Dynamic characteristics of early-age shotcrete-rock composite considering roughness

Investigating the dynamic properties of early-age shotcrete-rock composite body necessitates consideration of the roughness at the interface between shotcrete and rock. In this paper, impact tests were conducted on shotcrete-rock composite using a Split Hopkinson Pressure Bar (SHPB) testing apparatus, with a focus on both interface roughness and curing time. The results reveal a close correlation between the stress-strain curve of the composite specimens and factors such as roughness, curing age, and impact velocity. For curing ages under 5 days, the composite specimens exhibit characteristics of modest plastic deformation. Notably, a lower joint roughness coefficient (JRC) effectively enhances the dynamic compressive strength of the composite specimens. Furthermore, the dynamic strength of the composite specimens continuously increases with curing age, showing a rapid increase in the first three days followed by a slower rise. Within the composite, the shotcrete primarily undergoes compression-shear failure, while the rock predominantly experiences shear and tensile failure modes. A higher JRC corresponds to increased specimen fragmentation, particularly with a higher degree of concrete fragmentation. Moreover, extending the curing age enhances the impact resistance of the composite. When the curing age remains constant, the dissipated energy progressively diminishes as the JRC value increases. Conversely, as the curing period extends, the dissipated energy exhibits an exponential rise. Finally, a theoretical constitutive model of the shotcrete-rock composite is presented.