Characteristics of calcium silicate cement: Effects of CO<sub>2</sub> curing and CaCO<sub>3</sub> micro-filler addition

This study investigates the synergistic effects of adding calcium carbonate (CaCO3) micro-fillers and applying CO2 curing to mortars blended with Ordinary Portland Cement (OPC) and Calcium Silicate Cement (CSC). Specimens were prepared according to ASTM C109 and, after demolding, were subjected to CO2 curing for 12 h under conditions specified by ASTM C1910 (70 ± 5 % CO2, 30 ± 3 °C, 80 ± 10 % RH). The results showed that the Cc5 specimen, containing 30 wt.% OPC and 70 wt.% CSC with CaCO3 replacing fine aggregate (approx. 5 wt.%), exhibited a favorable balance of performance. Its compressive strength increased by 122 %, from 12.5 to 27.8 MPa, after 12 h of curing, with a net CO2 uptake of 8.3 wt.%. Thermogravimetric analysis (TGA) revealed that this performance enhancement was due to the CaCO3 filler acting as nucleation sites for carbonate formation, which simultaneously accelerated the carbonation of both OPC hydrates (portlandite, C–S–H) and non-hydraulic CSC phases (wollastonite, rankinite). The resulting dense microstructure was identified as the key factor for the improved strength and high CO2 sequestration capacity. These findings highlight the significant potential of the OPC-CSC blended binder system for developing CO2-utilized and low-carbon construction materials.