Valorization of mineral wool waste in Class F fly ash geopolymer: Geopolymerization, macro properties, and high temperature behavior

The tension between the non-recyclable nature of mineral wool wastes (MWW) and the scarcity of landfill space emphasizes the imperative to explore sustainable ways to valorize these wastes. In this work, the potential of utilizing MWW as both co-precursor and fiber reinforcement in Class F fly ash geopolymer is investigated. The phase composition and microstructure are systematically learned by multiscale physicochemical analysis, followed by the determination of macro properties and high temperature behavior. Results indicate that the ion dissolution and dimension of MWW have a synergetic effect on the microstructural formation and macro performance of the hybrid geopolymer. The inclusion of MWW, particularly in fine particle form, accelerates the geopolymerization process, leading to enhanced gel formation and increased Al uptake in the N-A-S-H gel. With increasing MWW content (0–12 wt%), a denser gel forms, but greater macropore formation increases porosity, subsequently reducing compressive strength. The desired pore structure with optimal MWW substitution significantly reduces drying shrinkage and enhances flexural properties. At elevated temperatures, MWW poses a healing effect on the matrix, achieving a 98.5% increase in compressive strength with MWW-m incorporation. While a drastic thermal shrinkage arises from the substantial mass loss and partial melting of MWW.