Bond between FRP and concrete in reinforced concrete beams strengthened with near surface mounted and externally bonded reinforcement

The paper concerns bond behaviour between composite carbon fibre reinforced polymer (CFRP) materials and concrete in externally bonded (EB) and near surface mounted (NSM) FRP strengthened reinforced concrete (RC) beams. Bond mechanism was investigated on the modified RILEM beam bond test in aspect of six parameters: beam’s span and depth, longitudinal steel reinforcement, type of the CFRP strips/sheets, CFRP bond length, and compressive concrete strength. The influence of the existing steel reinforcement on the FRP-to-concrete bond conditions was investigated in the beams with continuous longitudinal steel bars and in the beams with cut longitudinal reinforcement at the mid-span. The test confirmed a crucial rule of the internal steel bars on the FRP-to-concrete bond and failure modes.