Size effect of concrete samples on the kinetics of external sulfate attack

The external sulfate attack (ESA) of concrete is a disease related to expansive sulfate hydrate formation in a hardened cement matrix. The aim of this research is to study how the choice of a concrete sample size can impact on the kinetics of ESA, by exposing different types of specimen to constant immersion in a solution dosed with 5% Na₂SO₄⋅10H₂O. Monitoring involves mass, dynamic modulus and expansion measurements. It is concluded that 4 × 8 cm concrete cylinders (cored from 11 × 22 cm concrete cylinders) are more quickly damaged by ESA than usual sample types (11 × 22 cm concrete cylinders and 4 × 4 × 16 cm mortar prisms). For all sample types, damage is always limited to the periphery of the sample in the short run. The thickness of the damaged zone is in the region of the size of the largest aggregates. For 4 × 8 cm concrete cylinders, this periphery corresponds to the entire sample because the maximum aggregate size is of the order of the size of the specimen. In this situation, the percolating crack network resulting from swelling is assumed to dramatically damage the cement matrix and to give sulfate solution access to the whole sample. Hence, by using this original type of cored samples, the concrete resistance to sulfate attack can be studied under reliable conditions (concrete formulations and not mortar ones, good sensitivity to ultrasonic tests) and advantage can be taken of the increased kinetics of degradation.     

Long-term energy management optimization according to differenttypes of transactions

In this paper, we describe a method for the energy management, according to minimal costs criteria over one year (month after month), of an electrical utility, which has to deal with nuclear and hydro power plants, sale/purchase and exchange contracts, and spot market business. The chosen method for minimizing the costs is linear programming with most variables continuous, and a few binary ones. The results obtained allow us the management of every power plant, contract and the spot market business, in order to respect the economic, physical and environmental constraints     

Electronic and structural properties of cholesteryl acetates

Electronic and structural properties of the cholesteryl acetate are investigated using semi-empirical quantum calculation. In the present article we perform an energy minimization through series of different configurations and a particular attention is given to the steroid ring structures. Different orientations and directions for the acetyl and the iso-octyl groups are observed for the suggested configurations. A comparison between calculated and experimental data show that the method not often used for large molecules is reliable and yields to values of bond lengths and bond angles close to those obtained by neutron diffraction at low temperature.     

Sol–gel incorporation of silica nanofillers for tuning the anti-corrosion protection of acrylate-based coatings

The aim of the present work is to synthesize through sol–gel approach new hybrid polymeric nanocomposites to be used as coating materials. An acrylic-based polymer was prepared by free-radical copolymerization of two monomers widely used for coatings, namely 2-ethylhexylacrylate (EHA) and glycidyl methacrylate (GMA) bearing epoxy moieties, in which silica nanoparticles were incorporated by in situ acid hydrolysis and subsequent condensation of tetraethoxysilane (TEOS). Glycidoxypropyl trimethoxysilane (GPTS) was used as coupling agent to fine-tune the compatibility between organic and inorganic phases. The morphology, mechanical properties and corrosion resistance of thin films applied on aluminum alloys were optimized by varying the content of silica nanoparticles whose properties were strongly affected by the TEOS/GPTS ratios. Performances of the obtained hybrid materials were scrutinized by atomic force microscopy (AFM), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), and electrochemical impedance spectroscopy (EIS). Thus it was evidenced that an optimum amount of silica nanoparticles with a precise morphology and composition in term of TEOS/GPTS ratio is needed to maintain good coating barrier properties. Outstanding anti-corrosion protection was reached by using optimized hybrid films.     

The Oil from Mentha rotundifolia as Green Inhibitor of Carbon Steel Corrosion in Hydrochloric Acid

The corrosion inhibition potentials of Mentha rotundifolia oil on carbon steel in 1 M HCl was studied at different concentrations via gravimetric, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. Polarization curves reveal that Mentha rotundifolia oil is a mixed-type inhibitor. Changes in impedance parameters (charge transfer resistance R_t, and double-layer capacitance C_dl) were indicative of adsorption of Mentha rotundifolia on the metal surface, leading to the formation of a protective film. The effect of the temperature on the corrosion behavior with addition of the optimal concentration of Mentha rotundifolia oil was studied in the temperature range 308 and 338 K. Adsorption of oil on the carbon steel surface is found to obey the Langmuir adsorption isotherm. Attempts to explain the inhibitory action were carried out using density functional theory (DFT) at B3LYP/6-31G(d,p) level. Quantum chemical parameters most relevant to its potential action as corrosion inhibitor such as E_HOMO (highest occupied molecular orbital energy), E_LUMO (lowest unoccupied molecular orbital energy), energy gap (ΔE), and Mulliken charges have been calculated and discussed. The theoretical results were found to be consistent with the experimental data.     

An inverse problem methodology for design and optimization of an interior permanent magnetic BLDC motor

In the theory of inverse problem, the parameters identification by optimization is considered as one of its main applications. This paper presents an optimal design of a slotted permanent magnet Brushless DC (BLDC) motor with surface mounted magnets. The inverse problem method is applied by using a thriving solver afforded by the nonlinear optimization toolbox of Matlab ‘Fmincon’, this function is based on Active-Set and Sequential Quadratic Programming approaches with calculation of the Hessian from Quasi-Newton algorithm. The optimal magnetic field density considered as the main objective is obtained by picking several parameters and analyzing their effects. The proposed approach is highlighted by using the obtained parameters in the design of the motor. The Finite element method is applied on the motor for numerical analysis by using FEMM magnetic coupled with Matlab code. Effectiveness and robustness of the proposed approach are verified by a comparison between the initial and optimized design.     

