Dynamic properties and fiber effects of fiber‐reinforced coral concrete under dry‐wet cycling: Macro–micro experiment and simulation

The study of fiber‐reinforced coral aggregate seawater shotcrete (FRCASS) is essential for island and reef infrastructure development and maintenance. However, its behavior under simultaneous environmental degradation and dynamic loading is not well understood. In this study, a multi‐scale investigation combining nanoindentation, dynamic compression tests, and mesoscopic numerical simulation was conducted to evaluate the micromechanical properties, dynamic response, and degradation mechanisms of polypropylene fiber and steel fiber reinforced coral aggregate seawater shotcrete subjected to dry‐wet cycling. Nanoindentation tests quantitatively identified the coral aggregate as the weakest microphase (with elastic moduli primarily in the 0.3–1.0 GPa range), governing the distinctive “trans‐aggregate” cracking mode. Dynamic tests with a Split Hopkinson Pressure Bar showed that polypropylene fiber‐reinforced concrete (PFRC) consistently achieved a dynamic strength growth rate of about 12.5% under impact pressures of 0.2 to 0.4 MPa, while steel fiber‐reinforced concrete (SFRC) experienced a significant decrease in strength enhancement from 17.31% to 2.03%. After 30 dry‐wet cycles, SFRC suffered severe mechanical degradation, with fiber residual stress plummeting by 93.75% (from 400 to 25 MPa), while PFRC demonstrated superior durability, showing only a 68.4% reduction (from 380 to 120 MPa) and minimal mass loss due to the chemical inertness of polypropylene and salt crystallization clogging pores. A high‐fidelity 3D mesoscopic finite element model calibrated with nanoindentation‐derived parameters was developed using LS‐DYNA, which accurately replicated the macroscopic dynamic stress–strain response, cracking patterns and fiber effect. The results underscore the effectiveness of polypropylene fibers in enhancing damage resistance and durability of FRCASS under marine environmental conditions, providing critical insights for the design of sustainable marine infrastructure.