Conversion of CO2 and Its Utilization in the Preparation of Cement-Slag-CaCO3 Ternary Blends

A reduction in CO2 emissions is necessary in the concrete industry. This study proposes a CO2 conversion technique by which CO2 gas is converted into solid nano CaCO3 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 CaCO3 and the Al(2)O(3 )phase in the binder. XRD analysis revealed that at 28 days, the addition of nano CaCO3 can inhibit the transformation of ettringite (AFt) to monosulfate (AFm). As the contents of nano CaCO3 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 CO2 emissions (the ratio of CO2 emissions of the paste to its strength) was much higher than the replacement percentage of nano CaCO3. This was because nano CaCO3 increased the late strength and had a negative CO2 emission value. (c) 2022 American Society of Civil Engineers.