The mechanical, transport and chloride binding characteristics of ultra-high-performance concrete utilising seawater, sea sand and SCMs

While concrete production accounts for significant CO₂ emissions and natural resources (e.g., river sand and freshwater) depletion, the incorporation of sea sand, seawater, and industrial by-products in ultra-high-performance concrete (UHPC) manufacture could offset such impacts. However, the transport and durability performances of marine resource-based UHPC are not well documented. This paper presents an experimental investigation into the mechanical, transport, and chloride binding characteristics of seawater and sea sand-based ultra-high-performance concrete (SWSS-UHPC) with supplementary cementitious materials (SCM) (i.e., slag and silica fume). Mixes were developed with varying proportions of SCMs (up to 62.5%) and sources of aggregates. Early-age and long-term mechanical (i.e., modulus of elasticity, splitting tensile strength) and transport properties (i.e., water absorption, porosity, and ingress of chloride) were evaluated. Non-destructive tests (i.e., ultrasonic pulse velocity, and electrical resistivity) were correlated to the mechanical and durability properties. The chloride binding capacity was determined. Results reveal that although SCMs in SWSS-UHPC marginally improve its mechanical performance, it offers a significant enhancement in transport properties and durability, particularly at 50% cement replacement. The incorporation of marine resources can be beneficial against chloride diffusion and does not adversely affect the binding of external chloride. Electrical resistivity can successfully predict chloride penetration resistance. SCM-based SWSS-UHPC can be extremely durable for long-term exposure in spray and tidal/splash zones of maritime structures.