06 Décembre – Thesis defense - Agnès Zambon

14 h Amphi - building B18N (Université de Bordeaux / Talence)

Mix design method and physics characterization of lightweight air-foam concrete using clay - Valorization for dredged sediments.

A re-use of dredged sediments as raw material in the process of making of concrete directly on the site of the dredging is an interesting valorization as regards economy and environment. The present study aims at valuing the thin particles of sediments because they create a problem in the valorization of dredged sediments. Indeed the layer structure of the clay makes it prone to react to humidity conditions and confers it an important capacity to retain polluting agents. To optimize the valued volumes, a total substitution of aggregates in the concrete by the thin particles of sediments is envisaged. The results from the literature tend to favor an application in embankment such as the filling between two sheetpile walls, a geotech embankment, a quarry embankment. An incorporation of an air-foam made of animal protein during the making of the concrete is used to reduce the density of the material (density between 1.1 and 1.3). This material is classified in the category of lightweight foam concrete called by the English abbreviation LWFC (LightWeight Foamed Concrete). In this study the material is named BAMS acronym for “Béton Allégé par l’incorporation d’une Mousse et à base de Sediments”. The study was realized with a model soil composed of 80% of bentonite clay and 20% of calibrated sand  (diameter 0.125mm). The mix design method is based on the liquidity limit of the soil taking into account its swelling.
The characterization of the BAMS is split into three parts.
The first part corresponds to the characterization of the fresh state of the BAMS. It highlights an optimization of the reduction of the density from a quantity of added water with regard to the liquidity limit of  the soil. The incorporation of air foam modifies the characteristics of the fresh state of the material. It improves the workability and delays the setting of cement.
The second part corresponds to the mechanical characterization of the BAMS. The added water which optimizes the reduction of the density impacts the mechanical resistance which has to be over 0.5MPa. There is thus an inevitable compromise between mechanical resistance and density. For a cement treatment with C=12%, to get a mechanical resistance up to 0.5MPa, density cannot be lightened below 1.3. The possible combinations and the mix design to get them are known. Non-destructive tests are done to simply check the mechanical performances on construction site. The study of the linear shrinkage highlights an important variation of the dimension of the BAMS. This can be limited by a wet cure.
The third part corresponds to the durability by the study of the transfer properties of the BAMS. The results highlight a limited accessibility of the porous network. The release of polluting agents in sediments is estimated by a lixiviation test realized on BAMS made with a model soil artificially polluted (non immersible case). From the results we can conclude on the efficiency of the inerting of polluting agents by the cement treatment and therefore the use of the material is allowed without having an impact on environment.

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