CO2 adsorption on calcium silicate hydrate gel synthesized by double decomposition method

The calcium silicate hydrate gel (C–S–H) was synthesized by the double decomposition method because of the simplicity and the quickness of the procedure. The structure of the C–S–H gels after 1 week and 4 weeks in contact with the formation solution was studied through micro-Raman, Fourier transformed infrared spectroscopy and 29Si nuclear magnetic resonance. Simultaneous thermodifferential–thermogravimetric analysis and mass spectrometry (DTA/TG/MS) was used to identify the amount of calcium carbonate formed due to the reaction between the calcium and atmospheric CO2. With DTA/TG/MS, mass loss due to CO2 was observed to take place at temperatures below 400 °C, unidentified to date, which might be associated with the CO2 adsorbed on the C–S–H gel. Thus, in the TG analysis in the 300–430 °C range, both the loss of water due to the decomposition of the amorphous calcium carbonate and the loss of CO2 adsorbed on the gel must be considered. Additionally, polymerization of the gel and a decrease in the Ca/Si ratio was observed from the samples from 1 to 4 weeks.