The Leaching Of The Reactive Powder Concretes: Results on Transfer Properties
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MATITE ""',M. MORANVILLE' Laboratoire de M6canique et Technologie, ENS Cachan, 94235 Cachan CEDEX, France Bouygues, Direction Scientifique, Challenger, 78061 St-Quentin-Yvelines CEDEX, France Laboratoire d'6tudes des mat~riaux, CEA Saclay, 91191 Gif-sur-Yvette, France
ABSTRACT The properties of concrete can be altered in aggressive media such as pure water. A leaching test was performed for Reactive Powder Concretes (RPC) in order to evaluate their durability when used as storage of nuclear wastes. Emphasis is placed on the changes of their microstructure, on the tritium diffusion coefficient and on the porosity after leaching. Using mainly non destructive techniques such as SEM, BET and diffusion cell, we found that the leaching affects the RPC microstructure, particularly the anhydrous cement grains. The tritium diffusion coefficient, even lower than that of granite, is however ten times higher after a three month-leaching. INTRODUCTION Reactive Powder Concretes (RPC) are a new kind of cementitious composite (cement, silica fume, ground quartz, steel fibers, superplasticizer) with a very low water to cement ratio. The basic principles underlying their development are [ I] "* improvement of homogeneity by replacing traditional aggregates with quartz sand less than 600 microns in size ; "* increase of dry-compacted density by optimizing the gap-grading of the components; "* improvement of the microstructure by applying a heat treatment to the RPC (after demolding) which enhances the pozzolanic action of the silica fume ; "* achievement of ductile behavior by adding steel fibers and "* increase of durability (carbonation, freeze-thaw scaling, chloride diffusion, ...). In this paper, we will report the study of the RPC durability for radioactive waste storage through the leaching process. EXPERIMENT Materials The RPC composition for nuclear application is given in Table 1. The cement is an OPC type CEM I, the white silica fume has a BET specific area of 12000 m2/kg and the superplasticizer is a polyacrylate. The mixture was heat treated at 90'C for two days after demolding (two days).
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Mat. Res. Soc. Symp. Proc. Vol. 503 0 1998 Materials Research Society
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Its microstructure appears as a dense material (fig. 1).
cement grain
Fig. I Microstructure of an RPC. Backscattered Electron Image (BEI). This RPC has a compressive strength of 216 ±25 MPa and a porosity of 4 ±1% (as measured by Mercury Intrusion Porosimetry (MIP)). As almost 60% of the RPC is made of v inert materials *,such as the sand, quartz and fibers, we planned to investigate first the hydrates behavior in an aggressive medium. Matrixes (cement+silica fume+ground quartz) were studied. Methods The leaching test simulates the worst attack of a container confining radioactive wastes during its service life (300-500
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