21. Mechanical performance of timber connections made of thick flexible polyurethane adhesivesJaka Gašper Pečnik, Igor Gavrić, Václav Sebera, Meta Kržan, Arkadiusz Kwiecień, BogusŁaw Zając, Boris Azinović, 2021, izvirni znanstveni članek Povzetek: This study investigates timber connections with flexible polyurethane adhesives, which prove to have the po-tential for timber-adhesive composite structures without mechanical connections for seismic regions. Results of conducted cyclic double lap-shear adhesive timber joints tests were compared with available experimental re-sults on timber connections with standard mechanical dowel-type fasteners and with results of numerical finite element analysis. The study found that the shear strength, elastic stiffness and strength degradation capacity of the flexible adhesive connections were significantly higher compared to mechanical fasteners commonly used in seismic-resistant timber connections. The latter, however, manifested larger ultimate displacements but also yielded at lower displacements.
Ključne besede: flexible adhesive, timber connection, polyurethane, double lap-shear, cyclic loading, energy dissipation, open access
Objavljeno v DiRROS: 19.05.2023; Ogledov: 385; Prenosov: 249
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22. Influence of the deep cryogenic treatment on AISI 52100 and AISI D3 steelʼs corrosion resistancePatricia Jovičević Klug, Tjaša Kranjec, Matic Klug Jovičević, Tadeja Kosec, Bojan Podgornik, 2021, izvirni znanstveni članek Povzetek: The effect of deep cryogenic treatment (DCT) on corrosion resistance of steels AISI 52100 and AISI D3 is investigated and compared with conventional heat-treated counterparts. DCTʼs influence on microstructural changes is subsequently correlated to the corrosion resistance. DCT is confirmed to reduce the formation of corrosion products on steelsʼ surface, retard the corrosion products development and propagation. DCT reduces surface cracking, which is considered to be related to modified residual stress state of the material. DCTʼs influence on each steel results from the altered microstructure and alloying element concentration that depends on steel matrix and type. This study presents DCT as an effective method for corrosion resistance alteration of steels.
Ključne besede: steel, deep cryogenic treatment, corrosion, Raman, open access
Objavljeno v DiRROS: 19.05.2023; Ogledov: 304; Prenosov: 222
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23. Effect of laser texturing pattern on Ti6Al4Vtribocorrosion in a physiological solutionMarjetka Conradi, Tadeja Kosec, Bojan Podgornik, Aleksandra Kocijan, Janez Kovač, Damjan Klobčar, 2022, izvirni znanstveni članek Povzetek: Laser texturing is a process that alters a material’s surface properties by modifying its morphology, which can improve properties like adherence, wettability, thermal and electrical conductivity and friction. Here, the effect of laser texturing was studied on an alpha-beta titanium alloy (Ti6Al4V) biomedical material. Two types of patterned surfaces, cross-hatch with varying scan-line separations, Dx = 100, 180 and 280 μm and dimples of 200 μm size, were prepared on the surface of alpha-beta titanium alloy by laser technology. Prepared samples were characterised for their surface properties, such as corrosion, wear-induced corrosion, friction and wettability. Electrochemical and tribocorrosion properties in a physiological solution were studied on the samples with different texture densities of cross-hatch pattern and dimples and compared to the as-received alpha-beta titanium alloy surface. Corrosion rate decreased for laser-textured samples, especially for cross-hatch texture (down to 1 μm/year for Dx = 180 μm) when compared to the as-received alpha-beta titanium alloy surface due to the changed laser-induced surface film and wetting properties. Friction coefficient slightly decreased for all laser-textured surfaces, most noticeably for cross-hatch patterns, from 0.38 (as-received) down to 0.34 (Dx = 180 and 280 μm). The main contribution to total wear in physiological solution increased due to the mechanical wear, which is governed by the removal of the surface oxide layer induced by laser texturing.
Ključne besede: TiAIV, laser texturing, tribocorrosion, open access
Objavljeno v DiRROS: 17.05.2023; Ogledov: 294; Prenosov: 119
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24. An electrochemical and spectroscopic study of surfaces on bronze sculptures exposed to urban environmentDajana Mikić, Helena Otmačić Ćurković, Tadeja Kosec, Neven Peko, 2021, izvirni znanstveni članek Povzetek: Polluted urban environment enhances dissolution of patina and underlying bronze material of recent and historical bronze sculptures exposed outdoors. In this work, two bronze statues, situated in one of the most polluted Croatian cities, were examined in order to characterize composition of patina and its electrochemical stability. The composition of patina on several positions on each sculpture was determined by EDS, Raman spectroscopy, and FTIR measurements. Electrochemical impedance spectroscopy measurements were conducted in order to evaluate the corrosion stability of both patina and underlying bronze. Results obtained in this work show that the two examined bronze sculptures were covered with patina layer that was mainly composed of copper sulfides and sulphates, which is in accordance with the high concentrations of H2S and SO2 in the atmosphere. However, the variations in the appearance of FTIR and Raman spectra revealed that the amount of each species differed from spot to spot, as well as the fact that other compounds, such as carbonates, were present at some areas. This difference in patina composition was reflected in electrochemical behavior as observed by electrochemical impedance spectroscopy.
