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Etude du comportement des bétons bas-PH sous sollicitations chimiques

Abstract : The French national radioactive waste management agency is studying a deep underground repository as a solution for high and intermediate level long lived radioactive waste. The sealing system of the disposal is composed of a high-expansion bentonite confined between two massive concrete blocks. But, high pH solution, in contact with bentonite, is going to provoke a loss of its confinement properties. So, the use of low-pH cement is needed. At long term these low-pH concrete structures will be expose to leaching induced by a calcium poor water that can jeopardize the storage stability. The purpose of this work concerns the characterization of chemical behavior under chemical degradation and its influence on the physical and mechanical behavior of low-pH cement. From the chemical aspect, leaching leads to a progressive decalcification of C-S-H with degradation profiles, characterizable by the C/S ratio, which are linear in the degradation area. Kinetics degradation of low-pH paste are slower than kinetic degradation of ordinary binders (CEM I, CEM III, CEM V). Also, mineralogical structure of degraded area from an accelerated leaching test with ammonium nitrate solution are similar to those from a pure water leaching. This phenomenon allows to validate the use of this acceleration technique for physical and mechanical characterization of low-pH binders. Mechanical characterization of materials under chemical degradation are always complicated due to degradation fronts which do not allow homogeneous characterization of a degradation state at a macroscopic scale. Our study, with reverse analysis of physical and mechanical experiments at a macroscopic scale, propose evolution law of properties at a local scale according to the chemical state of the area investigated. Low pH binders show, for a same state of degradation, a smaller loss of mechanical properties than the one found on ordinary binders (for paste and concrete).
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  • HAL Id : tel-03468755, version 1

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Thomas Bes. Etude du comportement des bétons bas-PH sous sollicitations chimiques. Matériaux. Université Paul Sabatier - Toulouse III, 2019. Français. ⟨NNT : 2019TOU30337⟩. ⟨tel-03468755⟩

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