Bonding Fracture and Deformation Behaviors of Sandstone–Concrete Interface Subjected to Different Temperatures under Three-Point Bending

Thermal operations threaten the safety of geological engineering, especially the rock–concrete interface, as the link of in situ stress transmission is crucial to structural stability. In this study, three-point bending experiments were conducted on sandstone–concrete binary specimens to investigate the thermal effect on fracture behaviors of the rock–concrete bonding interface. The deformation evolution characteristics were analyzed by digital image correlation (DIC). The results demonstrated that the temperature has a remarkable degradation for the bonding capacity of sandstone–concrete interfaces, which can be classified into the rapid-damage stage and steady-damage stage with a critical temperature of 300°C. The phased degradation is closely related to the decline in interfacial adhesion and the thermal damage to concrete, instead of sandstone. By determining the strain inflection point of different positions on the crack path, a new idea is proposed to reveal the crack propagation process. During the loading process, the crack propagates slowly to a certain length and then coalescences violently when subjected to a small load increment. In addition, the crack initiation load is weakened by the elevated temperature or lower interface roughness.