Conversion of ${\mathbf{CO}}_{\mathbf{2}}$ and Its Utilization in the Preparation of Cement-Slag-${\mathbf{CaCO}}_{\mathbf{3}}$ Ternary Blends

A reduction in ${\mathrm{CO}}_2$ emissions is necessary in the concrete industry. This study proposes a ${\mathrm{CO}}_2$ conversion technique by which ${\mathrm{CO}}_2$ gas is converted into solid nano ${\mathrm{CaCO}}_3$ and used to replace the partial binder of cement-slag blends in ratios of 2%, 4%, and 6%. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy analyses confirmed the formation of hemicarboaluminate (Hc) and monocarboaluminate (Mc) due to the chemical reaction between nano ${\mathrm{CaCO}}_3$ and the ${\mathrm{Al}}_2{\mathrm{O}}_3$ phase in the binder. XRD analysis revealed that at 28 days, the addition of nano ${\mathrm{CaCO}}_3$ can inhibit the transformation of ettringite (AFt) to monosulfate (AFm). As the contents of nano ${\mathrm{CaCO}}_3$ increased, the hydration heat, strength, ultrasonic pulse velocity (UPV), electrical resistivity, and combined water content increased. The degree of increment of the electrical resistivity was more pronounced than that of the strength. For various specimens, the strength and combined water content presented a linear relationship, and the strength and UPV presented an exponential function. The reduction rate of normalized ${\mathrm{CO}}_2$ emissions (the ratio of ${\mathrm{CO}}_2$ emissions of the paste to its strength) was much higher than the replacement percentage of nano ${\mathrm{CaCO}}_3$. This was because nano ${\mathrm{CaCO}}_3$ increased the late strength and had a negative ${\mathrm{CO}}_2$ emission value.