Characterization of the effects of waste mullite powder on seawater sea sand cementitious materials

Maintaining the durability of coastal concrete structures while reducing construction costs remains a formidable challenge. Drawing inspiration from the volcanic concrete used by ancient Greeks and Romans, this study explores the feasibility of using waste mullite powder (WMP) with a high alumina content in seawater sea sand concrete to conserve natural resources and enhance durability. The experimental results demonstrate that the incorporation of seawater and WMP exerts detrimental impacts on the flow characteristics and workability of cementitious composites. While the sulfate content in seawater and sea sand can bolster the early strength of sea sand seawater concrete, sulfate attack compromises its long-term strength. Incorporating a small amount of WMP (3%, 5%) proved beneficial for compressive strength. To assess the chloride penetration resistance of SSC, the Rapid Iodide Migration test indicated that the alumina in WMP can adsorb and immobilize chloride ions. Microstructure characterizations show that the incorporation of WMP resulting in an increased content of calcium silicate hydrate gel and Friedel's salt in the hydration products. The observed modification substantially augments both the physicochemical binding mechanisms within the cementitious matrix, facilitating improved chloride ion immobilization through synergistic physical entrapment and chemical fixation processes.