Study on carbonation behavior and carbon footprint of steel slag-calcium carbide slag-desulfurization gypsum composite system

The carbonation of steel slag (SS) can enhance its performance while capturing CO₂. The synergistic effect of combining multi-solid waste materials improves SS's carbon sequestration efficiency, thereby contributing to reduce carbon emissions. This study investigates the synergistic carbonation mechanism of SS when combined with calcium carbide slag (CCS) and desulfurization gypsum (DG) under various water-to-binder ratios (w/bs). The mineral evolution, carbon sequestration performance, and carbon footprint of the multi-solid waste composite system are comprehensively analyzed. The results indicate that, at different w/bs, most SS-CCS-DG composite pastes exhibit a significant strength increase after carbonation compared to carbonated SS paste. Specifically, the strength of the 89%SS-5%CCS-6%DG paste is 44% and 60% higher than that of carbonated SS pastes at 0.15 and 0.3 w/bs, respectively. Carbon sequestration and carbon footprint analysis show that after carbonation, the composite system effectively sequesters 12.2% CO₂, with an actual carbon sequestration rate surpassing 70% of its theoretical value. Compared to the SS system, the composite system achieves a higher negative carbon emission of -279.93 kg CO₂/t.