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Terzic A.,Serbian Institute for Testing of Materials IMS | Pezo L.,University of Belgrade | Andric L.,Serbian Institute for Technology of Nuclear and Other Mineral Raw Materials
Composites Part B: Engineering | Year: 2017

Natural zeolites of clinoptilolite type from seven deposits were submitted to mechano-chemical activation in a Retsch ultra-centrifugal mill. The zeolite types and activation parameters were altered during the experiment with an aim to determine the optimal combination that would produce powder with adequate physico-chemical and microstructural properties for application as a binder replacement and an ion-exchanger in the construction composites. The effects of input variables (chemical composition of the samples) and process parameters (the rotor velocity and the activation period) on the efficiency of zeolite activation were investigated in terms of dependent parameters such as: specific surface area, grain size distribution, cation exchange capacity, melting point, compression strength, shrinking, water absorption and apparent porosity. Cluster analysis, Principal component analysis and Standard score analysis were applied in the assessment of the acquired product quality. Artificial neural networks (ANN) were developed in mathematical modeling of observed responses. Subsequently the ANN was compared to experimental results and the developed second order polynomial models. Developed models showed r2 values in the 0.822–0.998 range, meaning that they were able to predict the observed responses in a wide range of processing parameters. ANN models performed high prediction accuracy (0.975–0.993) and can be considered as precise and very useful for response variables prediction. The combination of the conducted mathematical analyses isolated Z5 zeolite as a preferable type, and 20000 rpm and 30 min as an optimal activation set of parameters. Mathematically derived conclusions were confirmed by results of instrumental analyses (XRD, DTA/TG, SEM). © 2016 Elsevier Ltd

Arsenovic M.,Serbian Institute for Testing of Materials IMS | Pezo L.,University of Belgrade | Mancic L.,Serbian Academy of Science and Arts | Radojevic Z.,Serbian Institute for Testing of Materials IMS
Thermochimica Acta | Year: 2014

This paper describes a study of 11 selected samples of loess soil from Serbia, by using differential scanning calorimetry, simultaneously with thermogravimetry and its differential calculation, known as simultaneous thermal analysis (STA). This survey is supplemented by chemical and mineralogical analysis, particle size distribution, and plasticity and drying susceptibility tests. Correlation analysis of major oxides content and certain technological test results were used for better understanding of the raw material composition and product physical properties. The results indicate that the samples were rich in carbonates, with the highest content of alevrite fraction and variable content of clay-sized particles. Mineralogical analysis confirms significant correlations between major oxides content and reveals that the most common non-clay mineral present is quartz, followed by calcite, dolomite and sodium feldspar. Major clay minerals include illite, chlorite, smectite and, in some cases, low quantities of kaolinite. Although STA method is well-known, this is the first time that it was used for discussion about its practical aspect, for characterization of the loess deposits, in terms of exploitation in brick industry. © 2014 Elsevier B.V.

Arsenovic M.,Serbian Institute for Testing of Materials IMS | Stankovic S.,University of Belgrade | Pezo L.,University of Belgrade | Mancic L.,Serbian Academy of Science and Arts | Radojevic Z.,Serbian Institute for Testing of Materials IMS
Ceramics International | Year: 2013

Loess clays are commonly used to produce bricks. Heavy clays, taken at location near Zrenjanin, Serbia, are used as a representative raw material in this study. The sample, containing about 28% of clay sized particles, is enriched using two more plastic heavy clays from neighboring locations. Chemical and mineralogical content of clays is determined, as well as particle size distribution. Optimization of the processing parameters during the bricks production, i. e. temperature (900-1100 °C), and concentration of 2 clays combined addition (both in the range of 0-10%), is done based on the following independent parameters: compressive strength (CS), water absorption (WA), firing shrinkage (FS), weight loss during firing (WLF) and apparent density expressed as volume mass of cubes (VMC). Developed models showed r2 values in the range of 0.822-0.998, and they were able to accurately predict CS, WA, FS, WLF and VMC in a wide range of processing parameters. The optimum conditions are determined by the response surface method (RSM), coupled with the fuzzy synthetic evaluation (FSE) algorithm, using membership trapezoidal function, with defined optimal interval values, depending on a final usage of the raw material in heavy clay brick industry. © 2012 Elsevier Ltd and Techna Group S.r.l.

