Search results

Filters

  • Journals
  • Keywords
  • Date

Search results

Number of results: 17
items per page: 25 50 75
Sort by:

Abstract

One of the main threats to constructions made from rammed earth is destruction due to exposure to water. The way to limit this dangerous phenomenon is to supplement the local soil mixtures with stabilizing agents. The main component used is Portland cement. This article analyses the results of research which focused on the resistance of rammed earth to water erosion. Because of the lack of national standards regarding the method of examining the durability of rammed earth, the research was based on the New Zealand standard NZS 4298: 1998. The results confirm the possibility of using rammed earth stabilized by cement in a temperate climate.
Go to article

Abstract

Concrete is generally produced using materials such as crushed stone and river sand to the extent of about 80‒90% combined with cement and water. These materials are quarried from natural sources. Their depletion will cause strain on the environment. To prevent this, bottom ash produced at thermal power plants by burning of coal has been utilized in this investigation into making concrete. The experimental investigation presents the development of concrete containing lignite coal bottom ash as fine aggregate in various percentages of 25, 50, and 100. Compressive, split tensile, and flexural strength as part of mechanical properties; acid, sulphate attack, and sustainability under elevated temperature as part of durability properties, were determined. These properties were compared with that of normal concrete. It was concluded from this investigation that bottom ash to an extent of 25% can be substituted in place of river sand in the production of concrete.
Go to article

Abstract

Self-curing concrete SC is a concrete type that can be cured without using any external curing regimes. It can perform by several methods such as using lightweight aggregate or chemical agents. In this research chemical curing agent is used to produce SC. This paper reports the results of a research study conducted to evaluate the effect of sulfates on the performance of self-curing concrete compared to ordinary concrete. Samples are immersed in sodium sulfate Na2S04 solution of 4% concentration. Results are measured in terms of compressive strength, tensile strength, flexural strength and mass loss. It was found that the rate of strength loss is noticed at ordinary concrete compared to SC concrete. Sulfate resistance is improved when using self-curing concrete. This improvement appears to be dependent on using a chemical curing agent.
Go to article

Abstract

The present paper is comparing the results of research studies carried out for three road acoustic screens of different design and different number of damping layers. For the tests, we selected timber or steel screens with a traditional multilayer structure and also one innovative type of simplified design. With respect to particular panels, their sound absorption properties were investigated in the reverberation chamber after they had been subjected to simulated weathering. In the process, two screens were subjected to the aging tests of 50–500 cycles in a special climatic chamber, and the innovative screens were subjected to 1000 cycles. The procedure was repeated every 50 or 100 cycles in order to obtain the changes of acoustic characteristics. The changes taking place in the absorbing material were also investigated with the use of scanning electron microscopy method (SEM). Basing on the obtained results and on the statistical analysis, the capability to maintain acoustic properties by the panels during their service life in natural conditions was estimated. For that purpose, linear statistical models were worked out, which were then applied to estimate the value of the single number sound absorption coefficient after successive aging cycles as well as the predicted time periods of acoustic class changes.
Go to article

Abstract

The paper analyses the influence of seasonal temperature variations on fatigue strength of flexible and semi-rigid pavement structures chosen for KR4 traffic flow category. The durability of pavement determined assuming a yearly equivalent temperature of 10˚C and assuming season-dependent equivalent temperatures was compared. Durability of pavement was determined with the use of Asphalt Institute Method and French Method. Finite Element Method was applied in order to obtain the strain and stress states by the means of ANSYS Mechanical software. Obtained results indicate a considerable drop in pavement durability if seasonal temperature variations are considered (up to 64% for flexible pavements and up to 80% for semi-rigid pavements). Durability obtained by the French Method presents lower dependence on the analysed aspect.
Go to article

Abstract

The paper presents a description of the phenomena occurring on the surface of the forging dies. A detailed analysis was made of 24 pre-forging dies due to the most intensive wear in this operation. To compare the results, new tools were also analysed. The research described in the study showed that the most dangerous factor for the hot forging process analysed is thermal-mechanical fatigue, which causes small cracks, which in turn quickly leads to the formation of a crack network on the entire contact surface of the tool with forged material. The second phenomenon is the tempering of the surface of the material for a long-term temperature effect. The presence of hard iron oxides in the form of scale from forging material is the accompanying phenomenon that intensifies the processes of tool wear. The paper presents the results of the analysis of the presence of residual magnetic field for forging tools and the results of laboratory tests of wear processes of tool steels for hot work in the presence of a magnetic field and in the presence of scale.
Go to article

