This paper aims to investigate the influence of coal fly ash (CFA) addition on the fireproof properties of the metakaolin-based geopolymer foams. The physical properties, thermal conductivity and fire resistance of the CFA-metakaolin-based geopolymer foams are discussed. The CFA-metakaolin-based geopolymer foams achieve a dry density between 259.43 kg/m³ and 349.73 kg/m³, a porosity between 71.78% and 72.98%, a thermal conductivity between 0.0871 W/(m·K) and 0.0944 W/(m·K) and a compressive strength between 0.38 MPa and 0.56 MPa, exhibiting better physical properties than that of the porous blocks without CFA addition. It is also found that the CFA addition could decrease the viscous sintering temperature and change the phase compositions of sintering products, resulting in the porous structure deterioration in a certain extent and obvious rise of the final reverse-side temperature during the fire-resistance tests. Fortunately, the conversion of the amorphous geopolymer gel to ceramics has helped to maintain the main skeleton structure stability. The CFA-metakaolin-based geopolymer foams still exhibit excellent fire resistance, and the reverse-side temperatures are always within 250 °C after 3 h fire-resistance tests.

This study aims to explore the solidification performance of municipal solid waste incineration fly ash (MSWIFA) through co-mechanical treatment with circulation fluidized bed combustion fly ash (CFBCFA). The mineral characterization, physical properties, and leaching resistance of the solidified bodies are investigated by X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FT-IR), Thermogravimetry-differential thermal analysis (TG-DTA), compressive strength, porosity, and leaching test, respectively. C–S–H, ettringite (AFt), and Friedel’s salt (FS) are the predominant hydrate products in the CFBCFA based solidified bodies, which are similar to the cement based solidified bodies. However, CFBCFA based solidified bodies exhibit higher compressive strength (36.7 MPa) than cement based solidified bodies (11.28 MPa), attributing to the three reasons: lower porosity and more compact internal structure of CFBCFA based solidified bodies; large amounts of Ca(OH)₂ originating from MSWIFA are conducive to promoting the hydration reaction extent and compressive strength of the CFBCFA based solidified bodies; excessive Ca(OH)₂ would cause compressive strength deterioration for the cement based solidified bodies. The heavy metals (Zn, Cu, Cr, Cd, and Pb) concentrations in the extraction solution of the CFBCFA based solidified bodies are far below the requirements of Chinese National Standard GB 5085.3-2007. The solidification of MSWIFA through co-mechanical treatment could be an ideal substitute for cement solidification technology.