Effect of Concrete Composition on Interfacial Parameters Governing FRP Debonding from the Concrete Substrate

For concrete beams strengthened with FRP plates, FRP debonding may occur from the bottom of an intermediate flexural or shear/flexural crack in the span. As debonding failure occurs within the concrete, interfacial friction resulted from aggregate interlocking between opposing surfaces of the debonded zone plays an important role in the debonding behavior. Interfacial debonding can be analyzed with a three-parameter model. To investigate the effect of concrete composition on the debonding behavior, the direct shear test was conducted with ten different compositions of concrete. Interfacial parameters corresponding to each concrete composition were then derived according to the analytical model. It is found that the concrete compressive or splitting tensile strength shows little correlation with interfacial parameters. However, the debonding initiation strength and residual shear strength correlates well with the surface tensile strength, and the maximum sliding between FRP and concrete is mainly governed by the aggregate content. Test results indicate that the composition of concrete should be considered explicitly in the investigation of FRP debonding from a concrete substrate.