Ouali Amiri

Determination of the macroscopic chloride diffusivity in cementitious by porous materials coupling periodic homogenization of Nernst-Planck equation with experimental protocol

In this paper, we propose a macroscopic migration model for cementitious porous media obtained from periodic homogenization technique. The dimensional analysis of Nernst-Planck equation leads to dimensionless numbers characterizing the problem. According to the order of magnitude of the dimensionless numbers, the homogenization of Nernst-Planck equation leads at the leading order to a macroscopic model where several rates can be coupled or not. For a large applied electrical field accelerating the transfer of ionic species, we obtain a macroscopic model only involving migration. A simple experimental procedure of measurement of the homogenized chlorides diffusivity is then proposed for cement-based materials.

Permeability Prediction of Soils Including Degree of Compaction and Microstructure

AbstractThe present paper deals with the proposition of an original analytical permeability model of compacted soils. The model involves the microstructure of the material through the porosity and the pore-size distribution obtained by mercury intrusion porosimetry (MIP), as well as the degree of compaction. Their effects on the morphological parameters of the porous network (tortuosity and interconnection of pore network) are studied. The model was developed and tested on various types of soil: a loamy sand, a gravelous sand, a clay, and an alterite. Samples were compacted with various degrees of compaction: 85, 95, 100, and 105% of the optimum dry density as determined by a standard compaction method. The experimental results obtained for both loamy and gravelous sands and for clay were well reproduced by the model, except for the alterite. Such results might be explained by the high brittleness of the alterite, leading to a crumbling phenomenon rather than to its densification during the compaction pro...

Influence of carbonation on ionic transport in unsaturated concrete: evolution of porosity and prediction of service life

Abstract In this paper, the effects of carbonation and moisture on chloride and ionic transport into concrete are studied. Based on the concrete composition and porosity as well as the physicochemical equilibrium, a comprehensive macroscopic model is proposed for this problem. The model features the chemical activity of ions, the interactions between chloride ions and concrete; and the ion–ion interactions in the solution. The governing equations of moisture and ionic transport into nonsaturated concrete are thoroughly described and solved numerically by the finite difference method in time and in space. Applications of the numerical model are demonstrated by predicting the evolution of the porosity and the service-life of a concrete specimen exposed to an aggressive environment containing chloride, carbon dioxide and moisture. A comparison of the model with a set of experimental data is finally proposed.

Modelling the mechanical strength development of treated fine sediments: a statistical approach

ABSTRACT Sediments valorization (recycling) has revealed limitations due to different restrains and practical difficulties. When it comes to different recovery methods, the possibility of valuing diverse types of sediments still needs to be defined. Using a statistical approach, the present study aims to quantitatively estimate the mechanical resistance of stabilized sediments. A database that included 22 fine sediments is selected and assembled from the literature. These sediments were treated with distinct types and quantities of additives (fillers and/or binders). The present study includes two parts. On one hand, using multivariate linear regression tool of XLstat software, an analytical model that highlights the effects of various parameters influencing the mechanical resistance of treated sediments after 28 days is obtained. This model showed that organic matter content and plasticity index are the most significant factors of sediments characteristics, while cement is the best mechanical strength booster. On the other hand, the evolution of treated sediments mechanical resistance over time is modelled by an exponential relationship using a least square regression method. Both models showed acceptable accuracies compared to a panel of selected experimental values.

Moisture transport in cementitious materials. Periodic homogenization and numerical analysis

This article presents a new approach based on periodic homogenisation for the computation of moisture diffusion coefficients in porous media. Experimental data allow fixing the parameters in the homogenised model. A series of parametric simulations are performed in order to compute the homogenised moisture diffusion coefficient through a gradual complexity of elementary cells approaching the microstructure of the cementitious materials tested.