Concrete's degradation mechanisms during a molten corium-concrete interaction

This thesis deals with the characterization of siliceous (S) and limestone-siliceous (SC) concretes when exposed to high temperatures. The understanding of the degradation of their properties, in advance of the melt front, is the hypothesis that motivates this work since it could bring new avenues to interpret the results of these experiments. Samples that have never been in contact with molten metals/oxides were first studied. Thermo-gravimetry, mercury intrusion porosimetry and complex impedancemetry were used to describe their properties after they were subjected to temperatures up to 1000 C. Thermo-gravimetric analyses allowed the identification of temperature domains in which specific degradation mechanisms are activated. Those of porosimetry showed that porous volumes and typical pore sizes increase significantly with the temperature. It is also demonstrated that at 1000 C, the exchange surface of SC concretes is twice as large as that of S concretes. Finally, the high tortuosity obtained by impedancemetry suggests a topology of porous networks of great complexity. In a second part of this thesis, the studied concrete samples were previously in contact with molten metals and/or oxides. They were analysed by X-ray tomography or scanning electron microscopy. No phenomenon of impregnation of the metal/oxide phases could be observed. Signatures of possible phenomena of percolation of these phases by de-carbonation mechanisms have however been demonstrated. (author)