Information of confining ability of rock is important for the geological disposal of radioactive wastes. To maintain or improve the confining ability of rocks, it is important to seal pores and cracks. Usually, pores and cracks in rock are sealed over geological time scales. If sealing of pores and cracks in rock can be accelerated and completed by precipitation of minerals, the method would be effective for use during radioactive waste disposal. In this study, we investigated the precipitation of minerals onto the rock surface, to consider whether sealing of pores and cracks in rock can be accelerated. As rock samples, we used Berea sandstone and Toki granite in this study. It was shown that precipitation occurred clearly on the surface of rock specimens kept in calcium hydroxide solution for 1 month if the concentration was high. Specifically, if the concentration of calcium hydroxide solution was higher than 589 mg/l, the precipitation occurred obviously. After keeping rock specimens in calcium hydroxide solution, the weight of the rock samples increased and the concentration of calcium ion decreased by the precipitation. It is considered that the calcium ion in water was used for the precipitation on rock surfaces. Since the precipitation has been recognized for rock specimens, it is concluded that the sealing of pores and cracks in rocks by the mineral precipitation is possible.
