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

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