Supercritical carbonation of steel slag and its impact on cement hydration

Supercritical carbonation is an effective way to improve steel slag utilization and CO 2 sequestration. The supercritical carbonation of steel slag was performed in an industrial autoclave device. With micromorphology and mineralogy analyses, the nano-CaCO 3 and amorphous SiO 2 were identified in the interior and surface of carbonated steel slag due to high diffusivity and reactivity of supercritical CO 2 ; the nano-CaCO 3 is in the proportion of 1%-28%, and amorphous SiO 2 accounts for 1%-7%. Carbonation mechanisms of a direct reaction model in gas-solid carbonation (moisture less than 0.02) and the surface coverage and interior generation model in aqueous carbonation (moisture more than 0.02) are established. Supercritical carbonation greatly improves the early compressive strength and soundness; the activity indexes are more than 80% and even above 90% at 3 days. The nano-CaCO 3 and -SiO 2 are involved in cement hydration to produce Mc and Fe-bearing C-S-H gel, contributing to lower porosity and enhanced strength.