Search results for: glass aggregate

Authors: Sultan Husein Bayqra, Ali Mardani Aghabaglou, Zia Ahmad Faqiri, Hassane Amidou Ouedraogo

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In this study, the effect of shape and size of the concrete specimen on the compressive and splitting tensile strength of the concrete mixtures in the absence and presence of steel fiber was investigated. For this aim, ten different concrete mixtures having w/c ratio of 0.3, 0.4, 0.5, 0.6 and 0.7 with and without fiber were prepared. In the mixtures containing steel fibers having aspect ratio (L/D) of 64 were used by 1% of the total mixture volume. In all concrete mixtures, CEM I 42,5R type Portland cement and crushed Lime-stone aggregates having different aggregate size fractions were used. The combined aggregate was obtained by mixing %40 0-5 mm, %30 5-12 mm and %30 12-22 mm aggregate size fraction. The slump values of concrete mixtures were kept constant as 17 ± 2 cm. To provide the desired slump value, a polycarboxylate ether-based high range water reducing admixture was used. In order to investigate the effect of size and shape of concrete specimen on strength properties 10 cm, 15 cm cubic specimens and 10×20 cm, 15×30 cm cylindrical specimens were prepared for each mixture. The specimens were cured under standard conditions until testing days. The 7- and 28-day compressive and splitting tensile strengths of mixtures were determined. The results obtained from the experimental study showed that the strength ratio between the cylinder and the cube specimens increased with the increase of the strength of the concrete. Regardless of the fiber utilization and specimen shape, strength values of concrete mixtures were increased by decreasing specimen size. However, the mentioned behaviour was not observed for the case that the mixtures having high W/C ratio and containing fiber. The compressive strength of cube specimens containing fiber was less affected by the size of the specimen compared to that of cube specimens containing no fibers.

Keywords: compressive strength, splitting tensile strength, fiber reinforced concrete, size effect, shape effect

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Authors: Kanchan Maji, Debasmita Pani, Sudip Dasgupta

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Calcium phosphate cement (CPC) due to its high bioactivity and optimum bioresorbability shows excellent bone regeneration capability. Despite it has limited applications as bone implant due to its macro-porous microstructure causing its poor mechanical strength. The reinforcement of apatitic CPCs with biocompatible fibre glass phase is an attractive area of research to improve its mechanical strength. Here we study the setting behaviour of Si-doped and un-doped alpha tri-calcium phosphate (α-TCP) based CPC and its reinforcement with the addition of E-glass fibre. Alpha tri-calcium phosphate powders were prepared by solid state sintering of CaCO3, CaHPO4 and tetra ethyl ortho silicate (TEOS) was used as silicon source to synthesise Si doped α-TCP powders. Alpha tri-calcium phosphate based CPC hydrolyzes to form hydroxyapatite (HA) crystals having excellent osteoconductivity and bone-replacement capability thus self-hardens through the entanglement of HA crystals. Setting time, phase composition, hydrolysis conversion rate, microstructure, and diametral tensile strength (DTS) of un-doped CPC and Si-doped CPC were studied and compared. Both initial and final setting time of the developed cement was delayed because of Si addition. Crystalline phases of HA (JCPDS 9-432), α-TCP (JCPDS 29-359) and β-TCP (JCPDS 9-169) were detected in the X-ray diffraction (XRD) pattern after immersion of CPC in simulated body fluid (SBF) for 0 hours to 10 days. The intensities of the α-TCP peaks of (201) and (161) at 2θ of 22.2°and 24.1° decreased when the time of immersion of CPC in SBF increased from 0 hours to 10 days, due to its transformation into HA. As Si incorporation in the crystal lattice stabilised the TCP phase, Si doped CPC showed a little slower rate of conversion into HA phase as compared to un-doped CPC. The SEM image of the microstructure of hardened CPC showed lower grain size of HA in un-doped CPC because of premature setting and faster hydrolysis of un-doped CPC in SBF as compared that in Si-doped CPC. Premature setting caused generation of micro and macro porosity in un-doped CPC structure which resulted in its lower mechanical strength as compared to that in Si-doped CPC. This lower porosity and greater compactness in the microstructure attributes to greater DTS values observed in Si-doped CPC. E-glass fibres of the average diameter of 12 μm were cut into approximately 1 mm in length and immersed in SBF to deposit carbonated apatite on its surface. This was performed to promote HA crystal growth and entanglement along the fibre surface to promote stronger interface between dispersed E-glass fibre and CPC matrix. It was found that addition of 10 wt% of E-glass fibre into Si-doped α-TCP increased the average DTS of CPC from 8 MPa to 15 MPa as the fibres could resist the propagation of crack by deflecting the crack tip. Our study shows that biocompatible E-glass fibre in optimum proportion in CPC matrix can enhance the mechanical strength of CPC without affecting its bioactivity.