New Computational Model Based on Finite Element Method to Quantify Damage Evolution Due to External Sulfate Attack on Self‐Compacting Concretes

Abstract: This work combines experimental and numerical investigations to study the mechanical degradation of self‐compacting concrete under accelerated aging conditions. Four different experimental treatments are tested among them constant immersion and immersion‐drying protocols allow an efficient external sulfate attack of the material. Significant damage is observed due to interfacial ettringite. A predictive analysis is then adopted to quantify the relationship between ettringite growth and mechanical damage evolution during aging. Typical 3D microstructures representing the cement paste‐aggregate structures are generated using Monte Carlo scheme. These images are converted into a finite element model to predict the mechanical performance under different criteria of damage kinetics. The effect of ettringite is then associated to the development of an interphase of lower mechanical properties. Our results show that the observed time evolution of Young's modulus is best described by a linear increase of the interphase content. Our model results indicate also that the interphase regions grow at maximum stress regions rather than exclusively at interfaces. Finally, constant immersion predicts a rate of damage growth five times lower than that of immersion‐drying protocol.     

Electrocoagulation process applied to wastewater containing dyes from textile industry

In the present work, electrocoagulation was applied for the colour removal of solutions containing Direct red 81. Experiments were performed for synthetic solutions in batch mode.     

A procedure for modelling the differences between the gravimetric geoid model and GPS/levelling data with an example in the north part of Algeria

Local gravimetric geoid models from a combination of a global geopotential model and local gravity data generally contain errors of dm-level on the long wavelengths and sometimes they may be significantly higher in areas lacking accurate gravity information like Algeria where only few gravity data from Bureau Gravimétrique International (BGI) have been included in the development of the recent geopotential models. Consequently, these models do not have the required accuracy to transform the GPS ellipsoidal heights to orthometric heights. One of the main causes for this is the limited precision of the global and detailed DTM models. On the other hand, we can now measure by means of the space techniques, on land through a combination of GPS positioning and precise levelling and at sea through satellite altimetry, the geoid on some points on the earth's surface with very high absolute accuracy. These points can be used to correct the systematic effects, the medium and longer wavelength errors in the gravimetric geoid. The main goal of this study is to propose a procedure, for combination of available gravimetric geoid and external data from GPS and levelling in an optimal way and for estimating the gravimetric geoid accuracy using the collocation approach. So, the question is to find what is the adequate functional representation of the correction that should be applied to the gravimetric geoid? Several functions have been tested and the most suitable will be selected in test area from a statistical testing procedure. For this purpose, the improved Algerian gravimetric geoid computed by the Geodetic Laboratory of the National Center of Space Techniques from the gravity data supplied by the Geophysical Exploration Technology Ltd. (GETECH), and the precise GPS data collected from the international TYRhenian GEOdynamical NETwork (TYRGEONET), ALGerian GEOdynamical NETwork (ALGEONET) projects with baseline length ranging from about 1 to 1000 km have been used. The comparisons based on different GPS campaigns provide after fitting a RMS of the differences ±1.9 cm and prove that a good fit in experimental area between the gravimetric geoid and GPS/levelling data using the seven-parameter model transformation has been reached. Moreover, the analysis of statistics shows that the residuals in benchmarks are due principally to gravimetric geoid errors. The main outlines of the Algerian geoid computation, the available GPS/levelling data, the developed procedure and the obtained results will be presented.     

Intercalation of halloysite from Djebel Debagh (Algeria) and adsorption of copper ions

Halloysite available in Djebel Debagh, Guelma (eastern region of Algeria) was characterised by XRF, SEM, XRD, FTIR and by CEC, specific surface area and electrokinetic measurements. The crude halloysite was modified with Mⁿ⁺(CH₃COO)_n (M = Na⁺, NH₄⁺ or Pb²⁺), and intercalation of NaCH₃COO was monitored with time. XRD showed that the intercalation rate exceeded 90% for NaCH₃COO at long reaction time. X-ray diffraction also showed an expansion of the interlamellar space of 5.5 and 6.3 Å due to the intercalation of Pb(CH₃COO)₂ and NH₄CH₃COO. FTIR proved that Mⁿ⁺(CH₃COO)_n reacted with the inner surface hydroxyl groups of halloysite, on the basis of disappearance of the frequence bands at 3676 and 3652 cm^− 1 and the appearance of new bands around 3699 and 3457 cm^− 1. Intercalation of Pb(CH₃COO)₂ and NH₄CH₃COO shifted the band at 1650 towards 1663 and 1671 cm^− 1, respectively. The untreated and intercalated halloysite samples were used for removing copper(II) ions from aqueous solutions. The adsorption isotherms were of L-type according to the classification of Giles et al. (Giles, C.H., Mac Ewan, T.H., Makhwa, S.N., Smith, D., 1960. Studies in adsorption. Part XI. A system of classification of solution adsorption isotherms and its use in diagnosis of adsorption mechanisms and in measurement of specific surface areas of solids. J. Colloid Interface Sci. 3, 3973–3993.). The adsorption of copper ions was explained by electrostatic interaction between the copper(II) ions and negatively charged binding sites on halloysite surface and ion-exchange of the cations associated with acetate within the interlayer space.