Enhancement of fly ash reactivity through triethanolamine addition and CO2 curing

This study investigated the effect of triethanolamine (TEA) on the hydration and carbonation of Class C fly ash (FA) varying its dosages (1 wt% and 5 wt%). From an early age, TEA enhanced the dissolution of calcium and alumina of FA, leading to improved hydration and carbonation. As a result, regardless of curing conditions, the reactivity of merwinite (C₃MS₂) and the formation of katoite (C₃AH₆) increased with TEA content. Furthermore, TEA remained in the pore solution for 7 days, affecting the hydration and carbonation products. Under wet curing, at 5 wt% of dosage, the complexation effect of TEA resulted in the preferential formation of ettringite over monosulfoaluminate, despite a high aluminate concentration. Meanwhile, under the carbonation curing in the presence of TEA, crystalline forms of calcium carbonate, as well as mono- or hemicarboaluminate, were not observed. Instead, spherical-shaped amorphous calcium carbonate was formed, with its quantity increasing with the TEA content, mineralizing CO₂ up to 2.55 g per 100 g of FA. In addition, combining TEA and carbonation improved the formation of C-A-S-H, significantly enhancing the compressive strength. Consequently, the addition of TEA along with carbonation curing to FA resulted in a remarkable increase in mechanical performance and pore structure refinement. The carbonated FA pastes with 1 wt% and 5 wt% of TEA achieved the strengths of 44.8 MPa and 70.2 MPa, respectively, after 7 days.