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. © 2023 Elsevier Ltd