Prediction of strength of rock after thermal treatment through dielectric property

Abstract

This study attempts to establish the feasibility of using the dielectric constant to evaluate the strength of sandstone after being subjected to high temperatures. The dielectric constant of red sandstone was determined after thermal treatment at temperatures ranging from 25 to 1200°C was applied to the rock. At the same time, the porosity, tensile strength, mineral composition and microstructure of the sandstone were determined and analysed. The results shows that the dielectric constant for sandstone decreases rapidly between 500 and 1000°C, increases substantially between 1000 and 1100°C, and then decreases slightly between 1100 and 1200°C. The variation trend of the tensile strength is basically consistent with the dielectric constant. Porosity is the main factor affecting the variations in the sandstone dielectric constant and the tensile strength. The volume expansion of minerals and the melting of the sandstone are the two main reasons for the variation in the porosity of the sandstone. There is a significant correlation between dielectric constant, porosity and tensile strength in the temperature range 25–1000°C. The relationship between dielectric constant and tensile strength increases linearly. Therefore, the dielectric constant can be used as a new non-destructive method to evaluate the strength of sandstone after its exposure to high temperatures.