Abstract:In order to study the deterioration characteristics of the microscopic structure of sandstones in freeze-thaw cycles, tests of 180 freeze-thaw cycles were performed on sandstone specimens. The nuclear magnetic resonance (NMR) technique was applied to the measurement of sandstone specimens and analysis of the magnetic resonance imaging. Then, the fractal theory was employed to compute the fractal dimension values of pore development of rocks after different freeze-thaw cycles. The results show that the mass and porosity of rocks grow with the increase of freeze-thaw cycles. According to the NMR T₂ distribution of sandstones, the pore sizes of rock specimens increase after 180 freeze-thaw cycles, especially that of the medium-sized and small-sized pores. The spatial distribution of sandstone pores after freeze-thaw cycles has fractal features within certain range, and the fractal dimension of sandstones tends to increase gradually.

Key words: nuclear magnetic resonance (NMR); freeze-thaw cycles; deterioration of rocks; microscopic structure; fractal dimension