Influence of inorganic salts on the hydration of tricalcium silicate

The influence of various chlorides and potassium salts on the hydration of alite (3CaO·SiO₂ solid solution) has been studied by conduction calorimetry and an explanation based on diffusion experiments in hardened Portland cement is presented. The mechanism of the action of inorganic electrolytes on cement hydration was also investigated. In hardened Portland cement the diffusion rate of the Cl^? ion was greater than that of the coexisting cations. The accelerating effect of inorganic electrolytes was dependent mainly on the mobility of anions. The higher the anion mobility, the greater was the accelerating effect on the hydration. It is shown that the hydration of alite is a topochemical reaction and that the rate of hydration of alite is controlled by the rate of the dissolution of Ca²⁺ or OH^? ions into a liquid phase. It is concluded that the dissolution of OH^? ions from the hydrate layer around the cement particle is increased when the reciprocal diffusion action of the anion accelerates the hydration.