Impact of high-temperature exposure on the mechanical properties and microstructure of seawater sea sand mortar

In recent years, seawater and sea sand have gradually become a research hotspot as alternative materials for concrete. Current research on seawater sea sand mortar (SSM) mainly focuses on its synergistic effect with Fibre Reinforced Polymer (FRP) bars, while studies on the high-temperature resistance of the material itself are relatively scarce. In this paper, flexural and compressive strength tests were carried out on SSM with different water-binder ratios and under different temperatures. The changes in hydration products and microstructure of SSM at different temperatures were studied by XRD, MIP and SEM. Comparative experiments were set up to compare the differences in high-temperature resistance between SSM and freshwater river sand mortar(FNM), and the high-temperature deterioration mechanism of SSM was summarized. The study found that the addition of seawater and sea sand has an adverse effect on the high-temperature resistance of mortar. The Cl - and SO 4 2- introduced by seawater and sea sand react with cement to form expansive products Fs and Aft respectively. The decomposition of Fs and Aft at different temperatures causes SSM to exhibit a looser and more porous microstructure compared to FNM, which ultimately leads to the flexural and compressive strengths of SSM being lower than those of FNM after exposure to high temperatures. • Studied the mechanical properties of Seawater Sea Sand Motar(SSM) after high temperature. • Analyzed hydration product changes of SSM after high temperature by XRD. • Analyzed microstructure changes of SSM after high temperature by SEM and MIP. • Summarized the degradation mechanism of SSM after high temperature.