Waste GFRP powder–GGBS geopolymer for sustainable stabilization of municipal sewage sludge: Engineering performance, contaminant immobilization and environmental assessment

Municipal sewage sludge (MSS) management remains a significant environmental challenge due to its high moisture content, contaminants, and reliance on carbon-intensive OPC stabilization. This study developed a GFRP powder–GGBS geopolymer for MSS stabilization and systematically evaluated its engineering, environmental, and resource-efficiency performance. The effects of GFRP powder replacement ratio, binder dosage, activator concentration, and activator-to-precursor ratio were investigated through unconfined compressive strength (UCS), hydraulic conductivity, pH, and contaminant leaching tests, complemented by XRD, FTIR, and SEM-EDS analyses. Increasing the geopolymer dosage from 10% to 20% increased UCS by 263% and 350% at 7 and 28 days, respectively, while increasing GFRP powder replacement from 10% to 20% reduced hydraulic conductivity by 31% and 33% at 7 and 28 days. At 28 days, the optimized GFRP powder–GGBS system achieved immobilization efficiencies of 99.72% for Ba, 95.97% for Pb, 79.52% for As, and 70.41% for Ni. Microstructural analyses revealed progressive phase dissolution, aluminosilicate network rearrangement, and formation of a dense Ca-rich aluminosilicate gel matrix, accounting for the improved strength, reduced permeability, and contaminant retention. Life cycle assessment further showed lower energy demand and environmental impacts than OPC stabilization, and the multi-criteria evaluation identified the GFRP powder–GGBS system as the best-performing option. The results demonstrate a circular approach for simultaneously valorizing waste GFRP and MSS toward low-carbon stabilization and resource recovery.