Dense suspensions such as fresh concrete consist of very polydisperse particles suspended in a viscous fluid. These materials are yield stress fluids: they flow only when the applied stress is large enough. When scale separation is possible between the large and small particles, these materials can be seen as suspensions of grains (noncolloidal particles) in a yield stress fluid (the colloidal paste). A good knowledge of the rheological properties of these materials, and of the link between these properties and their composition, is needed to ensure a good control of their casting properties (for industrial materials) and for the prediction of geophysical flows (e.g. debris flows). To date, the existing studies have focused only on very specific materials in link with their field of application. Therefore, a global understanding of their behavior still has to be achieved. To this end, one has to characterize their microstructure, their macroscopic properties, and the link between these two properties. Indeed, the particle distribution and their orientation in the suspension depend on the suspension flow history, which depends on the macroscopic properties of the suspension; these last properties depend in turn on the suspension microstructure. Moreover, at high particle volume fraction, contact networks may appear, which may lead to jamming. The final aim of our project is to build a constitutive law of yield stress suspensions that includes a characterization of its microstructure and of this microstructure evolution. As no standard rheometric technique exists to characterize the macroscopic and structural anisotropies, and as it is challenging to take the nonlinear properties of the interstitial fluid into account, we propose to develop original experimental, numerical and theoretical tools, the coupling of which will allow us to achieve our goal. We will study the macroscopic behavior of yield stress suspensions thanks to a new rheological test that will allow us to apply three-dimensional loadings. We will characterize the anisotropy of the macroscopic behavior for a given microstructure (obtained through a controlled strain history). On the other hand, we will develop a rheometrical device inserted in an X-ray microtomograph, which will allow us to characterize directly the suspension microstructure as a function of the strain history. A numerical tool devoted to simulate the flows of yield stress suspensions will also be developed; it will be used to predict the microstructure and its evolution as a function of the applied loading. Its strength will be its optimization and validation by comparison with the experiments succinctly described above. Finally, the link between the microstructure and the macroscopic behavior will be built through a change of scale method; it will be first validated experimentally, then numerically for complex flows. Finally, these coupled studies should allow us to build the link between the microstructure and the macroscopic behavior, and between the strain history and the microstructure evolution, providing in the end a complete model of macroscopic behavior of yield stress suspensions validated experimentally. This field of investigation being basically new, we will limit our study to the fundamental case of monodisperse spheres suspended into model yield stress fluids; we will nevertheless propose a validation of our approach on cementitious materials. The original tools that we will develop during this project and their ability to allow for the modeling of the behavior of model materials will naturally lead to study more complex materials.

The objective of this research project is to capture carbon dioxide inside crushed demolished concretes. The higher specific surfaces of these crushed concretes could allow for a far higher CO2 capturing speed via carbonation reactions than when the material is still part of a wall or a slab. The CO2 capture will moreover allow for an increase in the quality of the recycled aggregates formed by these crushed demolished concretes. Their porosity will indeed decrease whereas their chemical stability will increase. A part of the growing quantity of demolished concrete could therefore be used to prepare new concretes instead of being used in low grade applications such as road bases.

Le projet proposé a pour objectif de développer les stratégies de gestion du patrimoine et les outils technologiques et méthodologiques contribuant significativement à minimiser la gêne occasionnée par les chantiers conduits sur des infrasructures, sous fortes contraintes de circulation, d'exigence des riverains et d'impact environnemental. Cela concerne :_x000D_ - d'une part le développement d'outils amont permettant une évaluation pertinente des différentes stratégies d'entretien et de rénovation d'ouvrages existants sous circulation;_x000D_ - d'autre part la mise au point de stratégies de conception, de conduite de chantiers et d'exploitation prenant en compte l'ensemble du cycle de vie et les impacts socio-économiques, en particulier les coûts d'usage et les externalités.

With more than 70 % of the national population living in urban areas, the anthropisation of the urban water cycle is obvious and requires a holistic approach. Reaching the WFD (European Water Framework Directive) objective prescribing a good ecological status of water bodies will not be possible without an adequate operation of sewer systems. However, their functionning is rather unknown even if they represent a huge asset. According to the data provided by IFEN (French Environment Institute), 24.8 millions of flats and houses in France in 2004 were connected to sewer systems whose total length was above 280000 km. These figures reveal the economical signification of the operation and the management of sewer systems. From an environmental point of view, it is known since many years that pollutant loads discharged by urban water systems during storm weather significantly contribute to the degradation of the quality of water bodies. It is thus necessary to estimate these pollutant loads at both event and annual scales in order to better evaluate the functionning and to improve the operation of urban sewer systems, and to contribute to a better chemical and ecological quality of water bodies. The concepts of permanent diagnosis and self-monitoring of sewer systems have been introduced more than 15 years ago in order to improve the operation of sewer infrastructures, the planning of works and the regulatory and financial issues (e.g. to allocate investment costs within inter-municipal structures). Consequently, in situ measurements shall be carried out in order to evaluate, and then to improve, the real functionning of sewer systems. Measurement networks are a key instrument for monitoring and operation, with a increased interest in case of continuous on line measurements. However, an efficient operation of sewer systems also depends on the ability of both sewer systems and measurement networks to be resources for their operating organisations : how do they contribute to create economic and usage value ? The main objective of the MENTOR project consists to propose a methodology for the design and the audit of discharge and particulate pollutant loads measurement sites in sewer systems. MENTOR will also provide operational tools for data processing and use. The steps of the methodology are the following ones: 1. defining the characteristic parameters of the flow, 2. modelling the hydrodynamics of an existing or planned measurement site, 3. simulating various sensors configurations for this site, 4. qualifying or not the site, 5. defining appropriate methods for interpretation of measured data, 6. establishing organisational recommendations ensuring the implementation of best metrological practices.