Durability of Reactive Powder Composites: influence of silica fume on the leaching properties of very low water/binder pastes

Reactive Powder Composites are new cement-based materials which could be used for the storage of nuclear wastes thanks to their excellent microstructural properties. This paper studies their durability when submitted in the laboratory to a water leaching attack. In order to understand the behaviour of the hydrates (C-S-H), the study was carried out on a pure cement paste and on a cement+silica fume paste. The beneficial effect of silica fume is demonstrated from considerations on the calcium leaching, from XRD analysis, from SEM observations and from the tritium diffusion and pore distribution analysis. It was found that the leaching greatly affects the microstructure, especially that of the anhydrous cement grains remaining in the paste. (C) 1999 Elsevier Science Ltd. Ail rights reserved.