Modification of the Tournemire Argilite in Contact with Simplified Concrete Fluid

Argillaceous rocks are considered as potential host rocks for radioactive waste repositories. The design of an underground disposal often includes large amounts of concrete which are proposed as waste matrix, backfill material and structural components. The leaching of concrete by groundwater produces alkaline solutions that will react with the host rock inducing modifications of the geological barrier performances. In order to examine the effects of an alkaline plume on the properties of claystone, an experimental program is being developed in our institute involving batch, diffusion and percolation experiments. This paper presents the results obtained with first batch studies performed at 25°C and 70°C over 3 months. The effect of high pH solutions (corresponding to the early period of leaching) on the composition of a claystone (originating from Tournemire - France) was examined. The changes in solutions composition were monitored as a function of temperature and V/m ratio. In spite of the short contact time between solution and solid, some modifications in these two phases were noticed. The interactions between solids and solutions were more pronounced at 70°C than at 25°C, resulting in pH and potassium concentration decrease, while the sodium concentration remained constant. Moreover, the dissolution of mineral phases such as dolomite and kaolinite was proposed.