Study of seawater corrosion resistance of ordinary Portland cement–aluminate cement–gypsum mortar containing slag

A repair material for use in the marine environment is developed. The ternary cementitious system (TCS), which contains ordinary Portland cement, calcium aluminate cement and gypsum, causes rapid hardening and displays high strength, and hence can be used as a building repair material. However, the hydration products of the TCS contain a large amount of ettringite, calcium hydroxide and calcium aluminate hydrate, which can be easily corroded by the inorganic ions in seawater. Owing to its pozzolanic activity and ability to bind chloride, slag is added to the TCS. The content of slag in the TCS is a critical factor; hence, the effects of 0–35 wt% slag on the compressive strength, mass change, apparent porosity, and free and total chloride content of TCS immersed in seawater are investigated. The systems with slag show a higher compressive strength than the TCS in seawater, and the reduction in compressive strength of the system with 25 wt% slag is only 14·14% after 180 d. Also, the addition of slag significantly reduces the free and total chloride content of the TCS immersed in seawater. The optimum amount of slag in the TCS is determined to be about 25 wt%.