Journal of Materials and Engineering Structures
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Elaboration of geopolymer cement based on dredged sediment
Get PDFThis work aims to study the feasibility of making a geopolymer cement based on dredged sediments, from the Fergoug dam (Algeria). Sedimentary clays were characterized before and after calcination by X-ray diffraction, ATG / ATD, spectroscopy (FTIR) and XRF analysis. The reactivity of the calcined products was measured using isothermal calorimetric analysis (DSC) on pastes prepared by mixing an alkaline solution of sodium hydroxide (NaOH) 8 M in an amount allowing to have a Na / Al ratio close to 1. Also, cubic mortar samples were prepared with a ratio L / S: 0.8, sealed and cured for 24 hours at 60 ° C and then at room temperature. The results obtained allowed to optimize the calcination time of 5 hours for a better reactivity of these sediments, and a concentration of 8M of sodium hydroxide and more suitable to have the best mechanical performances
Approche numérique de l'endommagement des matériaux quasi-fragiles : Cas du béton
Get PDFLes matériaux hétérogènes à matrice fragile se comportent de manière adoucissante après la phase élastique. Cette dégradation peut être modélisée par la mécanique de l’endommagement continu par l’introduction d’une variable qui mesure la réduction de la surface résistante due à l’amorçage et à la propagation de fissures. Le modèle de Mazars choisi pour notre étude est isotrope et prend en compte le comportement dissymétrique du béton (traction-compression). Le modèle est implémenté dans un programme éléments finis travaillant avec interface GID, pour la simulation du comportement réel du matériau jusqu’à la ruine. L’application du programme à des structures simples montre la complexité du modèle à décrire avec précision le comportement d’un tel matériau. L’objectif principal de notre travail est justement, de mettre en évidence les limites d’une telle formulation en exploitant les résultats issus de la simulation.The heterogeneous materials with fragile matrix behave in a softening manner after the elastic phase. This degradation can be modeled by the mechanics of the continuous damage by the introduction of a variable which measures the reduction of the resistant surface due to the initiation and the propagation of cracks. The Mazars model chosen for our study is isotropic and takes in account the asymmetrical behavior of concrete (traction-compression). The model is implemented in a finite element program working with GID interface, for the simulation of the real behavior of the material up to ruin. The application of the program to simple structures shows the complexity of the model to accurately describe the behavior of such a material. The main objective of our work is then, to highlight the limits of such a formulation by exploiting the results resulting from the simulation.Les matériaux hétérogènes à matrice fragile se comportent de manière adoucissante après la phase élastique. Cette dégradation peut être modélisée par la mécanique de l’endommagement continu par l’introduction d’une variable qui mesure la réduction de la surface résistante due à l’amorçage et à la propagation de fissures. Le modèle de Mazars choisi pour notre étude est isotrope et prend en compte le comportement dissymétrique du béton (traction-compression). Le modèle est implémenté dans un programme éléments finis travaillant avec interface GID, pour la simulation du comportement réel du matériau jusqu’à la ruine. L’application du programme à des structures simples montre la complexité du modèle à décrire avec précision le comportement d’un tel matériau. L’objectif principal de notre travail est justement, de mettre en évidence les limites d’une telle formulation en exploitant les résultats issus de la simulation
Modulus of Elasticity of Lightweight Concrete Containing Different Ratios of PET as an Aggregate and Fiber
Get PDFIn this paper, the modulus of elasticity of lightweight concrete contains polyethylene terephthalate (PET) as fine, coarse aggregate and fiber was estimated by using experimental data from different literatures. The ratios of PET fiber range from 0.5% -1.5%. The modulus of elasticity increased by 8% for 0.5% PET fiber, and decreased by 45% when the concrete contains 1.5% PET fiber. The replacement of the fine or the coarse aggregate by using PET varies between 2.0% - 100%, and this caused decreasing the modulus of elasticity within range 1%-79%. This decreasing effected by shape and size of PET particles, strength of concrete, using of fly ash or silica fume, type of curing and ratio of aggregate to cement. More than 160 data sets, obtained by many investigators using various materials, have been collected and analyzed statistically to introduce the new formula of calculating the modulus of elasticity of concrete contained PET. The compressive strengths of the considered concretes range from 8.1 to 54 MPa. The modulus of elasticity of collected data range from 5.9 to 49 GPa. As a result, a practical equation, which is taken into consideration the ratio of PET as an aggregate or fiber, is proposed
