In-situ XRD study of the temperature-dependent early hydration of calcium aluminate cement in a mix with calcite

摘要

In the present work the hydration of white CAC, inert alumina-filler and CaCO3 was investigated at different temperatures with in-situ XRD. Experiments were performed at 10 degrees C, 23 degrees C, 40 degrees C and 60 degrees C. Overcoming or mitigating the phenomena of calcium aluminate hydrate conversion by adding reactive additives to calcium aluminate cement is often described in literature. When a sufficient amount of calcite is added, carbonate-AFm (monocarbonate and hemicarbonate) is expected to be the dominant hydrate phase. Calcite however, acts as an inert filler and barely influences the calcium aluminate hydration products at 10 degrees C. With rising temperature monocarbonate contents increase as well as the reaction rate of cement phases. At 60 degrees C minor amounts of C(3)AH(6) precipitate during the early hydration. Special attention is given to the role of CAH(10) and C(2)AH(x) during hydration. While CAH(10) is dominant at 10 degrees C, C(2)AH(x) precipitates in a temperature range between 23 and 60 degrees C as a precursor phase for carbonate-AFm phases. These are not found at 10 degrees C, which is probably due to the lack of the precursor phase (C(2)AH(x)). The hydration of the mix M 10 degrees C with an initial addition of C(2)AH(x) shows that carbonate-AFm-phases can be precipitated in addition to CAH(10) during the first 96 h.