Benefits of Fiber Hybridization on the Residual Performance of Ultra-High-Strength High Ductility Concrete at Elevated Temperatures

This study investigates the effects of fiber hybrid types, synthetic fiber types, and synthetic fiber replacement rate on the compressive and tensile properties of ultra-high-strength high-ductility concrete (UHSDC) at elevated temperatures. For the this, two types of synthetic fibers, i.e., polyethylene (PE) and polypropylene (PP), and single straight steel fiber (SF), were considered. The test results showed that the PP fiber was most effective in improving the high-temperature spalling resistance and compressive and tensile performance of UHSDC under its low dosage. The steel fiber also exhibited effectiveness in enhancing the high-temperature spalling resistance, whereas PE fiber was ineffective in improving the spalling resistance. The hybridization type with PP fiber (PP + SF, PP + PE + SF) significantly improved residual compressive and tensile properties specifically; the specimens exhibited positive synergy after exposure to 150 °C and approximately over 98 units of synergy value after exposure to 450 °C. Thus, the ternary fiber hybrid method (PP + PE + SF) can significantly improve the tensile strain capacity and explosive spalling resistance, which provides the possibility for developing refractory UHSDC.