CNRS Civil and geo-Environmental Engineering Laboratory

Artois, France

CNRS Civil and geo-Environmental Engineering Laboratory

Artois, France
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Belabbes A.,University of Science and Technology of Oran | Zaoui A.,CNRS Civil and geo-Environmental Engineering Laboratory | Ferhat M.,University of Science and Technology of Oran
Applied Physics Letters | Year: 2010

Density functional theory was applied to study the electronic and magnetic coupling of Cr-doped InN, in which magnetic configurations have been investigated. We found that the calculated ferromagnetic stabilizing energy is strongly linked to the Cr-Cr distance. The local magnetic moment of Cr is 2.3μB, and it weakly depends on the Cr-Cr distance. The coupling between the Cr d and the N p states is found to be the origin of ferromagnetism in the InCrN system. The generalized gradient approximation-1/2 correction procedure increases the polarization of InCrN, making this system a robust half-metallic ferromagnetic alloy. © 2010 American Institute of Physics.


Zaoui A.,CNRS Civil and geo-Environmental Engineering Laboratory
Cement and Concrete Research | Year: 2012

The present work relates to the study of structural and elastic properties of Tobermorite 11 Å as a function of external pressure and composition in terms of calcium to silicon ratio. Basing on the lattice dynamics method, the main aim of this work is precisely to shed light, for the first time, on the high pressure structural phase transition in Tobermorite 11 Å and the possible correlation with some elastic quantities. In order to check the transferability of the potentials used we have, additionally, performed a single calculation based on the density functional theory (DFT) for a pressure of 15 GPa in the case of Ca/Si = 1. The variation of the unit cell parameters with pressure indicates that Tobermorite 11 Å undergoes a structural instability around 15 GPa along b-axis and around 20 GPa along a-axis which is confirmed from our calculations of X-Rays diffraction patterns at various pressure values. We have also observed the anisotropic character of the Tobermorite structure for both cases (Ca/Si = 1 and Ca/Si = 0.83). Our results show that around 20 GPa an important change appears in the elastic behaviour of Tobermorite. As pressure increases the calculated elastic quantities for Ca/Si = 1 became closer to those evaluated for Ca/Si = 0.83, which may stimulate further experimental and theoretical research on the matter. © 2011 Elsevier Ltd. All rights reserved.


Zheng Y.,CNRS Civil and geo-Environmental Engineering Laboratory | Zaoui A.,CNRS Civil and geo-Environmental Engineering Laboratory
Solid State Ionics | Year: 2011

Molecular dynamics simulations have been performed to study the diffusive transport properties of water and counterions in 1-, 2- and 3-layer hydrated Wyoming-type montmorillonite (MMT). The considered counterions included in the clay are monovalent cations, such as Li +, Na +, K +, Rb +, Cs +, and divalent cations, such as Ca 2+, Ni 2+, Zn 2+ and Pb 2+. The diffusion simulation results of Li-, Na-, K-, Cs-MMT, based on NVE ensemble and SPC/E water model, compared well to available experimental quantities and previous simulations, which permit us to study the diffusion behaviour of heavy metal counterion including in the different hydrated montmorillonite. Our simulation results show that the diffusion coefficients of both water molecule and counterions increase versus the quantity of water content. At the same hydrated state, the diffusion of cations strongly depends on their size, weight and capacity of attracting water. Monovalent cations diffuse always much faster than divalent ones. Although the increasing of hydrate degree can raise the diffusion coefficient of divalent heavy cations, the activity of these heavy counterions is still very weak. The diffusion of cations in the interlayer space of clay is much weaker than that in bulk water. That means the presence of charged clay has great influence on the diffusion of cations, which change totally the diffusion behaviour of cations. © 2011 Elsevier B.V.


