Demand is growing for explosive-free and high efficiency rock breakage systems for mining, petroleum and civil engineering applications. Microwave irradiation is becoming a promising technique to deal with rock breakage due to its high efficiency, controllability and environmental friendliness. The cylindrical basalt samples with diameter of 50 mm and height of 100 mm and semi-disc specimens with diameter of 50 mm and thickness of 25 mm were irradiated using microwave apparatus (2.45 GHz, 2 kW). The mechanical properties of microwaved basalt have been tested and the micro fractures were quantitatively analyzed. The structural evolution and mechanical properties of basalt between 100 °C and 400 °C are assessed through the morphology, mineral characteristics and mechanical performance. It is found that the main damage modes of microwaved basalt are intergranular and transgranular fractures. Intergranular fractures generated rapidly at 100 °C, while transgranular fractures generated above 200 °C. Statistically, the length density of fractures grows fastest at 100 °C, while the width of fractures grows fastest at 200 °C. The intergranular and transgranular fractures develop rapidly and intersect each other over 400 °C, which results in rock failure. The length density of the fractures is the main factor inducing the decrease of compressive strength and fracture toughness of basalt which decrease fastest at 100 °C. The elastic modulus decreases fastest at 200 °C, which is closely related to the width of fractures. The Poisson's ratio of basalt is significantly improved by microwaves, and is not only affected by fractures size, but also closely relates to fracture type and distribution.
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