Dynamic response characteristics of coral reef sand concrete under impact loading

The dynamic mechanical properties, energy evolution characteristics, breakage modes, and damage mechanism of coral reef sand concrete (CRSC) are distinctly different from those of land-sourced aggregate concrete. Because structures made of CRSC may suffer damage due to earthquakes and artillery shells, it is significant to investigate the impact resistance and dynamic response characteristics of CRSC. In this study, macroscopic and microscopic testing techniques were used to compare the dynamic response characteristics of CRSC, CRSC with polypropylene fibers (PFs), and CRSC with basalt fibers (BFs) under impact loading. The results showed that with increasing strain rate, the dynamic compressive strength and dynamic increase factor (DIF) of the CRSC increased via power and logarithmic functions, respectively. Furthermore, the PFs and BFs improved the dynamic compressive strength at medium and low strain rates. The damage modes of the CRSC and CRSC with BFs were primarily fragmentation damage, while the damage mode of the CRSC with PFs was core retention damage. The failure cracks of all three types of concrete developed through the coral coarse aggregate, cement mortar, and slurry near the interfacial bonds. Nanoindentation test results revealed the great bonding performances at the coral aggregate–slurry bond. The incorporation of PFs or BFs changed the form and content of the C–S–H in the interfacial transition zone of the CRSC, which in turn affected the mechanical properties of the CRSC. In practical engineering, however, PFs and BFs could still improve the seismic and blast-resistant performances of CRSC.