Exploring the Effectiveness of Hybrid Fiber–Reinforced Geopolymer Concrete

This paper presents an experimental study evaluating the mechanical and durability properties of plain, steel fiber (SF), and polypropylene fiber (PPF) reinforced industrial fly ash (IFA)-based geopolymer concrete (GPC) and compares the results with those of ordinary Portland cement-based conventional concrete (CC). The incorporation of fibers in GPC resulted in a gradual reduction in workability, with slump values decreasing from 130 to 70 mm across GPC mixes. However, significant improvements were observed in mechanical properties. Compressive strength increased from 34 MPa in CC to a maximum of 46 MPa in the hybrid mix (GPC8). Likewise, notable enhancements in split tensile strength (7.90 MPa) and flexural strength (10.10 MPa) were achieved in GPC8, highlighting the synergistic effect of hybrid fibers in improving postcracking behavior. The modulus of elasticity also improved substantially, with GPC8 reaching 50.20×103 MPa compared to 24.60×103 MPa in CC. The GPC specimens demonstrated superior durability compared to the CC specimens. GPC showed 25% lower wear in abrasion tests, which improved to a 60% reduction with the addition of SF and PPF. In acid resistance tests, GPC exhibited less than 2.26% weight loss and a maximum 22.50% reduction in compressive strength after 6 months in 3% H2SO4. Both GPC and CC showed less than 1% weight loss under sulphate attack. Under wet–dry cycles in a marine environment, GPC maintained durability, with mass loss and strength reduction not exceeding 5.26% and 23.83%, respectively. The optimum percentage of SF, PPF, and a combination of hybrid fiber specimens was 0.4% PPF, 1% SF, and 0.4% PPF+1.0% SF, showing improvement in mechanical properties and durability properties over CC of the same grade. Scanning electron microscopy (SEM) and x-ray diffraction analyses were consistent with the observed mechanical and durability results. Furthermore, SEM images revealed a dense microstructure and a well-integrated interface between the GPC matrix and the fibers.