Investigation on variables affecting bond strength between FRP reinforcing bar and concrete by modified hinged beam tests

Abstract The bond strength between FRP reinforcement and concrete significantly affects the load bearing capacity and deformation ability of an FRP reinforced concrete member subjected to bending. There are numerous parameters affecting this bond. In the past, however, studies of FRP rebar-concrete bond strength have considered only one or more of the basalt, glass and carbon FRP reinforcement types, and generally only one or a limited number of surface properties. Since all variables affecting this bond were not set forth, experiments were not conducted on the basis of keeping other test variables constant to examine the effect of a single parameter. In this study, in order to conduct a proper experimental study on concrete-FRP bond by isolating a single parameter in the related tests, 90 hinged beam tests were carried out under transverse loading. The effects of reinforcement fiber type (basalt, glass, carbon), reinforcement surface property (ribbed, wrapped, wounded, sand coated), distance between rebars, bottom and side concrete cover, reinforcement diameter, reinforcement embedment length, presence of stirrups, concrete compressive strength on FRP -concrete bond strength were investigated. Experiments conducted within the scope of this study showed that the effects of concrete compressive strength and concrete cover (bottom and side) on this bond are limited. Moreover, the bond strength values of rebars with mechanical interlocking load-bearing mechanism were found to be higher than the respective values of the ones with friction mechanism. Finally, an increase in the modulus of elasticity of FRP resulted in an increase in bond strength and the presence of stirrups in the beams reduced the bond strength.