Flexural fracture behavior of ultra-high performance concrete after high-temperature exposure

Exposure to high-temperature environments can seriously affect the mechanical properties of UHPC. However, the fracture mechanism of UHPC after high-temperature exposure remains unclear. This study aims to understand the fracture performance of ultra-high performance concrete (UHPC) upon high-temperature damage. UHPC was designed with different volume ratios of steel fibers (SF) and tested under temperatures 200, 400, 600, and 800 ℃, respectively. Three-point bending tests were conducted with pre-cracked beams to investigate the bending and fracture properties of UHPC. The results show that the compressive strength and flexural strength of UHPC after high-temperature present a trend of first increasing and then decreasing with the increase in temperature, and high temperature reshapes the original development trajectory of the third stage P − δ and P − C M O D curves. High temperature reduces the bending toughness, double K fracture toughness, and fracture energy of UHPC, causing the original strengthening stage of UHPC to suddenly transform into a failure stage, resulting in brittle failure characteristics of UHPC—moreover, a prediction model for the fracture performance of UHPC after high temperature is proposed and validated. • High-temperature exposure reshapes the development trajectory of P − δ and P − C M O D curves. • Stress redistribution due to fiber drawing after high-temperature exposure severely reduces the its adhesion with matrix. • UHPC exhibits brittle fracture behavior at high temperatuare, SF volume ratio contributes to residual fracture performance. • A predictive model was established for strength and fracture performance of UHPC after high-temperature exposure.