Accelerated carbonation of low-lime calcium silicates: CaCO 3 seeding for polymorph control and strength enhancement

Low-lime calcium silicates such as wollastonite, rankinite and belite solidify by mineral carbonation, forming calcium carbonate and amorphous silica gel while offering lower process emissions and inherent CO2 sequestration compared with conventional cement. This paper evaluated whether 1.0 wt.% Mg-calcite and aragonite nucleation seeds can control carbonate phase evolution and improve early strength development during accelerated carbonation curing (20% CO2, 30 °C, 75–85% RH) of phase-pure calcium silicate phases. XRD, TG/DTA, FTIR, and SEM results revealed that seeding modified nucleation pathways and reaction kinetics, increasing total carbonate formation by 46–82%. Precursor calcium/silicon oxide (C/S) ratios controlled boundary-layer alkalinity, stabilizing vaterite in wollastonite, while suppressing it in rankinite and belite. Simultaneously, Mg-calcite seeds redirected precipitation into aragonite in rankinite and wollastonite, whereas aragonite seeds provided direct templates for aragonite growth in belite. Consequently, 7-day compressive strengths increased by 49.1–82.9% for wollastonite and rankinite and 44.0–72.5% for belite.