Quantification of pore structure evolution and its correlation with the macroscopic properties of sandstones under freeze–thaw action

Although freeze–thaw damage to rocks has been extensively studied in recent decades, the quantitative correlation between the microscopic pores and macroscopic physico-mechanical properties of rocks under freeze–thaw action has not yet been determined. In this study, the pore structure variation in three sandstones during the freeze–thaw process was continuously measured by the mercury intrusion porosimetry (MIP) test. The pore size distribution can be characterized by a multimodal exponential function. With increasing freeze–thaw cycles, the characteristic pore radii of the nanopores (d ≤ 5 × 10⁻⁵ mm), micropores (5 × 10⁻⁵ mm ≤ d ≤ 0.1 mm), and macropores (0.1 mm ≤ d ≤ 1 mm) increase. However, the volumetric fractions of nanopores and micropores decrease continuously during freeze–thaw cycles because a considerable number of nanopores and micropores develop into macropores. The fractal dimension of the pore structure gradually decreases as the number of freeze–thaw cycles increases. This implies that the pore size distribution gradually tends to be more homogeneous and that the complexity of the pore structure decreases. Finally, the relationship between microscopic pore structure parameters and macroscopic properties (porosity, P-wave velocity, and uniaxial compressive strength) was established. Through the analysis of microscopic structure evolution and loss of macroscopic properties, it can be concluded that the growth of macropores may play a dominant role in freeze–thaw damage and strength loss. This study can provide a better understanding of the macro-microscopic freeze–thaw damage mechanism of sandstones.