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Evaluation des interactions entre biodéchets en digestion anaérobie et matériaux cimentaires à base de différents liants en vue d'une meilleure durabilité des structures de méthanisation

Abstract : Anaerobic digestion allows the transformation of organic matter into biogas. In the current context of ecological transition towards renewable energies and the reduction of greenhouse gas emissions, the development of the sector is encouraged in Europe and the sector is growing fast. On an industrial scale, this bioprocess is implemented in concrete structures that are in direct contact with the biowastes being digested and undergo biodeterioration phenomena. Indeed, the liquid medium contains a wide variety of metabolites produced during digestion (volatile fatty acids, NH4+, dissolved CO2) whose concentrations can reach several grams per litre, as well as the microorganisms themselves, colonizing the surface of the concrete in the form of biofilm.This thesis, carried out within the framework of the ANR project BIBENdOM, aimed at (i) analysing the mechanisms of biogeochemical interactions between cementitious materials made from different types of binders, biowaste in digestion, and biofilm in the anaerobic digestion environment and (ii) providing a thorough experimental and numerical understanding of the mechanisms of alteration of cementitious materials in order to tend towards the prediction of the durability of concrete in these complex and variable environments.On one hand, the experimental work was carried out on complete environments in laboratory and highlighted local scale interaction mechanisms between a panel of materials (CEM I, CEM III/B, CAC, alkali-activated metakaolin and alkali-activated slag) and two substrates being digested (cattle manure and maize breakage) allowing to vary the composition and the aggressiveness of the environment toward the materials (during 5 digestion cycles, or about 6 months per experience). The anaerobic digestion process was monitored and analysed in terms of composition of the liquid medium and biogas production, microbial populations and microstructural, chemical and mineralogical modifications of the materials. On the other hand, the individual actions and combined effects of the chemical compounds metabolised during the digestion were finely studied in order to characterise the kinetics and thermodynamic equilibria governing degradation, with a view to proposing a model tending towards the prediction of deterioration in media of varied compositions. For this purpose, aggressive solutions were analysed (cation and anion concentrations) over time and the degradation of cementitious materials was characterised (mass loss, structural, mineralogical and chemical modifications).The work has shown that the presence of materials in the liquid phase only impacts the digestion process in the short term and on a local scale only. The use of substrates of agricultural origin generated environments rich in dissolved CO2 (1000 - 2000 mg.L-1) and favoured the carbonation of the materials, which seems to play a major role in the deterioration mechanisms of Portland based cements, ahead of those of other metabolites (organic acids, ammonium, phosphate salts...). Among the materials used, alkali-activated metakaolin stands out for its very good behaviour and low degradation. It is also the material that has had the greatest impact on digestion, in terms of the composition of the medium (NH4+), digestion kinetics and pH as well as the microbial populations developed. Finally, the experiments carried out on chemical metabolites alone have enabled the development of a thermodynamic model applied to the interactions between cement pastes and aggressive agents, allowing to predict the chemical evolution of the solid phase during degradation and as a function of the metabolite studied.
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Marie Giroudon. Evaluation des interactions entre biodéchets en digestion anaérobie et matériaux cimentaires à base de différents liants en vue d'une meilleure durabilité des structures de méthanisation. Génie civil. INSA de Toulouse, 2021. Français. ⟨NNT : 2021ISAT0001⟩. ⟨tel-03347568⟩

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