This paper presents a systematic experimental investigation to explore the effect of incorporating discarded hybrid steel fibers (DSF) on the rheological, mechanical, and hardened properties of high strength self-compacting concrete (HSCC). This study also covers the effect of elevated temperatures (300 °C, 500 °C, and 700 °C) in the furnace with a heating time of 2 h on residual mechanical and hardened properties of produced concrete.

The results revealed that adding DSF to the HSCC slightly reduced its filling ability and passing ability, while increasing its resistance to segregation. Although residual strength was decreased by exposure to elevated temperatures over 300 °C, residual mechanical properties of fiber-reinforced high strength self-compacting concrete (FRHSCC) was significantly higher than HSCC. There was a significant increase in the impact resistance, fracture energy, and toughness index of FRHSCC compared to HSCC, where the increase was about 130%, 500%, and 1300%, respectively. After exposure to 700 °C, it was found that concrete becomes more brittle, loses its strength, density, and changes color alongside the appearance of fine cracks on its surface at 500 °C. The results also indicated that elevated temperatures had a greater influence on impact resistance, toughness, and fracture energy compared to compressive strength. DSF almost doubled the impact resistance and tensile strength of HSCC, and the highest effect was on the toughness and fracture energy at both ambient and elevated temperatures. The ultra-pulse velocity test has also been shown to be a suitable technique to infer loss of strength and deterioration of fire-exposed concrete structures. Finally, this study confirms that DSF can be successfully used as a steel fiber in producing FRHSCC to be structurally used as well as improving residual hardened properties and resistance to heating effects.

本文提出了一项系统的实验研究，以探讨掺入废弃混合钢纤维（DSF）对高强度自密实混凝土（HSCC）的流变，机械和硬化性能的影响。这项研究还涵盖了加热时间为2小时的加热炉中的高温（300°C，500°C和700°C）对所生产混凝土的残余机械性能和硬化性能的影响。

结果表明，在HSCC中添加DSF会稍微降低其填充能力和通过能力，同时增加其抗偏析性。尽管暴露于300°C以上的高温会降低残余强度，但纤维增强高强度自密实混凝土（FRHSCC）的残余机械性能明显高于HSCC。与HSCC相比，FRHSCC的耐冲击性，断裂能和韧性指数显着提高，分别增加了130％，500％和1300％。暴露于700°C后，发现混凝土在500°C时会变得更脆，失去强度，密度并改变颜色，同时在其表面出现细小裂纹。结果还表明，高温对耐冲击性的影响更大，韧性，断裂能与抗压强度相比。DSF几乎使H​​SCC的抗冲击性和拉伸强度提高了一倍，并且在环境温度和高温下对韧性和断裂能的影响最大。超脉冲速度测试也已被证明是一种推断强度损失和着火混凝土结构劣化的合适技术。最后，这项研究证实了DSF可以成功地用作钢纤维，以生产结构上使用的FRHSCC以及改善残余硬化性能和耐热性。超脉冲速度测试也已被证明是推断强度损失和火灾混凝土结构恶化的合适技术。最后，这项研究证实了DSF可以成功地用作钢纤维，以生产结构上使用的FRHSCC以及改善残余硬化性能和耐热性。超脉冲速度测试也已被证明是一种推断强度损失和着火混凝土结构劣化的合适技术。最后，这项研究证实了DSF可以成功地用作钢纤维，以生产结构上使用的FRHSCC以及改善残余硬化性能和耐热性。