Fracture energy of high-performance concrete at high temperatures up to 450°C: the effects of heating temperatures and testing conditions (hot and cold)

Abstract

The fracture energy of high-performance concrete (HPC) with a compressive strength of 67·1 MPa was studied by conducting three-point bending tests on eighty notched beams of 500×100×100 mm at high temperatures up to 450°C (hot) and in cooled-down states (cold). The temperatures in the furnace and inside the concrete and the weight loss of concrete were continuously monitored. If the exposure time was long enough, 16 h in this study, both thermal and hygric equilibriums could be reached. The fracture energy sustained a decrease–increase tendency with the increasing heating temperature for the hot concrete, and an increase–decrease tendency for the cold concrete. The modulus of rupture generally decreased with the heating temperature for the hot concrete but sustained an increase–decrease tendency for the cold concrete. There was a sudden drop at 105°C for the hot concrete owing to high vapour pressure inside the concrete. The residual compressive and tensile strengths both decreased with the increasing heating temperature, with sudden drops between 105°C and 150°C owing to residual stresses caused by high vapour pressures inside the concrete during heating. The tensile strength decreased more rapidly than the compressive strength for the same heating scenario. The residual Young's modulus of concrete monotonically decreased with the increasing heating temperature and this could be expressed using a linear relationship. The fracture energy and other material properties of concrete could be closely related to the ultimate weight loss.