Modifying effects and mechanisms of superfine stainless wires on microstructures and mechanical properties of ultra-high performance seawater sea-sand concrete

Ultra-high-performance seawater sea-sand concrete (UHPSSC) presents a prospective solution to address the natural resource shortage in marine infrastructure construction. To eliminate the corrosion risk of steel fibers and broaden the applicability of UHPSSC, this study investigates the mechanical properties and free chloride ion content as well as microstructures of UHPSSC reinforced with superfine stainless wires (SSWs) under natural curing. The results indicate that 1.5% SSWs can remarkably improve the flexural strength and toughness of UHPSSC by 127% and 1724%, respectively, and mitigate the long-term strength degradation of UHPSSC. The strong interfacial bond between SSW and UHPSSC improves the compactness of UHPSSC, thus reducing the growth space for Ca(OH)₂ crystals and swelling hydration products generated by sulfate and magnesium ions. This can be supported by the observed reduction in the Ca/Si ratio of C–S–H gels, CH crystal orientation index, and porosity. Moreover, through mechanisms such as pull-out, rupture, overlapping network, and internal anchor interface, SSWs effectively prevent microcrack growth and propagation, transforming single long-connected microcracks into multiple-emission microcracks centered on SSW. Additionally, the free chloride ion content of the composites at 28 and 180 d meets the ACI 318-19 standard requirements for concrete exposed to seawater. This compliance is attributed to the chloride immobilization facilitated by Friedel’s salt and C–S–H gels within the interfaces around SSWs and sea-sand. Consequently, SSWs-reinforced UHPSSC exhibits considerable potential for applications in sustainable marine infrastructures, demanding long-term mechanical properties and high durability.