Polypropylene fiber-reinforced geopolymer mortar from coal washing waste and recycled glass powder: mechanical and microstructural performance.

In this study, a sustainable geopolymer mortar has been developed entirely from industrial waste materials, including coal washing waste (CWW) ash, recycled glass powder (RGP), and calcium carbide residue (CCR), reinforced with polypropylene fibers (PPF). A five-stage experimental approach was employed to optimize the binder composition, alkaline activator ratio (Na2SiO3/NaOH) (NS:NH), alkali solution-to-binder ratio (S:B), fiber content, and the heat-curing process, based on mechanical performance. The optimal binder consisted of 7% CWW ash, 10% RGP, and 20% CCR, activated at an NS:NH ratio of 1.5 and an S:B ratio of 0.65. Incorporation of 0.8% PPF increased flexural strength by approximately 7% compared to the unreinforced geopolymer mortar due to effective crack-bridging and improved matrix integrity. Heat curing at 100 °C for 24 h resulted in the highest performance, yielding a 28-day compressive strength of 42.15 MPa, flexural strength of 5.23 MPa, and UPV of 4746 m·s⁻¹, representing improvements of 50%, 45.2%, and 10.1%, respectively, over the Portland cement control sample. SEM, FTIR, and XRD analyses confirmed the formation of dense aluminosilicate and calcium-rich gel phases, which correlate with the enhanced mechanical properties. The novelty of this research lies in the synergistic utilization of three industrial wastes, combined with fiber reinforcement and optimized curing, to produce a high-performance, low-carbon geopolymer mortar suitable for both structural and non-structural engineering applications.