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Dusan B.,Serbian Institute for Materials Testing | Zoran B.,Highway Institute | Cebasek V.,University of Belgrade | Susic N.,Serbian Institute for Materials Testing
Engineering Geology | Year: 2014

Structural collapse and sudden volume changes represent a major geotechnical issue, particularly in loess soils. There are different criteria for assessing collapse potential based on laboratory test results, which require the collection of undisturbed samples from test pits. This can be a complicated and costly procedure, often financially unjustified for smaller projects. This paper presents the results of seismic dilatometer tests (SDMT) performed at a single location in a loess soil in Belgrade, in addition to the results of single oedometer collapse tests performed on high quality samples from test pits.After comparing laboratory test results it was possible to determine that in samples collected from boreholes, dry unit weight is approximately 20% higher than in block samples taken from test pits, while moisture content is between 1 and 4% higher. Unit weight estimated from DMT is on average 15% higher than the unit weight obtained from block samples.The constrained modulus (MDMT) determined by DMT are highly compatible with oedometer modulus (Eoed) obtained from samples at natural moisture content. This paper presents two possible ways of identifying collapsing loess based on intermediate DMT parameters and the ratio of G0/MDMT. The tests results indicate that if the ratio between the material index (ID) and the horizontal stress index (KD) is greater than 5, the danger of collapse is imminent. Simultaneous observation of the changes of ID and KD with depth on a semi-log graph in the same scale is recommended. In this way the relative distance between them may be clearly noticed; the larger the distance becomes, the greater the risk of collapse. In the collapsing loess ratio G0/MDMT is found to be higher than 21 for KD less than 0.6, while in non-collapsing loess G0/MDMT is less than 21 for higher values of KD. In terms of DMT, loess is considered as underconsolidated soil, which is one of the most common "definitions" of loess. © 2014 Elsevier B.V. All rights reserved.


Mitrovic A.,Serbian Institute for Materials Testing | Zdujic M.,Serbian Academy of Science and Arts
Journal of the Serbian Chemical Society | Year: 2013

Mechanochemical treatment of Serbian kaolin clay was performed in a planetary ball mill using two different milling media, hardened steel or zirconia vials and balls. The samples obtained after various milling times were characterized by particle size laser diffraction (PSLD), X-ray diffraction (XRD), differential scanning calorimetry/thermogravimetry (DTA/TGA) and Fouriertransform infrared (FTIR) analyses. The mechanochemical treatment induced amorphization of the kaolinite phase accompanied by dehydroxylation. It was found that for given milling parameters, amorphization mainly occurred in the milling period up to 15 min, and was completed after about 30 min of milling for both employed milling media. The pozzolanic activities were determined by the Chapelle method. Milling in the hardened steel milling medium had no significant influence on pozzolanic activity, even though there was accumulated iron contamination. For both milling media, a pozzolanic activity of 0.79 was obtained for the samples milled for 15 min and it remained almost unchanged with prolonged milling. The determined pozzolanic activity values were similar to those of commercial metakaolinite or metakaolinite obtained by calcination of the same clay, thereby, indicating that highly reactive pozzolana could be obtained by mechanochemical treatment of Serbian kaoline clay. Copyright (C)2013 SCS.


Bosnjak S.M.,University of Belgrade | Arsic M.A.,Serbian Institute for Materials Testing | Zrnic N.T.,University of Belgrade | Rakin M.P.,University of Belgrade | Pantelic M.P.,Kolubara Metal Ltd.
Engineering Failure Analysis | Year: 2011

The bucket wheel boom tie-rods are vital structural parts of the bucket wheel excavators (BWE). Their failures inevitably cause BWE collapse and are followed, among other things, by a substantial financial loss (millions of €). Non-destructive testing revealed a flaw in the butt welded joint of the body and eye-plate of the bucket wheel tie-rod. Its size exceeds the level allowed by current technical regulations. An integrity assessment of the bucket wheel tie-rod has been carried out, i.e. the remaining fatigue life has been determined based on the stress-state characteristics in the welded joint and defined by experimental research in real working conditions. The calculation results show that despite the excessive size of the internal flaw the welded joint integrity is not compromised. During periodical inspections of the welded joint in the past two years (BWE was put into operation in December 2007) changes that could compromise the structural integrity were not observed. In this way, by using a " fail-safe" philosophy design, a considerable financial saving (ca. 1,600,000 €) was achieved while at the same time there was no threat to the worker's safety and life, the safety of the machine and the production process in the open pit mine. © 2010 Elsevier Ltd.


