Synergistic effects of fiber hybridization in seawater sea-sand mortar: From microstructure evolution to life cycle sustainability

Seawater sea-sand mortar (SWSSM) shows great promise in sustainable marine construction, as it utilizes abundant locally-available marine resources to replace scarce freshwater and river sand, but its application is partially limited by its inherent brittleness. To overcome this structural drawback while further minimizing the environmental footprint, this study proposes a synergistic reinforcement strategy for SWSSM using a hybrid system of synthetic polymeric (polyvinyl alcohol, PVAF), inorganic (glass, GF), and natural plant (bamboo, BF) fibers. A comprehensive characterization method, employing X-ray computed tomography (X-CT), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and life cycle assessment (LCA), was adopted to establish the relationships among "microstructure-macroscopic performance-sustainability" of SWSSM. The results show that the hybrid system of rigid GF and coarse BF (SWSS-G0.25-B0.25) exhibited a negative hybridization effect, with the aggregation of interconnected extra-large pores (>300 μm, accounting for 16.56%), leading to a decrease of compressive strength to 23.27 MPa, lower than the baseline group (SWSS-0). Conversely, the SWSS-B0.25-P0.25 hybrid system exhibited a positive synergistic effect, achieving a high compressive strength of 37.70 MPa at 28 days. This enhancement is attributed to the micro-filling effect achieved by the combination of BF and PVAF, as well as strong chemical anchoring effect at the fiber-matrix interface. Although high-doped PVA (SWSS-P1) achieved the highest strength (44.43 MPa), LCA results showed that it had a significant environmental impact. Meanwhile, multi-criteria decision analysis based on the Simple additive weighting (SAW) suggested that the SWSS-B0.25-P0.25 group was the optimal green design scheme, achieving acceptable mechanical properties with minimal environmental impact, providing a sustainable solution for marine engineering.