Keywords: Calcium phosphate cement, biocompatibility, e-glass fibre, diametral tensile strength

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Authors: Huda Zakaria

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The concept of the glass ceiling persists as a barrier to women's advancement in leadership roles, shaped significantly by organizational culture and climate. This study examines the impact of organizational culture on advancing women to top leadership roles in the Egyptian banking sector. The research explores how varying organizational cultures and climates either facilitate or hinder women's progress in breaking through the glass ceiling. Data suggests that women are underrepresented in senior management positions globally, including in Egypt, indicating a barrier to their advancement. Organizational norms often align more with masculine traits, creating challenges for women in leadership. Stereotypes and biases affect how women are treated, leading to limited advancement opportunities and a lack of sponsors advocating for their skills. Female managers also exhibit lower levels of career confidence compared to male counterparts. To address these issues, organizations must tackle cultural biases and provide equal opportunities to promote genuine gender diversity and empower women in leadership roles. Understanding the impact of organizational culture is crucial for creating inclusive workplaces that foster gender equality and provide equal opportunities for women to succeed in leadership roles.

Keywords: glass ceiling, leadership, banking, bias

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Authors: Benmalek M. Larbi, R. Harbi, S. Boukor

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This paper reports an experimental work that aimed to investigate the effects of clay brick waste, as part of fine aggregate, on rendering mortar performance. The brick, in crushed form, was from a local brick manufacturer that was rejected due to being of-standard. It was used to replace 33.33 %, 50 %, 66.66 % and 100 % by weight of the quarry sand in mortar. Effects of the brick replacement on the mortar key properties intended for wall plastering were investigated; these are workability, compressive strength, flexural strength, linear shrinkage, water absorption by total immersion and by capillary suction. The results showed that as the brick replacement level increased, the mortar workability reduced. The linear shrinkage increases over time and decreases with the introduction of brick waste. The compressive and flexural strengths decrease with the increase of brick waste because of their great water absorption.

Keywords: clay brick waste, mortar, properties, quarry sand

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Authors: F. Onyango, Salim R. Wanjala, M. Ndege, L. Masu

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Asphalt concrete pavements have a short life cycle, failing mainly due to temperature changes, traffic loading and ageing. Modified asphalt mixtures provide the technology to produce a bituminous binder with improved viscoelastic properties which remain in balance over a wider temperature range and loading conditions. In this research, 60/70 penetration grade asphalt binder was modified by adding 2, 4, 6, 8, and 10 percent by weight of asphalt binder following the wet process and the mineral aggregate was modified by adding 1, 2, 3, 4, and 5 percent crumb rubber by volume of the mineral aggregate following the dry process. The LDPE modified asphalt binder Rheological properties were evaluated. The laboratory results showed an increase in viscosity, softening point and stiffness of the binder. The modified asphalt was then used in preparing asphalt mixtures by Marshall Mix design procedure. The Marshall stability values for mixes containing 2% crumb rubber and 4% LDPE were found to be 30% higher than the conventional asphalt concrete mix.

Keywords: crumb rubber, dry process, hot mix asphalt, wet process

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Authors: Mohammad A. Khasawneh

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The design of high pressure water jet based polishing equipment and its fabrication conducted in this study is reported herein, together with some preliminary test results for assessing its applicability for HMA surface polishing. This study also provides preliminary findings concerning the test variables, such as the rotational speed, the water jet pressure, the abrasive agent used, and the impact angel that were experimentally investigated in this study. The preliminary findings based on four trial tests (two on large slab specimens and two on small size gyratory compacted specimens), however, indicate that both friction and texture values tend to increase with the polishing durations for two combinations of pressure and rotation speed of the rotary deck. It seems that the more polishing action the specimen is subjected to; the aggregate edges are created such that the surface texture values are increased with the accompanied increase in friction values. It may be of interest (but which is outside the scope of this study) to investigate if the similar trend exist for HMA prepared with aggregate source that is sand and gravel.

Keywords: high-pressure, water jet, friction, texture, polishing, statistical analysis

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Authors: C. Chhorn, S. H. Han, S. W. Lee

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Roller-compacted concrete (RCC) has been used for decades in many pavement applications due to its economic cost and high construction speed. However, due to the lack of deep researches and experiences, this material has not been widely employed. An RCC mixture with appropriate consistency can induce high compacted density, while high density can induce good aggregate interlock and high strength. Consistency of RCC is mainly known to define its constructability. However, it was not well specified how this property may affect other properties of a constructed RCC pavement (RCCP). This study suggested the possibility of an ideal range of consistency that may provide adequate quality of RCCP. In this research, five sections of RCCP consisted of both 13 mm and 19 mm aggregate sections were investigated. The effects of consistency on compacted depth, strength, international roughness index (IRI), skid resistance are examined. From this study, a new range of consistency is suggested for RCCP application.

Keywords: compacted depth, consistency, international roughness index (IRI), pavement, roller-compacted concrete (RCC), skid resistance, strength

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Authors: SeyedMohammad Hosseini, Amirhossein Moghanian

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The main purpose of this research was to design a biomimetic system by freeze-drying method for evaluating the effect of adding 5 and 10 mol. % of zinc (Zn)in 58S bioactive glass and gelatin (5ZnBG/G and 10ZnBG/G) in terms of structural and biological changes. The structural analyses of samples were performed by X-Ray Diffraction (XRD), scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy (FTIR). Also, 3-(4,5dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide(MTT) and alkaline phosphate (ALP) activity test were carried out for investigation of MC3T3-E1cell behaviors. The SEM results demonstrated the spherical shape of the formed hydroxyapatite (HA) phases, and also HA characteristic peaks were detected by X-ray diffraction spectroscopy (XRD)after 3 days of immersion in the simulated body fluid (SBF) solution. Meanwhile, FTIR spectra proved that the intensity of P–O peaks for 5ZnBG/G was more than 10ZnBG/G and control samples. Moreover, the results of alkaline phosphatase activity (ALP) test illustrated that the optimal amount of Zn (5ZnBG/G) caused a considerable enhancement in bone cell growth. Taken together, the scaffold with 5 mol.% Zn was introduced as an optimal sample because of its higher biocompatibility, in vitro bioactivity, and growth of MC3T3-E1cellsin in comparison with other samples in bone tissue engineering.

