Development of low-carbon alkali-activated materials solely activated by flue gas residues (FGR) waste from incineration plants

Flue gas residues (FGR), a waste from incineration plant was utilized as an alternative alkaline activator to energy intensive and costly commercial activators. Fly ash (FA) and slag were used as precursors materials along with the FGR to produce low-carbon and cost-effective alkali-activated materials (AAMs). Reaction products and micromechanical properties were investigated by advanced microstructure analysis techniques. Results from the infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and nanoindentation indicated that reaction products were comprised of N-A-S-H gel as a major reaction product along with the hybrid gel (C–N-A-S-H) and C-A-S-H gel. SEM-EDS and nanoindentation results showed that the formation of C-A-S-H gel was directly related to the content of FGR. The increase in volume of Ca-based reaction products (C–N-A-S-H and C-A-S-H) was associated with the activation of slag in presence of Na₂SO₄. Besides N-A-S-H gel, some new reaction products (zeolite, apatite and berlinite) were also observed from XRD analysis of pastes. The compressive strength of AAMs was in the range of 33.5–39.6 MPa and was in line with microstructure analysis results. Leaching concentrations of Ag, Ba, Cd, Cu and Zn heavy metals in FGR were 0.10, 0.40, 0.63, 0.26 and 1.65 mg/L respectively and below the regulatory limits and it was classified as a non-hazardous material.