Effects of polypropylene fibre on the compressive and splitting tensile strength of concrete
Get PDFConcrete is a versatile construction material comprising of cement, aggregates, water and occasionally admixture. It is very good in compression and weak in tension. To complement for the deficiency in the tensile zone; cracks, reinforcements (steel, fibre, etc.) have been found suitable. A good example of fibre is polypropylene. A concrete grade (M20) was batched and synthetic fibre (polypropylene) was used. Two categories of concrete specimens; with and without propylene fibre. The fibre was introduced in varying percentages (0.2%, 0.4%, and 0.6%) by weight of concrete. The compressive strength of concrete containing 0.4% polypropylene fibre at 28 days has the highest value of 32.22N/mm2 as compared to 30.22N/mm2, 30.49N/mm2 and 30.39N/mm2 for 0%, 0.2%, and 0.6% respectively. The splitting tensile strength at 7 days increases from 6.176 N/mm2 to 8.386 N/mm2 as the percentage of fibre increases from 0% to 0.4%
Influence of Recycled Aggregate on Shear Behavior of Steel Fibrous SCC
Get PDFOf all the different kinds of failures in concrete, shear failure is a sudden and brittle and occurs abruptly without any prior warning. To avoid these types of failures in concrete, beams are traditionally reinforced with stirrups at closer spacing based on design. An experimental study was carried out to study the shear behavior of steel fiber reinforced self-compacting concrete (SCC) beams with recycled concrete aggregate (RCA) as a complete replacement of both natural coarse and fine aggregate. The experimental program consists of 24 beams of which 12 beams were cast with natural aggregate and remaining 12 beams were cast using recycled aggregates as a complete replacement of natural aggregates. Due to the use of recycled concrete aggregates as coarse and fine aggregates, the compressive strength reduced by 7.8% and 8% for 30 and 70 MPa Concrete. The ultimate shear strength reduced by 14% and 12% due to use of recycled concrete aggregates for SCC30 and SCC70 beams respectively. The investigation indicates that the ultimate load and ultimate shear strength decreases as the spacing of stirrups increased. It was observed from the experimental results that addition of steel fibers enhanced the mechanical properties of both natural aggregate based self-compacting concrete (NASCC) and recycled aggregate based self-compacting concrete (RASCC). Also due to the addition of steel fibers the performance of SCC beams has improved. The shear strength obtained experimentally was compared with the existing models in the literature and the correlation was found to be satisfactor
Study of concretes properties based on pre-saturated recycled aggregates
Get PDFThe aim of this study was concretes waste recovery by replacing natural aggregates (NA) by recycled aggregates (RA) at rates of 0%, 50% and 100%. Recycled aggregates coming from construction and demolition waste (CDW) present a low quality compared to natural aggregates, the water absorption being their main drawback. Quantities of water absorbed and their variations in times were measured according to the European standard (EN 1097-6). Adding absorbed water during mixing have caused concretes segregations and an excess volume of water was observed at the surface of the concrete. The added water was not totally absorbed by aggregates. The pre-saturation of aggregates 24 hours before mixing and introducing them as a component in concrete was the best method. The initially saturated aggregates did not consume concretes mixture water. Workability by slump test and mechanical strengths developed with pre-saturated aggregates (100 % RA) and (50% RA - 50% NA) were measured on concretes, and then were compared to those of the reference concretes made with 100 % of natural aggregates
Evaluation of the performance of local cement for oil well cementing operations in Algeria
Get PDFThe cementing of oil wells is done using special cement called ‘’class G cement’’, whose properties should meet the requirements of the American Petroleum Institute (API). Algeria, which ranks high among the oil and gas producing countries, has recently begun production of petroleum cement. The aim of this work is to characterize and evaluate the performance of a locally manufactured cement sample intended for oil and gas well cementing operations in Algeria. In this paper, significant properties (thickening time, compressive strength and free water) as well as the rheological behavior of the cement slurry under specific conditions have been experimentally examined. Apart from the initial consistency, which could be resolved by incorporating additives, the results indicated that the locally produced cement meets the requirements of the API standards and can therefore be used for cementing oil and gas wells
