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<p>This study presents a comprehensive durability assessment of slag-based geopolymer concretes reinforced with hybrid glass and steel fibers and modified with silica fume or metakaolin, under elevated temperatures up to 1000°C. The primary innovation lies in identifying the synergistic combination of 15% silica fume replacement with a low-volume hybrid fiber system (0.25% alkali-resistant glass + 0.75% hooked-end steel fibers), which substantially enhances both ambient mechanical properties and high-temperature resilience. A total of 15 mix designs were evaluated for compressive and splitting tensile strength, flexural performance, ultrasonic pulse velocity, mass loss, and post-fire load–displacement behavior. Results demonstrate that the optimized mix (SF15-GF0.25-ST0.75) achieves a 90-day compressive strength of 130.7 MPa and retains 26.0 MPa (19.9%) after 1000 °C exposure—nearly six times higher than the unreinforced control. Crucially, it exhibits exceptional residual tensile (3.80 MPa, 42.9% retention) and flexural strength (4.30 MPa, 33.2% retention), alongside markedly reduced mass loss (13.8%) and microstructural degradation (UPV loss limited to ~ 71%). Microstructural analyses (X-ray diffraction (XRD), X-ray fluorescence (XRF), Mercury intrusion porosimetry (MIP), Thermogravimetric analysis–differential thermal analysis (TGA-DTA), and Scanning electron microscopy (SEM)) suggest that silica fume densifies the matrix and strengthens the fiber–matrix interface, while hybrid fibers mitigate spalling and enable pseudo-ductile post-peak behavior even after extreme thermal exposure. In contrast, metakaolin-based mixes showed inferior thermal performance due to alumina-induced phase instability. These findings establish a new benchmark for fire-resistant geopolymer concretes, demonstrating that targeted precursor modification combined with balanced hybrid fiber reinforcement can overcome the intrinsic brittleness of geopolymers and significantly extend their applicability in high-temperature structural environments.</p>

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Low-Volume Hybrid Glass–Steel Fibers and Silica Fume Synergy: A Sustainable Innovation for Fire-Resistant, High-Performance Geopolymer Concrete

  • 期刊论文

  • 发表日期：

    2026年6月15日

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  • Arian DarvishaliNezhad,
  • Omid Bamohabbat,
  • Seyed Hosein Ghasemzadeh Mousavinejad,
  • Mohammadreza Raoufi Zaklehbari

摘要

This study presents a comprehensive durability assessment of slag-based geopolymer concretes reinforced with hybrid glass and steel fibers and modified with silica fume or metakaolin, under elevated temperatures up to 1000°C. The primary innovation lies in identifying the synergistic combination of 15% silica fume replacement with a low-volume hybrid fiber system (0.25% alkali-resistant glass + 0.75% hooked-end steel fibers), which substantially enhances both ambient mechanical properties and high-temperature resilience. A total of 15 mix designs were evaluated for compressive and splitting tensile strength, flexural performance, ultrasonic pulse velocity, mass loss, and post-fire load–displacement behavior. Results demonstrate that the optimized mix (SF15-GF0.25-ST0.75) achieves a 90-day compressive strength of 130.7 MPa and retains 26.0 MPa (19.9%) after 1000 °C exposure—nearly six times higher than the unreinforced control. Crucially, it exhibits exceptional residual tensile (3.80 MPa, 42.9% retention) and flexural strength (4.30 MPa, 33.2% retention), alongside markedly reduced mass loss (13.8%) and microstructural degradation (UPV loss limited to ~ 71%). Microstructural analyses (X-ray diffraction (XRD), X-ray fluorescence (XRF), Mercury intrusion porosimetry (MIP), Thermogravimetric analysis–differential thermal analysis (TGA-DTA), and Scanning electron microscopy (SEM)) suggest that silica fume densifies the matrix and strengthens the fiber–matrix interface, while hybrid fibers mitigate spalling and enable pseudo-ductile post-peak behavior even after extreme thermal exposure. In contrast, metakaolin-based mixes showed inferior thermal performance due to alumina-induced phase instability. These findings establish a new benchmark for fire-resistant geopolymer concretes, demonstrating that targeted precursor modification combined with balanced hybrid fiber reinforcement can overcome the intrinsic brittleness of geopolymers and significantly extend their applicability in high-temperature structural environments.