A green approach to construction: Fly ash-based one-part geopolymer foam concrete reinforced with waste concrete powder and polypropylene fibers

Abstract

Making concrete in the usual way produces a lot of carbon dioxide, so we need new ways to make building materials that are better for the environment. This study investigates the feasibility of producing one-part geopolymer foam concrete (GFC), utilizing Class F fly ash partially replaced by waste concrete powder (WCP) and reinforced with polypropylene (PP) fibers. Twelve mixes were prepared with 0-50 % WCP (by fly-ash mass) and 0-0.9 % PP fibers (by volume). The effects of these variations on fresh state properties, mechanical strength, density, thermal conductivity, porosity, chemical durability (against acid and sulfate attack), freeze-thaw resistance, and thermal durability were systematically evaluated. Replacing 25 % of fly ash with WCP maximized 28-day compressive strength at 5.97 MPa, an 80 % improvement over the control mix. Durability peaked when WCP and fibers were combined: the 10 % WCP + 0.9 % PP fiber mix retained 3.65 MPa and 3.35 MPa after 120 days in H2SO4 and MgSO4 attack, respectively, while the 25 % WCP + 0.3 % PP fiber mix lost only 1.02 % mass after 25 freeze-thaw cycles. Thermal stability was highest for the 25 % WCP + 0.9 % PP fiber blend, which preserved 76.5 % of its original strength at 900 degrees C. These results demonstrate that moderate WCP substitution governs strength, whereas PP fiber dosage controls durability. Integrating both waste valorization and fiber reinforcement in GFC yields a lightweight, low-carbon concrete with balanced mechanical performance and robust resistance to chemical, thermal, and freeze-thaw degradation.