Influence of limestone filler and of the size of the aggregates on DEF

This experimental study aims to determine the effect of limestone filler on concrete expansion due to delayed ettringite formation (DEF). Different mortars made with different sizes and percentages of limestone filler and Portland cement CEM I 52.5N are conserved in water. The expansion of the specimens is measured. Results show that DEF is not inhibited by limestone filler. The kinetics and the amplitude of the swelling depend on the size of the limestone filler. The volume fraction of aggregates changes only the kinetics: the relation between swelling and water uptake depends only on the size of the aggregates.Comment: 16 pages, 9 figures, 4 table

Multi-scale failure of heterogeneous materials: A double kinematics enhancement for Embedded Finite Element Method

International audienceThis paper presents a Finite Element model for the modeling of the failure of heterogeneous material at the meso-scale. This model is cast into the framework of the Enhanced Finite Element Method (E-FEM). Two kinds of enhancement are performed: (1) in the displace-ment field (strong discontinuity approach) in order to take into account micro-cracks, (2) in the strain field (weak discontinuity) in order to take into account heterogeneities without any mesh adaptation. Mechanical applications (uniaxial tension and compression loading, non-proportional loading) are performed in the context of cementitious materials such as concrete. We show the capability of the model to represent some of the main features of such materials observed at macro-scale

Implementation of Multidimensional Databases with Document-Oriented NoSQL

International audienceNoSQL (Not Only SQL) systems are becoming popular due to known advantages such as horizontal scalability and elasticity. In this paper, we study the implementation of data warehouses with document-oriented NoSQL systems. We propose mapping rules that transform the multidimensional data model to logical document-oriented models. We consider three different logical models and we use them to instantiate data warehouses. We focus on data loading, model-to-model conversion and OLAP cuboid computation

Experimental investigation of the variability of concrete durability properties

One of the main objectives of the APPLET project was to quantify the variability of concrete properties to allow for a probabilistic performance-based approach regarding the service lifetime prediction of concrete structures. The characterization of concrete variability was the subject of an experimental program which included a significant number of tests allowing the characterization of durability indicators or performance tests. Two construction sites were selected from which concrete specimens were periodically taken and tested by the different project partners. The obtained results (mechanical behavior, chloride migration, accelerated carbonation, gas permeability, desorption isotherms, porosity) are discussed and a statistical analysis was performed to characterize these results through appropriate probability density functions

Suction Anchors for Deepwater Moorings at Nkossa and Girassol in 200 and 1,400M of Water

A new type of anchor, composed of steel caissons installed into the soil by suction under-pressure, presently finds a strong interest in the offshore oil industry, in particular for deepwater sites because of its vertical loading capability in taut-leg moorings, and the reduced installation equipment required. Two case histories are presented in the paper, describing the installation of the moorings for the Nkossa barge in Congo in 1995 and for the Girassol FPSO in Angola in 2001. In both cases, the paper gives the general soil conditions and design assumptions, together with the results of the installation operations, with a comparison between the predictions and the monitored site installation results. For the Nkossa barge anchors in about 200m of water, the results obtained in soft normally consolidated clays were in perfect agreement with the predictions, thus demonstrating the reliability of the design installation procedure. For the Girassol FPSO anchors in 1,400m of water, the measured anchor penetration resistance in soft highly plastic clays was lower than predicted, raising concern about the actual anchor holding capacity in a taut-leg mooring system with a significant vertical loading component. Following a third party review of the design assumptions, the holding capacity of the FPSO anchors was validated, and an improved installation prediction method was proposed

Complexation interfaciale de polymères : propriétés et stabilité d'émulsions millimétriques

