Development of a Method for Accelerated Ageing of Cementitious Materials Used in Repositories for Nuclear Waste

Sammanfattning: The Swedish nuclear fuel and waste management company (SKB), is required to validate the service life prediction of the concrete structures in nuclear waste repositories. Considering the repository being in contact with water , the decalcification process of cementitious materials although being very slow can during the very long operational lifetime of the repository (up to 100000 years), cause the degradation of chemical and mechanical properties of the concrete structures. In order to predict the long-term service life of the structures without extrapolating short-term experimental results, methods that accelerate the leaching process of calcium from cementitious materials are required. In this work the development process of an electro-chemical migration method for acceleration of the calcium leaching from cementitious specimens is presented. The method enables ageing of cementitious specimens with sufficiently large sizes suitable for testing mechanical and transport properties. In this method, the cementitious specimen is placed in an electrochemical cell as a porous path way through which ions can migrate at a rate far higher than diffusion process. The results show that, by a careful adjustment of the experimental parameters such as the magnitude of electrical field and choice of anolyte and catholyte solutions, an effective leaching of calcium with an acceleration factor of >600 can be obtained. According to instrumental analysis the chemical and mineralogical properties of the treated specimens are comparable with the characteristics of the aged specimens in natural decalcification process