The meso-mechanism study of gypsum rock weakening in brine solutions

The effects of aqueous solutions on the behavior of rocks are of great concern in many geotechnical applications. Many factors regarding the corrosion process should be considered, including temperature and the solute. In this paper, the evolution of the meso-structure of gypsum from Xishan, Taiyuan, China, with a purity of 95.86 %, is studied under the coupling effect of brine solution (with concentrations of 0, 3.08 and 5.989 mol/L) and temperature (23, 40 and 70 °C) using scanning electron microscopy. Results indicate that an aqueous solution can significantly soften gypsum rocks. Unaltered gypsum rock is initially compact in structure and fissures or fractures are less obvious. After being corroded by an aqueous solution, the original compact gypsum is largely damaged in structure and the gypsum's crystal clusters change from jointed connections to separated connections. Moreover, some of the crystal clusters are broken into pieces and layers, or split into small columns. In this study, ∂ is defined as the corrosion damage ratio representing the corroding effect of the aqueous solution on the gypsum rock. The lager the value of ∂, the more serious the gypsum structure damage. Study results show that with a rising temperature, the corrosion damage ratio ∂ also gradually increases. The corrosion damage ratio ∂ increases with the brine changing from a fresh concentration to a half-saturated concentration. However, when the brine concentration is changed from half-saturated to saturated, the damage ratio ∂ decreases, partly due to halite crystallization of the saturated brine on the gypsum's surface. This study enhances insight into the micro-structure development mechanism of soluble rock under different aqueous solution conditions.