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<p>Concrete structures exposed to fire experience significant degradation, while the residual mechanical behavior of hybrid fiber systems across dosage gradients remains insufficiently quantified. This study systematically investigates the effects of steel fiber (SF) and carbon fiber (CF), used individually and in hybrid combinations, on the residual mechanical properties and thermomechanical damage evolution of fiber-reinforced concrete after high-temperature exposure. Ten mixtures were prepared by varying SF and CF dosages (0–1.5 vol%). Specimens were heated from 25&#xa0;°C to 800&#xa0;°C and evaluated for residual compressive, splitting tensile, and flexural strengths. Damage characteristics were analyzed using scanning electron microscopy (SEM) together with ultrasonic pulse velocity (UPV) and resonant frequency (RF) measurements to link microstructural deterioration with macroscopic performance. A multi-parameter polynomial model was established to correlate temperature, fiber dosage, and relative wave velocity for post-fire performance prediction. Residual strength showed a slight increase between 25–400&#xa0;°C, followed by pronounced degradation beyond 400&#xa0;°C. The hybrid mixture containing 1.0 vol% SF + 1.0 vol% CF exhibited the best overall compressive and flexural retention, whereas 1.5 vol% SF + 1.0 vol% CF achieved the highest splitting tensile strength. Microstructural observations and wave velocity measurements consistently revealed progressive matrix cracking and interfacial debonding with increasing temperature. The proposed three-stage thermomechanical damage model elucidates the synergistic mechanism of hybrid fibers and provides a practical framework for rapid assessment of residual performance after fire exposure.</p>

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Research on the properties of carbon-steel hybrid fiber concrete after elevated temperatures

  • 期刊论文

  • 发表日期：

    2026年6月19日

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  • Yikai Wang,
  • Qimeng Tian,
  • Guofeng Du,
  • Jicheng Zhang,
  • Xia He

摘要

Concrete structures exposed to fire experience significant degradation, while the residual mechanical behavior of hybrid fiber systems across dosage gradients remains insufficiently quantified. This study systematically investigates the effects of steel fiber (SF) and carbon fiber (CF), used individually and in hybrid combinations, on the residual mechanical properties and thermomechanical damage evolution of fiber-reinforced concrete after high-temperature exposure. Ten mixtures were prepared by varying SF and CF dosages (0–1.5 vol%). Specimens were heated from 25 °C to 800 °C and evaluated for residual compressive, splitting tensile, and flexural strengths. Damage characteristics were analyzed using scanning electron microscopy (SEM) together with ultrasonic pulse velocity (UPV) and resonant frequency (RF) measurements to link microstructural deterioration with macroscopic performance. A multi-parameter polynomial model was established to correlate temperature, fiber dosage, and relative wave velocity for post-fire performance prediction. Residual strength showed a slight increase between 25–400 °C, followed by pronounced degradation beyond 400 °C. The hybrid mixture containing 1.0 vol% SF + 1.0 vol% CF exhibited the best overall compressive and flexural retention, whereas 1.5 vol% SF + 1.0 vol% CF achieved the highest splitting tensile strength. Microstructural observations and wave velocity measurements consistently revealed progressive matrix cracking and interfacial debonding with increasing temperature. The proposed three-stage thermomechanical damage model elucidates the synergistic mechanism of hybrid fibers and provides a practical framework for rapid assessment of residual performance after fire exposure.