Influence of Thermal and Mechanical Loading on Development of Microcracks in Granite

Abstract

Fire safety is one of the most important concerns in underground engineering projects. Exposure to high temperature can weaken rocks and potentially cause catastrophic failure of the rock mass, either during the fire, or after the fire. In this study, Brazilian tensile tests were conducted on unheated and heat-treated Bukit Timah Granite. The microcrack length distribution and orientation were then recorded and analyzed through the fluorescent dye impregnation technique. The amount of microcracks generated was found to be proportional to the heating temperature. However, other factors such as the mineralogy and the texture of the rock were also found to influence the length and orientation of the microcracks. The modal microcrack lengths of the specimens were found to be similar despite different thermal and mechanical treatments of the specimens, while the orientation of the microcracks was found to be influenced by the type of minerals. Besides the average grain size, another factor which played a key role in determining the microcrack characteristics is the size and shape of the individual mineral grains.