Thermal and dynamic response of hybrid fiber-reinforced concrete to fire exposure: Experimental and computational approaches

Fire and explosive events pose significant threats to infrastructure, leading to devastating human and economic losses. To address this, Hybrid Fiber-Reinforced Concrete (HFRC) has emerged as a promising material due to its exceptional compressive strength (CS) and durability. However, its performance under extreme heat remains a critical concern. This study delves into the fire resistance of HFRC, exploring how it withstands high temperatures and dynamic loading conditions. Experimental tests were conducted on HFRC samples, incorporating steel fibers, synthetic fibers, superplasticizer, and fly ash, exposed to temperatures of 200°C, 400°C, 600°C, and 800°C for durations of 30, 60, 90, and 120 min. The results reveal intriguing trends: dynamic compressive strength (fcd) and specific energy absorption (SEA) initially increase, peaking at 200°C, before declining at higher temperatures, while strain rate effects (ε) consistently rise. The optimal fcd threshold is identified at 400°C, with synthetic fibers significantly enhancing dynamic properties, particularly at a 1.5 % fiber content. To further advance understanding, this study employs cutting-edge machine learning techniques, developing XGBoost models using 213 experimental data points. These models demonstrate remarkable predictive accuracy, with R-values of 0.998 (training), 0.920 (validation), and 0.899 (testing). Global Sensitivity Analysis underscores temperature and high strain rate as the most influential factors. By combining experimental insights with advanced predictive modelling, this research offers a comprehensive understanding of HFRC's behaviour under extreme conditions, paving the way for designing resilient, fire-resistant infrastructure. This work not only bridges critical knowledge gaps but also provides actionable tools for engineers and researchers striving to enhance structural safety in high-risk environments.