Abstract

The experimental material consisted of semi-finished products of high-grade, medium-carbon constructional steel with: manganese, chromium, nickel, molybdenum and boron. The experimental material consisted of steel products obtained in three metallurgical processes: electric and desulfurized (E), electric and desulfurized with argon-refined (EA) and oxygen converter with vacuum degassed of steel (KP). The production process involved two melting technologies: in a 140-ton basic arc furnace with desulphurisation and argon refining variants, and in a 100-ton oxygen converter. Billet samples were collected to analyze: relative volume of impurities, microstructure and fatigue tests. The samples were quenched and austenitized at a temperature of 880o C for 30 minutes. They were then cooled in water and tempered by holding the sections at a temperature of 200, 300, 400, 500 and 600o C for 120 minutes and air-cooled. Fatigue tests were performed with the use of a rotary bending machine at a frequency of 6000 cpm. The results were statistical processed and presented in graphic form. This paper discusses the results of microstructural analyses, the distribution of the relative volume of impurities in different size ranges, the fatigue strength characteristics of different production processes, the average number of sampledamaging cycles and the average values of the fatigue strength coefficient for various heat processing options.
Go to article

Abstract

The paper deals with evaluation of a 3D scanning method elaborated by the authors, by applying it to the analysis of the wear of forging tools. The 3D scanning method in the first place consists in the application of scanning to the analysis of changes in geometry of a forging tool by way of comparing the images of a worn tool with a CAD model or an image of a new tool. The method was evaluated in the context of the important measurement problems resulting from the extreme conditions present during the industrial hot forging processes. The method was used to evaluate wear of tools with an increasing wear degree, which made it possible to determine the wear characteristics in a function of the number of produced forgings. The following stage was the use it for a direct control of the quality and geometry changes of forging tools (without their disassembly) by way of a direct measurement of the geometry of periodically collected forgings (indirect method based on forgings). The final part of the study points to the advantages and disadvantages of the elaborated method as well as the potential directions of its further development.
Go to article

Abstract

The phase composition of the cement paste phase of concrete containing fly ash from circulating fluidized bed combustion (CFBC) was studied. The motivation was to broaden the knowledge concerning the microstructure and the durability of concrete containing new by-products from the power industry. Several air-entrained concrete mixes were designed with constant water to binder ratio and with substitution of a part of the cement by CFBC fly ash (20%, 30% or 40% by weight). X-ray diffraction tests and thermal analysis (DTG, DTA and TG) were performed on cement paste specimens taken from concrete either stored in water at 18° C or subjected to aggressive freeze-thaw cyclic action. The evaluation of the phase composition as a function of CFBC fly ash content revealed significant changes in portlandite content and only slight changes in the content of ettringite. The cyclic freeze-thaw exposure did not have any significant influence on the phase composition of concrete with and without the CFBC fly ash.
Go to article

Abstract

Bearings of three-bearing shafts are usually treated as ideally-rigid articulated supports. In literature, the reactions of supports and bending moments of multibearing shafts are calculated taking into consideration only shaft elasticity. In fact, also deformation is present in these bearings, and it changes the shaft bending line. The deformation thus influences distribution of bending moment and reaction of supports. It is the most important difference when comparing two-bearing with three-bearing shafts. Moreover, in most types of bearings, a reactive bending moment is the response of bearing to unparallel position of inner bearing rings in relation to outer rings, that is to the tilt angle. As a result, real loads of rolling elements differ from theoretical ones. The aim of the paper is to develop a method of calculating generalized loads in rolling bearings of a three-bearing shaft taking into consideration shaft deformation, deformations in bearings and reactive moments of bearings caused by tilt angle.
Go to article

Abstract

Commonly used computations of basic rating life of a bearing system are based on the ISO 281:1990 standard. These computations include dynamic load capacity of a given bearing, its effective load and average rotational speed, whereas they omit distribution of external load acting upon particular rolling parts depending, among other things, on: - displacement in bearing (displacements in three directions and declination in two planes), - slackness in bearings. The aim of the presented theoretical research is to solve a problem of fatigue life of a ball bearing taking into consideration displacement in bearing resulting from elasticity of a three-bearing shaft, elasticity of bearings and their internal slackness.
Go to article

Abstract

In the recent years a tendency for design of increasingly slender structures with the use of high performance concrete has been observed. Moreover, the use of high performance concrete in tunnel structures, subject to high loads with possibility of extreme loads occurrence such as fire, has an increasing significance. Presented studies aimed at improving high performance concrete properties in high temperature conditions (close to fire conditions) by aeration process, and determining high temperature impact on the concretes features related to their durability. In this paper it has been proven that it is possible to obtain high performance concretes resistant to high temperatures, and additionally that modification of the concrete mix with aerating additive does not result in deterioration of concrete properties when subject to water impact in various form.
Go to article

