Roles of CO2 curing induced calcium carbonates on high temperature properties of dry-mixed cement paste

Abstract

CO2 curing represents a promising way to enhance the mechanical strength of cement-based materials. Since the calcium carbonates (CaCO3) induced by CO2 curing has a higher decomposition temperature compared with most cement hydration products (such as calcium silicate hydrate (C-S-H) and calcium hydroxide (Ca(OH)2)), the performance of those carbonated cement pastes is expected to react differently when exposed to elevated temperatures (in particular temperature above 400 °C). In this study, dry-mixed cement pastes prepared with different water to cement ratios (w/c) was first CO2 cured for different ages, followed by exposure to 200 °C, 400 °C, 600 °C and 800 °C. The residual compressive strengths, microstructure evolution and physicochemical properties before and after exposure to elevated temperatures were studied and compared with the control group cured with natural air. The results showed that CO2 curing enhanced the thermal stability of cement pastes, and the 7 and 28 days residual compressive strength of the carbonated samples after exposure to 600 °C was higher than that of the 28-day original strength (tested at 20 °C) of the natural air cured samples. This is because the presence of CaCO3 can prevent the expansion of micro-cracks at temperatures up to 600 °C. In addition, the generated CaCO3 reduced the water absorption of those samples before and after exposure to elevated temperatures, but its synergetic impact lowered with an increase the heating temperature.