Cement-based salt concrete (mass concrete with crushed salt filler) and MgO (sorel) concrete are the building materials used for seals in repositories in salt formations. These structures are important elements to prevent the access of aqueous solutions to emplaced waste containments. The post-closure evolution of such cements is studied in detail at GRS in order to understand the long-term changes in their hydraulic conductivity. This includes CHM-coupled interactions between the concrete material and the host rock and formation water. This paper presents results from laboratory investigations of the sealing capacity of seal systems at laboratory scale in contact with various saline solutions.