Mechanical and Mineralogical Properties of Concrete Incorporating Low-Lime Calcium Silicate Cement Under Accelerated Carbonation Curing

Low-lime calcium silicate cement (CSC) offers the potential to reduce CO2 emissions during cement production and sequester CO2 through carbonation curing. However, the relationship between CSC replacement, strength development, and CO2 uptake requires clarification at the concrete scale. This study evaluated the effects of replacing OPC with 0%, 25%, and 50% CSC on compressive strength, carbonation behavior, phase evolution, and CO2 sequestration in concrete. Following initial steam curing, specimens underwent carbonation curing under 20% CO2 for up to 14 days. Compressive strength and carbonation depth were measured, while phase evolution and CO2 uptake were examined using X-ray diffraction, Fourier-transform infrared spectroscopy, and thermogravimetric analysis (TGA). After 14 days, compressive strengths were 35.46, 29.84, and 27.95 MPa, respectively. Although final strength decreased with increasing CSC replacement, the 50% mixture exhibited an approximately 398% increase from its pre-carbonation strength of 5.61 MPa. Corresponding carbonation depths were 8.8, 18.2, and 27.1 mm, and TGA-based net CO2 uptakes were 18.2, 34.0, and 50.5 kg CO2/t-concrete. Calcite and vaterite were identified, while infrared spectral changes suggested the formation of silica-rich reaction products. Thus, 50% OPC replacement achieved approximately 28 MPa and 2.8 times the CO2 uptake of the control under the investigated conditions. These findings demonstrate the potential to combine OPC substitution with mineral CO2 sequestration, while highlighting a trade-off between compressive strength and CO2 uptake. Further mechanical and durability evaluations and a comprehensive life-cycle assessment are required to establish structural applicability and net greenhouse gas emission reductions.