Ključne besede: bronze, corrosion, spectroscopy, FTIR, Raman, EIS, open access
Objavljeno v DiRROS: 16.05.2023; Ogledov: 293; Prenosov: 173
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25. Innovative circular economy models for the european pulp and paper industry : a reference framework for a resource recovery scenarioAmaia Sopelana, Camille Auriault, Anurag Bansal, Karmen Fifer Bizjak, Helena Paiva, Christian Maurice, Gunnar Westin, Javier Rios, Asier Oleaga, Antonio Cañas, 2021, izvirni znanstveni članek Povzetek: According to recent literature in the field of sustainability, the circular economy (CE) appears to be a thriving opportunity for creating new businesses, although less attention has been paid to the form in which its principles fit into a comprehensive framework that enables companies to design it in a practical way. This paper presents the methodology that has been adopted to pave the way to a coherent reference framework for circular business model innovation and its outstanding design and implementation, taking into consideration the entire value and supply chain. A unique analysis of recent innovations in circular economy models is provided herein, together with an exhaustive analysis of those elements that enable or hinder their implementation. The main interactions among all those critical elements influencing how organisations innovate and operate cooperatively within a CE ecosystem are also evaluated. In addition, a study of five industrial cases in the pulp and paper industry allowed searching for industrial insights and empirical evidence of the relevance of those elements, including observation, document analysis, and interviews. Lastly, the main outcomes of this research are illustrated using the CE reference framework designed when applied to the aforementioned industrial cases, and relevant insights into future improvements are also provided.
Ključne besede: circular economy business models, pulp and paper industry, construction sector, open access
Objavljeno v DiRROS: 12.05.2023; Ogledov: 308; Prenosov: 172
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26. Potential usage of hybrid polymers binders based on fly ash with the addition of PVA with satisfying mechanical and radiological propertiesMiljana Mirković, Ljiljana Kljajević, Sabina Dolenec, Miloš Nenadović, Vladimir Pavlović, Milica Rajačić, Snežana B. Nenadović, 2021, izvirni znanstveni članek Povzetek: Since recycled technologies usage is mandatory for environmental safety, and in this regard, it is important to examine new materials that can be used in construction and are primarily produced from fly ash. In addition to characteristics such as hardness and compressive strength, the given materials must also be radiologically and environmentally safe. The main concept of engineered geopolymer gel composites based on fly ash residues is focused on developing binder materials via gel formation processes that can replace ordinary cement materials. This study is unique in researching the potential use of fly ash from the Nikola Tesla thermal power plant in Serbia, where the hybrid geopolymeric materials synthesized from fly ash are experimentally examined with the addition 1 wt% and 2 wt% of polyvinyl alcohol (PVA). This paper aims to investigate the structural, morphological, mechanical, and radiological properties of hybrid materials with the addition of PVA and without additive in the period of ageing for 28 days at room temperature. The phase composition was investigated using X-ray powder diffraction (XRPD) analysis, while morphological characteristics of these materials were examined using scanning electron microscopy and energy dispersive X-ray analysis (SEM-EDS). Vibrational spectra of obtained samples are investigated using diffuse reflectance infrared Fourier transform (DRIFT) and Fourier transform infrared (FTIR) techniques. The hardness and compressive strength are also examined, indicating that the 1 wt% addition in geopolymeric matrix results in the best mechanical properties. Radiological measurements of investigated all geopolymer samples show decreasing activity concentrations of radionuclides for 50% compared to fly ash.
Ključne besede: geopolymer gel, inorganic binders, hybrid materials, fly ash, radiological properties, strength, open access
Objavljeno v DiRROS: 12.05.2023; Ogledov: 294; Prenosov: 135
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27. Investigation of surface treatment effects on the environmentally-assisted cracking behaviour of Alloy 182 in boiling water reactor environmentZaiqing Que, Bojan Zajec, Stefan Ritter, Tommi Seppänen, Timo Saario, Aki Toivonen, Aleksandra Treichel, Valentin Lautaru, Fabio Scenini, 2022, izvirni znanstveni članek Povzetek: Surface treatments of primary circuit components in light water reactors are regarded as possible ways to mitigate environmentally-assisted cracking (EAC). To date, it is not fully conclusive which surface condition is suitable to reduce the EAC initiation susceptibility. Constant extension rate tensile (CERT) tests were performed by several labs using flat tapered tensile specimens with different surface conditions (ground, industrial face milled, advanced face milled and shot peened), exposed to a boiling water reactor normal water chemistry environment at 288°C. Despite some scatter in the results, the CERT tests revealed that the EAC initiation susceptibility seems lowest for the advanced face milled surface and highest for the shot peened surface. However, it must be emphasised that the differences were moderate and that the surprising behaviour of the shot peened surface can be explained. The mechanical grinding of the surface did not significantly retard EAC initiation compared to industrial face milling.