Andric L.,Serbian Institute for Technology of Nuclear and Other Mineral Raw Materials | Terzic A.,Serbian Institute for Materials Testing | Acimovic-Pavlovic Z.,University of Belgrade | Pavlovic L.,Serbian Institute for Technology of Nuclear and Other Mineral Raw Materials | Petrov M.,Serbian Institute for Technology of Nuclear and Other Mineral Raw Materials
Composites Part B: Engineering | Year: 2014

Mica and talc have wide areas of application as a raw material in a number of industrial branches. Mechanically activated mica has specific applications such as: capacitors, insulators, and pearlescent pigments. Talc is widely used as either a basic raw material or as filler. This paper presents a comparative analysis of mechanically activated samples of mica and talc in ultra-centrifugal mechano-activator "Retsch ZM-1". The following mechano-activator parameters were variable: number of rotor revolutions (rpm); sieve mesh size (μm); current intensity (A). In addition, the following parameters were monitored: duration of mechanical activation, t (min); circumferential rotor speed, v (m/s); capacity of mechano-activator, Q (kg/h); and specific energy consumption, We (kW h/t). It was observed that effect of mechanical activation of mica and talc increased with an increase of the load and rotor revolution of ultra-centrifugal mechano-activator. Both mica and talc were successfully treated by mechanical activation procedure. In the processing of mica, mechanical activation is suggested to be applied as a post-treatment, and in the talc processing as a pre-treatment, as the high quality talc is obtained by means of hydrometallurgical concentration method. © 2013 Elsevier Ltd. All rights reserved.


Terzic A.,Serbian Institute for Materials Testing | Pezo L.,University of Belgrade | Andric L.,Serbian Institute for Technology of Nuclear and other Raw Mineral Materials
Ceramics International | Year: 2015

The differences in the set of the process parameters measured before and after mica mechanical activation and their influence on the grain size distribution related characteristics have been studied. The modification of the behavior for activated samples has been correlated to the particle size distribution effect produced by activation via an ultra centrifugal mill. The mechanical treatments are energetically and economically unsustainable procedures, therefore the mica activation was optimized on basis of assessment of the process variables effect on the final quality of product parameters. Response surface method, standard score analysis and principal component analysis were used as means of the optimization. Developed models showed r2 values in the range of 0.816-0.988 and they were able to accurately predict quality parameters in a wide range of processing parameters. Standard score analysis highlighted that the optimal sample was obtained using sieve mesh of 80 μm set of processing parameters (SS=0.81). Multiple comparison tests revealed that the optimal variation in the processing parameters could reduce the negative effect of mica samples inherent properties on the final score and improve activation procedure energetic and economic sustainability. © 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.


Terzic A.,Serbian Institute for Materials Testing | Andric L.,Serbian Institute of Technical Sciences | Mitic V.,Serbian Institute for Technology of Nuclear and other Raw Mineral Materials
Ceramics International | Year: 2014

A growing demand for refractory castables with advanced properties has given rise to a continuous technological evolution and highlighted the necessity for secondary raw materials reapplication even in refractory industry. For the experiment, refractory shotcretes with the same matrix composition were prepared from 30 wt% of high aluminate cement, 40 wt% of bauxite aggregate and 30 wt% of chamotte filler. The request for obtaining a low-cement castable is fulfilled by application of mechanically activated coal ash as microfiller in one of the bauxite shotcretes. The fly ash was activated by means of vibratory disc mill and ultra-centrifugal mill, and results were compared. The shotcrete samples were dried at 110 °C during 24 h to create specimens for investigation of mechanical and thermal properties. The properties have been studied at temperatures ranging from room temperature to adopted maximal temperature 1400 °C. At maximal 1400 °C, the bauxite shotcretes were mainly composed of anorthite, corundum, mullite and cristobalite. Mechanisms of hydration and sintering were investigated by means of differential thermal analysis (DTA) at three different heating rates. DTA measurements showed different activation energies for ordinary bauxite shotcrete and shotcrete with microfiller. The evolution of the refractory shotcretes properties was investigated and correlated with microstructural changes induced by temperature and microfiller addition. The combination of advantages in investigated refractory shotcretes makes them suitable for use in severe conditions at high temperature applications especially in refractory industries. © 2014 Elsevier Ltd and Techna Group S.r.l.


