Mechanical properties and chloride resistance of ultra-high-performance seawater sea-sand concrete with limestone and calcined clay cement (UHPSSC-LC3) under various curing conditions

Although the application of ultra-high performance seawater sea-sand concrete with limestone calcined clay cement (UHPSSC-LC³) provides a promising solution for sustainable marine structures, research on the mechanical properties of UHPSSC-LC³ is quite limited, and no research has been conducted on its chloride resistance performance. In this study, the effect of four curing regimes (i.e. standard curing, 20 °C seawater curing, 40 °C fresh water curing, and 80 °C fresh water curing) on the compressive and flexural strength of UHPSSC-LC³ is experimentally investigated. Rapid chloride migration test and chloride titration test are conducted to determine the chloride diffusion and distribution of UHPSSC-LC³, considering the effects of curing conditions and calcined clay (CC) dosage. In addition, XRD analysis is performed to show the differences in the composition of UHPC, UHPSSC, and UHPSSC-LC³. The obtained results demonstrate that UHPSSC-LC³ attains higher mechanical strength than UHPC and UHPSSC under various curing conditions. The incorporation of LC³ makes the free chloride concentration of UHPSSC-LC³ close to that of UHPC, especially when the heated water curing is applied. The free chloride concentrations of UHPSSC- LC³ cured with 40 °C and 80 °C water are only 10.1 % and 2.9 % higher, respectively, than that of UHPC cured under standard condition. Besides, UHPSSC-LC³ achieves the lowest chloride ion diffusion rate, which is 40.4 % lower than that of UHPSSC, due to the denser matrix resulting from the carboaluminate products and the pozzolanic effects of the calcined clay. Furthermore, the application of heated water curing regimes is recommended for UHPSSC-LC³ when the early strength and chloride resistance are the main concerns.