Mechanisms of Mechanical Property Degradation and Dynamic Response Characteristics of Hybrid Fiber Reinforced Concrete under High-Temperature Conditions

In the context of building fire scenarios, this paper thoroughly investigates the degradation patterns of mechanical properties, dynamic response characteristics, and microstructural evolution of hybrid fiber reinforced concrete (HFRC) under high-temperature conditions. A series of orthogonal design experiments were conducted to quantitatively explore the regulatory effects of rice husk ash content, polypropylene fiber, and steel fiber volume fractions on the mechanical properties of HFRC. Using the Split Hopkinson Pressure Bar (SHPB) technique, the dynamic mechanical behavior of HFRC and ordinary concrete (OC) under various temperature gradients was examined, revealing the interactive influence mechanisms of temperature and strain rate on the dynamic mechanical properties of HFRC. Scanning Electron Microscopy (SEM) was utilized to analyze the microstructure of OC and HFRC samples subjected to high-temperature treatment, elucidating the micro-damage mechanisms behind the mechanical property degradation of HFRC in high-temperature environments. The results indicate that the steel fiber content predominantly determines the compressive and tensile strengths of HFRC, while polypropylene fiber plays a crucial role in enhancing the tensile performance of HFRC. Optimal mechanical performance was achieved with 12% rice husk ash content, 0.1% polypropylene fiber volume fraction, and 0.5% steel fiber volume fraction, resulting in a 10.41% and 50.22% increase in compressive and tensile strengths, respectively. Under high-temperature conditions, HFRC exhibited significantly superior mechanical properties compared to OC, particularly in terms of dynamic response characteristics. As the temperature increased, the dynamic compressive strength, dynamic increase factor, and peak toughness of HFRC initially decreased and then increased, consistently maintaining levels higher than those of OC. The study highlights the critical importance of the interaction between temperature and strain rate on the high-temperature dynamic response characteristics of HFRC, and the significant deteriorative impact of elevated temperatures on its microstructure. This research provides a solid scientific basis for enhancing the disaster resistance of concrete structures in fire environments and offers theoretical support for the effective application of hybrid fiber reinforced concrete in practical engineering.