Incorporation of limestone calcined clay cement (LC3), seawater and sea-sand in ultra-high-performance engineered cementitious composites (UHPECC): Mechanical properties, hydration and microstructure

This study investigates the use of Limestone powder calcined clay cement (LC 3 ), seawater , and sea-sand in ultra-high-performance engineered cementitious composites (UHPECC) to development high-strength, highly ductile materials that can reduce construction costs and carbon footprints in coastal areas . The mechanical properties of UHPECC made with different materials (freshwater, quartz sand , seawater, sea-sand, metakaolin (MK) and limestone powder (LP)) were evaluated, including workability, mechanical performance and microstructure. Results show that seawater and sea-sand improve mechanical properties but reduce flowability compared to freshwater-based UHPECC. LC 3 -based UHPECC also has lower flowability but better mechanical performance. Additionally, seawater, sea-sand, and LC 3 increase the number of crack density while reducing crack width and spacing, enhancing ductility. MK and LP can replace up to 45 % of cement without sacrificing performance. Isothermal calorimetry shows that MK and LP accelerate hydration, while chloride ions in seawater promote the formation of Friedel’s salt, increasing heat release and strength . X-ray diffraction (XRD) confirmed the presence of Friedel’s salt in seawater samples and calcium aluminate phases in LC 3 mixtures. Scanning electron microscopy (SEM) images showed improved pore filling, and densification in seawater and LC 3 samples, leading to better mechanical properties. Overall, the combined use of seawater, sea-sand, MK and LP significantly enhances the mechanical performance and durability of UHPECC, offering promising applications for marine and coastal infrastructures.