Influence of crack density on energy dissipation and damage evolution in rock–concrete composites under cyclic loading paths

Abstract

Rock-concrete composite structures are commonly encountered in engineering projects such as tunnels and dams, where pre-existing cracks significantly influence structural stability. Under engineering disturbances, their load-bearing mechanisms become more complex. This study conducted loading-unloading tests via Path I (constant lower limit with stepwise cyclic loading) and Path II (varying upper and lower limits with constant amplitude cycles), combined with acoustic emission monitoring. Based on the division of dissipated energy into damping energy and damage energy, a damage characterization model was established. Results indicate that the number of cracks is the dominant factor affecting macroscopic properties, as it accelerates microcrack coalescence through stress concentration at crack tips, significantly reducing peak strength and stiffness. Path II induced “interface hardening” in single-crack specimens but exacerbated damage in multi-crack specimens due to stress field superposition. The failure mode shifted from tensile failure to tensile-shear composite failure, with Path II being more prone to inducing shear cracks. Acoustic emission results showed a “silent-outburst” pattern in Path I, while damage accumulation was more uniform in Path II. The damage model revealed that when the number of cracks is ≥2, the damage rate under Path II is significantly higher than under Path I, owing to the synergistic effect of variable amplitude loading and stress fields. This study elucidates the coupled damage mechanism of cracks and loading paths, providing a theoretical basis for engineering stability assessment.