Effects of High Temperature on Carbonated Calcium Silicate Cement (CSC) and Ordinary Portland Cement (OPC) Paste

This paper presents a comparative study on the effects of high temperature (~500°C) on carbonated calcium silicate-based cement (CSC), hydrated ordinary Portland cement (OPC), and hydrated OPC with 20% fly ash (FA) paste samples. The CSC is primarily composed of calcium–silicate minerals with different calcium to silica atomic ratios, such as wollastonite, rankinite, and pseudowollastonite. The major difference between CSCand OPC-based systems is that the CSC system generates strength from the carbonation reaction, while strength development of OPC-based systems depends on the hydration reaction. The microstructure of the carbonated CSC paste consist mainly of calcium carbonate, polymerized silica gel, and unreacted cement grains. The loss of stiffness due to the high-temperature exposure was found to be substantially lower for CSC samples compared with that of the hydrated OPC and OPC + FA paste samples. This observation was also consistent with the observed mass losses of these paste samples upon their exposure to high temperatures during the thermogravimetric analysis (TGA). The higher resistance of CSC paste samples to high temperature is attributed to the presence of microscopic phases which have higher decomposition temperatures than the phases present in the OPC. For the same reason, the increases in total porosities (measured using helium pycnometer) of the hydrated paste samples after exposure to 510°C were significantly higher than those of the CSC paste samples.