Modelling of Short-Term Interactions Between Concrete Support and the Excavated Damage Zone Around Galleries Drilled in Callovo–Oxfordian Claystone

peer reviewedProduction of energy from nuclear power plants generates high-level radioactive nuclear waste, harmful during dozens of thousand years. Deep geological disposal of nuclear waste represents the most reliable solutions for its safe isolation. Confinement of radioactive wastes relies on the multi-barrier concept in which isolation is provided by a series of engineered (canister, backfill) and natural (host rock) barriers. Few underground research laboratories have been built all over the world to test and validate storage solutions. The underground drilling process of disposal drifts may generate cracks, fractures/strain localisation in shear bands within the rock surrounding the gallery especially in argillaceous rocks. These degradations affect the hydro-mechanical properties of the material, such as permeability, e.g. creating a preferential flow path for radionuclide migration. Hydraulic conductivity increase within this zone must remain limited to preserve the natural barrier. In addition galleries are currently reinforced by different types of concrete supports such as shotcrete and/or prefab elements. Their purpose is twofold: avoiding partial collapse of the tunnel during drilling operations and limiting convergence of the surrounding rock. Properties of both concrete and rock mass are time dependent, due to shotcrete hydration and hydromechanical couplings within the host rock. By the use of a hydro-mechanical coupled Finite Element Code with a Second Gradient regularization, this paper aims at investigating and predicting support and rock interactions (convergence, stress field). The effect of shotcrete hydration evolution, spraying time and use of compressible wedges is studied in order to determine their relative influence

Application of thermo-hydro-chemo-mechanical model for early age behaviour of concrete to experimental massive reinforced structures with strain-restraining system

WOS:000338768400008International audienceThis paper presents the application of a thermo-hydro-chemo-mechanical (THCM) model to the design of actual massive structures with a system to restrain the strain at early age (thermal strains and autogenous shrinkage). The experimental campaign was performed in the French national project CEOS.fr. The modelling of early-age behaviour of reinforced concrete is first based on a hydration model, which is able to reproduce the variations of temperature, water content and mechanical properties according to hydration. Then a non-linear mechanical model is used (combining creep and damage models, both adapted to hardening concrete). The comparison between numerical results (obtained with a calculation time of around 12 h on an ordinary computer) shows that the models are able to reproduce the early-age behaviour of restrained reinforcement concrete structures (in terms of strains, global forces and crack patterns). Using steel-concrete interface elements (adapted to early age), the models are also able to reproduce the influence of reinforcement on cracking

Effets d’un déficit hydrique sur certains paramètres morphologiques, physiologiques et de rendement chez le cotonnier (Gossypium hirsutulm L. CV STAM129A) cultivé au Togo

Le cotonnier est connu pour sa sensibilité au déficit hydrique. Le présent travail a été initié afin de mesurer les effets de ce facteur chez la variété STAM129A de cotonnier vulgarisée au Togo. L'étude porte sur certains paramètres tels que la hauteur des plantes, la longueur des entrenoeuds, le taux de rétention des capsules, le rendement en coton graine, la teneur en protéines solubles foliaires et en chlorophylles totales ainsi que la perméabilité membranaire des cellules foliaires. Pour cela, un déficit hydrique strict a été induit entre les 45 et 75èmes jours après levée. Les résultats ont montré que le déficit hydrique a entrainé une diminution de la croissance en hauteur des plantes à partir du 65ème jour après levée et du taux de rétention des capsules sur certaines branches fructifères. Le rendement en coton graine a chuté de 56 %. Le déficit hydrique n'a pas affecté la teneur en protéines solubles totales mais il a partiellement diminué le taux de chlorophylles et l'intégrité membranaire cellulaire. Ces données montrent que le cotonnier STAM129A est sensible au déficit hydrique. Elles devront être prises en compte dans les futurs programmes de gestion du cotonnier en particulier dans les zones du Togo à faible pluviométrie.Mots clés : Déficit hydrique, cotonnier, organes fructifères, rendement

In vitro efficacy of two biopesticides formulated on the development of tomato pathogenic fungi and comparison with Mancozeb, a synthetic pesticide

