions of the CHDBC and ACI 440.2R. CFRP strengthening techniques have been proposed to address the flexure and shear deficient capacity of deteriorated girders. It is concluded that by using a suitable repair methodology employing CFRP, it is possible to upgrade the bridge to comply with the latest requirements of the code and increase the service life of the structure which otherwise would have needed imminent replacement.

The seismic performance of reinforced concrete (RC) bridge columns subjected to multidirectional ground motions is a critical issue, as these columns can experience axial compression, bending, and torsional loading. Moreover, steel corrosion is a significant concern in existing bridges, leading to deficiencies in steel-RC structural members. The use of glass fiber-reinforced polymer (GFRP) reinforcement has been established as a practical and effective solution to mitigate the corrosion-related issues associated with traditional steel reinforcement in concrete structures. However, the dissimilar mechanical properties of GFRP and steel have raised apprehensions regarding its feasibility in seismic-resistant structures. The current study involves conducting an experimental investigation to assess the feasibility of utilizing GFRP reinforcement as a substitute for conventional steel reinforcement in circular RC bridge columns subjected to cyclic lateral loading, which induces shear, bending, and torsion. One column was reinforced with GFRP bars and stirrups, while the other column, served as a control and was reinforced with conventional steel reinforcement. The aim of this investigation was to analyze the lateral displacement deformability and energy dissipation characteristics of the GFRP-RC column. The results showed that GFRP-RC column exhibited stable post-peak behavior and high levels of deformability under the applied combined loading. Additionally, with a torsion-to-bending moment ratio of 0.2, both columns reached similar lateral load and torsional moment capacities and were able to attain lateral-drift capacities exceeding the minimum requirements of North American design codes and guidelines.