Synthesis of Concrete Waste Powder in Fly Ash Based Geopolymer Mortar: Assessing Strength, Durability Properties and Environmental Impact

The sustainable reuse of concrete waste in the form of aggregates and finely milled Concrete Water Powder (CWP) in Geopolymer Mortar (GPM) is an emerging area of research. This study examines the influence of CWP and Silica Fume (SF) on the strength, durability, and sustainability of Fly Ash (FA)-based GPM. This way, the potential for coupled valorisation fly ash and demolition wastes was assessed, thus promoting circularity in construction sector. GPM was substituted with CWP at 0%, 10%, 20%, 30%, and 40%, while SF substitution was maintained at 10% in all mixes except the control. Workability decreased with increasing CWP content, whereas compressive strength peaked at 20% CWP substitution. This mix also demonstrated superior durability, attributed to a densified microstructure and enhanced calcium hydroxide formation, as evidenced by SEM analysis. Environmental and economic assessments indicated that the 20% CWP–10% SF mix achieved the highest Sustainability Index (SI) and Economic Index (EI), supporting its viability. These findings highlight the potential of CWP as a precursor in sustainable GPM production.