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This work offers in-depth understanding about the behavior of different M-S-H phases under carbonation. Here, we carbonated 8-year-old M-S-H samples under i) wet carbonation and ii) dried or steamed pressurized CO2. Both solid and liquids samples were analyzed using various techniques while thermodynamic modelling was coupled to shed light on the response of M-S-H phases under carbonation. We found that M-S-H with Mg/Si = 0.8 showed excellent carbonation resistance in which the phase remained stable in all investigated conditions. M-S-Hs with higher Mg/Si ratios (1.1 and 1.5) released Mg2+ to obtain the stable M-S-H (Mg/Si = 0.8) while the released Mg2+ dissolved in water or formed Mg‑carbonates under wet carbonation or pressurized carbonation, respectively. Hence, high temperature and/or pressure are needed to carbonate M-S-H with high Mg/Si ratios to form Mg‑carbonates. The remarkable stability of the strength-forming M-S-H phase under carbonation holds promising potential for future applications of such cements.
Bernard et al. (Tue,) studied this question.