High-performance geopolymer production using reclaimed fly ash: A sustainable approach to landfilled fly ash management?

The growing disparity between the supply and demand for fly ash (FA), which is increasingly used in sustainable building materials, contrasts with the large quantities of FA already in landfills, contributing to environmental pollution and disasters. Meanwhile, geopolymer technology offers significant environmental and financial benefits for managing waste. Therefore, this research examines the potential for producing high-performance geopolymers using reclaimed FA (RFA) (from landfilled FA recycling) and ground granulated blast furnace slag (GGBFS) through hot water curing. The characteristics and performance of these geopolymers were evaluated based on strength, transport properties, durability, and microstructural analysis. The results revealed that the strength of geopolymers is approximately unaffected by replacing up to 60 % of GGBFS with RFA, and increasing the RFA dosage to 80 % still yielded material suitable for at least medium-grade applications. Specifically, inclusion of 20-80 % RFA resulted in a 28-day compressive strength ranging from 81.1 to 38 MPa. While RFA slightly increased water absorption and decreased surface electrical resistivity of geopolymers, indicating vulnerability to environmental agents, excessive GGBFS reduced resistance to acid attack, suggesting that 40-60 % RFA is needed for adequate chemical resistance. Similarly, adding RFA led to lower drying shrinkage and improved resistance to elevated temperatures. Also, RFA posed no leaching problem, and neither raw RFA nor RFA-based geopolymers exceeded solid inert or hazardous waste thresholds, with the latter more effective at immobilizing heavy metals. The findings support high-performance geopolymer production containing RFA to manage landfilled FA, reduce environmental burden, and encourage the circular economy in construction.