Rheology of cement pastes with calcium carbonate polymorphs

Naturally occurring limestone currently used for concrete production mainly consists of calcite, and the other two metastable forms of anhydrous calcium carbonate include aragonite and vaterite. In this research, all three calcium carbonate polymorphs were synthesized in laboratory conditions and their effects on cement rheology were investigated. After comprehensive characterization of the polymorphs, they were used as cement sub-stitutes (20 wt%) to prepare pastes for rheological testing. Aragonite was found to increase the initial static yield stress, dynamic yield stress, and storage modulus of cement pastes, while calcite and vaterite did not. The rate of structural build-up was also enhanced by aragonite, as indicated by higher rates of static yield stress development and storage modulus increase over time. The underlying mechanisms of the rheological changes induced by the calcium carbonate polymorphs - geometric features, hydration kinetics, and surface charge - were discussed and supported with experimental evidence.