Accepted Papers to Appear in Future Issues

A Study of Cr / CrN and Cr / CrN / CrAlN Multilayer Coatings for Permanent Mold Castings of Aluminum Alloys: Wear and Soldering Tendency

Mohammed Said BOUAMERENE, Corinne NOUVEAU, Hamid AKNOUCHE, Abdelatif ZERIZER, Taous Doria ATMANI, Mohand Oulhadj CHALLALI
Abstract :
Physical vapor deposition (PVD) coatings namely Cr/CrN, Cr/ CrN / CrAlN multilayers (period of μ = 4 with a Cr bonding layer 138 nm thick), have been synthesized on a quenched and tempered X38CrMoV8 steel to test their ability to avoid soldering during casting of aluminum alloys. Wear tests, optical profilemetry observations and demolding stress tests were carried out. Intermetallic compounds were formed and aluminum cast alloy soldering layer was found on surfaces of all tested pins, which were observed and quantified by SEM/EDS. Cr/CrN multilayers have been found to exhibit the best performance among all materials and coatings considered here. The results showed low friction coefficient of Cr/ CrN multilayers and the amounts of intermetallic compounds were lower than those formed on Cr/CrN/CrAlN ones.
Accepted : 2020-10-31

Prevention of alkali silica reaction risks in mortars by mineral admixtures.
Abstract :
The experimental study aims to prevent the alkali-silica reaction (ASR) of mortars made with reactive aggregates, where the volume rates of cement ranging from 10% to 50% are substituted by mineral admixtures such as Granulated Slag, Natural Pozzolan and Silica Fume. Their effectiveness in countering the ASR adverse effects; such as weight and dimensional variations, the width and density of cracks and mechanical performance losses was studied.
The results obtained show that the rate and the nature of the mineral admixtures influence their effectiveness, for Granulated Slag and Natural Pozzolan the ideal rate is 30%, for Silica Fume the 10% rate seems effective in countering ASR adverse effects. This effectiveness is ensured by the pozzolanic reaction favored by the high temperature of the test and the alkalinity of the system.
Accepted : 2020-11-16

Numerical simulation of heat losses from a slab-on-ground structure using Comsol-Multiphysics
Bouraoui WISSEM, Laredj NADIA, Maliki MUSTAPHA, Missoum HANIFI
Abstract :
Heat loss occurring through the slab-on-ground structure represents more than 10% of the total heat loss in residential buildings.
In this article, a transient two-dimensional numerical simulation using the COMSOL-Multiphysics software, is carried out for an experimental structure (Minnesota Experiment), and using the same thermo-physical properties of the soil and the same indoor and outdoor climatic conditions. The general heat transfer equation in unsaturated porous media has been used to simulate energy losses. A mathematical approach has also been developed in order to calculate the thermal conductivity of different materials with the aim of making them closer to real values.
The main goal is to compare the results of the simulated temperatures with the values measured in-situ. An excellent correlation between the simulated temperatures and those resulting from the experimental structure was obtained. At the same time, the exhaustive analysis of heat fluxes crossing the soil-structure interface has enabled us to propose practical solutions for reducing losses through the slab-on-ground.
Accepted : 2020-11-24

Reuse of Dam sediments in road engineering – Application to Mascara Dams, Algeria
Abstract :
Present study focuses on the characterization of sediments dredged from Mascara dams in the north west region of Algeria for a reuse in road material. Chemical and geotechnical properties of Bouhanifia and Fergoug dams are investigated showing the high level of silica and alumina in the composition of sediments. Geotechnical characteristics are defined according to the GTR (2000) recommendations allowing the identification of sediments and the classification in class A3F11. Immediate Bearing Indexes (IBI) are measured at the optimum water content. Compaction tests are performed on raw sediments (RS) and IBI results were lower than 25%. A such value imposes to improve the quality of raw sediments by an adequate treatment. Treatments with binders (lime and/or cement) and an addition of sand are proposed. As the two dams have similar properties and for a recovery in road engineering, only the Fergoug dam sediment was treated. Types of treatment have consisted in an addition of 30% of quarry sand and treated with 7% cement and/or 2% lime.The 2 mixtures proposed have shown clear improved properties for sublayer road materials. An acceptable road class was obtained demonstrating a possible reuse in road engineering.
Accepted : 2020-12-22

Evaluation of Mechanical Properties and Chemical Composition of Some Selected Steel Reinforcements Used in Nigeria
Mutiu A. AKINPELU, Ash-Shu’ara M. SALMAN, Ibrahim A. RAHEEM
Abstract :
Mechanical properties and chemical composition of some selected steel reinforcement bars used for construction works in Nigeria were investigated.Six nominal sizes of bars from four selected brands, including: Real steel reinforcing pty Limited, code name Red; Phoenix steel mills, code name White; Pulkit alloy and steel limited, code name Blue; and African foundries limited, code name Black were evaluated. The tensile test was carried out at the mechanical engineering department, University of Ilorin using Universal Testing Machine (UTM) while the chemical compositions of the steel samples were analyzed using optical emission spectrometer at the laboratory of African foundries limited, Ikorodu Lagos State. The results obtained were compared with BS 449:2005 +A3:2016 standard provision. The outcome of the study showed that 70.8 % of the tested steel bars failed the characteristic tensile strength test, though with a very good percentage elongation satisfying the required specification. Chemical composition tests revealed that most of the failed samples contained low carbon content or excess phosphorus composition plus other impurities.
Accepted : 2021-01-03

