Shear failure behavior and interfacial bonding mechanism of fiber/epoxy resin grouting concrete

The bonding interface between repair materials and existing concrete governs the structural integrity of rehabilitated systems, while the underlying mechanisms linking material composition, interfacial microstructure, and macroscopic shear performance remain inadequately understood. This study systematically investigates the shear failure behavior and interfacial bonding mechanisms of epoxy resin grouted concrete. The effects of curing agent types (JH45, T31, and JH593), interface moisture, grouting thickness, and fiber characteristics are quantitatively evaluated through direct shear tests. Micromechanical properties and microstructural evolution across the interfacial transition zone (ITZ) are characterized using nanoindentation, Fourier-transform infrared spectroscopy, and scanning electron microscopy with energy-dispersive X-ray spectroscopy. The results reveal that the curing agent plays a dominant role in governing the interfacial structure and failure behavior. JH45 leads to a sharp and mechanically weak interface that is susceptible to debonding, whereas T31 promotes the formation of a graded ITZ with mixed failure modes, and JH593 enables deep resin penetration, forming a micromechanically reinforced zone that induces cohesive failure within concrete. Interface moisture significantly deteriorates bonding performance, with its influence strongly dependent on the curing agent. The incorporation of fibers effectively transforms the failure mode from interfacial debonding to cohesive failure of the resin by mitigating defects, bridging stress, and enhancing interfacial bond. A strong correlation is identified between the micromechanical property gradient across the ITZ and the macroscopic failure path. This provides a fundamental, mechanism-based framework for designing high-performance epoxy repair systems by tailoring curing agent selection, fiber addition, and grouting parameters to engineer durable, shear-resistant concrete interfaces.