Material property and constitutive model of C120 hybrid fiber ultra-high performance concrete at elevated temperatures

This paper uses a purpose-built rigid element-assisted loading system to conduct uniaxial compression tests on C120 hybrid fiber ultra-high performance concrete (HF-UHPC) at elevated temperatures. The test results show that C120 HF-UHPC exhibits brittle failure characteristics at elevated temperatures within the range of 100 °C to 400 °C, while the plastic damage characteristics are obvious at room temperature and within the range of 400 °C to 800 °C. The compressive strength of C120 HF-UHPC increases with the temperature from 20 °C to 200 °C and decreases with the temperature within the range of 200 °C to 800 °C. Based on the experimental data, the uniaxial compression strength and elastic modulus reduction factors, as well as the peak strain of C120 HF-UHPC variation factors at elevated temperatures, are proposed as functions of the temperature. Besides, the elevated-temperature constitutive model of C120 HF-UHPC is proposed. The comparison of the proposed model, experimental data, and existing models indicates that the proposed model is more accurate and reasonable. The findings of this research can lay an essential foundation for the structural analysis of HF-UHPC structures under fire conditions.