Comparative study of hydration of monocalcium aluminate and quaternary phase and the amorphous AH3 phase in their hydrates.

Monocalcium aluminate (CaAl₂O₄, CA) and quaternary (Q) phase (Ca₂₀Al₂₆Mg₃Si₃O₆₈) are the two principal hydraulic phases in calcium aluminate cement. Their strength development has been reported. However, little information about the difference of their hydration and hydrates composition is available. For this reason, the hydration process of CA and Q phase was investigated and compared. Results of conductometry indicate that the rate of Q phase hydrates precipitation is much slower than that CA latter. Hydrates identification demonstrates that the most prominent difference between the hydrates for these two compounds is the amorphous AH₃ content. The quantity of amorphous AH₃ (A=Al₂O₃, H=H₂O) in Q phase hydrates is evidently less than that of CA, as confirmed by FTIR, TG and BSE. Even-distributed amorphous AH₃ fills in the crystalline skeleton of calcium aluminate hydrates (C–A–H) enhancing the compactness of CA paste. Hence, CA exhibits a higher 72-day compressive strength than Q phase. [ABSTRACT FROM AUTHOR]