The influence of carbon dioxide concentration on carbonation behavior in cement paste

Accelerated carbonation is the main method of simulating carbonation in the laboratory, but there are significant differences in the CO2 concentrations adopted for accelerated carbonation testing among the various standards currently. In this work, X-ray imaging technology was used to study the distribution of the carbonation zone in samples at different CO2 concentrations and used for imaging, which was followed by quantitative analyses of the carbonation profile and the material compositions of the entire carbonation zone in combination with thermogravimetric analysis (TGA) and 29Si nuclear magnetic resonance (29Si NMR) analyses. The results showed that the carbonation profiles of cement paste were similar under 3% and 10% concentration, with the front line of carbonation developing parallel to the soffit of the sample. However, when the concentration was increased to 20%, the carbonation profile at partial carbonation zone could be changed due to shrinkage cracking. In addition, the compositions of the complete carbonation zone under different concentrations were similar, and the development of this zone followed Fick's law.