Pore structure change and physico-mechanical properties deterioration of sandstone suffering freeze-thaw actions

Abstract

Although the strength loss of natural stone materials was widely investigated in the previous decades, the change law of pore structure characteristic and their correction with the strength loss under freeze-thaw was not completely understood. In this study, the pore structure change of red sandstone under freeze-thaw was continuously monitored by MIP (mercury intrusion porosimetry). The pore size distribution was characterized by a developed tri-modal exponential function. The characteristic pore radii in this function corresponding to nanopores (d < 0.05 μm), micropores (0.05 μm < d < 100 μm) and macropores (100 μm < d < 1000 μm) increased with increasing freeze-thaw cycles. However, the volumetric fractions of nanopores and micropores reduced, because some of them had developed into macropores under freeze-thaw. Fractal dimension was a good indicator to characterize the complex of pore structure, which had an obvious reduction trend against the freeze-thaw number. It illustrated that the distribution of pore size turned to be uniform, and the complexity of the pore structure decreased after repeated freeze-thaw cycles. Triaxial compression strengths of sandstones after different freeze-thaw cycles were measured. The UCS and TCS decreased due to the growth of macropores, but the confined pressure had an inhibitory effect on the freeze-thaw damage. In addition, the cohesion of sandstones decreased while the internal friction angle increased with increasing the freeze-thaw number. At last, the relationship between the mechanical strength loss and fractal dimension change was built. By analysis of the microscopic pore structure evolution and macroscopic strength loss, it can be concluded that the growth of macropores may play a dominant role in the freeze-thaw damage and strength loss. This study provides a better understanding of the macro-micro freeze-thaw damage mechanism of stone materials.