Effects of low-lime calcium silicate cement addition on the hydration, carbonation, and microstructural characteristics of OPC pastes by carbonation curing

Low-lime calcium silicate cement (CSC) is a promising alternative binder characterized by its non-hydraulic properties and low-lime content, requiring a carbon dioxide-enriched environment for effective curing. In the current study, CSC powder was blended into ordinary Portland cement (OPC) pastes to investigate its impact on phase evolution, microstructural pore characteristics, and strength development. The amount of CSC added to the OPC pastes varied from 0 % to 50 % by weight. For carbonation curing, the concentration of gaseous carbon dioxide was fixed at 20 %. Phase evolution, hydration reactions, carbonation reactions, microstructural pore characteristics, and strength development were analyzed using X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), compressive strength testing, and thermodynamic modelling. The analysis indicated an increase in the amount of calcium carbonate due to the consumption of portlandite, calcium-silicate-hydrate (C-S-H), and ettringite under carbonation curing conditions. The reaction of low-lime CSC was observed between one and three days of curing, resulting in a significant increase in calcium carbonate formation. The OPC paste containing 50 % CSC powder demonstrated the highest compressive strength of 45.6 MPa, representing a 75 % increase compared to the pure OPC paste, which achieved a compressive strength of 26.0 MPa after seven days of carbonation curing. • Primary reaction in OPC-CSC pastes occurs within 1–3 days of carbonation curing. • The addition of CSC increased the compressive strength of the OPC paste. • The C50 sample exhibits a denser microstructure. • Carbonation consumes key hydration products: portlandite, C-S-H, and ettringite.