Characterization of interfacial bond failure in PVA fiber-reinforced concrete repair for sulfate-attacked concrete

Reinforced concrete structures in sulfate-rich environments are vulnerable to sulfate ions. Sulfate attack can seriously deteriorate concrete, so efficient repair methods are needed. Concrete structures often experience different levels of sulfate attack and washout. In this study, we investigated the interfacial bonding strength of the interface between polyvinyl alcohol (PVA) coarse fiber concrete and concrete. Splitting tensile tests were conducted with different numbers of sulfate dry–wet cycles and different interface roughness levels. In addition, the strain evolution at the interface was explored using digital image correlation. The microstructural evolution at the interface was examined using scanning electron microscopy. The results indicated that 88.89% of the bond failure samples exhibited interface failure. Therefore, the splitting tensile test can effectively characterize the interfacial bond strength. As sulfate dry-wet cycles increased, the accumulation of ettringite led to crystallographic coarsening and interfacial stress. Consequently, the splitting tensile strength at the interface decreased exponentially. Among them, the repair effect of Type III roughness (coarse aggregate with a certain exposed height) samples was most affected by sulfate erosion, with the repair effect decreasing from +45.84% to −29.48%. With the increase in roughness, the splitting tensile strength of the repaired specimen interface increased. For specimens not subjected to sulfate dry-wet cycles, the strength of Type II (initial exposure of coarse aggregate) showed a 10.23% increase compared to Type I (natural molded surface). Furthermore, the strength of Type III exhibited a more substantial increase of 40.68% over Type II. Specimens with low roughness exhibited progressive failure through micro-damage energy dissipation. By contrast, specimens with high roughness failed abruptly. This behavior was attributed to strain concentration induced by the development of complex stress-transfer paths. As the sulfate attack on the concrete substrate intensified, the enhancing effect of roughness on interfacial bonding performance was significantly reduced.