Keywords: scaffold, gelatin, modified bioactive glass, alp, bone tissue engineering

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Authors: P. Charvin, R. Bourrou, F. Lemont, C. Lafon, A. Russello

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For nuclear waste treatment and confinement, a specific IN-CAN melting module based on low-frequency induction heating have been designed. The frequency of 50Hz has been chosen to improve penetration length through metal. In this design, the liquid metal, strongly stirred by electromagnetic effects, presents shape of a dome caused by strong Laplace forces developing in the bulk of bath. Because of a lower density, the glass phase is located above the metal phase and is heated and stirred by metal through interface. Electric parameters (Intensity, frequency) give precious information about metal load and composition (resistivity of alloy) through impedance modification. Then, power supply can be adapted to energy transfer efficiency for suitable process supervision. Modeling of this system allows prediction of metal dome shape (in agreement with experimental measurement with a specific device), glass and metal velocity, heat and motion transfer through interface. MHD modeling is achieved with COMSOL and Fluent. First, a simplified model is used to obtain the shape of the metal dome. Then the shape is fixed to calculate the fluid flow and the thermal part.

Keywords: electromagnetic stirring, induction heating, interface modeling, metal load

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Authors: Sallehan Ismail, Mahyuddin Ramli

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This study examined the properties of fresh and hardened concretes as influenced by the moisture state of the coarse recycled concrete aggregates (RCA) after surface treatment. Surface treatment was performed by immersing the coarse RCA in a calcium metasilicate (CM) solution. The treated coarse RCA was maintained in three controlled moisture states, namely, air-dried, oven-dried, and saturated surface-dried (SSD), prior to its use in a concrete mix. The physical properties of coarse RCA were evaluated after surface treatment during the first phase of the experiment to determine the density and the water absorption characteristics of the RCA. The second phase involved the evaluation of the slump, slump loss, density, and compressive strength of the concretes that were prepared with different proportions of natural and treated coarse RCA. Controlling the moisture state of the coarse RCA after surface treatment was found to significantly influence the properties of the fresh and hardened concretes.

Keywords: moisture state, recycled concrete aggregate, surface treatment

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Authors: Bhavna Malik

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The study is build on a theoretical framework that links characteristics of job, key attitudes and intention to leave, why faculty may be disengaging from institutional service. The literature indicates that job characteristics, key attitudes and intention to leave are very important for effective organizational functioning. In general, the literature showed that some job characteristics might be the antecedents of job satisfaction and the aggregate variable job scope was positively associated with organizational commitment, and these key attitudes predicted intention to leave negatively. The present study attempted to propose a new integrative model of the relationships among job characteristics, key attitudes, and intention to leave. The main purpose of the present study is to examine the effects of job characteristics on intention to leave. While examining the role of job characteristics, the mediating roles of key attitudes were taken into account in order to better understand how job characteristics affect the exhibition of intention to leave. The secondary purpose is to investigate the effects of job characteristics on key attitudes, and the effects of key attitudes on intention to leave. Job characteristics of remuneration, resource for professional activities, career opportunities were positively associated with the work attitude of job satisfaction. The aggregate job scope was positively associated with the work attitude of organizational commitment although no single job characteristic was significantly associated with organizational commitment. Commitment, however, did not significantly affect time spent on institutional service. Two job characteristics—time spent on research and time spent on teaching—were negatively associated with this behavior. In general, the literature showed that some job characteristics might be the antecedents of job satisfaction and the aggregate variable job scope was positively associated with organizational commitment, and these key attiudes predicted intention to leave negatively. In turn, job satisfaction and organizational commitment were negatively associated with the intention to leave. In addition to these, organizational commitment was negatively associated with the intention to leave. However, no significant direct association was found between job characteristics and intention to leave.

Keywords: Job Characteristics Model, job satisfaction, organizational commitment, intention to leave

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Authors: J. Kosikova, B. Vacenovska, M. Vyhnankova

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The paper reports on the subject of recycling and further use of secondary raw materials obtained from solar panels, which is becoming a very up to date topic in recent years. Recycling these panels is very difficult and complex, and the use of resulting secondary raw materials is still not fully resolved. Within the research carried out at the Brno University of Technology, new polymer materials used for industrial floors are being developed. Secondary raw materials are incorporated into these polymers as fillers. One of the tested filler materials was glass obtained from solar panels. The following text describes procedures and results of the tests that were performed on these materials, confirming the possibility of the use of solar panel glass in industrial polymer flooring systems.

