Study on carbonation reactivity of silicates in steel slag accelerated by Bacillus mucilaginosus

Abstract Using steel slag to fix CO2 to prepare building materials is beneficial to reducing carbon emissions and recycling industrial waste. A novel approach for accelerating CO2 fixation and improving the mechanical properties of steel slag-based materials was proposed based on using microorganisms. Silicates are the main mineral phases of steel slag. This paper focused on the effects of microorganisms on carbonated conversion rate, compressive strength, and products of β-C2S and C3S. The results showed that microorganisms could accelerate carbonation and improve the conversion of β-C2S and C3S. The conversion level of β-C2S and C3S were increased by 16% and 12%, respectively, the compressive strength increased by 48.13% and 32.13%. The mineralization and carbonation products of β-C2S and C3S were characterized by XRD, FTIR, TG-DTC, and MIP methods. The main products of mineralized β-C2S and C3S were CaCO3, and the main crystal types were calcite and vaterite. The amorphous phases were silica and C-S-H gel. Compared with carbonation products, mineralization products had higher calcium carbonate content, a larger proportion of calcite, higher decomposition temperature, smaller crystal grain size, and lower porosity of paste samples. Besides, the compressive strength of mineralized steel slag samples was significantly higher than that of carbonated samples, showing a good strength improvement effect.