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

Artikel i vetenskaplig tidskrift, 2022

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 degrees 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 degrees C and completely decomposed at 600 degrees C, while the decomposition of calcite started at 600 degrees C and finished at 720 degrees C. Meanwhile, the depolymerization of the calcium modified silica gel to the silicate phases with a lower degree of polymerization was initiated at 500 degrees C, which led to the crystallization of beta-C2S at 600 degrees C. The generation of beta-C2S was found to increase with the elevation in temperature and became the dominant phase at 950 degrees C. In conclusion, the high temperature could affect the stability of carbonated cement pastes at 500 degrees 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 nondestructive way, which should be more consistent with the true condition in the material.