Effect of pre-carbonation on the properties of cement paste subjected to high temperatures

The paper studied the effect of pre-carbonation on the C–S–H structure and investigated the positive effect of pre-carbonation on enhancing the stability of cement paste at high temperatures. OPC samples with a w/c of 0.45 were precarbonated under 20% CO2, 80% RH, and 30 °C for one week. By comparing the performance of pre-carbonation cement paste samples with un-carbonated samples subjected to 25 °C (room temperature), 450 °C, 650 °C, and 800 °C, the mineral and microstructure of the cement paste after exposure to different temperatures were investigated through TG, XRD and SEM measurements and observations. The results indicated that adequate pre-carbonation can not only consume almost all Ca(OH)2 and produce CaCO3, resulting in a denser C–S–H microstructure, but also transform the ettringite into calcium carboaluminate in cement paste, which is considered to have a better thermal stability. •Pre-carbonation consumed almost all Ca(OH)2 and produced CaCO3, which makes the cement paste more stable when subjected to high temperature.•Pre-carbonation transformed the ettringite into calcium carboaluminate, which is stable at 800 °C in cement paste.•Pre-carbonation makes the C–S–H structure more compact under high temperatures and enhances the stability of cement paste.