Effects of CO₂ Curing on Alkali-Activated Slag Paste Cured in Different Curing Conditions

The effect of CO₂ curing on alkali-activated slag paste activated by a mixture of sodium hydroxide and sodium silicate solutions is reported in this paper. The paste samples after demolding were cured in three different curing environments as follows: (1) environmental chamber maintained at 85% relative humidity (RH) and 25 °C; (2) 3-bar CO₂ pressure vessel; and (3) CO₂ chamber maintained at 20% CO₂ concentration, 70% RH and 25 °C. The hardened samples were then subjected to compressive strength measurement, X-ray diffraction analysis, and thermogravimetry. All curing conditions used in this study were beneficial for the strength development of the alkali-activated slag paste samples. Among the curing environments, the 20% CO₂ chamber was the most effective on compressive strength development; this is attributed to the simultaneous supply of moisture and CO₂ within the chamber. The results of X-ray diffraction and thermogravimetry show that the alkali-activated slag cured in the 20% CO₂ chamber received a higher amount of calcium silicate hydrate (C-S-H), while calcite formed at an early age was consumed with time. C-S-H was formed by associating the calcite generated by CO₂ curing with the silica gel dissolved from alkali-activated slag.