SCECC-confined seawater coral concrete for island and reef structures: Dynamic mechanical properties and damage evolution

Abstract

Seawater coral aggregate concrete (SCAC) is an economical material for island and reef engineering due to in-situ resource utilization, but its high brittleness leads to poor impact resistance and safety concerns. This study employs seawater coral sand engineered cementitious composite (SCECC) as an external confinement layer to enhance the impact performance of SCAC. The synergistic effects of confinement-layer thickness (12.5/ 37.5 mm) and coral sand gradation (maximum particle size 0.60/1.18/2.36 mm) on SCECC-SCAC composite cylinders are systematically investigated using split Hopkinson pressure bar (SHPB) tests and finite element analysis. Quasi-static tests show that SCECC confinement markedly increases the compressive strength of SCAC (up to 65.7 %) while maintaining core integrity. Under impact loading, both SCAC and SCECC-SCAC exhibit pronounced strain-rate sensitivity. The maximum average dynamic strengths of SCECC-SCAC reach 109.0 MPa and 123.4 MPa for the two thicknesses. The SCECC layer increases the ultimate compressive strain by up to ∼70 % and raises the energy dissipation density to 2234.8 kJ/m³, effectively suppressing unstable crack propagation at high strain rates (>120 s⁻¹) and transforming the failure mode from catastrophic fragmentation to controlled multi-crack damage. Based on SHPB data, a logarithmic DIF prediction model is established, capturing the dependence of dynamic strength on strain rate. Three-dimensional finite element models incorporating JH-2, modified CDP and CZM interfaces reproduce dynamic stress-strain curves with peak-stress errors within ∼3 % and reasonably capture damage evolution. The proposed SCECC-SCAC system offers a feasible solution for impact-resistant design in island and reef engineering.