Dynamic tensile behavior and crack propagation in coral aggregate seawater shotcrete: Experimental investigation and numerical simulation

Coral aggregate seawater shotcrete (CASS) is crucial for maintaining the stability of island infrastructure subjected to dynamic forces. In this study, nanoindentation tests were conducted to evaluate the micromechanical properties of CASS, and the Split Hopkinson Pressure Bar (SHPB) apparatus was used to investigate its dynamic mechanical behavior. Dynamic splitting tests were performed at impact pressures of 0.10, 0.20, 0.30, and 0.40 MPa to analyze the failure modes, fractal dimensions, and energy characteristics of CASS under different loading conditions. To further explore its fracture mechanisms, a coupled numerical model integrating the finite difference method (FDM) and discrete element method (DEM) was developed to simulate the dynamic response of CASS, and the model was calibrated using nanoindentation results. The results revealed that CASS exhibited strong rate-dependent behavior, and its dynamic splitting tensile strength (DSTS) increased from 9.6 ± 0.1 MPa to 17.1 ± 0.1 MPa as the loading rate increased from 78 ± 1 GPa s⁻¹ to 182 ± 1 GPa s⁻¹. However, the rate of strength enhancement diminished beyond a critical loading rate, indicating a saturation effect. Cracks preferentially propagated through the coral aggregates rather than along the interfacial transition zone (ITZ), as evidenced by nanoindentation-derived fracture toughness measurements. The fractal dimension of the cracks increased with loading rate, but its growth rate slowed at higher rates, indicating energy saturation. With increasing loading rate, the absorbed energy increased by 314.81 %, the reflected energy ratio also increased, and the absorbed energy efficiency decreased. Furthermore, the numerical model effectively replicated the crack propagation patterns and failure characteristics observed in the experiments, demonstrating its reliability for predicting CASS behavior under dynamic loads. These findings provide essential insights into the fracture behavior and energy dissipation characteristics of CASS can be used to aid in their optimization in marine infrastructure applications.