Keywords: fillers, industrial floors, recycling, secondary raw material, solar panel

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Authors: Lenka Bodnárová, Rudolf Hela, Michala Hubertová, Iveta Nováková

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This paper is concerning the issues of behaviour of lightweight expanded clay aggregates concrete exposed to high temperature. Lightweight aggregates from expanded clay are produced by firing of row material up to temperature 1050°C. Lightweight aggregates have suitable properties in terms of volume stability, when exposed to temperatures up to 1050°C, which could indicate their suitability for construction applications with higher risk of fire. The test samples were exposed to heat by using the standard temperature-time curve ISO 834. Negative changes in resulting mechanical properties, such as compressive strength, tensile strength, and flexural strength were evaluated. Also visual evaluation of the specimen was performed. On specimen exposed to excessive heat, an explosive spalling could be observed, due to evaporation of considerable amount of unbounded water from the inner structure of the concrete.

Keywords: expanded clay aggregate, explosive spalling, high temperature, lightweight concrete, temperature-time curve ISO 834

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Authors: Priyanka Kumari Gupta, Punya Prasanna Paltani, Shrivishal Tripathi

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This paper proposes a nonlinear photonic crystal ring resonator-based all-optical 2 × 2 switch. The nonlinear Kerr effect is used to evaluate the essential 2 x 2 components of the photonic crystal-based optical switch, including the bar and cross states. The photonic crystal comprises a two-dimensional square lattice of dielectric rods in an air background. In the background air, two different dielectric materials are used for this comparison study separately. Initially with chalcogenide glass rods, then with GaAs rods. For both materials, the operating wavelength, bandgap diagram, operating power intensities, and performance parameters, such as the extinction ratio, insertion loss, and cross-talk of an optical switch, have also been estimated using the plane wave expansion and the finite-difference time-domain method. The chalcogenide glass material (Ag20As32Se48) has a high refractive index of 3.1 which is highly suitable for switching operations. This dielectric material is immersed in an air background with a nonlinear Kerr coefficient of 9.1 x 10-17 m2/W. The resonance wavelength is at 1552 nm, with the operating power intensities at the cross-state and bar state around 60 W/μm2 and 690 W/μm2. The extinction ratio, insertion loss, and cross-talk value for the chalcogenide glass at the cross-state are 17.19 dB, 0.051 dB, and -17.14 dB, and the bar state, the values are 11.32 dB, 0.025 dB, and -11.35 dB respectively. The gallium arsenide (GaAs) dielectric material has a high refractive index of 3.4, a direct bandgap semiconductor material highly preferred nowadays for switching operations. This dielectric material is immersed in an air background with a nonlinear Kerr coefficient of 3.1 x 10-16 m2/W. The resonance wavelength is at 1558 nm, with the operating power intensities at the cross-state and bar state around 110 W/μm2 and 200 W/μm2. The extinction ratio, insertion loss, and cross-talk value for the chalcogenide glass at the cross-state are found to be 3.36.19 dB, 2.436 dB, and -5.8 dB, and for the bar state, the values are 15.60 dB, 0.985 dB, and -16.59 dB respectively. This paper proposes an all-optical 2 × 2 switch based on a nonlinear photonic crystal using a ring resonator. The two-dimensional photonic crystal comprises a square lattice of dielectric rods in an air background. The resonance wavelength is in the range of photonic bandgap. Later, another widely used material, GaAs, is also considered, and its performance is compared with the chalcogenide glass. Our presented structure can be potentially applicable in optical integration circuits and information processing.

Keywords: photonic crystal, FDTD, ring resonator, optical switch

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Authors: Ibrahim Al-Suraihy, Abdellaziz Doghmane, Zahia Hadjoub

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We discuss in this work the elastic properties by using acoustic microscopes to measure Rayleigh and longitudinal wave velocities in a no radiated and radiated sodium borate glasses X2Na2O-X2B2O3 with 0 ≤ x ≤ 27 (mol %) at microscopic resolution. The acoustic material signatures were first measured, from which the characteristic surface velocities were determined.Longitudinal and shear ultrasonic velocities were measured in a different composition of sodium borate glass samples before and after irradiation with γ-rays. Results showed that the effect due to increasing sodium oxide content on the ultrasonic velocity appeared more clearly than due to γ-radiation. It was found that as Na2O composition increases, longitudinal velocities vary from 3832 to 5636 m/s in irradiated sample and it vary from 4010 to 5836 m/s in high radiated sample by 10 dose whereas shear velocities vary from 2223 to 3269 m/s in irradiated sample and it vary from 2326 m/s in low radiation to 3385 m/s in high radiated sample by 10 dose. The effect of increasing sodium oxide content on ultrasonic velocity was very clear. The increase of velocity was attributed to the gradual increase in the rigidity of glass and hence strengthening of network due to gradual change of boron atoms from the three-fold to the four-fold coordination of oxygen atoms. The ultrasonic velocities data of glass samples have been used to find the elastic modulus. It was found that ultrasonic velocity, elastic modulus and microhardness increase with increasing barium oxide content and increasing γ-radiation dose.

