Effects of concrete composition on the interfacial parameters governing FRP debonding from the concrete substrate

For the concrete beam strengthened with FRP, failure may occur from the bottom of a major flexural/shear crack along 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 debonding behavior, the direct shear test was conducted with ten different compositions of concrete. Interfacial parameters were then derived according to a three-parameter model. The test results show little correlation between interfacial parameters and concrete compressive or splitting tensile strength. However, the debonding initiation strength and residual shear strength correlates well with the surface tensile strength and the maximum crack opening is mainly governed by the aggregate content. According to our results, the composition of the concrete is an important factor that should be considered explicitly in the investigation of FRP debonding from a concrete substrate.