Internal carbonation of calcium silicate cement incorporated with Na₂CO₃ and NaHCO₃

This study investigates internal carbonation in calcium silicate cement (CSC) paste using sodium carbonate (Na₂CO₃) and sodium bicarbonate (NaHCO₃). CSC slurries, with 2.5–10 % Na₂CO₃ and NaHCO₃ were cured under a 60 °C atmosphere along with CSC slurries cured under a 10 % CO₂ environment. Microstructure and carbonation kinetics were studied using analytical tools such as TGA, XRD, FT-IR and ITC. CSC primarily comprises non-hydraulic phases such as CS, β-C₂S, C₃S₂ and γ-C₂S, which are depleted with increased Na₂CO₃ and NaHCO₃ content due to the carbonation reaction. This reaction is exothermic and accompanied by a higher heat release than CSC slurries. The inclusion of NaHCO₃ in the CSC matrix promotes the formation of strength-giving phases such as CaCO₃ and amorphous phases. Moreover, the IR spectra show the consumption of Q⁰ and Q¹ silicate species accompanied by a subsequent increase in carbonate absorption dip during carbonation.