Effect on structural properties and behavior of beam column joint retrofitted using carbon fiber reinforced polymer
Anuja S. JAPE, Sudhir B. GAYAKE, Pravinchandra D. DHAKE
Abstract :
Beam column joints are one of the most critical components of reinforced concrete (RC) structures since it is subjected to large forces during severe ground shaking. The present study comprises four exterior beam-column joint specimens having different reinforcement arrangements detailed as per IS 13920: 1993, tested under reversed cyclic loading up_to failure. The test was force-controlled and the specimen was loaded by increasing the load level during each cycle. The load was applied forward cyclic and reverse cyclic and deflection, were measured from every 5kN by using a linear variable digital transducer (LVDT) with the digital arrangement. The deflection was measured at the loading point and at the centre of the beam. Damaged specimens were repaired and retrofitted with carbon fibre reinforced polymer (CFRP) to prevent shear damage and strength deterioration and to achieve a more ductile response. Retrofitted specimens were subjected to similar cyclic loading. Results for displacement were obtained. Hysteresis behaviour of non-retrofitted and retrofitted specimens were studied with respect to ultimate load, maximum displacement, energy dissipation capacity, stiffness degradation and general failure pattern. The comparisons showed that CFRP sheets improved the shear resistance of the joint and increased its energy dissipation capacity. Retrofitting makes the joint so strong that failure is directed towards the beams as it helps the structure in energy dissipation through plastic hinge formation in the beam.
Accepted : 2021-01-04

Experimental assessment of mechanical behavior of a compressed stabilized earth blocks (CSEB) and walls
Abstract :
The use of compacted stabilized earth blocks (CSEB) in load-bearing masonry is largely developed during these last decades. This paper reports on an experimental study of the chemical and mechanical stabilization effects on the compressive strength of earth blocks and triplet/walls. The blocks prepared with a high sandy soil mixed with rising cement and/or lime contents and compacted at 7 MPa are tested in uniaxial compression. The triplet and walls built with these CSEB units were joined with a cement/earth mortar.
Static uniaxial compression tests are typically undertaken on samples of earth mortars, on single earth blocks, on triplets of blocks with and without mortar, and lastly on masonry specimens made of CSEB. Compression tests were performed on CSEB blocks and mortar by using a video extensometer for accurate contactless strain measurement. Mechanical parameters were thus determined, including compressive strength, Poisson’s ratio, and elastic modulus. The results show that the compressive strength values of earth blocks treated with stabilizers were generally increased by rising the additive content. The increase of earth/cement blocks resistances was found more marked in comparison with those of earth/lime. It was also observed that the blocks prepared with an optimal content of lime along with cement have led to continuous increases of mechanical strength up to values greater than 5 MPa. The relationship between the blocks and triplets' compressive strengths as a function of stabilizer content (cement/lime) is linear. In the range of cement content from 6 to 8 %, the compressive strength of triplets is respectively 16 % and 20 % higher than those of walls. The observed failure of triplets and walls occurred essentially by the propagation of vertical and diagonal cracks
Accepted : 2021-01-08

Evaluation of variations of coarse aggregate types on hardened properties of concrete
Abstract :
Variation in coarse aggregate types, shape, texture and means of production are known to have a profound effect on mechanical properties of concrete such as compressive and flexural strengths. Two coarse aggregates; uncrushed gravel (UG) and crushed granite (CG) were used as coarse aggregates. Coarse aggregates were partially replaced with crushed granite at the incremental rate of 20% by weight of total coarse aggregate from 0% to 100%. Mix proportion of 1:2:4 and the water-cement ratio of 0.65 were used. The concrete design targeted compressive strength of 20Mpa onthe 28th day. Aggregate Crushing Value (ACV) test was conducted on various coarse aggregate combinations. Compressive strength and modulus of rupture were determined at various mix proportion of concrete containing different percent of coarse aggregates replacements at curing ages; 7th, 14th, and 28th days. Across curing ages, an increase in percent of crushed granite lead to an increase in compressive strength (CS) and modulus of rupture (MOR). Statistical analysis established strong positive relationship between percent of CG replacement and CS at 28th day(R2 = 0.908 & p < 0.01), between percent of CG replacement and MOR at 28th day (R2 = 0.832 & p < 0.05), and between CS at 28th day and MOR at 28th day for different mix proportions (R2 = 0.878 & p < 0.01).
Accepted : 2021-01-22

Numerical simulation and reliability of behaviour until the rupture of reinforced concrete spacial structure members with circular cross section
Abstract :
Numerical simulation of simple and composed bending behaviour of reinforced concrete spatial structure elements with circular cross section in the field of nonlinear elasticity, require a particular modeling’s technique of the cross section shape by a subdivision of the latter into trapezoids to best approximate the contour of the cross section. The input and output parameters of the materials behaviour modeling are simulated by random and deterministic variables. The present study aims at proposing a technique of the behaviour’s simulation up to failure taking into account the material non-linearity on the reinforced concrete structural elements with a circular cross section; a comparison was made between our simulation results and the experimental results. On the other hand, a numerical method has been modeled which makes it possible to estimate the reliability and the probability of failure of our simulation. To validate this modeling, we performed another comparison of the results obtained from our mechanical model by a Monte Carlo simulation with a reliable Hasofer-Lind method
Accepted : 2021-01-29