Characterisation of the behaviour of high performance mortar subjected to high temperatures

An experimental investigation was conducted to evaluate the performance of mortar mixed with silica fume (SF) when exposed to high temperatures. A three-point bending test apparatus was developed to test concrete-like materials at high temperatures. Notched specimens were first heated at a rate of 3.3 °C/min to various target temperatures from room temperature to 900 °C and then maintained under constant temperature during 2 h. They were then subjected to a three-point bending test while the temperature was held constant. The maximum peak load occurred at 300 °C and decreased sharply at higher temperatures. The experimental results demonstrated a noticeable influence of the temperature on the fracture resistance of the high-performance mortar. The toughness parameters, such as intensity factor or fracture energy, evolved nonlinearly with the target temperature, and reached their maximum value at 300 °C; at higher temperature, their values decreased considerably. SEM micrographs of the heated specimens after the mechanical tests and cooling and TGA/DTA analysis of the dried material matrix facilitated the understanding of the material’s macroscopic behaviour.