Keywords: mechanical properties X2Na2O-X2B2O3, acoustic signature, SAW velocities, additives, gamma-radiation dose

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Authors: Sangmo Jon, Ganghyok Kim, Kwanghyok Jong, Ilnam Jo, Hyangsun Kim, Kukhyon Pae, GyeChol Sin

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The back contact dye solar cells (BCDSCs), in which the transparent conductive oxide (TCO) is omitted, have the potential to use intact low-cost general substrates such as glass, metal foil, and papers. Herein, we introduce a facile manufacturing method of a Ti back contact electrode for the BCDSCs. We found that the polylinkers such as poly(butyl titanate) have a strong binding property to make Ti particles connect with one another. A porous Ti film, which consists of Ti particles of ≤10㎛ size connected by a small amount of polylinkers, has an excellent low sheet resistance of 10 ohm sq⁻¹ for an efficient electron collection for DSCs. This Ti back contact electrode can be prepared by using a facile printing method under normal ambient conditions. Conjugating the new back contact electrode technology with the traditional monolithic structure using the carbon counter electrode, we fabricated all TCO-less DSCs. These four-layer structured DSCs consist of a dye-adsorbed nanocrystalline TiO₂ film on a glass substrate, a porous Ti back contact layer, a ZrO₂ spacer layer, and a carbon counter electrode in a layered structure. Under AM 1.5G and 100mWcm⁻² simulated sunlight illumination, the four-layer structured DSCs with N719 dyes and I⁻/I₃⁻ redox electrolytes achieved PCEs up to 5.21%.

Keywords: dye solar cells, TCO-less, back contact, printing, porous Ti film

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Authors: Brahim Safi, Mohammed Saidi, A. Benmounah, Jozef Mitterpach

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The aim of this work is to study the rheological and physico-mechanical properties of a self-compacting concrete elaborated with sea shells as an addition cementitious (total replacement of limestone fillers) and sand (partial and total substitution fine aggregate). Also, this present study is registered in the context of sustainable development by using this waste type which caused environmental problems. After preparation the crushed shells (obtaining fine aggregate) and finely crushed shells (obtaining end powder), concretes were manufactured using these two products. Rheological characterization tests (fluidity, filling capacity and segregation) and physico-mechanical properties (density and strength) were carried on these concretes. The results obtained show that it can be used as fin addition (by total replacement of limestone) or also used as sand by total substitution of natural sand.

Keywords: seashells, limestone, sand, self-compacting concrete, fluidity, compressive strength, flexural strength

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Authors: Nagri Sateesh, Kundavarapu Vengalrao, Kopparthi Phaneendra Kumar

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Vacuum assisted resin transfer molding (VARTM) is one of the manufacturing technique that is viable for production of fiber reinforced polymer composite components suitable for aerospace, marine and commercial applications. However, the repeatable quality of the product can be achieved by critically fixing the process parameters such as Vacuum Pressure (VP) and permeability of the preform. The present investigation is aimed at studying the effect of permeability for production of Glass Fiber Reinforced Plastic (GFRP) components with consistent quality. The VARTM mould is made with an acrylic transparent top cover to observe and record the resin flow pattern. Six layers of randomly placed glass fiber under five different vacuum pressures VP1 = 0.013, VP2 = 0.026, VP3 = 0.039, VP4 = 0.053 and VP5 = 0.066 MPa were studied. The laminates produced by this process under the above mentioned conditions were characterized with ASTM D procedures so as to study the effect of these process parameters on the quality of the laminate. Moreover, as mentioned there is a considerable effect of permeability on the impact strength and the void content in the laminates under different vacuum pressures. SEM analysis of the impact tested fractured GFRP composites showed the bonding of fiber and matrix.

Keywords: permeability, vacuum assisted resin transfer molding (VARTM), ASTM D standards, SEM

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Authors: Eliott Guérin, Remi Daudin, Georges Kalepsi, Alexis Lenain, Sebastien Gravier, Benoit Ter-Ovanessian, Damien Fabregue, Jean-Jacques Blandin

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Due to interesting compromise between mechanical and corrosion properties, Zr-based BMGs are attractive for biomedical applications. However, the enhancement of their glass forming ability (GFA) is often achieved by addition of toxic elements like Ni or Be, which is of course a problem for such applications. Consequently, the development of Ni-free Be-free Zr-based BMGs is of great interest. We have developed a Zr-based (Ni and Be-free) amorphous metallic alloy with an elastic limit twice the one of Ti-6Al-4V. The Zr56Co28Al16 composition exhibits a yield strength close to 2 GPa and low Young’s modulus (close to 90 GPa) [1-2]. In this work, we investigated Niobium (Nb) addition through substitution of Zr up to 8 at%. Cobalt substitution has already been reported [3], but we chose Zr substitution to preserve the glass forming ability. In this case, we show that the glass forming ability for 5 mm diameters rods is maintained up to 3 at% of Nb substitution using suction casting in cooper moulds. Concerning the thermal stability, we measure a strong compositional dependence on the glass transition (Tg). Using DSC analysis (heating rate 20 K/min), we show that the Tg rises from 752 K for 0 at% of Nb to 759 K for 3 at% of Nb. Yet, the thermal range between Tg and the crystallisation temperature (Tx) remains almost unchanged from 33 K to 35 K. Uniaxial compression tests on 2 mm diameter pillars and 3 points bending (3PB) tests on 1 mm thick plates are performed to study the Nb addition on the mechanical properties and the plastic behaviour. With these tests, an optimal Nb concentration is found, improving both plasticity and fatigue resistance. Through interpretations of DSC measurements, an attempt is made to correlate the modifications of the mechanical properties with the structural changes. The optimized chemical, structural and mechanical properties through Nb addition are encouraging to develop the potential of this BMG alloy for biomedical applications. For this purpose, we performed polarisation, immersion and cytotoxicity tests. The figure illustrates the polarisation response of Zr56Co28Al16, Zr54Co28Al16Nb2 and TA6V as a reference after 2h of open circuit potential. The results show that the substitution of Zr by a small amount of Nb significantly improves the corrosion resistance of the alloy.

