On the tensile mechanical characteristics of fine-grained granite after heating/cooling treatments with different cooling rates

This study discusses the results from tests performed to investigate the tensile mechanical characteristics of granite after exposure to heating and cooling treatments. The samples, which were previously heated to various elevated temperatures and then cooled at various cooling rates, were tested using the Brazilian disc method. The variations in the P-wave velocities, microscopic cracks, tensile strengths and fracture surface roughnesses of the samples as a result of the various heating/cooling treatments were analysed. The results show that the water-cooled samples exhibited the largest decrease in P-wave velocity and the largest numbers of newly generated cracks (including both inter-granular and intra-granular cracks) on the surface, which indicates that the samples heated and cooled at higher cooling rates were more susceptible to the heating/cooling treatments. The cooling rate had less influence on the tensile strengths of the samples when they were heated to 400 degrees C or less. Nevertheless, when the heating temperature was 600 degrees C or greater, the water-cooled samples exhibited the lowest tensile strengths, followed by the air-cooled samples and the oven-cooled samples. After the heating/cooling treatment, the samples with lower tensile strengths had rougher fracture surfaces, which are potentially attributed to the thermally-induced microcracks generated during the heating and cooling process. Finally, the relationship between the tensile strength and fracture surface roughness can be well fitted using an exponential decay function.