Mechanical properties of interface between concrete structure and repair mortar under multivariate conditions

In the repair of concrete structures, the interface bonding performance between the repair material and concrete matrix directly determines the reinforcement effect and long-term durability. However, the mechanical behavior and bonding mechanism under multiple factors are not yet clear. In this study, 3D printing was used to prepare different roughness templates combined with the solid mold method to fabricate seven groups of repair material–concrete interface specimens. The flexural and shear tests revealed the effects of repair material type, curing conditions, interface roughness, and normal load on the interface bonding performance, and its mechanism was revealed. The results showed that the failure modes of interface are sliding, shear, and tensile, and the failure mode was mainly influenced by interface roughness and normal stress. The interface roughness was significantly positively correlated with the bond strength, and the rough interface greatly improved the bonding performance through anchoring and friction effects. The effect of curing conditions on strength was seawater curing > freshwater curing > standard curing. The salinization and cementation effects of the seawater environment can strengthen interface bonding. The interfacial bonding strength of the modified mortar was significantly higher than that of the ordinary mortar, and the PTB emulsion contained in the modified mortar could optimize the interface microstructure and play a reinforcing role. The normal load was the dominant factor affecting the shear strength of the interface, and its effect was much greater than that of the type of repair material, curing conditions, and interface roughness. Based on the shear mechanical behavior of the structural plane, a shear strength calculation method for the three failure modes was established. This study provides theoretical support and design basis for the optimization of the interface treatment process in concrete structure repair, and has important theoretical and practical significance for improving the long-term service performance of repaired structures.