Keywords: metallic glasses, amorphous metal, medical, mechanical resistance, biocompatibility

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Authors: Eya Hentati, Mona Lamine, Jalel Bouzid

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In this study, a laboratory-scale was designed and fabricated to treat single house greywater in the north of Tunisia with a combination of physical and natural treatments systems. The combined system includes a bio-filter composed of LECA® (lightweight expanded clay aggregate) followed by a vertical up-flow constructed wetland planted with Iris pseudacorus and Typha Latifolia. Applied two hydraulic retention times (HRTs) with two different plants types showed that a bio-filter planted with Typha Latifolia has an optimum removal efficiency for degradation of organic matter and transformation of nitrogen and phosphate at HRT of 30 h. The optimum removal efficiency of biochemical oxygen demand (BOD), chemical oxygen demand (COD), and suspended solids (SS) ranged between 48-65%, between while the nutrients removal was in the range of 70% to 90%. Fecal coliforms dropped by three to four orders of magnitude from their initial concentration, but this steel does not meet current regulations for unlimited irrigation. Hence further improvement procedures are suggested.

Keywords: constructed wetland, greywater treatment, nutriments, organics

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Authors: O. M. Omar, G. D. Abd Elhameed, A. M. Heniegal, H. A. Mohamadien

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Green concrete are generally composed of recycling materials as hundred or partial percent substitutes for aggregate, cement, and admixture in concrete. To reduce greenhouse gas emissions, efforts are needed to develop environmentally friendly construction materials. Using of fly ash based geopolymer as an alternative binder can help reduce CO2 emission of concrete. The binder of geopolymer concrete is different from the ordinary Portland cement concrete. Geopolymer Concrete specimens were prepared with different concentration of NaOH solution M10, M14, and, M16 and cured at 60 ºC in duration of 24 hours and 8 hours, in addition to the curing in direct sunlight. Thus, it is necessary to study the effects of the geopolymer binder on the behavior of concrete. Concrete is made by using geopolymer technology is environmental friendly and could be considered as part of the sustainable development. In this study the Local Alkaline Activator in Egypt and dolomite as coarse aggregate in fly ash based-geopolymer concrete was investigated. This paper illustrates the development of mechanical properties. Since the gained compressive strength for geopolymer concrete at 28 days was in the range of 22.5MPa – 43.9MPa.

Keywords: geopolymer, molarity, sodium hydroxide, sodium silicate

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Authors: Suhaib Salahuddin Alzubair Suliman

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This paper examines the mechanical strength of different binders including pure ordinary Portland cement (OPC) and others having OPC supplemented by two maximum sizes of waste glass powder (GP) of 75-μm and 150μm. Chemical analysis of the GPs using PCEDX test analysis has revealed it silica (SiO2 ) content % is 86.883 and Calcium oxide (CaO) is 12.203%while there are traces of other impurities . Furthermore, the specific gravity of GP was measured. The experiments have been conducted on 63 specimens mortar made with standard sand with 20%,25%, and 30% of GP levels of substituting OPC. The specimens are tested at 3, 7 and 28 days for compressive strength and flexural strength. The specimens made with maximum GP size of 75-μm have outperformed the control OPC mortar at 28 days test age than size 150-μm at various replacement levels. In addition to that, the mechanical strengths were evaluated compressive strength and flexural strength tests were conducted for GPs. The findings from this study indicated that the mortars modified with GP 75μm and replacement ratio of 20% showed an improvement in compressive strength and flexural strength compared to the control mortar at the 28 days of curing with significant development between 7 and 28 days. Mortar with GP size 75-μm containing 30% & 20% replacement of cement have exhibited the highest flexural strength among all mortar mixtures. The improvement in the mechanical strength of the mortars modified with GP can be attributed to the pozzolanic property of GPs, which leads to a more densified microstructure and improved interfacial bonding between sand and cement paste matrix in mortars.

Keywords: glass powder, pozzolana, compressive strength, flexural strength, mortar

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Authors: Chukwuebuka Vincent Azuka, Chidimma Peace Odoh

