Abstract

The effect of thermal damage on the physical and mechanical properties of gneiss has been experimentally investigated. The cylindrical samples prepared from this rock were gradually heated to a specific temperature level of 100, 200, 300, 400, 500, 700, and 900°C and gradually cooled down to room temperature without causing thermal cracking in order to investigate the effect of thermal treatment on physical properties and mechanical properties. The mechanical tests conducted on the sample were the Brazilian test and the uniaxial compressive test. Microscopic analyses from thin section were done to better understand the reasons for the mechanical behavior observed from the mechanical test results. Our study confirms that the thermal treatment reduces the strength of gneiss and increases its porosity. Moreover, it is found that above 600°C of heating, gneiss rock specimens can loss 80% of its original mechanical performances. This is due to a micro crack network connection and their propagation. However between 300 and 400°C we observe an increase in the strength of gneiss. Microscopic examination shows the abundance of feldspar and pyroxene minerals in the gneiss, which in turn show high mineralogical phase changes at 300-400°C compared to change at temperatures above 400°C.

Keywords: Fneiss rock; Thin section; Porosity; Thermal damage; Tensile strength; Uniaxial compressive strength