Temperature-dependent late hydration of calcium aluminate cement in a mix with calcite – Potential of G-factor quantification combined with GEMS-predicted phase content

In continuation of earlier work on early hydration, this study evaluates the late hydration of CAC and CaCO₃ using QXRD and thermodynamic modelling at different temperatures. Experiments were performed at 5, 23, 40 and 60 °C for up to one year. As stated in the preceding study, C₂AH_X might act as a precursor for monocarbonate in early hydration, and thus no or only little monocarbonate should form at temperatures below 20 °C. At 5 °C, monocarbonate starts precipitating after 7 d and remains alongside CAH₁₀. At all other investigated temperatures, monocarbonate is the dominant hydrate phase. Primarily formed CAH₁₀ at 23 °C is visible up to 14 d but then becomes unstable with respect to monocarbonate. At 23 °C and 40 °C the thermodynamically stable phase assemblage is reached within one year. However, the precipitation of C₃AH₆ is detected in all samples at 60 °C, which results from an insufficient w/CAC ratio for carbonate-AFm in the paste due to the inevitable evaporation of mixing water for this condition. However, C₃AH₆ can partly be “re-converted” at 60 °C when the sample is subsequently stored under water and monocarbonate is stable again.