Experimental investigation on mechanical behaviors of granites after high-temperature exposure

To investigate the influence of temperature on the physical, mechanical and acoustic emission characteristics of granites, uniaxial compression test, variable-angle shear test, acoustic emission signal monitoring and the measurement of physical parameters including mass, size and P-wave velocity were carried out on granite samples treated at temperatures T ranging from 25 to 900 degrees C. The results show that the density and P-wave velocity decrease gradually with increasing T. As the temperature increases, the peak compressive stress decreases while the peak strain increases, due to the fact that a high temperature induces the escaping of waters within granites, the expanding of mineral grains and the generations of fractures. With the increment of T, both the peak shear stress and the cohesion decrease, whereas the frictional angle increases. During the compressing and shearing tests, the maximum acoustic emission counts show a decreasing trend when T increases from 25 to 900 degrees C. When T exceeds 573 degrees C, the crystal lattice structure of quartz changes from alpha-phase to beta-phase, decreasing the mechanical behavior of granites to a great extent. In addition, the results also indicate that T=500-600 degrees C is the critical temperature ramge to characterize the influence of temperature on the physical, mechanical and acoustic emission characteristics of granites.