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°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.