Microstructural phase evolution and strength development of low-lime calcium silicate cement (CSC) paste incorporating ordinary Portland cement under an accelerated carbonation curing environment

Low-lime calcium silicate cement (CSC) is a CO2-reactive cement that utilizes the carbonation products of low-or non-hydraulic C2S, C3S2, and CS phases under H2O-and CO2-rich conditions. However, the reactivity and compressive strength of the CSC require further improvement. Therefore, this study aims to investigate the effects of blending ordinary Portland cement (OPC) as a reactive source into CSC on the initial reaction kinetics, phase evolution, and compressive strength development during carbonation curing. To assess the effects of blending CSC and OPC, CSC was substituted by OPC with the incremental ratio of 20 wt%. Notably, the CSC sample with 20 wt% OPC incorporation exhibited the highest compressive strength, which increased by up to 2.5 times compared to the pure CSC paste. Analysis of the microstructural phase evolution revealed that this significant increase in compressive strength was attributed to the strong mechanical interlocks between the rhombic CaCO3 crystals, which were reinforced by a substantial amount of vaterite.