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

The early-age impacts of CO 2 activation (using a dose of 0.3% CO 2 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 CO 2 accelerated the hydration of both the systems, with the effect being more pronounced in cement. During the first 30 min of hydration, the CO 2 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 CO 2 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. • CO 2 catalyzes hydration of tricalcium silicate and cement paste systems. • A rapid formation of CaCO 3 coincides with a temporary drop in the solution pH. • SEM analysis confirms calcite rhombs in the CO 2 -activated tricalcium silicate. • The total reaction is the same in the hydration and CO 2 activated cases at 3 h. • 15–30% less calcium hydroxide and calcium silicate hydrate gel in activated case.