Abstract

Industrial utilization of fly ash from various kinds of fuel plays an important role in the envi-ronmentally clean and cost effective power production. The primary market for fly ash utilizationis as a pozzolanic addition in concrete production. The paper concerns the concretes containingfly ash called Fly Ash from Biomass (FAB) from co-combustion of hard coal and wood biomass(wood chips). Characterization of the fly ash was carried on by means of X-ray diffractometryand E-SEM/EDS analysis. The results of laboratory studies undertaken to evaluate the influence of FAB on concrete resistance to surface scaling due to cyclic freezing and thawing in the presenceof NaCl solution were presented. The tests were carried out for concretes containing up to 25% offly ash related to cement mass. Additionally, the microstructure of air-voids was described. It was concluded that the FAB has significant effect on concrete freeze/thaw durability. The re-placement of cement by fly ash from co-combustion progressively transformed the concrete mi-crostructure into less resistant against freeze/thaw cycles and excessive dosage (over 15%) maydangerously increase the scaling.
Go to article

Abstract

The objective of this investigation was comparing the penetration of chloride ions in ordinary and air-entrained concretes containing a waste material Fluidized Bed Combustion Fly Ash (FBCFA). All concretes were tested with 15% and 30% cement replacement by FBCFA, with the same water-binder ratio of 0.45. Two kinds of fly ash coming from fluid bed combustion in two power plants in Poland have been used. In this study the rapid chloride permeability test – Nordtest Method BUILD 492 method – was used. The microstructure of the concrete was analyzed on thin polished sections and the measurement of air voids sizes and their distribution, using digital image analysis, was carried on according to PN-EN 480-11:2008. Obtained results have shown a significant influence of partial cement replacement by FBCFA on the chloride ions movements in concrete. It has been found that this kind of addition reduced considerably the chloride ion penetration. The influence of air entrainment on the chloride diffusion coefficients was also measured and it was shown that application of air-entraining admixture for concretes with FBCFA reduce the chloride diffusion coefficient but it should be used with caution.
Go to article

Abstract

The study presents a durability analysis of dies used in the first operation of producing a valve-type forging from high nickel steel assigned to be applied in motor truck engines. The analyzed process of producing exhaust valves is realized in the forward extrusion technology and next through forging in closed dies. It is difficult to master, mainly due to the increased adhesion of the charge material (high nickel steel) to the tool’s substrate. The mean durability of tools made of tool steel W360, subjected to thermal treatment and nitriding, equals about 1000 forgings. In order to perform a thorough analysis, complex investigations were carried out, which included: a macroscopic analysis combined with laser scanning, numerical modelling by FEM, microstructural tests on a scanning electron microscopy and light microscopy (metallographic), as well as hardness tests. The preliminary results showed the presence of traces of abrasive wear, fatigue cracks as well as traces of adhesive wear and plastic deformation on the surface of the dies. Also, the effect of the forging material being stuck to the tool surface was observed, caused by the excessive friction in the forging’s contact with the tool and the presence of intermetallic phases in the nickel-chromium steel. The obtained results demonstrated numerous tool cracks, excessive friction, especially in the area of sectional reduction, as well as sticking of the forging material, which, with insufficient control of the tribological conditions, may be the cause of premature wear of the dies.
Go to article

Abstract

Optimum values of preload can be achieved in well-tried constructions and then applied in similar structures. For new structures, it is recommended to calculate the preload force and to test the correctness of calculation by means of experiments. In practice it may be necessary to introduce corrections, because not all real work parameters can be precisely known. Credibility of calculations depends, first of all, on the consistence between the assumptions concerning temperature conditions during work and elastic deformations of cooperating elements – first of all of a holder – and the real work conditions. The aim of the study is to determine how preload influences the work of a system of angular ball bearings, in relation to durability of bearing, moment of friction and rigidity of the bearing.
Go to article

Abstract

This paper presents the concept and modern technological approach to the fabrication of discrete, integrated and integral micropassives. The role of these components in modern electronic circuits is discussed too. The material, technological and constructional solutions and their relation with electrical and stability properties are analyzed in details for linear and nonlinear microresistors made and characterized at the Faculty of Microsystem Technology, Wrocław University of Technology.
Go to article

This page uses 'cookies'. Learn more