Aqueous carbonation of ground granulated blast furnace slag and calcium carbide slag blends: CO₂ sequestration and application as mineral admixtures in cementitious materials

The cement industry is a major contributor to global CO₂ emissions, making the reduction of carbon emissions an urgent priority. This study explores the aqueous carbonation of ground granulated blast furnace slag (GGBS) and calcium carbide slag (CCS) blends as a method to sequester CO₂ and utilize the carbonation products as mineral admixtures (ADs) in cement pastes. The effects of key reaction parameters—liquid-solid ratio, CO₂ flow rate, and carbonation time—on CO₂ sequestration were systematically investigated. The carbonated GGBS/CCS blends were characterized for particle size distribution (PSD), morphology, and phase assemblage. The influence of the carbonated ADs on blended cement paste was evaluated through mechanical properties, hydration heat, phase assemblage, and microstructure. The results demonstrate that the carbonated GGBS/CCS blends exhibit significant CO₂ sequestration capacity and enhanced mechanical properties, including improved compressive strength and densified microstructure. Specifically, the carbonated blends showed a 16.34 % increase in compressive strength at 3d and a 21.40 % increase at 7d compared to non-carbonated blends. These findings suggest that the use of carbonated GGBS/CCS blends as ADs has the potential to reduce the carbon footprint of the cement industry without affecting performance. • Aqueous carbonation of GGBS and CCS blends for CO₂ sequestration and use as ADs. • CaCO3 adsorbs on the GGBS surface and the synergistic carbonation effect is observed. • Carbonated ADs increase the mechanical properties mainly in the early stages.