Influence du séchage sur le développement des hétérogénéités dans les structures à base de matériaux cimentaires : Impact sur les propriétés mécaniques

Ce travail décrit l’ensemble des phénomènes qui gouvernent le développement des hétérogénéités dans les structures à base de matériaux cimentaires lorsqu’elles sont soumises au séchage ainsi que leur influence sur les propriétés mécaniques du matériau mis en oeuvre. Il s’agit notamment des facteurs influents tels que la porosité, la teneur en humidité, le degré d’hydratation. Tous ces facteurs contribuent à la tenue du matériau in situ ainsi que son comportement au regard de la  fissuration. Il a été démontré pour ces matériaux que, les fissures s’amorcent dans la partie du matériau qui présente les propriétés les plus médiocres et qu’elles se propagent par la suite dans le reste du volume. Dans cette étude, nous nous sommes intéressés à la caractérisation et la quantification des gradients de propriétés tels que les gradients hydriques, les gradients d’hydratation et les gradients de porosités. Pour finir nous avons étudié leur impact sur l’évolution des propriétés mécaniques des matériaux mis en oeuvre. L’étude a révélé une parfaite adéquation entre la progression du front de séchage et les différentes hétérogénéités observées en terme de caractéristiques mécaniques.Mots-clés : matériaux cimentaires, béton, mortier, séchage, hétérogénéités, propriétés mécaniques

Non-Metabolic Membrane Tubulation and Permeability Induced by Bioactive Peptides

BACKGROUND: Basic cell-penetrating peptides are potential vectors for therapeutic molecules and display antimicrobial activity. The peptide-membrane contact is the first step of the sequential processes leading to peptide internalization and cell activity. However, the molecular mechanisms involved in peptide-membrane interaction are not well understood and are frequently controversial. Herein, we compared the membrane activities of six basic peptides with different size, charge density and amphipaticity: Two cell-penetrating peptides (penetratin and R9), three amphipathic peptides and the neuromodulator substance P. METHODOLOGY/PRINCIPAL FINDINGS: Experiments of X ray diffraction, video-microscopy of giant vesicles, fluorescence spectroscopy, turbidimetry and calcein leakage from large vesicles are reported. Permeability and toxicity experiments were performed on cultured cells. The peptides showed differences in bilayer thickness perturbations, vesicles aggregation and local bending properties which form lipidic tubular structures. These structures invade the vesicle lumen in the absence of exogenous energy. CONCLUSIONS/SIGNIFICANCE: We showed that the degree of membrane permeabilization with amphipathic peptides is dependent on both peptide size and hydrophobic nature of the residues. We propose a model for peptide-induced membrane perturbations that explains the differences in peptide membrane activities and suggests the existence of a facilitated “physical endocytosis,” which represents a new pathway for peptide cellular internalization

Durability diagnosis of a concrete structure in tidal zone by combining NDT methods: laboratory tests and case study

To successfully implement non-destructive techniques (NDTs) for surveying concrete structures in marine environments, non-destructive measurement results must be correlated with concrete durability indicators such as porosity and water and chloride contents. For this purpose, tests introducing two elec- tromagnetic methods (GPR and the capacitive technique), as well as the impact-echo method, were run on six different concrete mixes containing various porosities, with five water content values and three chloride concentrations. A reinforced concrete beam, extracted from the wharf of the Nantes-Saint-Nazaire Port, exposed to ocean tides was also tested under actual conditions. The NDT laboratory results exhibit linear correlations with concrete indicators, which in turn allows building a three-dimensional empirical model. This 3D cross-correlation model, coupled with onsite NDT results, is then used to perform a dura- bility diagnosis of the actual structure. Moreover, these results serve to illustrate the advantages of the 2D data fusion models developed during this project

Non Destructive Evaluation of Containment Walls in Nuclear Power Plants

Two functions are regularly tested on the containment walls in order to anticipate a possible accident. The first is mechanical to resist at a possible internal over-pressure and the second is to prevent leakage. The reference accident LLOCA (Large Loss of Coolant Accident) is the rupture of a pipe in the primary circuit of a nuclear plant. In this case, the pressure and temperature can reach 5 bar and 180°C in 20 seconds. The national project ‘Non-destructive testing of the containment structures of nuclear plants’ aims at studying the non-destructive techniques capable to evaluate the concrete properties and its damaging or progression of cracks. This 4-year-project is segmented into two parts. The first consists in developing and selecting the most relevant NDEs (Non Destructive Evaluations) in the laboratory to reach these goals. These evaluations are developed in conditions representing the real conditions of the stresses generated during ten-yearly visits of the plants or those related to an accident. The second part consists in applying the selected techniques to two containment structures under pressure. The first (technique) is proposed by the ONERA (National Office for Aerospace Studies and Research of France) and the second is a mock-up of a containment wall on a 1/3 scale made by EDF (Electricity of France) within the VeRCoRs program. Communication bears on the part of the project that concerns the damaging and cracking follow-up. The tests are done in bending on 3 or 4 points in order to study the cracks’ generation, their propagation, as well as their opening and closing. The mostly ultrasonic techniques developed concern linear or non-linear acoustic: acoustic emission [1], LOCADIFF (Locating with diffuse ultrasound) [2], energy diffusion, surface waves velocity and attenuation, DAET (Dynamic Acousto-Elasticity Testing) [3]. The data contribute to providing the mapping of the parameters searched for, either in volume, in surface or globally. Image correlation is an important additional asset to validate the coherence of the data. The spatial normalization of the data allows proposing algorithms on the combination of the experimental data. The tests results are presented and they show the capacity and the limits of the evaluation of the volume, surface or global data. A data fusion procedure is associated with these results.</p