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 microstructure, 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.