The antifungal activity of Cymbopogon schoenanthus and Azadirachta indica products based on emulsifiable concentrate (EC) formulation on Alternaria solani and Fusarium oxysporum, collar rot fungi of tomato was studied in vitro. Five concentrations (0.2%; 0.4%; 0.6%; 0.8% and 1%) were tested using agar dilution and diffusion methods. The botanical activity was more effective with the agar dilution than diffusion method, and when the concentration increased. The antifungal activity decreased with the incubation time and a high activity was recorded on the 3rd day of incubation with mycelial growth inhibition varying from 63.60 to 77.76% and 80.08 to 100% for Alternaria solani, then from 47.72 to 74.83 and 78.8 to 100% for Fusarium oxysporum, with agar dilution and diffusion methods, respectively.   French title: Efficacité in vitro de deux biopesticides formulés sur le développement des champignons pathogènes de la tomate et comparaison avec Mancozeb, un pesticide synthétique L'activité antifongique de deux types de formulation en concentré émulsionnable (CE) à base d’huile essentielle de Cymbopogon schoenanthus et d’huile d’Azadirachta indica a été évaluée en laboratoire sur deux champignons de la pourriture du collet de la tomate, Alternaria solani et Fusarium oxysporum. Cinq différentes concentrations (0,2% ; 0,4%; 0,6% ; 0,8% et 1%) ont été testées selon les méthodes de dilution et de diffusion sur agar. L'activité fongique était plus efficace avec la méthode de dilution que celle de diffusion sur agar et lorsque la concentration en huile essentielle de Cymbopogon schoenanthus augmente. L'activité antifongique a diminué en fonction du temps d'incubation avec une forte activité enregistrée le 3e jour d'incubation avec une inhibition de la croissance mycélienne variant de 63,60 à 77,76% et de 80,08 à 100% pour A. solani, puis de 47,72 à 74,83 et 78,8 à 100% pour F. oxysporum, respectivement selon les méthodes de dilution et de diffusion sur l'agar.&nbsp

Hydration of slag-blended cements

International audienceIn this paper, the hydration of slag in blended cements is investigated through the measurement of hydration reaction indicators such as portlandite content, non-evaporable and free water, and hydration heat. Three substitution rates of cement by slag were used (30%, 50% and 70%). The tests were performed at two constant temperatures (20 °C and 40 °C) in order to assess the activation energy of the different components. A multiphasic hydratation model is proposed to take account of the difference of kinetics of each main phase (clinker and slag) and the hydration kinetic law proposed considers interactions between the two phases. It includes the activation of the dissolution of slag by alkalis released by the clinker phases in the pore solution, the portlandite consumption by slag and the effect of temperature and moisture content on the reaction kinetics. The model is able to simulate the evolution of hydration products and adjust the hydration product stoechimetry to the rates of slag and the current temperature automatically and instantaneously. Its reliability is shown through its ability to fit the whole experimental plan results with a single parameter set. Among these parameters are the hydration heat of slag and its water consumption. The model and its parameters should be useful to simulate other types of slag-blended cement

Restrained shrinkage of massive reinforced concrete structures: results of the project CEOS.fr

International audienceWithin the CEOS.fr national research project, several experiments on massive concrete structures were conducted to improve the knowledge on the cracking phenomenon. In this paper, experiments where deformations at early age are restrained are presented. Testing bodies are I-shaped and two largely dimensioned steel struts are placed laterally between the two transverse heads to prevent almost any shrinkage. Three testing bodies were realized: RG8, the reference one; RG9, with a reduced reinforcement and RG10, with an increased cover. A full set of measurement was used for auscultation of these beams during early age. Optical long base fibres gave information on the relative displacement of the central part of the beam. Local measurements of strains in concrete were given thanks to Vibrating Wire Extensometers. Gauges on rebars produced data of the strain on the first reinforcement layer, and the force in struts was monitored. With this, the force and stresses in concrete and rebars could be deduced. This huge amount of data allows verifying the phenomenology of the concrete. Various hypotheses were analysed to explain the strain measured and the corresponding forces in each component during specific period of early age. A first analysis of the cracking process shows that the cracks could appear for stresses below the tensile strength