Engineering-oriented mechanical and environmental evaluation of polyurethane-stabilized recycled sea sand for coastal and marine infrastructure

This study investigates the mechanical behavior, microstructural evolution, and early-stage environmental sustainability of sea sand stabilized with two-component polyurethane as an engineering-oriented material system for coastal and marine infrastructure applications. Slump flow tests were conducted as an initial step to determine the optimal moisture content for effective curing. Polyurethane-cured sea sand (PCSS) specimens with varying curing agent contents were prepared and tested through unconfined compression and direct tensile tests to evaluate early-age mechanical strength. FTIR, XRD, and SEM analyses were employed to elucidate the curing mechanisms of the polyurethane. Results showed that increasing polyurethane content significantly increased both compressive and tensile strengths, with a proportional relationship observed between the two strength indexes. Microscopic analyses revealed that the curing process is governed by physical bonding, with polyurethane filling voids and forming a spatial bonding network, thereby enhancing the microstructure and resulting in improved mechanical performance. A cradle-to-site Life Cycle Assessment (LCA) of polyurethane curing process was conducted across 15 impact categories to quantify the environmental impacts under defined assumptions. The production stage was found to dominate most environmental burdens, especially carbon emissions, which exhibited a linear increase with polyurethane content. The findings offer insights into the mechanical response, microstructural reinforcement, and environmental characteristics of polyurethane-stabilized sea sand.