Investigation on the Microscopic Deterioration Characteristics of Anhydrite Rock Exposed to Freeze–Thaw Cycles

Abstract

Freeze–thaw cycles induced deterioration on rocks begins with the damage in microstructures such as pores and pore throats. This paper was devoted to providing a fundamental understanding of the microscopic deterioration characteristics of anhydrite rock exposed to freeze–thaw attacks by using a series of laboratory tests. Meanwhile, the relation between the microstructure evolution and the mechanical resistance deterioration was revealed. Results indicated that with the increase of freeze–thaw cycles, the proportion of micropores (r < 0.1 μm) and the pore throat radius within 0–0.1 μm (PT-I) decrease exponentially, while the proportion of mesopores (0.1 μm < r < 1 μm), macropores (r > 1 μm), the pore throat radius within 0.1–4 μm (PT-II), and porosity increase exponentially. Meanwhile, the pore fractal dimension and pore throat fractal dimension decrease exponentially with the freeze–thaw cycles. As the freeze–thaw cycles increase, the surface roughness and the area of micropores increase. It is characterized that the expansion and dissolution of anhydrite minerals in the water plays a crucial role in the morphology evolution. With the increase of freeze–thaw cycles, the mass variation increases, the average uniaxial compressive strength (UCS) and elastic modulus decrease exponentially. Furthermore, the average UCS and elastic modulus decrease exponentially with the damage variable represented by the porosity and increase exponentially with the pore structure fractal dimension. Finally, it is revealed that the proportion of the PT-II plays the leading role in the mechanical resistance evolution of anhydrite rock under freeze–thaw cycles. The experimental results presented are promoting the comprehending of the microscopic deterioration of anhydrite rock projects in cold districts.