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Geotehnički uslovi izgradnje nadvožnjaka "Balajnac" na autoputu E-80 deonica: Niš - Merošina
No full textU sklopu prve deonice autoputa E-80 Niš – Merošina, izgrađen je nadvožnjak u zoni sela Balajnac koji je oslonjen na tri stubna mesta na međusobnom rastojanju od oko 26 m. Svaki stub je fundiran na šipovima i to sa predloženim rasporedom od 2 šipa u grupi na međusobnom rastojanju od 3.6 m. U radu su na osnovu izvršenih geotehničkih istraživanja terena, analizirani rezultati nosivosti vertikalno opterećenog šipa prečnika 1.2 m i dužine šipa od L = 23 m. Analiza je izvršena primenom različitih metoda koristeći rezultate statičke i standardne penetracije, laboratorijskih ispitivanja tla kao i probnog opterećenja šipa.As part of the first section of the E-80 highway Niš - Merošina, an overbridge was built in the area of the village of Balajnac, which is supported by three piles at a distance of about 26 m. Each pillar is founded on piles with the proposed arrangement of 2 piles in a group at a distance of 3.6 m. Based on the geotechnical investigations of the terrain, the results of the bearing capacity of a vertically loaded pile with a diameter of 1.2 m and a pile length of L = 23 m were analyzed in the paper. The analysis was performed by applying different methods using the results of static and standard penetration test, laboratory soil tests as well as pile load test
Sustainable approach to raw clays for ceramic and refractory applications: insights from updated traditional ternary diagrams
No full textThe study analysed 93 samples from four Serbian clay deposits to determine their suitability for ceramics production. The samples were
mainly composed of illite and kaolinite. Ternary diagrams were used to classify the samples and evaluate their applicability. Winkler’s
diagrams, ternary graphs and mineralogical compositions were analysed. The results showed a broader area in these graphs than previously
determined for structural ceramics, as well as the potential of these clays for ceramic production. The study used dry-milled,
hydraulically semi-dry, pressed and fired samples to assess water absorption and flexural strength and statistical analysis to determine
the key parameters influencing final product quality, including that of refractory, wall and floor tiles. This paper evaluates the raw clay
materials’ applicability in ceramic production, promoting sustainable use through rapid initial tests, energy savings through dry milling
and ecologically sound principles through resource-efficient evaluation
Geopolymer Composites with Waste Materials Incorporation
No full textThis study investigates and critically evaluates the possibility of using various waste materials (e.g., ceramic tile powder, eggshell, Fe-slag, and fly ash) as a supplementary resource in the production of geopolymer composites, examining their physiochemical properties and bonding mechanisms. Since the late 1970s, researchers have been looking into geopolymers as a potential new class of aluminosilicate binders that could someday take the place of conventional structural materials based on cement. Principles of the Green Agenda and Circular Economy, as well as the call for a reduction in CO2 emissions, accelerated the search for a new sustainable bonding agent. Geopolymers are three-dimensional synthetic inorganic polymers that have amorphous or semi-amorphous crystal microstructures. In this paper, fly ash, which is known as a standard precursor for geopolymerization, was substituted with zeolite and bentonite in order to evaluate their proneness to alkali activation. Three composites have been prepared with different precursors: fly ash, zeolite, and bentonite. Particle size distributions of zeolite and bentonite were comparable to those of fly ash, which suggests that they can enhance densification, nucleation, and finally geopolymerization. Sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) solutions were used as alkaline activators. Biowaste (eggshell), construction and demolition waste (pulverized ceramic tiles), and industrial waste (Fe-slag) were added in the following quantities: 20%, 20%, and 10%. Thermally induced changes were analyzed by the DTA/DCS/TG method. Mineralogical phases were assessed via XRD. FTIR spectroscopy was employed in the assessment of the major reaction zones of Si-O and Al-O geopolymers. The microstructure was analyzed by means of scanning electron microscopy. Economically, the cost of employing raw materials is comparable to the cost of fly ash. Also, their environmental footprint is comparable, thereby making these composites a sustainable and cost-effective alternative. Notwithstanding, there is a necessity for further research on the mechanical performance and durability of these geopolymer composites
Effect of temperature treatments on microhardness of additively manufactured PETG
No full textThe specimens were made using an additive technology. Polyethylene terephthalate glycol
(PETG) filament was used as the primary material. Three series with nine different printing
specimens (different printing parameters) were made. The Vickers microhardness (HV) of all
specimens was tested. The temperature treatments of specimens were done in a mold with NaCl
powder (230°C, 30 min), and in a chamber at low temperature (-200 °C, 30 cycles). It was
observed that the HV values oscillated, depending on the printing parameters, temperature
treatment, and locations. The microhardness was slightly higher on the bottom surface of the
specimens than on the top surface. For untreated specimens, the average microhardness measured
on the top and bottom surfaces was between 10.2 and 12.6 HV. For specimens treated in mold
with NaCl powder, changes in geometry were observed, together with an increased
microhardness of 11.0 to 13.5 HV. The treatment in a chamber at low temperature induced a
decrease in microhardness, and the values were in the range of 9.0-9.5 HV. It is commonly
recognized that the microstructural alterations in amorphous polymers are directly correlated with
microhardness. In this connection, the basic idea is to show treatments that can significantly
improve/degrade the mechanical properties of this material in daily use
Influence of temperature and specimen orientation on the impact toughness of microalloyed steel
No full textNIOMOL 490 microalloyed steel, used for welded pressure vessels subjected to dynamic loads and operating at sub-zero temperatures, exhibits acceptable toughness. This paper presents the experimental analysis, which includes an impact toughness test. The analysis resulted in impact energy values and represents the first phase of a comprehensive investigation into behavior of NIOMOL 490 steel. the aim was to determine the effects of temperature and the effects of specimen orientation with respect to rolling direction on impact toughness and the relationship between its components
