Experimental study on mechanical and fracture characteristics of rock–concrete interface under dynamic direct tension

Abstract Rock–concrete interface is common in rock engineering, such as shotcreting in underground cavern, socketed pile, bridge anchorage etc. These rock–concrete interfaces are often subjected to dynamic tension, which can be induced by the compressive wave reflected by the free surface, and results in interfacial spalling even the collapse of rock–concrete structure. However, the dynamic tensile behavior of the rock–concrete interface under different loading directions, particularly the failure mechanism, is still unclear. This study employs split Hopkinson tension bar testing on rock–concrete specimens to investigate the influence of rock type, loading rate and direction on these tensile behaviors. Results show that rock–concrete interfaces exhibit distinct tensile behaviors depending on the rock type, primarily influenced by the interfacial tensile force. With increasing loading rate, both the dynamic tensile strength and average dynamic modulus of the granite–concrete interface increase, while the dynamic peak strain shows a decreasing trend. Loading direction has a significant effect on dynamic tensile behaviors of granite–concrete specimens. The dynamic tensile strength increases with the loading direction angle, and the failure mode changes accordingly from interfacial tensile failure to mixed tensile failure. Macro and micro morphologies indicate that the effect of loading direction and loading rate is attributed to the interfacial contact area and unit interfacial tensile strength, respectively. The findings can contribute to a deeper understanding of the dynamic tensile behavior of rock–concrete structures under different loading directions and can be applied to the design and reinforcement of practical engineering.