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Changes in agricultural practices and land use influence the storage and release of soil organic carbon and soil structural dynamics. To investigate this in Nsukka, southeastern Nigeria, soil samples were collected at 0-10 cm, 10-20 cm and 20-30 cm from three locations; Ovoko (OV), Obukpa (OB) and University of Nigeria, Nsukka (UNN) and three land use types; cultivated land (CL), forest land (FL) and grassland (GL)). Data were subjected to analysis of variance (ANOVA) using SPSS. Also, correlations between organic carbon stock, structural stability indices and other soil properties were established. The result showed that Ksat was significantly (p < 0.05) influenced by location with mean values of 68 cmhr⁻¹,121.63 cmhr⁻¹, 8.42 cmhr⁻¹ in OV, OB and UNN respectively. The MWD and aggregate stability (AS) were significantly (p < 0.05) influenced by land use and depth. The mean values of MWD are 0.85 (CL), 1.35 (FL) and 1.45 (GL), and 1.66 at 0-10 cm, 1.08 at 10-20 cm and 0.88 mm at 20-30 cm. The mean values of AS are; 27.66% (CL), 46.39% (FL) and 49.81% (GL), and 53.96% at 0-10cm, 40.22% at 10-20cm and 29.57% at 20-30cm. Clay flocculation (CFI) and dispersion indices (CDI) differed significantly (p < 0.05) among the land use. Soil pH differed significantly (p < 0.05) across the land use and locations with mean values ranging from 3.90-6.14. Soil organic carbon (SOC) significantly (p < 0.05) differed across locations and depths. SOC decreases as depth increases depth with mean values of 15.6 gkg⁻¹, 10.1 gkg⁻¹, and 8.6 gkg⁻¹ at 0-10 cm, 10-20 cm, and 20-30 cm respectively. SOC in the three land use was 8.8 g kg-1, 15.2 gkg⁻¹ and 10.4 gkg⁻¹ at CL, FL, and GL respectively. The highest aggregate-associated carbon was recorded in 0.5 mm across the land use and depth except in cultivated land and at 20-30 cm which recorded their highest SOC at 1mm. SOC stock, total nitrogen (TN) and CEC were significantly (p < 0.05) different across the locations with highest values of 23.43 t/ha, 0.07g/kg and 14.27 Cmol/kg respectively recorded in UNN. SOC stock was significantly (p < 0.05) influenced by depth as follows; 0-10>10-20>20-30 cm. TN was low with mean values ranging from 0.03-0.07 across the locations, land use and depths. The mean values of CEC ranged from 9.96-14.27 Cmol kg⁻¹ across the locations and land use. SOC stock showed correlation with silt, coarse sand, N and CEC (r = 0.40*, -0.39*, -0.65** and 0.64** respectively. AS showed correlation with BD, Ksat, pH in water and KCl, and SOC (r = -0.42*, 0.54**, -0.44*, -0.45* and 0.49** respectively. Thus, land use and location play a significant role in sustainable management of soil resources.

Keywords: agricultural practices, structural dynamics, sequestration, soil resources, management

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Authors: A. Umar, A. Tamimi

Abstract:

Development of new types of concrete with improved performance is a very important issue for the whole building industry. The development is based on the optimization of the concrete mix design, with an emphasis not only on the workability and mechanical properties but also to the durability and the reliability of the concrete structure in general. Self-compacting concrete (SCC) is a high-performance material designed to flow into formwork under its own weight and without the aid of mechanical vibration. At the same time it is cohesive enough to fill spaces of almost any size and shape without segregation or bleeding. Construction time is shorter and production of SCC is environmentally friendly (no noise, no vibration). Furthermore, SCC produces a good surface finish. Despite these advantages, SCC has not gained much local acceptance though it has been promoted in the Middle East for the last ten to twelve years. The reluctance in utilizing the advantages of SCC, in Bahrain, may be due to lack of research or published data pertaining to locally produced SCC. Therefore, there is a need to conduct studies on SCC using locally available material supplies. From the literature, it has been observed that the use of viscosity modifying admixtures (VMA), micro silica and glass fibers have proved to be very effective in stabilizing the rheological properties and the strength of fresh and hardened properties of self-compacting concrete (SCC). Therefore, in the present study, it is proposed to carry out investigations of SCC with combinations of various dosages of VMAs with and without micro silica and glass fibers and to study their influence on the properties of fresh and hardened concrete.

Keywords: self-compacting concrete, viscosity modifying admixture, micro silica, glass fibers

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Authors: Yogesh S. Patel

Abstract:

Novel polyimides were synthesized by Diels–Alder polymerization. Bisfuran was reacted with a couple of bismaleimides containing diglycidyl ether of bisphenol-A and F (epoxy) segment to obtain Diels–Alder polyadducts. Polyadducts were then aromatized and imidized (i.e. cyclized) through carboxylic and amide groups to afford polyimides. Synthesized polyadducts and polyimides were characterized by elemental analysis, spectral features, the number of average molecular weight (Mn) and thermal analysis. The ‘in situ’ glass fiber reinforced composites were prepared and characterized by mechanical, electrical, and chemical properties. These properties were compared with the other reported polyimides. All the composites showed good mechanical and electrical properties and good resistance to organic solvents and mineral acids.

Keywords: Diels-Alder reaction, bisfuran, bismaleimides, polyimide

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Authors: Innocent Kafodya, Guijun Xian

Abstract:

This paper presents effects of distilled water, seawater and sustained bending strains of 30% and 50% ultimate strain at room temperature, on the durability of unidirectional pultruded carbon fiber reinforced polymer (CFRP) plates. In this study, dynamic mechanical analyzer (DMA) was used to investigate the synergic effects of the immersions and bending strains on the visco-elastic properties of (CFRP) such as storage modulus, tan delta and glass transition temperature. The study reveals that the storage modulus and glass transition temperature increase while tan delta peak decreases in the initial stage of both immersions due to the progression of curing. The storage modulus and Tg subsequently decrease and tan delta increases due to the matrix plasticization. The blister induced damages in the unstrained seawater samples enhance water uptake and cause more serious degradation of Tg and storage modulus than in water immersion. Increasing sustained bending decreases Tg and storage modulus in a long run for both immersions due to resin matrix cracking and debonding. The combined effects of immersions and strains are not clearly reflected due to the statistical effects of DMA sample sizes and competing processes of molecular reorientation and postcuring.

