Development of sustainable ultra‐high‐performance engineered cementitious composites by synergistic utilization of seawater, sea‐sand, and limestone calcined clay cement

This study aims to optimize the performance of ultra‐high‐performance engineered cementitious composites (UHPECC) by innovatively incorporating limestone calcined clay cement (LC 3 ) with seawater and sea‐sand commonly found in marine environments. A systematic investigation was conducted to explore the underlying mechanisms through which this composite system influences the tensile performance and microstructural evolution of UHPECC. A series of tests were performed, including uniaxial tensile tests, single‐fiber pull‐out test, single‐crack tensile test, and matrix toughness test, combined with microstructural characterizations using thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and mercury intrusion porosimetry. The results revealed that the synergistic incorporation of seawater and LC 3 not only significantly enhanced the tensile strength and tensile strain capacity of UHPECC but also effectively improved the fiber–matrix interfacial bonding and crack resistance. Notably, when 30 wt% calcined clay and 15 wt% limestone powder were used to partially replace cement and seawater was used in place of freshwater, the tensile strength and tensile strain capacity of the specimens increased by 39.4% and 33.8%, respectively, compared to the control group composed of cement and freshwater. TGA results indicated that the combined use of seawater and LC 3 markedly promoted the degree of hydration. SEM images confirmed the formation of denser and more continuous C‐(A)‐S‐H gels, Friedel's salts, and carboaluminates, which contributed to a more compact and refined microstructure. This study not only deepens the scientific understanding of the synergistic effects between multicomponent cementitious systems and marine environments but also provides essential theoretical and technical guidance for the sustainable development and practical application of high‐performance concrete in marine engineering.