The potential of Fiber Reinforced Polymer (FRP) in the reinforcement of concrete structures has been shown in many studies and practical applications. However, few works have focused systematically on the development of quantitative criteria to measure surface roughness and relate this parameter to the bonding mechanical property. Moreover, some researchers have declared that, if the concrete interface is rougher, the bond performance between FRP and concrete will be increase, However, there is no answer to how rough the surface is. There are limited application standards for engineers to conduct in FRP reinforcement projects. This work evaluated several concrete specimens with three different strengths and six types of interface roughness. A single shear test was conducted to study the influence of surface roughness on the interfacial bonding performance of a carbon fiber-reinforced composite (CFRP)-concrete beam. The results show that, among the six interfaces, a concrete interface with the roughness of 0.44 has the best interfacial bonding performance. An interfacial appearance with the cement mortar almost cleaned away, and almost one fifth of the single coarse aggregate bared will get the best bond performance. Roughness parameters significantly influenced the effective bond length. The effective bond length of the six interfaces experienced an overall decreasing trend as the roughness increased. The bond–slip curves of concrete interfaces with roughness of 0.25–0.44 did not significantly change the rigidity within the brittle region. The rougher the interface was, the shorter the brittle region was. After entering a plasticity stage, the bond–slip curves for the six types of interfaces all declined with different slopes, and the max slip values were 0.04–0.35 mm when debonding failure occurred.
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