Ameur El Amine Hamami

Assessment of the variability of moisture transfer properties of High Performance Concrete from a multi-stage drying experiment

This article aims to assess the characterisation of the water vapour desorption process and its variability under site conditions. It presents a probabilistic approach allowing the assessment of the distribution laws for the water vapour desorption isotherms (WVDI) and the moisture diffusion coefficient. These two parameters were evaluated from multistage drying experiment. For each stage, the analysis of the equilibrium state allows the determination of WVDI whereas the analysis of the desiccation kinetic makes possible the evaluation of the moisture diffusion coefficient. In order to have a representative variability, the study was carried out on two different High Performance Concretes (HPC) during a large-scale construction: overall, more than 300 specimens were tested. Results indicate that Gaussian distribution can be used for modelling the statistical variability of desorption isotherm while log-normal distribution is more appropriate for describing the variability of moisture diffusion coefficient. Furthermore, whatever the concrete, the coefficient of variation on the water content at equilibrium remain very similar. Cet article a pour but la caractérisation du processus de désorption de la vapeur d’eau et de sa variabilité dans des conditions in-situ. Il présente une approche probabiliste permettant l’évaluation des lois de distribution des Isothermes de Désorption de la Vapeur d’Eau (IDVE) ainsi que celles des coefficients de diffusion d’humidité. Ces deux paramètres ont été évalués expérimentalement à partir d’essais de séchage par palier réalisés sur des bétons à haute performance (BHP), confectionnés in-situ. Pour chaque palier de séchage, l’exploitation des états d’équilibres hydriques a permis la détermination de l’IDVE. De plus, l’analyse des cinétiques de transfert a permis l’évaluation du coefficient de diffusion d’humidité. La campagne expérimentale a été réalisée sur plus de 300 échantillons. Les résultats obtenus ont révélés que la variabilité des isothermes de désorption peuvent être modélisés par une distribution Gaussienne tandis qu’une distribution de type log-normale s’avère plus appropriée pour décrire la variabilité du coefficient de diffusion d’humidité. En outre, quel que soit le béton testé, les coefficients de variation de la teneur en eau pour les différents états d’équilibre hydrique demeurent proches.

Effect of Variability of Porous Media Properties on Drying Kinetics: Application to Cement-based Materials

Abstract: Structures’ durability and their degradation mechanisms have received much interest from the scientific community and project owners. Cementitious materials are the most common building materials. They have a complex microstructure with a highly heterogeneous and random character of their mechanical and physical properties. Various processes affect their properties: chemical, such as cement hydration, and physical, such as heat and moisture exchange. The latter, which relate to variations in the water content and its distribution in the material, have an important influence on the global behavior of cementitious materials. The process of convective drying is a commonly encountered solicitation in the Civil Engineering field. It can be either natural, such as drying of concrete structural elements, or forced, such as drying in a research laboratory during the sample preparation and characterization.

Investigation of some electrochemical phenomena induced during chloride migration test on cementitious materials

This paper investigates electrochemical phenomena induced during accelerated chloride diffusion tests using a migration cell. By monitoring of electrical current time evolution coupled with electrochemical impedance spectroscopy measurements, it was set that the electrical current measured between the two sides of cement-based samples during migration tests increases continually even after reaching steady state checked by a constant chloride flux at the downstream of the cell. This is found to be due to the decrease in the samples’ electrical impedance (resistance). Furthermore, the cell charge phenomenon which appears during polarisation was quantified through cell discharges in electrical resistors after polarisation.

Influence of the initial water saturation of aggregates on concrete shrinkage

The study presented in this paper deals with the influence of the water saturation of natural aggregates on shrinkage and cracking sensitivity of concrete at early age. Limestone crushed gravels were specially chosen for this study due to their high porosity. The degree of water saturation of gravels varied, from a given concrete mixture, keeping the total water content constant. Significant variations of the plastic shrinkage and early age autogenous deformations were observed. Due to the kinetics of absorption of gravels, the water content remaining in cement paste was different from the effective water content. This was confirmed by the values of mechanical properties and porosimetry. The evolutions of elastic modulus and tensile strength were experimentally assessed and used to compare the cracking sensitivity of the three studied concretes by evaluating the self generated stresses.