Influence on compressive strength and CO2 capture after accelerated carbonation of combination β-C2S with γ-C2S

In order to deal with the current global climate crisis, it is urgent to reduce greenhouse gas emissions and store CO2 in the atmosphere through Carbon Capture and Storage (CCS) technology. Both C3S and C2S are the main mineral components of Ordinary Portland Cement; through accelerated carbonation reaction, C2S could sequestrate more CO2 and gain a rapid development of early strength. β-C2S and γ-C2S, as two stable crystallines of C2S, can both capture CO2. Compared to β-C2S, the γ-C2S essentially shows no hydration activity, but γ-C2S shows higher reactivity to CO2 during the carbonation process. The conversion of β-C2S to γ-C2S would cause volume expansion, saving electricity during the grinding process and reducing CO2 emissions. To synthetic different proportions of β and γ polymorphic of C2 S, the different weight content of B2O3 (B2O3 wt%) was mixed with the analytical pure chemical reagent of CaCO3 and SiO2, and different cooling rates were used. The synthetic C2S (F1, S1, F2, S2) were exposed to pure CO2 gas with 2 bar pressure for 2 h. After carbonation, compressive strength was tested, carbonation degree was calculated. The synthetic C2S (S2) containing 57.8 wt% β-C2S and 42.2 wt% γ-C2S showed the highest compressive strength and the higher CO2 sequestration capacity, with the compressive strength of 46.3 MPa and the 14.14% CO2 uptake. The XRD results and TG-DTG analysis have proved that different calcium carbonates, including calcite, aragonite, vaterite, and ACC (amorphous calcium carbonate), were formed after carbonation. FT-IR observed the characteristic vibration of calcium carbonate, the microstructure of different calcium carbonate crystals was observed by FE-SEM. The calcite in the S2-C group showed more thermodynamic stability, confirmed by TG analysis at the temperature stage of 680℃～820℃. The mechanical bond force of rhombic calcite contributed to the high compressive strength. And S2-C group had the lowest porosity, which contained the highest volume of capillary pores and the lowest volume of macropores among the 4 groups. The combination of β-C2S with γ-C2S exhibited rapid strength development and high sequestration of CO2 after carbonation. The carbonation of combination of β-C2S and γ-C2S was able to devote to the rapid development of compressive strength and rather a high capacity of capturing CO2, and the proper proportions of β-C2S and γ-C2S were beneficial to develop belite-rich cement, as well as speed up the absorption and storage of CO2 in the atmosphere.