Early age impacts of CO2 activation on the tricalcium silicate and cement systems

The early-age impacts of CO2 activation (using a dose of 0.3% CO2 by weight of cement) on two binder systems (tricalcium silicate and cement) were studied, principally across the first 3 h of hydration. The investigation included calorimetry, ICP-OES, TGA, and SEM. The in-situ mineralization of CO2 accelerated the hydration of both the systems, with the effect being more pronounced in cement. During the first 30 min of hydration, the CO2 addition impacted the solution phase pH and certain elemental concentrations (Ca, Mg, S). At later times of observation, the values were comparable to the level of the reference sample. Thermodynamic modeling revealed that the presence of CO2 resulted in stronger undersaturation with respect to the binder phases, which implies a strong driving force for their dissolution. The carbonates were observed in SEM micrographs as a multitude of rhombohedral-shaped calcite crystals while TGA confirmed an increased quantity of carbonates in both binder systems.