The protective layer and decalcification of C-S-H in the mechanism of chloride corrosion of cement paste

Abstract

Two processes of the chloride corrosion of cement paste are discussed: decalcification of C-S-H and the formation of the skin on the paste surface. Decalcification is relatively quick in the magnesium chloride solution, and brucite as well as basic magnesium chloride are formed. Taylor pointed out the possibility of magnesium silicate hydrate, which was proved in the works of other authors. A skin is formed on durable mortars immersed in the strong chloride solution. It is composed of brucite and basic magnesium chloride. The protective role of this skin, as foreseen by Taylor, was temporary, and sooner or later, the skin was destroyed. The alkali activated slag (AAS) mortar became then quickly destroyed. However, in high-alumina cement (HAC) paste, the dense layer was formed near the surface, which protected the paste, thus hindering the corrosion process.