Uniaxial creep behavior and constitutive model of rock-concrete composites with different interface roughness

Uniaxial compression and stepwise loading creep tests were conducted on rock-concrete composites with different interface roughness levels (JRC-0, JRC-2, JRC-4, and JRC-6) to systematically investigate the influence of interface characteristics on the mechanical properties and long-term creep behavior of the composites. The results show that interface roughness significantly enhances the load-bearing capacity and stiffness of the composites. As JRC increases, the uniaxial compressive strength and elastic modulus increase by approximately 75% and more than 100%, respectively. Digital image correlation (DIC) results reveal that increasing interface roughness effectively inhibits interfacial sliding and promotes the transition of strain distribution from a relatively uniform state to localized shear bands. Accordingly, the failure mode gradually evolves from interfacial failure to matrix shear-splitting failure. The creep test results indicate that all specimens exhibit typical stepwise creep characteristics, with creep strain and creep rate increasing markedly with increasing stress level. Interface roughness has a dual effect on creep behavior. It increases the creep failure stress and delays the time to instability, while simultaneously intensifying local stress concentration, resulting in greater deformation accumulation in specimens with higher roughness. The steady-state creep rates show only minor differences in the low-stress range, whereas they are significantly regulated by interface roughness in the high-stress range. Among the tested specimens, the medium-roughness specimen (JRC-2) exhibits the highest creep sensitivity. These findings provide a theoretical basis for evaluating the long-term stability and optimizing the interface design of rock-concrete composite structures.