Arsic M.,Serbian Institute for Testing of Materials IMS | Bosnjak S.,University of Belgrade | Zrnic N.,University of Belgrade | Sedmak A.,University of Belgrade | Gnjatovic N.,University of Belgrade
Engineering Failure Analysis | Year: 2011

Cracks in the welded joints on the bucket wheel (BW) body of the bucket wheel excavator (BWE) SRs 1300 were discovered after merely 1800 h of operation. Investigations are carried out in order to detect the causes of cracks occurrence and thus prevent possible heavy damages to the machine.Working stresses in the BW body are defined by using FEM. Methods of strain gauges are used for the experimental stress analysis in real working conditions. Measurements of welding residual stresses are carried out by applying the centre hole drilling method. Additionally, experimental investigations defined the chemical composition, tensile properties, hardness, impact toughness, as well as the susceptibility to cracking (measurement of residual hydrogen, FISCO, Tekken and CTS methods).External loads induced by the resistance-to-excavation are determined by following a model that encompasses all relevant structural parameters and also the BWE duty cycle parameters. By using FEM, it was identified that the maximum values of equivalent stress in the zones of cracks occurrence are lower than the allowable values. This conclusion is confirmed by measurements. The measured values of welding residual stresses reach the value of yield strength in critical zones. Non-compliances during grooving (clearance in the root is substantially larger than the prescribed one) caused large filler material deposition and heat input. Such welded joints are susceptible to cold cracking.Based on the results of the numerical-experimental analysis, findings show that in critical zones the combination of working (dynamic) and residual (static) stress can be above the limit lines of modified Goodman's diagrams i.e. that the fatigue safety of the BW body structure was insufficient. © 2010 Elsevier Ltd.

Pezo L.,University of Belgrade | Arsenovic M.,Serbian Institute for Testing of Materials IMS | Radojevic Z.,Serbian Institute for Testing of Materials IMS
Ceramics International | Year: 2014

Mineralogical composition of heavy clays is one of the most important properties when stadying raw materials in brick industry. Within this study, quantitative determination of minerals using LPNORM calculation was performed, using the first algorithm among the so-called norms that allows the introduction of a list of minerals and their configuration. This algorithm is implemented for the first time in practice, in order to calculate the minerals content in brick raw materials. The influence of minerals quantity, along with the firing temperature (800-1100 °C), and several shape formats of laboratory brick samples were investigated, and the acquired data were used to build Artificial Neural Network (ANN) model. ANN model was developed in order to predict the final products parameters, and its results have been afterwards compared to experimental data. ANN model, coupled with sensitivity analysis, was obtained with high prediction accuracy, according to coefficient of determination, r 2: 0.880-0.884 in compressive strength calculation, 0.954-0.960 for water absorption, 0.869 for firing shrinkage, 0.979-0.984 for water loss during firing and 0.907 for volume mass of cubes model. © 2014 Elsevier Ltd and Techna Group S.r.l.

Arsenovic M.,Serbian Institute for Testing of Materials IMS | Pezo L.,University of Belgrade | Stankovic S.,University of Belgrade | Radojevic Z.,Serbian Institute for Testing of Materials IMS
Ceramics International | Year: 2013

Compressive strength and water absorption of fired heavy clay products varies with firing temperatures, but not entirely according to linear function, as it is mostly reported in literature. Also, differential thermo-gravimetric curve shows many turnovers in all the samples tested, within observed temperature range (820-920 °C). The aim of this research was to find a cause for such behaviour. Except derivative weight (DW), compressive strength (CS) and water absorption (WA) are chosen as outputs that represent properties of the fired samples. These parameters can be calculated using second order polynomial models (SOPs), on the basis of content of major oxides and firing temperature, as shown in our previous research. Sensitivity analysis was used as the effective approach in testing changes observed in the SOP outputs, due to the variation of content of major oxides for +1% or -1% of their nominal value. This study reveals in more detail the most significant influence of inputs (SiO 2, Al2O3, Fe2O3 and CaO content) over the outputs (DW, CS and WA) in every observed firing temperature. Addition or lowering of content of major oxides can both increase and decrease all the observed outputs, as revealed using sensitivity analysis. © 2013 Elsevier Ltd and Techna Group S.r.l.

