Rapid hardening of ternesite and microstructural changes activated by carbonation curing and ye'elimite

This study investigates the effects of carbonation curing and ye'elimite on the physical and chemical properties of ternesite to improve its hardening rate. The results showed that ternesite had a high carbonation activity and the additional benefit of CO2 sequestration. The carbonation products included amorphous calcium carbonate, calcite, aragonite, gypsum, and either C-S-H gel or silica gel. The large amount of carbonated products improved the structure, densified the matrix, and was primarily responsible for the strong relationship between the mechanical strength and pore structure of the ternesite and its carbonation level. The strong carbonation activity of ternesite was caused by the rapid dissolution of calcium ions in the presence of CO2. Ye'elimite was added, and the aluminium hydroxide produced by the carbonation reaction of ye'elimite appeared in the slurry, accelerating the hydration rate of ternesite and causing the carbonation and hydration reactions of ternesite to occur simultaneously. This significantly increased the carbonation rate and mechanical strength of ternesite at the early stage. The hardening rate of ternesite significantly increased under the simultaneous action of ye'elimite and carbonation curing.