Development of low-carbon cement: Carbonation of compounded C2S by β-C2S and γ-C2S

Widespread utilization of Portland cement (PC) with a large-scale carbon footprint has caused a vital climate crisis. The application of low-carbon materials rich in belite is hindered by the low hydraulic activity of C2S. Both β-C2S and γ-C2S can rapidly develop compressive strength and sequestrate CO2 after carbonation. To explore the role of β-C2S and γ-C2S played on compressive strength and carbonation degree in C2S paste, several groups of C2S samples composed of pure β-C2S and pure γ-C2S in different weight contents (wt.%) were homogenized and carbonated. Compressive strength was tested, and XRD, TGA, FT-IR, and SEM analysis methods were applied to observe the carbonation properties. Experimental results showed that compressive strength positively correlated with the proportion of β-C2S content, and the carbonation degree positively correlated with the proportion of γ-C2S content. Different ratios of β-C2S and γ-C2S mainly affected the growth rates of compressive strength and carbonation degree. When β-C2S was 60 wt% and γ-C2S was 40 wt%, both compressive strength (54.4 MPa) and carbonation degree (36.7%) of carbonated samples can reach an optimum value. The calcite content increased with γ-C2S content, while the crystallite size of calcite decreased with the γ-C2S content. Through the established carbonation kinetics equation and the measured carbonation heat curves of compounded C2S, the possible synery effect of β-C2S and γ-C2S was proposed. Combined β-C2S and γ-C2S in cement clinker can reduce CO2 emissions. Carbonating high-belite cement composed of a certain proportion of β-C2S and γ-C2S will contribute to developing early compressive strength and improving CO2 sequestration of this low-carbon cementitious material.