Modelling the long-term durability of concrete barriers for radioactive waste disposals

In the past decades, cement-based materials have been increasingly used for the construction of radioactive-waste barriers. The design of durable structures for this specific application requires a precise knowledge of the evolution of the engineering properties of the materials over a 1000-year period. Given the intricate nature of the physical mechanisms involved, a reliable prediction of the long term behavior of the concrete barriers can only be made through modelling and numerical developments. After a brief literature survey in which the main aspects of the problem are outlined, the features of a new modelling approach are presented. The main originality of this approach resides in the fact that the model considers the various chemical and mechanical solicitations and their eventual couplings. The physical and thermodynamical bases behind the development of the model are detailed. A section of the paper is specifically devoted to the experimental techniques (accelerated leaching test, assessment of the permeability and mechanical behavior of concretes under tensile loading, characterization of the concrete microstructure and microcracking by image-analysis) designed to validate the model. Results of selected numerical simulations are presented in the last section of the paper. The main difficulties associated with the implantation of such a model in a finite-element code are discussed. (author)