Experimental studies on mechanical properties and brittleness of granite treated with different microwave heating times

Abstract

Microwave-induced strength weakening and brittle reduction of rock are significant for improving hard rock breaking efficiency. Uniaxial compression tests and microscopic analysis were conducted on granite treated with various microwave heating times (0 s, 60 s, 120 s, 180 s, 240 s, 300 s). The results demonstrate that a considerable change occurs in the mechanical properties of granite when irradiated at a power of 5.4 kW for 120 s. Combining the acoustic emission (AE) data, the crack initiation and damage stresses are identified and found to decrease linearly with increasing exposure time. According to microscopic analysis, the weakening behavior of granite under microwave heating is attributed to an increase in crack density. The opening of intergranular cracks after 120 s of heating results in a rise of 0.6% in crack density, and the development of thermal cracks after 300 s increases the crack density to 8.62%. The reduction in stress threshold ratios and the transition from tensile to shear failure mode of granite after microwave treatment indicate a decrease in rock brittleness. Quantitative brittleness indexes, especially the index based on the crack initiation stress, confirm that rock brittleness degrades as the duration of microwave processing increases.

Keywords

microwave heating / acoustic emission / stress threshold / brittleness / microcracking

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