Decomposition of synthesized ettringite by carbonation

The stability of ettringite (3CaO·Al2O3·3CaSO4·32H2O) in contact with CO2 gas has been studied using synthesized ettringite. Carbonation were carried out at water/solid ratios(W/S) of 0.6∼3.5 in a moist CO2-incubator. According to the SEM-EDAX examination, the carbonation without water makes compositional changes slightly in ettringite, maintaining fibrous form. By the carbonation with excess water, ettringite clearly decomposed to gypsum, calcium carbonate, and alumina gel. The apparent carbonation rates were calculated from the amount of calcium carbonate. Jander equation was taken to model the carbonation kinetics.