This work focuses on the study of an oil-water interface where the complexation of two polymers takes place. The aqueous phase is a solution of cross-linked polyacrylic acid microgels (carbomer) and the oil phase contains a polyelectrolyte possessing amine groups (amodimethicone). The stabilization of an emulsion of millimeter-sized droplets is achieved with this polymeric interface. Designed by millifluidic, the droplets are made one by one and a calibrated emulsion of oil in water is obtained. The process was developed by the company Capsum, with the objective to encapsulate perfumes or active ingredients for cosmetics. First, we characterize the adsorption and complexation of the polyelectrolytes at the oil-water interface with both static and dynamic tensiometry methods. Then, we study the mechanical properties of the polymeric membrane along with its capacity to stabilize emulsions, at the level of a collection of droplets undergoing compression which is applied either by gravity or by centrifugation, and also at the level of single droplets flowing through a glass capillary. Thanks to those various experimental methods, and depending on the physico-chemical conditions, the different emulsion stabilization regimes are highlighted. A major observation is that the amount of amodimethicone controls the anchoring of the carbomer at the interface, setting the interface state from fluid to solid, and therefore the corresponding emulsion stability. Moreover, when the membrane is solid, that is to say when the microgels are electrostatically cross-linked with the amodimethicone, a remarkable propagation of membrane rupture within an emulsion undergoing compression is revealed.Ce travail de thèse porte sur l’étude d’une interface eau-huile où a lieu une complexation de deux polymères. La phase aqueuse est une solution de microgels de polyacide acrylique réticulé (carbomer) et la phase organique comprend un polyélectrolyte possédant des fonctions amines (amodiméthicone). Cette interface polymérique permet la stabilisation d’émulsions directes dont la taille des gouttes atteint le millimètre. Les gouttes sont ici fabriquées une à une via une technique millifluidique, ce qui permet d’obtenir une émulsion calibrée. Ce procédé a été mis au point par la société Capsum afin d’encapsuler des parfums ou bien des principes actifs pour la cosmétique. L’adsorption et la complexation des polyélectrolytes à l’interface eau-huile sont tout d’abord caractérisées à l’aide de méthodes de tensiométrie, en statique et en dynamique. Les propriétés mécaniques de la membrane polymérique ainsi que son potentiel stabilisateur d’émulsions sont ensuite étudiés à l’échelle d’une collection de gouttes, en compression par gravité ou bien par centrifugation, ainsi que pour des gouttes uniques en écoulement dans un tube. Ces diverses approches expérimentales permettent de mettre en lumière différents régimes de stabilisation des émulsions en fonction des conditions physico-chimiques. Une observation majeure est que la quantité d’amodiméthicone contrôle l’ancrage du carbomer à l’interface ainsi que l’état fluide ou bien solide de l’interface et donc la stabilité de l’émulsion correspondante. De plus, lorsque la membrane est solide, c’est-à-dire lorsqu’il y a réticulation des microgels via l’amodiméthicone, un phénomène remarquable de propagation de la rupture de la membrane au sein d’une émulsion sous compression est révélé

Meso-macro numerical approach to macroscopic permeability of fractured concrete – COMPLAS XI

In this paper, a sequential multi-scale framework to solve mass (air or water) transfer problems is described. Numerical results are checked against mechanical and permeation experimental datas from a reinforced concrete specimen under tensile load designed by C. Desmettre and J.P. Charron [2

Methodology and numerical strategy for forecasting the leakage rate evolution of nuclear reactor buildings inner containments

The containment building represents the third and last protection barrier of nuclear reactors buildings (NRB). Yet ageing mechanisms of prestressed concrete could strongly affect the tightness capacity of the inner containment of a double-wall reactor building over time. That is a major issue considering the long-term operation and the potential life extension of NRBs while ensuring safety and regulatory requirements. Considering the size of those structures and the complexity of all interacting phenomena (such as drying, creep, shrinkage and cracking), it is very difficult from a computational perspective to build an industrial and operational tool modeling efficiently all the strong couplings occurring at different scales. In that context, a simple yet physically representative chained weakly-coupled strategy based on a macro-element discretization is implemented and applied to the VeRCoRs mock-up (scale 1:3). The proposed methodology adapts to feedback and data collected with time. It enables operators to take into account variabilities and uncertainties of main parameters in order to quantify their impact on the total leakage rate, to manually introduce defects coming from visual inspections and to preempt and optimize leak mitigation actions in order to avoid outage extensions and associated losses of income

Modélisation à l’échelle mésoscopique du comportement hydro-mécanique des matériaux à matrice cimentaire

L’objectif des travaux présentés est de simuler des problèmes hydro-mécaniques couplés dans les matériaux cimentaires, à une échelle mésoscopique, permettant de considérer l’hétérogénéité de ces matériaux. La mésostructure représentative de ces matériaux est discrétisée à l’aide d’un maillage EF 3D, de type treillis, non adapté à la géométrie du problème. L’hétérogénéité de ces matériaux est représentée par l’introduction de discontinuités hydriques et mécaniques faibles. Un couplage hydro-mécanique faible est retenu pour la résolution du problème