Study on Mechanical Properties and Fracture Behavior of Granite after Thermal Treatment under Brazilian Splitting Test

In this paper, the effects of thermal treatment on the mechanical properties, fracture characteristics, and roughness of the fracture surface of granite under the Brazilian splitting test are studied using an electro-hydraulic servo testing machine with an acoustic emission (AE) and digital image correlation (DIC) system. The test results show that: 1) Thermal treatment degrades the physical and mechanical properties. Density, P-wave velocity, and peak load of granite decrease with the increase in thermal treatment temperature (T). 2) With the increasing T, the fracture pattern changes from "I" type tensile fractures to "Y" type tensile-shear mixed failure. The DIC results show that the fracture process changes from transient to progressive. 3) AE counts show that granite gradually changes from brittleness to ductility with the increase of T. Furthermore, the variations in the RA and AF values of the AE events indicate that the increasing T leads to an increase in shear cracks in granite. After the test, 4) the roughness of the fracture surface of the specimen was analyzed using a spatial digitizer. The results show that thermal treatment significantly improved the fracture surface's asperity height and roughness. 5) Scanning electron microscopy (SEM) results revealed that thermal treatment leads to the generation of micro-cracks in granite and the desquamation of mineral grains, which influences the macro properties of granite.