Mortar Research and Design – Preserving the Values of the Danube Limes in Serbia
No full textThe research project Mortar Design for Conservation - Danube Roman Frontier 2000 Years After (MoDeCo2000) explores Roman mortars of the former Danube Limes in Serbia. It aims to fill in some missing pieces of the puzzle about life in the Roman period in the border territory by examining the creation of fortifications, and public and residential buildings. Finally, the project designs tailor-made conservation mortar mixtures in accordance with these precious data. The project concept is based on the prevailing idea of modern architectural conservation, which requires a holistic approach, combining old building practice and new scientific knowledge about building constructions, technologies, and materials used in the Roman period in the mentioned territory, with the aim of giving science-based recommendations for future practical conservation
A Correlation Relating the Residual Strength Parameters to the Proportions of Clay Fractions and Plasticity Characteristics of Overburden Sediments from the Open-Pit Mine Drmno
No full textOne of the prerequisites for the safe exploitation of surface mines is the stability of the
working and final slopes of the mine. In order to ensure this, it is necessary to carry out detailed field
and laboratory geomechanical tests of the soil and, based on the obtained results, make calculations
related to stability analyses. The results obtained in this way are used for dimensioning the slope of
exploitation slopes (excavation). Landslides occur when the ultimate shear strength is reached, and
therefore, the adequate definition of shear strength parameters is one of the essential prerequisites
for successfully solving the stability problem. Unlike earlier tests in Serbia, when the residual
shear strength parameters were determined based on the usual conventional methods (direct shear
apparatus, triaxial apparatus), this time, in addition to the direct shear apparatus, a ring shear
apparatus was also chosen for testing. The paper shows the method of determining the residual shear
strength parameters of high plasticity gray clays and siltstones of roof sediments from open pit mine
Drmno, using direct and ring shear apparatus. The results show that the residual angle of internal
friction for gray clays obtained with the ring shear apparatus is 9.9–10.8◦, and for the siltstone, it
is 11.8–12.9◦, both of which are lower than the values obtained with the direct shear apparatus. In
addition, correlations between the residual parameters of soil shear resistance and some physical
indicators (plasticity index, clay content) are provided, showing high correlation coefficients. The
proposed correlations should be used only when time and financial constraints prevent the execution
of actual tests to determine residual shear strength, as concrete experimental procedures provide a
much more reliable assessment of the residual strength properties of the soil
Remaining life assessment of 1Cr-0.5Mo boiler steel by replica method
No full textA key ingredient in plant life extension is the remaining life assessment technology. Replication metallography is a Non-Destructive Evaluation (NDE) tool to assess the metallurgical degradation in high temperature components and further it can help in calculating the remaining life by Neubauer and Wedel classification method. Creep life assessment based on a simplified cavity classification is limited to the four different grades - i.e., isolated cavities, oriented cavities, linked cavities (microcracks), and macrocracks.
A steam boiler is responsible for the efficient and rapid production of steam from water This steam is then used to rotate turbines, generating electrical power. Boilers consist of various components such as tubes, pipes, headers, valves and they are exposed to high temperatures during operation. Materials widely used in boiler construction are carbon steels, low alloy steels and stainless steels. Due to prolonged exposure to high temperatures and pressures, the low alloy steel components undergo creep metallurgical deformation. Boiler tube failure is the main cause of forced shutdown of the boiler. Evaluation of microstructural evolution in exposed to service high-temperature materials is a key tool for a correct evaluation of material status and allowable service extension.
In this paper, test results are discussed for replication metallography carried out in high-temperature 1Cr-0.5Mo boiler steel. The operating parameters boiler are - pressure: 13,72 MPa and temperature: 540°C. Replication for metallographic examination was carried out at different spots of base & weld metal of boiler tubes. The microstructure developed on the boiler tubes was transferred to a thin film and preserved for laboratory microstructural analysis at higher magnification. The weld metal revealed the microstructure as undamaged degradation level, while the right/left base material revealed an "A" degradation level. The undamaged level of degradation microstructure of base metal is close to the original microstructure of ferrite and pearlitic structure. The microstructure of "A" level degradation consists of initial deformation of pearlite with pearlite colonies intact and some isolated cavities are also seen in the microstructure. Remaining life was calculated based on correlation between creep damage classification and expended life fraction for "A" degradation level. According to the recommendations formulated for the four cavitation grades, for class "A" damage, no remedial action would be required. Based on extensive observations on boiler components in power plants, the approximate time interval required for damage to progress from one stage to another under typical plant conditions can be estimated
The Mechanical Modeling of Thermomechanical Processes for Thin-Walled Cylinders
No full textThe problem of stress in perforated thin-walled cylinders due to
mechanical and thermal load was analyzed for cases where the load of the
system varies both along the cylinder circumference and axially. Starting
from the solution and considerations for a smooth thin-walled cylinder, the
concept was expanded and the distribution of deformations caused by
thermal loads on the cylinder and the resulting stresses in the structure of
the thin-walled perforated cylinder was observed for a specific form of
perforation.
The cylindrical perforated burner is one of the main elements of premixed
condensing boiler for home heating systems. The quality of combustion,
and thus the heat load on the outer sheath of the burner, largely depends
on the layout, shape and dimensions of the perforation.
This paper presents the mechanical modeling of thermomechanical
processes of a cylindrical gas burner with premixing for a triangular
layout or the so-called checkerboard shape of perforation