Speaker
Description
The hydration reaction and transformation behavior of a calcium aluminate cement (CAC) mixed with reactive calcium carbonate (Cc) were investigated at different temperatures. By introducing CO32- into the pore solution of the hydrating CAC through calcite dissolution, a promising way was investigated to avoid or limit the metastable hydrate phases (CAH10, C2AHx) that typically occur during the hydration of pure CAC.
Instead, the precipitation of carbonate-AFm phases, mainly monocarbonate, is favoured. Analysis of the extensive data base (10-90°C) has shown the general conditions and temperature limits under which the calcium aluminate hydrate phase monocarbonate is formed and stabilized. At 60°C, no thermodynamic stability or formation limit of monocarbonate is found. No conversion of monocarbonate to C3AH6 (or dissolution-precipitation) was observed up to 80°C, this probably only happens above a critical temperature, which is specified in databases as approximately 90°C.
We were able to demonstrate that C2AHX acts as a precursor for monocarbonate in the early hydration of mixtures of CAC with Cc. Below 20°C no or only a small amount of C2AHx and thus also no or only minor monocarbonate should initially form in CA-dominated CAC-pastes. Here, CAH10 is prevailing. At elevated temperatures (40°C and 60°C), when CAH10 does not initially precipitate, monocarbonate is formed as result from the rapid conversion of the precursor phase C2AHx.
Affiliations
FAU Erlangen-Nürnberg, GeoZentrum Nordbayern, Mineralogy, 91054 Erlangen, Schlossgarten 5a, Germany
friedlinde.goetz@fau.de
| Keywords | Hydration, C2AHx, Monocarbonate, Conversion, Reactive Calcite |
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