The Performance of Monolithic Reinforced Concrete Structure Includes Slab, Beam and Column against Blast Load
Get PDFThe numerical investigations has been carried out on reinforced concrete structures against blast loading to demonstrate the accuracy and effectiveness of the finite element based numerical models. The size of building was considered 3 ×3 × 3 m and whereas the size of beam and column was 0.3 m, arbitrary. The thickness of roof slab was 120 mm, whereas the reinforced concrete wall on all four sides was 0.2 m. The simulations were carried out through finite element code ABAQUS/CAE. The inelastic behavior of concrete has been incorporated through concrete damage plasticity model and the model includes compressive and tensile behavior. The elastic and plastic behavior of steel reinforcement bar has been incorporated using Johnson-cook model includes the effect of state of stress, temperature and strain rate. The simulations were carried out against varying standoff distance, mass of TNT, locations of blast origin and thickness of roof slab to examine the resistance of building. The response of structural elements were studied in light of deflection, impulsive velocity, von-Mises stresses, compression and tension damage of concrete. The results indicate that the standoff distance has great influence on the survivability of reinforced concrete slab and wall
Modeling the erosion of the upper and middle Cheliff basin by the Model builder application on ArcGis
Get PDFL’objectif de cette étude est de réaliser une carte de répartition des degrés de vulnérabilité à l’érosion au niveau du bassin haut et moyen Cheliff, en faisant appel au modèle de superposition des cartes « model builder » sur ArcGisTM. Cette zone d’étude est confrontée à un grave problème de dégradation des sols ; ce qui a provoqué une augmentation considérable du taux d’envasement de la majorité des barrages répartis sur ce bassin. En effet, quatre classes de vulnérabilité à l’érosion ont été distinguées (faible, moyenne, forte et très forte). La carte élaborée a permis de disposer d’une vue d'ensemble des zones menacées. Elle fournit un excellent outil d’aide à la prise de décision pour les gestionnaires, afin de mieux cibler leurs stratégies d’interventions préventives.L’objectif de ce présent travail est de réaliser une carte synthétique de répartition des degrés de sensibilité à l’érosion au niveau du bassin haut et moyen Cheliff, en faisant appel au modèle de superposition des cartes « model builder » sur ArcMapTM. Ce bassin est exposé à un grave problème de dégradation du sol, ce qui provoque l’envasement de la majorité des barrages répartis sur son ensemble. En effet, quatre classes de vulnérabilité à l’érosion ont été distinguées (faible, moyenne, forte et très forte) où les zones fortement vulnérables couvrent la majeur partie du bassin. La carte produite fournit un excellent outil d’aide à la prise de décision pour les gestionnaires, afin de mieux cibler leurs stratégies d’interventions préventives.The objective of this present work is to produce a synthetic distribution map of sensitivity degrees to erosion on the level of the high and middle Cheliff basin, by using the superposition model of cards “model builder” on ArcMapTM. The latter is exposed to a serious problem of soil degradation causes siltation of the majority of the dams distributed on his whole. Indeed, four classes of erosion vulnerability have been distinguished (weak, average, strong and very strong) where the strongly vulnerable areas cover the most part of the basin. The map produced provides an excellent decision-making tool for managers, in order to better target their preventive intervention strategies
Finite Elements Analysis of a Butterfly-Shaped Composite patch Repair and its Comparison to the Usual Shapes
No full textA 3-D finite element analysis was conducted on a thin aluminum plate with a 45 ° inclined central crack. A modeling of the bonding repair with composite patch of different shapes was carried out. In addition to the patch shapes studied in the literature, a new butterfly shape was proposed. The latter is defined by a length H, a width B and a neck C in the middle. The main objective is to analyze the effect of patch geometry on the rate of decrease of stress intensity factors. This rate is characterized by a coefficient R which combines between the mode I and the mode II of the rupture (KI and KII). Thus, an optimization of the patch shape is made with respect to the effectiveness in decreasing the stress intensity factor. The comparison between the results obtained with the different patch shapes has shown that the butterfly-shaped patch is more effective for relatively small surfaces. On the other hand, the extended octagon shape has been shown to be more effective for higher patch surfaces