Assessment of FRP–Concrete Interfacial Debonding with Coupled Mixed-Mode Cohesive Zone Model

External bonding (EB) of fiber–reinforced polymer (FRP) laminates has emerged as a popular method to strengthen reinforced concrete (RC) structures. The premature failure of these structures is induced by debonding across the FRP–concrete interface. The mixed-mode debonding of the FRP–concrete interface will be analyzed by a cohesive zone model (CZM) derived from the modified Mohr–Coulomb strength criterion. The partial derivatives of the normal and tangential stresses that concern the interfacial separations will be presented in this study, which will facilitate the program coding to implement the proposed model. The coupled mixed-mode CZM provided a detailed description of the initial debonding and propagation of the FRP–concrete interface through a full range mixed-mode debonding process. Parametric studies will be conducted to provide a clear understanding of the mixed-mode loading-dependent debonding process of the FRP–concrete interface. The proposed model could be utilized to effectively and efficiently analyze the mixed-mode debonding of the FRP–concrete interface.