The formation of monosulphate from tetracalcium aluminoferrite and magnesium sulphate

The formation of monosulphate, by hydration of a tetracalcium aluminoferrite powder, was investigated by isothermal calorimetry and X-ray diffraction (XRD) analyses. Hydration reactions were carried out isothermally at temperatures ranging from 25 to 80°C in 0·25 M, 0·5 M, 1·0 M, 2·0 M, and 3·0 M magnesium sulphate solutions. Gypsum was the initial hydration product in all magnesium sulphate concentrations and was the only crystalline hydration product in 2·0 M and 3·0 M magnesium sulphate solutions. Monosulphate was the dominant crystalline phase produced over the entire temperature range when hydration was carried out in magnesium sulphate concentrations between 0·25 M and 1·0 M. XRD and calorimetry also demonstrated that small amounts of calcium aluminium hydroxide, calcium aluminate carbonate hydrate and magnesium aluminate hydrate phases formed at the lower temperatures and in low (0·25 M and 0·5 M) magnesium sulphate concentrations. No crystalline phases incorporating iron were observed regardless of magnesium sulphate concentration or temperature.