Terzic A.,Serbian Institute for Materials Testing | Pavlovic L.,Serbian Institute for Technology of Nuclear and other Raw Mineral Materials | Milicic L.,Serbian Institute for Materials Testing
International Journal of Coal Preparation and Utilization | Year: 2013

Utilization potential of fly ash, as the main residue in the lignite coal combustion in Serbian power plants, was investigated in present study. High production of fly ash represents extreme hazard for environment. Question of storage of this waste material is disclosed. Recycling and reapplication of fly ash in construction materials industry is only economic solution for ongoing problem. Fly ash can be used as a component in cement, mortar, concrete, bricks, and tiles. In this study, characterization of three different Serbian fly ash capacities was used as base for further fly ash utilization possibilities investigation. Investigation of fly ash mineralogical components as well as chemical composition analysis was emphasized. Macroperformance was correlated to the microstructure of fly ash studied by means of XRD and SEM analysis. Furthermore, thermal stability of crystalline phases, content of trace elements, physico-chemical characteristics, and leaching toxicity were tested. Highlight was placed on the determination of the influence of the fly ash grain-size and its microstructure on the performances of the fly-ash-based products. Comparison of Serbian fly ash properties with characteristics of foreign fly ashes led to the presumption that Serbian fly ash has equal if not better characteristics and that it can be reapplied in production of high-value products manufacturing worldwide. © 2013 Taylor and Francis Group, LLC.


Mitrovic A.A.,Serbian Institute for Materials Testing
AIP Conference Proceedings | Year: 2011

Pozzolans are supplementary materials added to Portland cement in order to increase the mechanical strength and durability of concrete structures. A number of thermal, mechanical and chemical methods have been used to activate the reactive potential of pozzolanic materials. The aim of the study is to obtain pozzolana, from Serbian kaolinite clay by mechanochemical treatment. Kaolinite clay Garaši was subjected to mechanical treatment during different times of milling. The changes were monitored using particle size distribution (PSD) analyses, thermal methods [thermogravimetric analysis (TGA), and differential thermal analysis (DTA)] and X-ray diffraction methods (XRD). The pozzolanic activity was determined using Chapelle method. Milling withing 20 min influences particle size decrease and after that time continuous increase. XDR analysis indicates gradual decrease of cristallinity with prolonged milling time. The higher values for pozzolanic activitie, expressed through consumption of gCa(OH) 2 per gPozzolana are 0.78 and 0.77, and they were obtained for milling times 20 and 40 min, respectively. The values are comparable with commercial pozzolan - metakaolin. The results indicates that milling has caused the disintegration of particles and the consequent formation of new active surfaces in addition to changes in its physico-chemical properties that decrease its crystallinity (through amorphization) and increase it reactivity. © 2011 American Institute of Physics.


Jankovic K.,Serbian Institute for Materials Testing | Nikolic D.,Serbian Institute for Materials Testing | Bojovic D.,Serbian Institute for Materials Testing
Construction and Building Materials | Year: 2012

Demolition of old buildings in urban cores has produced a large amount of waste material. Since they are mostly masonry structures the largest part of the waste material is ceramic waste. Besides that, ceramic waste is obtained as a byproduct in the ceramic industry. All of this initiated a research for the application of concrete with recycled brick as aggregate. In this paper, the possibility of using crushed bricks in the production of concrete elements for the pedestrian zone is shown. The application of recycled brick as aggregate, produces concrete of less density and strength, and of increased absorption. All of this also has an effect on the quality of concrete flags and paving blocks. Based on the results obtained by testing the resistance to frost of concrete it was assumed that it is possible to get the products comply with European standards. The results show that replacing up to a 32.5% of natural aggregate with crushed brick aggregate produces concrete blocks, and up to 65% of it produces concrete paving flags which meet the requirements of European standards. © 2011 Elsevier Ltd. All rights reserved.


Kuresevic L.,Serbian Institute for Materials Testing
Acta Montanistica Slovaca | Year: 2013

Five Tertiary granitoid plutons of central and western Serbia Vardar zone are examined in order to establish their potentiality for use as dimension stone. Field studies aimed at establishing the geological factors - presence of fractures, harmful minerals, jointing, alterations, fabric homogeneity Laboratory examinations comprised petrological analyses and testing of technical properties. Evaluation of results of technical properties laboratory testing is performed according to technical requirements of the Serbian standard B.B3.200 and it has shown that stone from these plutons can be used as dimension stone for production of slabs for exterior and interior paving and cladding.

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