Assessment of compositional changes of carbonated cement pastes subjected to high temperatures using in-situ Raman mapping and XPS

This paper presents a new method for assessing the compositional changes of carbonated cement pastes subjected to high temperatures. In this new method, in-situ Raman mapping combined with X-ray photoelectron spectroscopy (XPS) was used to monitor the phase transformation in carbonated cement pastes subjected to various high temperatures from 30 to 950 °C. Two kinds of carbonated areas, i.e., vaterite dominated and calcite dominated, were found in the in-situ Raman measurements. With the elevation in temperature, most of the vaterite was converted to calcite at 500 °C and completely decomposed at 600 °C, while the decomposition of calcite started at 600 °C and finished at 720 °C. Meanwhile, the depolymerization of the calcium modified silica gel to the silicate phases with a lower degree of polymerization was initiated at 500 °C, which led to the crystallization of β-C₂S at 600 °C. The generation of β-C₂S was found to increase with the elevation in temperature and became the dominant phase at 950 °C. In conclusion, the high temperature could affect the stability of carbonated cement pastes at 500 °C and above. The in-situ Raman mapping measurement has provided an extraordinary view of the spatial distribution of interesting phases subjected to high temperatures in a non-destructive way, which should be more consistent with the true condition in the material.