Experimental investigation on structural evolution of granite at high temperature induced by microwave irradiation

The microwave high-temperature irradiation was introduced to deal with the low efficiency of traditional microwave treatments for breaking granite. Structural evolution of granite between 300 degrees C and 800 degrees C was assessed through the morphology, mineral characteristics and mechanical performance. A spherical melt cavity with radial cracks formed near the biotite-rich area at 600 degrees C and the rock completely disintegrated at 800 degrees C. Intergranular crack was the main mode of micro-cracks. Besides, the micro crack propagation at 600 degrees C was affected by the distribution and shapes of mineral grains and original cracks. Furthermore, the intergranular crack in the biotite grain boundary induced many secondary smaller cracks. Feldspar and biotite melted at 800 degrees C. Thus, the melt probably initiated from the cracked-intensive feldspar near biotite-rich area. The uniaxial compressive strength of granite decreased from 88.17 MPa at 25 degrees C to 18.61 MPa at 800 degrees C. Between 300 and 600 degrees C, the decrease in the uniaxial compressive strength was associated with moisture releasing, quartz transition and thermal induced cracks, and 600-800 degrees C, the decrease was mainly contributed by the partial melt of rock, and magma intruding and solidifying.