Atomistic insights into the debonding of Epoxy–Concrete interface with water presence

In this study, molecular models are developed to investigate the water-induced bond degradation of the epoxy–concrete interface. Concrete is simulated using the C[sbnd]S[sbnd]H binder. The results indicate that the interfacial chemical bonds, including Ca–O, Ca–N, and H-bond, are reduced due to the existence of water at the interface. Two different roles of water molecules are characterized in the interfacial structure, including the filling and enlarging roles. The water presence degrades the interfacial bond strength and accelerates the interface debonding process, attributed to the weakened interaction between the epoxy and the C[sbnd]S[sbnd]H and the weakened load transfer of water molecules. The fracture position is transferred from the internal epoxy to the interface between the epoxy and the C[sbnd]S[sbnd]H. These atomic-level findings facilitate a better understanding of the interfacial deterioration of epoxy-bonded systems, e.g., fiber-reinforced polymer (FRP)-strengthened concrete structures with water presence at the interface.