Dynamic behavior and energy dissipation mechanisms of coral aggregate concrete under high strain rate impact loading

To improve the impact resistance of coral aggregate concrete (CAC) used in island-reef engineering, this study investigated its dynamic mechanical behavior, failure mechanisms, and energy dissipation characteristics under impact compression and impact splitting tension. Tests were performed using a 100 mm Split Hopkinson Pressure Bar (SHPB) system combined with Digital Image Correlation (DIC) for real-time strain observation. The applied strain-rate ranges were 24–128 s⁻¹ for compression and 16–98 s⁻¹ for tension. Results show that CAC exhibits strong strain-rate sensitivity: the peak compressive stress increased from 39.5 MPa to 64.1 MPa and the peak tensile stress from 3.9 MPa to 7.7 MPa, with maximum DIFs of 1.73 and 2.26, respectively. DIC analyses showed that cracks under impact compression initiated in the core and transformed from tensile to shear modes with increasing strain rate, forming intersecting fracture networks, whereas under impact splitting tension, a central crack expanded into a triangular crushed zone with higher strain rates accelerating crack growth. Energy analysis revealed that the total strain energy increased from 16.54 J to 45.97 J under impact compression, while the energy dissipation ratio rose from 4.23% to 44.59%; in impact splitting tension, the maximum dissipation ratio reached 40.83%. These results clarify the rate-dependent strength enhancement and energy absorption mechanisms of CAC and provide quantitative parameters (DIFs, energy dissipation ratios, and fracture patterns) that can be incorporated into the impact-resistant design and protective performance evaluation of island-reef infrastructures such as pile foundations, breakwaters, and coastal defense components.