The flexural response of concrete beams retrofitted with FRP and fibrous cementitious composites : a comparative experimental and analytical investigation

Abstract

The main objective of this study is to compare the flexural behavior of beams retrofitted at the tension face with Fiber Reinforced Polymers (FRP) such as Glass Fiber Reinforced Polymer (GFRP), Carbon Fiber Reinforced Polymer (CFRP), with cementitious fibrous composites such as Fiber Reinforced Concrete (FRC) and Slurry Infiltrated Fiber Reinforced Concrete (SIFCON). The tests were conducted on cast-in-place concrete beams in a single-point load bending application. Two batches of beams were considered unreinforced and reinforced with steel reinforcement at the tension face. The study aimed to examine their flexural behavior after retrofitting with the composite materials identified above. Theoretical models will be developed to compute the theoretical loads and deflections of beams retrofitted with GFRP, CFRP, FRC, and SIFCON to validate the experimental load-deflection curves. Mechanical parameters were obtained experimentally including ultimate load, ultimate deflection, rupture load, rupture deflection, stiffness, and toughness. This thesis aims to develop frameworks and guidelines for designing unreinforced and reinforced concrete beams retrofitted with different composite materials including cementitious fibrous and reinforced fiber polymers and to compare the results for constructability and application issues. The results of SIFCON Parallel and SIFCON Perpendicular extremely differ, having the only difference between the two composites being the fiber’s orientation. This simple direction transforms the composite from the best to the worst composite between all other retrofits. Polymers are mainly recommended to handle gravity loads and SIFCON Parallel is suitable for earthquake and high impulse loadings. From the study above, it was noted that the performance of SIFCON parallel with steel reinforcement had a higher ultimate load capacity than without steel of around 22.54%. SIFCON parallel reached the highest load capacity of 58.416 kN among all steel-reinforced specimens. SIFCON perpendicular and FRC resulted in the lowest and similar ultimate load capacity in the range of 29 kN, excluding regular concrete. From the comparison of polymers and cementitious composites without steel reinforcement, polymers primarily control the highest loads ranging from 40 to 50 kN as well as SIFCON parallel with 47.67 kN. It was discovered, however, that cementitious composites can maintain a significant amount of strength beyond peak levels in contrast to polymers, which tend to have a rapid failure right after peak loads. The rupture strains of SIFCON with fibers parallel to the load direction reached values of 8.1 mm compared to FRP reaching values of 4.4 mm.