High strength and ultra low permeability concrete (HSULPC) is considered as a material used to confine transuranic (TRU) waste for disposal in geological repositories. Therefore, information of the permeability of HSULPC is essential. In general, water migrates through the network of fractures and pores in a solid. It has been reported that the precipitation of calcium compounds occurred on the surfaces of fractures and pores in cementitious materials kept in water, which brought about the fracture closure. However, none has investigated the influence of such precipitation on the permeability. In this study, we have conducted permeability measurements on a macro-fractured HSULPC. In particular, we kept the macro-fractured HSULPC specimen in an artificial seawater, and investigated the influence of calcium compound precipitation on the hydraulic conductivity. It was shown that the introduction of macroscopic fracture increased the hydraulic conductivity. In addition, when the macro-fractured HSULPC was kept in artificial seawater, the fracture was filled partly by the precipitation of calcium compounds, which decreased the hydraulic conductivity. Especially, the fracture closure was observed mainly for the upstream part of the specimen. When HSULPC is put in the underground condition, the fracture closure in HSULPC can occur due to the existence of groundwater with high electrolyte concentration.
