Micro-structural, petro-graphical and mechanical studies of schist rocks under the freezing-thawing cycles

Abstract

Freezing-thawing (F-T) process significantly affects the mechanical parameters of rocks in cold regions. Consequently, the effect of this phenomenon on rock properties should be evaluated before and during the construction of any engineering projects. In this regard, uniaxial compressive strength (UCS) of rocks is a good criterion for assessing the rock durability against the weathering factors. In this paper, some boreholes were drilled in the schist rock of Angouran open-pit mine of Iran to prepare the required specimens. Then, 25 specimens were cut and polished to perform the UCS tests. These tests were implemented in 0, 7, 15, 40 and 75 F-T cycles. For this purpose, samples were put in a freezer for about 12 h at −20 °C and then moved them to the water bath for 12 h at 20 °C. For any F-T cycle, 5 specimens were tested under the unconfined compressive conditions. In addition, optical microscopy and X-ray diffraction (XRD) analysis were used to determine the specimen's mineralogical composition and textural properties. According to the obtained results, Chlorite, Biotite, Calcite and Quartz are the main constitutive minerals of the schist rocks. To evaluate the effect of weathering on the micro-structure of the rock, the texture of specimens was also studied using a scanning electron microscope (SEM). The SEM results showed that after 75 F-T cycles, new cracks are created in samples body and their porosity are increased. Furthermore, uniaxial compressive tests results showed that rock UCS and elastic modulus (E) are decreased exponentially by increasing the number of F-T cycles. However, Poisson ratio (ν) of specimens was increased by increasing the weathering grade. Finally, to calculate the UCS, E and ν of the schist specimens, new empirical equations were developed and proposed at different F-T cycles.