Experimental study on the influence of water on fracture toughness in microwave-irradiated granite

Microwave-assisted rock breaking presents promising prospects in mining and geotechnical engineering for hard rock fragmentation. Water is a crucial factor influencing microwave rock breaking. However, the mechanism of rock water content on microwave-induced rock fracture remains unclear. This study examines the semi-circular bend (SCB) of granite with varying water saturations, heated by microwave, while monitoring acoustic emission (AE) signals in real time. This approach investigates the changes and mechanisms in mode I fracture toughness post-heating. The findings reveal that under 1 kW microwave exposure for 6 min, water expansion and escape lead to the growth of mineral crystal defects, causing thermal damage to the sample. The fracture energy of saturated samples decreases most significantly, by approximately 25%. The extent of fracture damage correlates positively with water saturation, exhibiting a linear correlation above 0.85. The Weakening Over Microwave Energy (WOME) increases significantly with the rise in water saturation. As heating time increases, the correlation between damage and water weakens, reducing mode I fracture toughness and fracture energy, and increasing the fractal dimension of crack propagation paths. The acoustic emission (AE) energy release characteristics of samples with different water saturations during microwave heating can be classified into a quiet period, an active period, and an attenuation period. The energy release density of acoustic emission (AE) in the quiet period escalate with water saturation.