Fracture characteristics and failure mechanisms of concrete under high-pressure water jet impact with varying coarse aggregate properties

High-pressure water jet (HPWJ) is an efficient, eco-friendly method for concrete demolition. However, the influences of coarse aggregates, a key heterogeneous component, and their characteristics (content, gradation, etc.) are often oversimplified or overlooked in existing models, leading to inaccuracies in predicting demolition precision. This study investigated the fracture behavior of concrete subjected to HPWJ under varying aggregate content and gradation through fragmentation experiments. Surface strain patterns influenced by aggregates were also examined. Using an SPH-FEM coupled algorithm, we quantitatively analyze the fracture behavior and energy evolution of concrete under different aggregate conditions (content, grading, particle size, and shape). The comprehensive damage and breakage coefficient ( D cdb ), is introduced to quantify internal damage distribution of concrete. The damage and failure mechanisms of coarse-aggregate concrete under HPWJ impact were revealed. The results show that a regular hole forms on the surface at aggregate content below 30 %, with broken pit depth decreasing exponentially as content increases. Beyond 45 % aggregate content, a typical "bowl-shaped" pit is formed. At low aggregate content, sparsely distributed interfacial transition zones (ITZs) guide energy flow, promoting crack propagation. Increasing aggregate content suppresses energy absorption, as the "rigid skeleton" formed by the aggregates forces lateral energy dissipation and induces high-pressure backflow, leading to secondary erosion of the surface layer, which results in shallower and wider broken pits. Smaller aggregate particles accelerate the damage process, creating deeper and wider broken pits. Angular aggregates enhance energy penetration due to stress concentration, while spherical aggregates distribute stress uniformly, reducing concrete damage. Secondary cracks were preferentially formed within ITZs due to tensile stress concentration. The study results could provide theoretical guidance for optimizing process parameters and controlling the range of HPWJ demolition on coarse-aggregate concrete. • Fracture and deformation traits of concrete with different aggregates under water jet impact were obtained. • Effects of aggregate on fracture and energy evolution were quantified through numerical simulation. • Initiation and propagation mechanism of secondary cracks under impact was revealed. • Damage and failure mechanisms of concrete with different aggregate properties were elucidated.