Preparation of Nano Calcite by the Carbon Capture Technology to Improve the Performance of Ultrahigh-Performance Concrete Containing Calcined Clay

Ultrahigh-performance concrete (UHPC) has been widely used because of its outstanding mechanical properties and durability. However, the high demand for cement leads to higher carbon dioxide emissions. In this study, solid nano-calcium carbonate (nano-CaCO3) derived from gaseous carbon dioxide is used as an admixture to UHPC, which indirectly realizes the capture and storage of carbon dioxide by UHPC. This study investigated the effect of the nano-CaCO3 on the macroscopic and hydration properties of the UHPC, characterized its micro-structure, and calculated the carbon dioxide emission. The experimental and analytical results show that the mechanical properties and durability of the UHPC are significantly improved with the nano-CaCO3 addition. Microscopic experimental analysis reveals that the presence of nano-CaCO3 significantly increases the hydration rate of the mixture. During the middle and late stages, the nano-CaCO3 reacted with the aluminum in Hwangtoh clay to form monocarboaluminate, which made the UHPC internal structure denser. Furthermore, the calculation results show that the nano-CaCO3 has a significant effect on reducing the UHPC CO2 emission, owing to the CO2 capture and sequestration during the conversion of gaseous CO2 into solid nano-CaCO3.