Wet carbonation of C3A and pre-hydrated C3A

The carbonation of C(3)A and pre-hydrated C(3)A was studied at different initial pH values, temperatures, pre-hydration and carbonation times. Based on these investigations, the reaction kinetics of C(3)A under humid conditions were considered in more detail. The reaction products were characterized by quantitative X-ray diffraction (QXRD) and thermogravimetric analysis (TGA). C(3)A shows no significant reaction when carbonated directly in suspension, however, it has been observed that pre-hydrated C(3)A can be carbonated. A higher reaction degree was obtained with increasing hydration time. Consistent with reaching a stable pH, no further reaction of the hydrate phases was detected after similar to 20 min, indicating fast kinetics of the carbonation reaction. At temperatures <= 21 degrees C, the CaCO3 polymorph vaterite was found to be the main phase. At a pre-hydration temperature of 40 degrees C, C(3)AH(6) appeared as a stable hydrate phase, but showed no reaction with CO2 under our experimental conditions.