Microwave heating and fracturing of granite: Insights from infrared thermal imaging

Abstract

Microwave heating has been considered as one of the promising rock breaking technologies. However, the non-uniform temperature distribution of microwave treated rocks has not been quantitatively studied and the microwave rock fracturing mechanisms have not been systematically revealed. In this paper, microwave heating tests were implemented using a 6 kW industrial microwave system. The ratio of maximum temperature to average temperature () was studied to characterize the non-uniformity of temperature. The temperature gradient and maximum temperature difference were calculated to quantitatively characterize the thermal stress. Experimental results indicate that the granite fracture temperature threshold is about 200 °C and cracking typically occurs at a minimum temperature gradient of 6 °C/mm. As either power level or irradiation time increases, the thermal gradient and temperature difference increase. For a fixed microwave energy, microwave heating at higher power levels for a shorter duration has a higher and a greater temperature difference and temperature gradient, which explains that the combination of high power and short heating time yields better rock weakening effects.