Carbonation of the synthetic calcium silicate hydrate (C-S-H) under different concentrations of CO2: Chemical phases analysis and kinetics

• Published in: Journal of CO2 utilization Vol. 35; pp. 303 - 313
• Main Authors: Li, Yongqiang, Liu, Wei, Xing, Feng, Wang, Shuping, Tang, Luping, Lin, Shifa, Dong, Zhijun
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.01.2020
• Subjects: Carbonation; Chemical phases; Different CO concentration 2; Different CO2concentration; Kinetics; Synthetic C-S-H; Carbonation; Different CO2concentration; Kinetics; Synthetic C-S-H; Chemical phases
• ISSN: 2212-9820; 2212-9839
• DOI: 10.1016/j.jcou.2019.10.001

•C-S-H would be partly decalcified under the natural condition but completely under the accelerated conditions. Two equations related to the carbonation kinetics under natural and accelerated conditions were proposed respectively.•The compositions in decalcified C-S-H were not affected by the CO2 concentration. The XRD analysis showed that vaterite, aragonite and calcite were coexistent after carbonation, which would be transformed to aragonite and calcite with further carbonation. The preferential formation of the allotropic calcium carbonate was not impacted by the concentration of CO2 either.•A carbonation kinetics model was proposed to learn the carbonation kinetics of C-S-H carbonated in different CO2 concentrations. The experimental data fitted well with the model. The carbonation kinetics between 3% and 20% CO2 are similar, but different from that under 50% and 100% CO2. In this study, the chemical phases analysis and the kinetics of synthetic calcium silicate hydrate (C-S-H) under differentCO2concentrations (natural (0.03%), 3%, 10%, 20%, 50%, 100%) were investigated. For this aim, the scanning electron microscope (SEM) and transmission electron microscope (TEM) were employed for microstructure characterisation. The 29Si magic angle spinning nuclear magnetic resonance (29Si MAS NMR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) coupled with mass spectrometer (MS) were used for characterising the chemical phases before and after carbonation. From the NMR results, it was found that C-S-H would be partly decalcified under the natural condition but completely under the accelerated conditions. Two equations related to the carbonation kinetics under natural and accelerated conditions were proposed respectively. The compositions in decalcified C-S-H were not affected by the CO2 concentration. The XRD analysis showed that vaterite, aragonite and calcite were coexistent after carbonation, which would be transformed to aragonite and calcite with further carbonation. The preferential formation of the allotropic calcium carbonate was not impacted by the concentration of CO2 either. Based on the TGA-MS test, the stoichiometric formula of synthetic C-S-H was determined with CaO∙SiO2∙0.87H2O or C⋅S⋅H0.87. In addition, a carbonation kinetics model was proposed to learn the carbonation kinetics of C-S-H carbonated in different CO2 concentrations. The experimental data fitted well with the model. The carbonation kinetics between 3% and 20% CO2 are similar, but different from that under 50% and 100% CO2.