Civil Engineering and Materials

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Authors: Y.A. Minaev
Abstract: The thermodynamic analysis of a ceramic compound solubility was carried out for ceramic compounds which may be used for dispersion hardening of advanced nickel alloys. The thermodynamic description of stability conditions was completed for a disperse heterophase systems consists of metal melt – nanosize phases (NSP). For a thermodynamic criterion (К) of stability was selected the specific variation of a free energy of the process of a disperse system degradation (referred to change of unit of a surface phases contact). The analysis was executed in view of formation of thick and thin elastic wetting films and takes in account a disjoining pressure. The above definition of new thermodynamically rigorous criterions becomes physically real, if the isotherm of a disjoining pressure is measured. The derived criterions are simplified in the Young approximation. In this case the criterion are expressed through measurable interfacial performances - interfacial tension and wetting angles. The application of a stability condition gives a simple outcome: aggregation of NSP does not happen at a wetting angles ≤ 600. On a basis of own experimental data the evaluations are carried out for possibility of using of some compounds as exogenous modifiers of a nickel alloys. The example of dispersion hardening of high-temperature strength nickel alloy and improving its heat resisting properties is reduced.
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Authors: Dashnor Hoxha, Vladimir Nicolae Ungureanu, Naima Belayachi, Duc Phi Do, Jean Baptiste Thevard
Abstract: This paper presents results of hydromechanical characterization tests performed on some mortars used in eco-construction practice. Typically, such mortars could be found in buildings constructed following so called GREB technique that uses straw bales as structural and insulating elements in addition to a wood frame. The full experimental program includes thermal, mechanical and hydraulic – hygroscopic tests. Mechanical tests, including uniaxial compression test and three point bending test and hydraulic tests including water and vapor water permeability, retention curve and unsaturated water permeability have been performed on three earth-cement mortars with sawdust additive. Tests were performed in age of 7, 14, 28 and 120 days. For retention curve and so called relative permeability a simple method has been used based on measurements of masse variations of samples on a controlled humidity environment and an inverse problem approach. Using of sawdust improves hydraulic properties of these mortars but the early age strength of these mortars has to be improved by cement additives.
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Authors: Moaz H. Ali, Basim A. Khidhir, Bashir Mohamed
Abstract: Titanium (Ti-6Al-4V) alloy is a desirable material for the aircraft industry because of their excellent properties behaves of high specific strength, fracture resistant characteristics, lightweight and general corrosion resistance. This paper presents a study on a two-dimensional orthogonal cutting process by using a face-milling operation through ABAQUS/EXPLICIT finite-element software. Several tests were performed at various feed rates and cutting speeds while the depth of cut remains constant. The results led to the conclusion that the stress components at integration points (Von - Mises) and the equivalent strain (PEEQ) were increased with increasing the feed rate and cutting speed during the machining process.
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Authors: Rui Barbosa, Diogo Dias, Nuno Lapa, Benilde Mendes
Abstract: The main aim of this work was to assess the possibility of using biomass ashes as substitutes for cement and natural aggregates in concretes without compromising their mechanical and chemical properties. Thirteen concrete formulations were prepared with different percentages of bottom and fly ashes produced at a forest biomass power plant. These formulations were submitted to mechanical compressive strength assays, after 28, 60 and 90 days of maturation. The reference formulation F1 that was produced without biomass ashes and one formulation incorporating fly and bottom ashes, F4, were selected for further characterization. After 90 days of maturation, the selected formulations were submitted to the leaching test described in the European Standard EN12457-2 (L/S ratio of 10 L/kg, in a batch extraction cycle of 24h) by using two different leaching agents: a synthetic marine medium (ASPM medium) and a synthetic freshwater medium (ISO 6341 medium). The eluates produced were submitted to chemical characterization which comprised a set of metals (As, Sb, Se, Cu, Zn, Ba, Hg, Cd, Mo, Pb, Ni, Cr, Cr VI, Al, Fe, Mg, Na, K and Ca), pH, SO42-, F-, dissolved organic carbon, chlorides, phenolic compounds and total dissolved solids. The substitution of 10% cement by fly ashes has not promoted the reduction of the compressive strength of concrete. The new formulation F4 has presented emission levels of chemical species similar or even lower to those observed for the reference formulation F1.
