Distribution of sulphate and aluminium in hydrated cement pastes

Sulphate and aluminium play important roles in cement paste chemistry. They are closely linked through AFm, ettringite, and C-A-S-H. This study quantifies the distributions of sulphate and aluminium in cement pastes with limestone, fly ash, and a volcanic pozzolan, cured for 180 days at 20, 38, and 60 °C. Elevated temperatures convert carbonate AFm and ettringite to sulphate AFm and calcite. Only minor amounts of sulphate and aluminium are in the pore solution. SCMs increases the total aluminium content of the paste but do not increase greatly the amounts of aluminium present in AFm and ettringite. Instead, the additional aluminium is mainly incorporated in the C-A-S-H. C-A-S-H incorporates 25–55 % of sulphate and 20–40 % of aluminium in hydrated cement pastes. This is a significant portion that must be accounted for in thermodynamic models and mass balances.