The evolution of Young's modulus versus temperature has been evaluated in SiC-based hydraulically bonded refractories used in waste-to-energy (WTE) plants. Two types of low cement castables (LCC) with 60 and 85 wt% of SiC aggregates have been considered. The study was conducted by the way of a high temperature ultrasonic pulse-echo technique which allowed in situ measurement of Young's modulus during heat treatment starting from the as-cured state up to 1400 A degrees C in air or in neutral atmosphere (Ar) and during thermal cycles at intermediate temperatures (1000 and 1200 A degrees C). For comparison in order to facilitate interpretation, thermal expansion has also been followed by dilatometry performed in the same conditions. Results are discussed in correlation with phase transformations occurring in the oxide matrix (dehydration at low temperature, crystallization of phases in the CaO-Al2O3-SiO2 system) above 800 A degrees C and damage occurring when cooling. The influence of oxidation of SiC aggregates on elastic properties is also discussed.