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Thèse Année : 2022

Use of oyster shell (Crassostrea gigas) as aggregate replacement for producing environmentally-friendly concrete

Utilisation de broyats de coquille d'huître (Crassostrea gigas) en remplacement complet des granulats pour la production de bétons à faible coût environnemental

Résumé

Due to the depletion of resources, by-products claim attention to be reused or reincorporated in other materials. Cementitious materials are on the top of the list of the most consumed materials which traditionally leads to a high demand for raw materials. In the actual context of net zero emissions target and circularity economy, building materials must be reinvented through a more sustainable approach. Based on this, bio-based materials have been attracting attention to be incorporated into building materials, improving materials properties and providing lower environmental burdens. Within this context, the Nouvelle-Aquitaine region (France), the Arcachon bay shellfish farming Comittee and France University Institute funded the BECCoH project, which aims to assess the potential use of crushed oyster shells (OS) in concrete. The oyster farming activity is largely developed in this region and generates a high amount of waste (shells) due to the maintenance and cleaning process in the farming area on top of food consumption. In general, the shells represent over 70% of the oyster weight, leading to over 700 kilograms of waste per ton of production. Therefore, the BECCoH project has been built to evaluate the reuse of crushed oyster shells as aggregate replacement in cementitious materials, raising awareness in the local community about alternative sustainable solutions for local by-products. In this context, this PhD thesis aims to investigate the use of crushed oyster shells to fully replace fine and coarse aggregate in concrete and to characterise the change of material properties and the potential environmental benefits from this substitution. A new approach is developed to optimise the granular skeleton obtained after oyster shell crushing. This approach consists in combining particle classes in different proportions to obtain better particle packing. Because of the flatness of the crushed OS, traditional methods designed for spherical particles cannot be used for this purpose. Consequently, our strategy is to directly minimise the intergranular porosity, which can be estimated through loose bulk and oven-dried densities of particle classes. A statistical software is used to analyse the particle classes combination and to optimise the mixture proportion in order to decrease the intergranular porosity. The crushed OS is optimised into fine (0/4 mm) and coarse (4/10 mm) aggregates. Once this optimisation is determined, a self-compacting concrete formulation is set with a full replacement of conventional aggregate (sand and gravel) by OS. To limit further environmental impacts, low clinker cement (CEM V/A) is chosen for concrete mixes. As conventional aggregates are substituted by OS, the formulation goes beyond the prescriptions of NF EN 206/CN for classical concretes. Therefore, the performance-based approach is applied to evaluate whether the concrete meets the performance and durability requirements or not. In this aim, the mechanical properties considered are the compressive strength, the flexural strength, the tensile splitting strength and the elastic modulus. In sequence, relevant durability indicators are chosen to evaluate the ageing of the OS concrete: carbonation, chloride migration, gas permeability, capillary water absorption and porosity accessible to water. Going further on the sustainable approach, the environmental impacts related to the replacement of conventional aggregates by crushed OS in concrete are investigated. We aim to evaluate the potential environmental impacts and possibilities for improvement in these processes. The energy demand, fuel consumption, water used and solid waste were the main indicators chosen to be assessed.
Ce projet vise à formuler un béton avec des coquilles d'huîtres en substitution des granulats pour diminuer l'impact environnemental. Dans un premier temps, l'optimisation du squelette granulaire a été menée et validée sur des mortiers. Puis, une large campagne expérimentale est conduite sur le matériau béton selon l'approche performantielle pour justifier de son utilisation: essais mécaniques et de durabilité. Pour finir, une analyse de cycle de vie évalue la diminution des impacts environnementaux de la solution proposée.
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Origine : Version validée par le jury (STAR)

Dates et versions

tel-03703837 , version 1 (24-06-2022)
tel-03703837 , version 2 (13-01-2023)

Identifiants

  • HAL Id : tel-03703837 , version 2

Citer

Ana Claudia Pinto Dabes Guimaraes. Use of oyster shell (Crassostrea gigas) as aggregate replacement for producing environmentally-friendly concrete. Chemical and Process Engineering. Université de Pau et des Pays de l'Adour, 2022. English. ⟨NNT : 2022PAUU3009⟩. ⟨tel-03703837v2⟩

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