Effects of pre-existing fissures on surface macro-crack characteristics of granite subjected to elevated temperatures

Abstract

In order to study thermal macro-cracks on granite surface, experiments were conducted to heat orthoclase granite samples under 25-800 °C. This paper reports a method for evaluating thermal damage of rock by indexes of thermal macro-cracks characteristics, including the width of macro-cracks, the length of macro-cracks, the density of macro-cracks and fractal analysis of macro-cracks. The major findings are as follows: (1) As treatment temperature increases from 500 °C to 800 °C, the average macro-crack width increases from 0.05 to 0.22 mm. And the average macro-crack length increases from 34.36 to 771.86 mm at 600-800 °C. In addition, the linear density is from 0.20 to 1.05 mm-1 and the surface density increases from 0.07 to 1.54 mm/mm 2 at 600-800 °C. (2) The temperature has an important influence on the thermal fracture fractal of the granite surface. As treatment temperature increases from 600 °C to 800 °C, the fractal dimension of macro-cracks changes from 0.47 to 1.43. (3) 400-500 °C is the threshold temperature of the thermal macro-cracks generated on the granite surface and the high temperature causes the unpenetrated fissures connect with each other.