Vasic M.,Serbian Institute for Testing of Materials IMS | Grbavcic Z.,University of Belgrade | Radojevic Z.,Serbian Institute for Testing of Materials IMS
Drying Technology | Year: 2014

The description of the drying process was reduced to the establishment of a series of theoretical and empirical drying models. The complex processes of simultaneous moisture and heat transfer, which are often nonstationary, and the distinct nature and properties of the material to be dried further complicate the description of the drying process. Three theories-diffusion theory, capillary flow theory, and evaporation-condensation theory-have won general recognition for the explanation of moisture transfer in porous media. The mechanisms of moisture movement during drying in the constant and especially in the falling drying period are rather complex and, hitherto, there have been no generally accepted explanations that could identify the exact transition between possible drying mechanisms, such as liquid movement due to capillary forces, liquid diffusion due to concentration gradients, liquid and vapor flow due to differences in total pressure, vapor diffusion due to difference in vapor concentration, vapor diffusion due to partial vapor pressure gradients, Knudsen diffusion, thermodiffusion, and the evaporation-condensation mechanism. The goal of this study was to find a way to better understand the different drying mechanisms, to identify the exact transition between them, and to estimate the time-dependent effective diffusivity. The results presented in this article confirmed that the effective diffusivity represents an overall mass transport property of moisture that includes all possible moisture transport mechanisms that are simultaneously controlling the moisture migration process in a material during drying. The experimental investigations were performed on clay tiles in a laboratory recirculation dryer, for which the drying parameters (humidity, temperature, and velocity) could be programmed, controlled, and monitored during drying. © 2014 Taylor & Francis Group, LLC.

Vasic M.,Serbian Institute for Testing of Materials IMS | Grbavcic T.,University of Belgrade | Radojevic Z.,Serbian Institute for Testing of Materials IMS
Chemical Engineering and Processing: Process Intensification | Year: 2014

Drying plays an important role in the production of clay tiles. In the present article, drying process is analyzed taking experimental data for several masonry clays obtained from different clay tile manufacturers and published data for different clay slabs. Calculation methods and computer programs designed for the calculation of the effective diffusion coefficient are developed. The first calculation method represents the analytical solution of the Crank equation, while the second one represents the analytical solution of the Efremov equation with boundary conditions in the form of the flux. Unlike other materials, clay tiles exhibit shrinkage during the drying process. For this reason, a shrinkage correction is included in both calculation methods. Four models (A1, A2, B1 and B2) for predicting the drying behavior are obtained as the result of the calculation cited programs. It is shown that the calculated effective diffusion coefficient determined by the designed computer programs, using experimentally obtained and selected published data sets have similar values to those of the same coefficient reported in the literature. Based on the mathematically determined prognostic values of the effective diffusion coefficient, it was concluded that there is more than 90% agreement between the experimentally recorded and the calculated drying curves. © 2013 Elsevier B.V.

Arsenovic M.,Serbian Institute for Testing of Materials IMS | Radojevic Z.,Serbian Institute for Testing of Materials IMS | Stankovic S.,University of Belgrade
Construction and Building Materials | Year: 2012

The aim of this study was to test utilization possibilities of industrial sludge in masonry industry, as well as risk of toxic elements leaching potential. Sludge is generated in a hot-dip galvanizing process after waste water neutralization. This waste is considered to be hazardous due to the presence of toxic elements, which can be fixed within heavy clay matrix after thermal treatment. Relatively large amounts of toxic metals were found in used raw materials, but their leachability reduces to a negligible level after firing at 1020 °C. The results show that sludge can be used to produce eco-friendly bricks. © 2012 Elsevier Ltd. All rights reserved.

Savkovic M.,University of Kragujevac | Gasic M.,University of Kragujevac | Arsic M.,Serbian Institute for Testing of Materials IMS | Petrovic R.,University of Kragujevac
Engineering Failure Analysis | Year: 2011

The common design of the bucket wheel drive mechanism in some bucket wheel excavators (BWE) consists of a gearbox and a hollow shaft, while the bucket wheel is supported by the axle passing through the hollow shaft. Improper maintenance and inadequate elimination of axis misalignment of the hollow shaft and the bucket wheel axle are the main causes of excavator failure and axle fracture. The paper examines the causes of bucket wheel axle fractures.Experimental testing of the chemical composition and mechanical properties of the material used to make the bucket wheel axle and metallographic inspections of the fracture surfaces in the bucket wheel axle by means of electronic and light microscope carried out in the first part of the paper have shown that there are no significant inhomogeneities and errors in the material of the axle.The second part of the paper presents the FEM analysis of influences of disturbances on the manner of support of the bucket wheel axle on the fracture. It shows that the negative influences of support of the axle reflected through the increase in the stress concentration and occurence of the initial crack are the main causes of the axle fracture. © 2010 Elsevier Ltd.

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