Benazzouz B.K.,CNRS Civil and geo-Environmental Engineering Laboratory | Zaoui A.,CNRS Civil and geo-Environmental Engineering Laboratory
Applied Clay Science | Year: 2012

The aim of the present work is the investigation of the thermodynamics properties of kaolinite by means of molecular dynamics calculations based on the CLAYFF force field. The obtained results give various thermodynamical quantities, not yet estimated for kaolinite, such as the linear thermal expansion coefficient in the three directions, heat capacities C p and C v in the temperature range between 100 and 2088K and enthalpy. We focussed our efforts, in particular, on the calculation of the superheating point, which is estimated at 1572K. This value was deduced from the variation of the lattice parameters, volume and enthalpy with temperature. In addition, the solid-liquid transformation was also seen from the flattening of the atomic density profiles and radial distribution functions, where the order is lost in the bulk structure. © 2012 Elsevier B.V.


Zaoui A.,CNRS Civil and geo-Environmental Engineering Laboratory | Shahrour I.,CNRS Civil and geo-Environmental Engineering Laboratory
Philosophical Magazine Letters | Year: 2010

We report a computational study of BaCO3 at high pressure using molecular dynamics simulation based on a recent potential model. The first phase transition from the witherite to the post-aragonite phase is observed at 9.67 GPa with a resistance to shear along the [0 0 1] direction and a high compressibility in a direction perpendicular to the layers. This stable phase is also found through the variation of the bulk modulus, the shear moduli, and the compressional and shear wave velocities with pressure. A softening mode is noticed at a pressure around 10 GPa. The computed X-ray diffraction pattern of the post-aragonite phase at 16 GPa shows favorable agreement with the available experimental data. © 2010 Taylor & Francis.


Yang W.,CNRS Civil and geo-Environmental Engineering Laboratory | Zaoui A.,CNRS Civil and geo-Environmental Engineering Laboratory
Journal of Hazardous Materials | Year: 2013

We have performed molecular dynamics simulations to investigate the adsorption of radionuclide elements species onto substituted Montmorillonite (001) surface in the presence of different counterions. The structure and the dynamics of uranyl ion as well as its aquo, chloride ion, and carbonate complexes are analyzed. In addition, we have studied the surface energy between layered Montmorillonite sheets and the work of adhesion between radionuclide and charged Montmorillonite. The clay model used here is a Wyoming-type Montmorillonite with 0.75e negative charge per unit cell resulting from substitutions in Octahedral and Tetrahedral sheets. The system model was constructed based on CLAYFF force field potential model. To evaluate the thermodynamic work of adhesion, each surface and clay layer regions are converted to a thin film model. One and two species of radionuclide elements (UO2(H2O)5,UO2CO3(H2O)5, and UO2Cl2(H2O)5) were deposited near the clay surface in a pseudo-two-dimensional periodic cell. Analysis shows that the uranyl ion structure is preserved with two axial oxygen atoms detected at 1.8Å. Radial distribution functions results indicate that average UOw distances are 2.45-2.61Å, and 2.29-2.40Å for UOc distance. Average UCl distances are 2.78-3.08Å, which is relatively larger than that of Uranium atom-Oxygen atom because of electrostatic factors. © 2013 Elsevier B.V.


Benazzouz B.K.,CNRS Civil and geo-Environmental Engineering Laboratory | Zaoui A.,CNRS Civil and geo-Environmental Engineering Laboratory
Materials Chemistry and Physics | Year: 2012

In this paper, Molecular dynamics simulation based on energy minimization technique has been used to study the structural and mechanical properties of kaolinite under pressure from 0 GPa to 25 GPa. Using the shell model, we have optimized the potential parameters according to Newton-Raphson procedure. Various mechanical properties have been calculated, such as the elastic constants, bulk modulus, shear modulus, Young modulus along a, b and c directions. Moreover the S-and P-wave velocities as well as Poisson ratio were also evaluated. Results reveal that kaolinite is quite compressible compared to the other clays. This reflects the possible uses in several applications including external constraints. In addition, we study the pressure effect on the elasticity of kaolinite. Results show that the elastic constants such as C 33, C 13, C 23 and C 34 have a positive slope under pressure with 15%, 6%, 6% and 1.3%, respectively. The remaining elastic constants are almost stable with a small change. A decrease of the Young modulus is noticed in a and b directions, whereas an increase in c direction appears with a slope equal to 10%. The ratio of the S-and P-wave velocities, which are key in the interpretation of seismic behaviours, gives V p/V s = 1.787, a value in favourable agreement with experimental data. © 2011 Elsevier B.V. All rights reserved.