Ključne besede: crack initiation, environmentally-assisted cracking, Alloy 182, surface machining, boiling water reactor, open access
Objavljeno v DiRROS: 05.05.2023; Ogledov: 360; Prenosov: 151
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28. Bioleaching process for copper extraction from waste in alkaline and acid mediumIvica Ristović, Darina Štyriaková, Iveta Štyriakova, Jaroslav Šuba, Emilija Širadović, 2022, izvirni znanstveni članek Povzetek: Flotation wastes are becoming a valuable secondary raw material and source of many metals and semimetals worldwide with the possibilities of industrial recycling. The flotation tailings contain oxide and sulfide minerals that have not been sufficiently stabilized and form acidic mine waters, which in turn contaminate groundwater, rivers, and reservoi6sediments. An effective way to recycle these mine wastes is to recover the metals through leaching. While the focus is on acid bioleaching by iron- and sulfur-oxidizing bacteria, alkaline leaching, and the removal of iron- containing surface coatings on sulfide minerals contribute significantly to the overall environmental efficiency of leaching. For this study, static and percolate bioleaching of copper from flotation waste at the Bor copper mine in Serbia was investigated in alkaline and then acidic environments. The aim of the study was to verify the effect of alkaline pH and nutrient stimulation on the bioleaching process and element extraction. A sample was taken from a mine waste site, which was characterized by XRF analyses. The concentration of leached copper was increased when copper oxide minerals dissolved during alkaline bioleaching. The highest copper yield during alkaline bioleaching was achieved after 9 days and reached 67%. The addition of nutrients in acidic medium enhanced the degradation of sulfide minerals and increased Cu recovery to 74%, while Fe and Ag recoveries were not significantly affected. Combined bioleaching with alkaline media and iron- and sulfur-oxidizing bacteria in acidic media should be a good reference for ecological Cu recovery from copper oxide and sulfide wastes.
Ključne besede: copper, alkaline, acidic bioleaching, secondary raw materials, open access
Objavljeno v DiRROS: 05.05.2023; Ogledov: 304; Prenosov: 155
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29. Impact of leaching on chloride ingress profiles in concreteAlisa Machner, Marie Helene Bjørndal, Aljoša Šajna, Nikola Mikanovic, Klaartje De Weerdt, 2022, izvirni znanstveni članek Povzetek: To investigate the effect of leaching on chloride ingress profiles in concrete and mortar, we exposed concrete and mortar specimens for 90 and 180 days to two different exposure solutions: 3% NaCl, and 3% NaCl with KOH added to limit leaching. The solutions were replaced weekly. After exposure, we determined total chloride profiles to investigate the chloride ingress, and portlandite profiles to assess the extent of leaching. The results showed that leaching during exposure greatly affects the chloride ingress profiles in mortar and concrete. We found that leaching leads to considerably higher maximum total chloride content and deeper chloride penetration into the concrete than in the specimens where leaching was limited. We recommend therefore that leaching should be taken into account in standard laboratory testing and that more mechanistic service life models should be used to take into account the impact of leaching.
Ključne besede: chloride ingress, service life prediction, leaching, concrete, portlandite, open access
Objavljeno v DiRROS: 04.05.2023; Ogledov: 302; Prenosov: 188
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30. Innovative calcium carbonate-based products to repair cracked cement mortarsMartina Zuena, Andreja Pondelak, Enrico Garbin, Matteo Panizza, Luca Nodari, Andrijana Sever Škapin, Luka Škrlep, Gilberto Artioli, Patrizia Tomasin, 2022, izvirni znanstveni članek Povzetek: The durability of Portland cement mortars is often affected by environmental factors, which can cause physicochemical and mechanical degradation processes. In this study, the performance of three products, calcium acetoacetate and calcium tetrahydrofurfuryloxide dissolved in two different solvents developed and tested as stone consolidants, was evaluated in terms of crack filling or sealing and consolidation. Realistic cracks were induced in quasibrittle cement mortar prisms using a custom-designed test rig. The effectiveness and the performance of the considered treatments, investigated on specimens, were evaluated by optical and scanning electron microscopy, colourimetry, water absorption rate, ultrasonic pulse velocity, and surface hardness measurements. Results revealed that, in the examined conditions, the products were more suitable as surface consolidants than as crack fillers.
Ključne besede: cement mortars, 20th century architecture conservation, calcium acetoacetate, calcium alkoxide, concrete repair, open access
Objavljeno v DiRROS: 04.05.2023; Ogledov: 359; Prenosov: 205
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