Abstract:

Clay minerals play important roles in hydration process, while the role was lack of quantitative evaluation at present. Therefore, SEM and X-ray powder diffractometry technology were used to analyze the microstructure, components and contents of clay minerals, and the change of microstructures in dry condition and different wetting times. At the same time, expansion experiments in different conditions were performed to study the variation of mass and the structure during the hydration process. These experiments show that: (1) The inner factors affected the hydration process are the contents of clay minerals such as montmorillonite, kaolinite, chlorite and illite in shales and slates. (2) Water-weakening effect is more distinctive when clay minerals array in order than in disorder. (3) Hydration progress of shales and slates happens in a gradual course. That is to say, clay minerals on the surface absorbed water and expanded firstly, which made the shale and slate fallen；then fluids filtered into the rock inside along the layer surfaces or cracks with time prolonged, and the inner minerals expanded, which made the fall occurred when without confining pressures. (4) During hydration progress, addition of inorganic chemical components in slurry and pressure increase will constrain the water-weakening effect; while the temperature will accelerate the water-weakening rate.

Key words: shale, clay mineral, microstructure, hydration process