Turning hazardous waste into sustainable pavement blocks: Life cycle assessment of geopolymer incorporating MSW incineration fly ash and bauxite residue

This study presents the first cradle-to-gate life cycle assessment of compressed and heated geopolymer pavement blocks incorporating 100% hazardous industrial by-products (municipal solid waste incineration fly ash and red mud) as aluminosilicate precursors, benchmarked against mould-cast cement-based and geopolymer systems from the literature using the midpoint methodology across 18 impact categories. The compressed geopolymer formulations achieved global warming potential of 0.051–0.066 kg CO₂eq/kg block, representing reductions of 55–76% relative to cement-based comparators, with consistently superior performance across all 18 categories. Embodied energy (0.52–0.57 MJ/kg) and material cost (0.028–0.037 US$/kg) were the lowest among all systems evaluated. TOPSIS multi-criteria analysis ranked all three compressed formulations in the top three positions. Sensitivity analysis also confirmed that the environmental superiority is statistically robust across alkali activator dosage variation and transport distance scenarios. These findings establish pressurised and heated geopolymer technology as a systemically superior and cost-competitive pathway for hazardous waste valorisation in pavement block manufacturing.