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.

Automated summary

This study investigated the feasibility of using flue gas residues (FGR) and commercial sodium silicate (CSS) as hybrid activators (HA) for the preparation of alkali-activated materials (AAMs). The results showed that the use of hybrid activators led to the formation of more C-A-S-H gel compared to the control paste, which contained a higher amount of N-A-S-H gel. The analysis also revealed the presence of calcium-rich cross-linked gel (C-(N)-A-S-H) in all the pastes.