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Authors: Brabha H. Nagaratnam, M.E. Rahman, M.A. Mannan
Abstract: The aim of this research is to investigate hardened state properties of Self Compacting Concrete (SCC) containing low calcium based fly ash. The mixtures were prepared using various proportions of Class F fly ash ranging from 0% to 30% cement replacement. Water to powder ratio is 0.38 – 0.39 and powder content was kept constant at 540 kg/m3. Properties investigated were strength properties (compressive strength and splitting tensile strength), and durability properties (complete immersion water absorption, apparent volume of permeable voids (AVPV), sorptivity, and RCIPT tests. These tests were done at various days. Results showed that fly ash replacement of up to 30% gave acceptable strength and durability properties for medium strength SCC.
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Authors: Vit Černý, Rostislav Drochytka, Jan Jandora
Abstract: Power supplying industry in the Czech Republic is still dependent on thermal power plants. Due to the on-going and completed renovation of the existing power plant units, it is expected that they will be serviceable for the following 30 years. It is therefore necessary to look for suitable use of the by-products of these plants. Using the energy by-products during construction of dikes is currently limited to creation of little protective dikes on unloading yards of fly ash stabilizers. Here we can take advantage of the binding abilities of the energy by-product to stabilize the unloading yards and protect the environment. This method is technologically less effective for constructions of anti-flood dikes. Therefore we use the soils from the vicinity of the building area. A suitable method of using fly ash in water building industry lies in repairs of existing earth dams by using fly-ash and clay grouting that increase homogeneity, stability and impermeability of the dam. This paper deals with laboratory verification of suitability of different types of fly-ash in the mixture with special sealing clay. It also deals with designing optimal recipes for "on-site" testing. Results of the tests clearly recommend classical fly ash as the most suitable raw material. On the other hand, the bedding ash marked is not suitable for this technology.
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Authors: Jitka Hroudová, Jiří Zach
Abstract: Thermal insulation systems of ETICS are now mostly solved in the building industry, whether in terms of insulating the structures, choices of materials and subsequent recycling after the end of their life period. From the environmental point of view and also in the perspective of sustainable development, it is essential to look for other suitable material bases which relate only to easily renewable sources of raw materials or to industrial wastes which have long been available in sufficient quantity and quality. It is important that production of the insulation systems is energetically efficient modest in terms of manufacturing facilities. The aim of this paper is to verify the possibility of using natural insulation materials for thermal insulation systems ETICS. This paper describes the results of studies of key properties of insulations based on industrial hemp and flax and the results of computational simulations of the behavior of these insulations incorporated in the real systems ETICS.
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Authors: S.F.A. Rafeeqi, S.U. Khan, N.S. Zafar, T. Ayub
Abstract: In this paper, behaviour of nine (09) RC beams (including two control beams) after unbonding and exposing flexural reinforcement has been studied which were intentionally designed and detailed to observe flexural and shear failure. Beams have been divided into three groups based on failure mode and unbounded and exposed reinforcement. Beams have been tested under two-point loading up to failure. Experimental results are compared in terms of beam behaviour with respect to flexural capacity and failure mode which revealed that the exposed reinforcement does not altered flexural capacity significantly and unbondedness positively influences shear strength; however, serviceability performance of beams with unbonded and exposed reinforcement is less.
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Authors: Šárka Keprdová, Jiří Bydžovský, Tomáš Melichar
Abstract: Cement-chip boards are building elements that combine the advantageous properties of wood and cement. It is this synergistic effect which determines the versatile use in the building industry. The boards can be used in any place where the favourable properties of this construction material can fully be appreciated. The disadvantage of the cement-chip boards remains in their relatively high price. Reduction of the price and possible improvement of physical and mechanical properties can be achieved by partial substitution of the raw materials. The basic ingredients of the cement-chip board include the binding material (cement) and filler (wood). The filling material may be partially replaced by secondary raw materials or completely replaced by other herbal sources, such as technical hemp. As the individual components mutually influence each other and, as their effects may not only be added up (additive effect), but also mutually reinforced (synergistic effect), it is not so easy to determine the optimal recipe as it may seem at first sight. This article deals with the use of technical hemp shives as a replacement of filling component of the cement-chip boards. To evaluate the possibility of future use of the boards in building structures, the physical and mechanical properties were monitored. Special emphasis was placed on tests of flexural strength, modulus of elasticity and volume weight. The mixture must meet the technical parameters related to the cement-chip boards.
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