Alkali-activated materials partially activated using flue gas residues: An insight into reaction products

This study explored the feasibility of using flue gas residues (FGR) and commercial sodium silicate (CSS) as hybrid activators (HA) to prepare alkali-activated materials (AAMs). The CSS was replaced by 8, 16, and 24% FGR for a fixed amount of Na₂O. Results from selective dissolution techniques showed that control paste (CP-0F, 0% FGR) contained a slightly higher amount of N-A-S-H gel as compared to pastes prepared by hybrid activators (HAPs), whereas the amount of C-A-S-H gel was higher in HAPs containing 16% and 24% FGR. These findings were further corroborated by SEM-EDS analysis results. TGA, XRF and SEM-EDS analysis on paste residues confirmed the efficacy of HCl and SAM dissolution approaches to selectively dissolve the reaction products (N-A-S-H and C-A-S-H gels). SEM-EDS analysis showed that calcium-rich cross-linked gel (C-(N)-A-S-H) was present in all pastes. The gradual increase in reaction products of alkali-actived fly ash/slag (AAFS) pastes with the increase in curing age was observed by XRD analysis. The ²⁹Si MAS NMR analysis revealed the formation of a higher amount of Q⁴(0Al) and Q⁴(1Al) species in HAPs as compared to control paste however a decline in the amount of Q⁴(3Al) and Q⁴(4Al) species was observed.