ACOUSTIC EMISSION AND P WAVE VELOCITY MONITORING DURING THERMAL CRACKING IN A LOCALLY-HEATED GRANITE BLOCK

An electric heater was inserted into a hole bored in the center of a 300mm cubic granite block, and the temperature of the heater was increased to 500°C at the rate of 200°C/h. An visible crack was produced from a lateral surface to the center hole through the block at 107 minutes after the start of heating. The distribution of temperature measured with thermocouples located at various points in the block indicated that this cracking was caused by the thermal tensile stress in the circumferential direction. Acoustic emission activity and P wave velocity were monitored during this experiment. These monitoring results corresponded to the cracking in the specimen, therefore it was assured that these monitoring methods are useful for thermal cracking of granite.