The effect of cations and metakaolin on chloride binding properties of mortars using simulated desalinated sea sand

With the scarcity of river sand resources, sea sand is also increasingly being used to prepare cementitious materials. Considering the threat of chloride salts still present in desalinated sea sand, this study investigates the effect of Na+, Mg2+, Ca2+ (contained on the surface of simulated desalinated sea sand) and metakaolin (MK) additions on the chloride binding properties of simulated desalinated sea sand mortar. The chloride binding capacity of the mortar and the hydration products of the mortar were analysed by chloride content measurement, X-ray diffraction, differential thermogravimetry, Fourier transform infrared spectroscopy and energy dispersive spectroscopy. The results show that Ca2+ and Mg2+ have a greater positive effect on improving the chloride binding capacity of mortar than Na+. This is because Ca2+ promotes the positive potential of the C–S–H gel in the mortar and Mg2+ facilitates the generation of a solid solution of Friedel’s salts and AFm in the mortar. The addition of MK in mortar improves the physical binding ability of the mortar to chloride ions. This improvement is primarily attributed to the increased production of C–S–H gel and C–A–S–H gel resulting from the addition of MK. This study is expected to provide theoretical support to facilitate the application of desalinated sea sand.