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Aptitude des granulats issus des bétons de déconstruction à la réutilisation, vis-à-vis du CrVI : Impact des propriétés de la matrice cimentaire et identification des mécanismes de relargage

Abstract : In France, it has been numerated more than 340 Million Tons of deconstruction wastes in the field of civil and public works.Among of these wastes, which are prone to be recycled if they are inert, are old aggregates concretes, especially which were produced in the 1960’s. The manufacturing process of cement on an industrial scale was similar to what is done today. Where, it cannot be excluded that these concretes may contain hexavalent chromium. However, the directive 2003/CE/53 concerning the production of cement limits the content of hexavalent chromium to 2 mg per kg of dry matter. Therefore, it is essential to study, before any upgrading project, the atmospheric interactions with the cement matrix and the degradation by rainwater during their landfill or during their life cycle.The thesis work takes part of a feasibility study on the recycling of waste deconstruction containing Cr (VI) and having undergone different types of natural degradations, including atmospheric carbonation. An environmental impact study has been performed on the basis of leaching tests on monolithic and granular materials. In addition, pH impact study on release conditions was also performed. The interpretation of the experimental results is based on the use of kinetic models, in particular the model of Côte & Constable (1985), as well as the solutions of interpretations graphs of the known different standards.The experimental campaign is focused on mortars confectioned from aggregates recycled at 30% and 100% substitution rates as well as recycled aggregates in the gross state. The obtained results are shown that the materials studied (mortars or aggregates alone) are inert with respect to the release of hexavalent chromium. t has been shown, independently from the origin of the recycled aggregates, their chemical composition, their mineralogy and their substitution rate in mortars, that the release of chromium hexavalent remains negligible. Similarly, an in-depth study was conducted on the chromium structure within the cementitious matrix under these two stable forms, trivalent and hexavalent. The results showed that chromium tends to stabilize in ettringite, with structure called Cr-ettringite in the case of Cr (VI) and in bentorite structure in the case of Cr (III).Finally, it has been shown that the cement matrix carbonation has an aptitude to trap and immobilize Cr (VI).
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Oumeima Ben Maaouia. Aptitude des granulats issus des bétons de déconstruction à la réutilisation, vis-à-vis du CrVI : Impact des propriétés de la matrice cimentaire et identification des mécanismes de relargage. Génie civil. Université Paris-Est, 2018. Français. ⟨NNT : 2018PESC1164⟩. ⟨tel-02469324⟩

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