Zheng Y.,CNRS Civil and geo-Environmental Engineering Laboratory | Zaoui A.,CNRS Civil and geo-Environmental Engineering Laboratory
Physica A: Statistical Mechanics and its Applications | Year: 2013

We investigate here the effect of temperature on the diffusion of water and cations in the Wyoming-type montmorillonite clay. The considered cations are monovalent compensating ions, such as Li+, Na+, K +, Rb+ and Cs+ in one-, two- and three-hydration states. For this purpose, molecular dynamics simulations have been performed to obtain the dynamic behaviour regarding the interlayer ions and water molecules under a temperature range between 260 and 400 K. The diffusion coefficient of water and cations in different hydrated clays increases with temperature. The influence of temperature on the diffusion of water is much greater than that of cations in one-, two- or three-hydrated clay. The degree of hydration plays an important role on the diffusion behaviour of water and counterions. We found that the effect of temperature is negligible in weakly hydrated clay, whereas it became significant in highly hydrated one. Besides, the size and mass of cations' hydrate also affect the diffusion behaviour of water and cations in the interlayer space of hydrated clay. © 2013 Elsevier B.V. All rights reserved.


Yang W.,CNRS Civil and geo-Environmental Engineering Laboratory | Zaoui A.,CNRS Civil and geo-Environmental Engineering Laboratory
Applied Clay Science | Year: 2013

The aim of the present paper is to investigate the adsorption of uranyl species (UO2)2+(H2O)5 onto kaolinite (001) surfaces. To this end we have employed molecular dynamic simulations based on CLAYFF force field potential. Various types of surface model for inner-sphere adsorption complexes and one model for outer-sphere adsorption complexes were optimized. In order to have a neutral structure, the uranyl (UO2)2+(H2O)5 or the kaolinite was deprotonated to form the outer-sphere or inner-sphere adsorption complexes. Both singly protonated and partially deprotonated states of the Al(0) kaolinite surface were considered for adsorption in the model of inner-sphere complexes. The first uranyl coordination shell exhibits pentagonal bi-pyramidal symmetry with the pentagonal formed by 5 water molecules. We show that the average U-OW distances are between 2.49 and 2.57Å for water molecules. The bond of uranyl with deprotonated O- center is always short because of the charge attraction. The obtained results agree well with density functional calculations and EXAFS measurements, and show how and why the adsorption of uranyl appears on the surface of kaolinite. © 2013 Elsevier B.V.


Bouharoun S.,CNRS Civil and geo-Environmental Engineering Laboratory
Journal of Civil Engineering and Management | Year: 2016

Concrete surface quality is generally linked to the development conditions of concrete close to the formwork. This work aims to study the influence of the nature of release agent and the quantity of fine elements on the chemical interactions at the concrete/oil/formwork interface. Five concretes were prepared at 28, 30, 32, 34, and 36% of paste to study the influence of paste volume on the friction between formwork and fresh concrete. The friction tests were performed using an apparatus which can reproduce the same conditions of construction sites. In addition, a physicochemical investigation was achieved to identify the effect of fine elements on the ability to form the interstitial mediums at the interface. The formation of soap in the vicinity of the formwork surfaces was also studied as a function of the content and the nature of oils. The results showed that the friction between fresh concrete and formwork depends on the pore solution content present at the interface. © 2016 Vilnius Gediminas Technical University (VGTU) Press.

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