Preparation and carbonation hardening of low calcium CO2 sequestration materials from waste concrete powder and calcium carbide slag

A series of new low calcium CO2 sequestration cementitious materials (LCC) with different Ca/Si ratios were prepared by sintering waste concrete fine powder (WCP) and calcium carbide slag (CCS) at different ratios. Their carbonation reaction activity, carbonation hardening properties, phase assemblages, and microstructure were systematically characterized. The results showed that when the WCP: CCS ratio was 70:30, the compressive strength of LCC reached 38 MPa after carbonation for 24h. With the decrease in the WCP: CCS ratio, the carbonation activity of LCC increased significantly. When the WCP: CCS ratio was 45:55, the compressive strength was increased to 109 MPa. Microstructure tests showed that the minerals of LCC gradually changed from CS and C2AS to C3S2 and C2S. After carbonation, unreacted clinker particles, crystalline CaCO3, and highly polymerized silica formed a dense microstructure, and the impurities of Mg element in the LCC triggered the formation of aragonite.