Thermal analysis of hydrated calcium aluminates

Differential scanning calorimeter (DSC) has been used to study the dehydration characteristics of hydrated calcium aluminates such as CA, CA₂ and C₁₂A₇ where C and A stand for CaO and Al₂O₃ respectively. Dehydration of CAH₁0 and C₂AH₈ (whereH=H₂O) occur at 160–180°C and 200–280°C respectively. These two phases are unstable and ultimately get transformed to AH₃ and C₃AH₆. Dehydration of AH₃ and C₃AH₆ occur between 290 and 350°C and overlap at lower scanning rate. The activation energy for dehydration of the stable AH₃ and C₂AH₆ phases has been found to be 107.16 and 35.58 kJ mol^–1 respectively. The compressive strength of the hydrated calcium aluminates has been determined. The result shows that in the case of CA, almost 90% of ultimate strength has been attained in 1 day whereas in CA₂, ultimate strength has been attained in 14 days and in C₁₂A₇ in 1 day. DSC results have been correlated with the rate of strength developments.