Microstructural characteristics and CO2 uptake of calcium sulfoaluminate cement by carbonation curing at different water-to-cement ratios

The present study investigates the effect of carbonation curing and the water-cement ratio on the microstructural characteristics and CO2 uptake of calcium sulfoaluminate (CSA) cement. Low-pH carbonic acid promoted ettringite participation in CaCO3 formation. Different CaCO3 polymorphs, Al(OH)3, and unreacted ye'elimite occupied the higher proportion of the phase assemblage of carbonation-cured sample. Ettringite and strätlingite were the major phases of the water-cured sample. A maximum fourfold increase in the CO2 uptake capacity per gram of the carbonation-cured paste at the highest water-cement ratio was observed. 27Al NMR demonstrates the strätlingite formation after 1 day of water curing, while unreacted ye'elimite was observed in the carbonation-cured sample. The dissolution of hydrated phases leading to the formation of CaCO3, moderately affects the strength. The maximum proportion of weight was reached within 1 day of water curing due to the reaction of ye'elimite and belite to the formation of ettringite and strätlingite, respectively.