Keywords: pultruded CFRP plate, bending strain, glass transition temperature, storage modulus, tan delta

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Authors: Selin Kunc, Srinivas Koushik Gundimeda, John A. Gallagher, Roselita Fragoudakis

Abstract:

This study investigates the behavior of Glass Fiber Reinforced Plastic (GFRP) laminated beams additionally reinforced with piezoelectric fibers. The electromechanical behavior of piezoelectric materials coupled with high strength/low weight GFRP laminated beams can have significant application in a wide range of industries. Energy scavenging through mechanical vibrations is the focus of this study, and possible applications can be seen in the automotive industry. This study examines the behavior of such composite laminates using Classical Lamination Theory (CLT) under three-point bending conditions. Fiber orientation is optimized for the desired stiffness and deflection that yield maximum energy output. Finite element models using ABAQUS/CAE are verified through experimental testing. The optimum stacking sequences examined are [0o]s, [ 0/45o]s, and [45/-45o]s. Results show the superiority of the stacking sequence [0/45o]s, providing higher strength at a lower weight, and maximum energy output. Furthermore, laminated GFRP beams additionally reinforced with piezoelectric fibers can be used under bending to not only replace metallic component while providing similar strength at a lower weight but also provide an energy output.

Keywords: classical lamination theory (CLT), energy scavenging, glass fiber reinforced plastics (GFRP), piezoelectric fibers

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Authors: T. D. Gunneswara Rao, Mudimby Andal

Abstract:

Research on the utilization of fly ash will no longer refer the fly ash as a waste material of thermal power plants. Use of fly ash in concrete making, makes the concrete economical as well as durable. The fly ash is being added to the concrete in three ways namely, as partial replacement to cement, partial replacement to fine aggregates and admixture. Addition of fly ash to the concrete in each one of the form mentioned above, makes the concrete more workable and durable than the conventional concrete. Studies on fly ash as partial replacement to cement gained momentum as such replacement makes the concrete economical. In the present study, an attempt has been made to understand the effects of fly ash on the workability characteristics and strength aspects of fly ash concretes. In India, major number of thermal power plants are producing low calcium fly ash. Hence, in the present investigation, low calcium fly ash has been used. Fly ash in concrete was considered for the partial replacement of cement. The percentage replacement of cement by fly ash varied from 0% to 40% at regular intervals of 10%. Moreover the fine aggregate to coarse aggregate ratio also has been varied as 1:1, 1:2, and 1:3. The workability tests revealed that up to 30% replacement of cement by fly ash in concrete mixes water demand for reduces and beyond 30% replacement of cement by fly ash demanded more water content for constant workability.

Keywords: cementing efficiency, compressive strength, low calcium fly ash, workability

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Authors: A. Sivakumar, K. Srinivasan

Abstract:

The main objective of the study is focused in producing slag based geopolymer concrete obtained with the addition of alkali activator. Test results indicated that the reaction of silicates in slag is based on the reaction potential of sodium hydroxide and the formation of alumino-silicates. The study also comprises on the evaluation of the efficiency of polymer reaction in terms of the strength gain properties for different geopolymer mixtures. Geopolymer mixture proportions were designed for different binder to total aggregate ratio (0.3 & 0.45) and fine to coarse aggregate ratio (0.4 & 0.8). Geopolymer concrete specimens casted with normal curing conditions reported a maximum 28 days compressive strength of 54.75 MPa. The addition of glued steel fibres at 1.0% Vf in geopolymer concrete showed reasonable improvements on the compressive strength, split tensile strength and flexural properties of different geopolymer mixtures. Further, comparative assessment was made for different geopolymer mixtures and the reinforcing effects of steel fibres were investigated in different concrete matrix.

Keywords: accelerators, alkali activators, geopolymer, hot air oven curing, polypropylene fibres, slag, steam curing, steel fibres

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Authors: Shams Ul Khaliq, Mushtaq Zeb, Fawad Bilal, Faizan Akbar, Syed Aamir Abbas

Abstract:

Self Compacting Concrete as the name implies--is the concrete requiring a very little or no vibration to fill the form homogeneously. Self Compacting Concrete (SCC) is defined by two primary properties: Ability to flow or deform under its own weight (with or without obstructions) and the ability to remain homogeneous while doing so. Flow ability is achieved by utilizing high range water reducing admixtures and segregation resistance is ensured by introducing a chemical viscosity modifying admixture (VMA) or increasing the amount of fines in the concrete. The study explores the use waste marble dust (WMD) to increase the amount of fines and hence achieve self-compatibility in an economical way, suitable for Pakistani construction industry. The study focuses on comparison of fresh properties of SCC containing varying amounts of waste marble dust (WMD) with that containing commercially available viscosity modifying admixture. The comparison is done at different dosages of super plasticizer keeping cement, water, coarse aggregate, and fine aggregate contents constant.

Keywords: self compacting concrete, waste marble dust (WMD), flow ability, segregation resistance

Procedia PDF Downloads 328