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Povzetek: This study presents research on the effect of Portland cement (PC) replacement with metakaolin on the mechanical behavior of flax textile-reinforced cementitious matrices (TRCM). The composition of cementitious matrices and in-situ flax fibres was determined using X-ray diffraction and thermogravimetric analysis, while the reinforcement efficiency of the textile and mechanical behavior of TRCMs was investigated by three-point bending tests and finite element analysis. High amounts of PC replacement with metakaolin provided a calcium hydroxide-free environment, more suitable for the natural fibres, to avoid their degradation and embrittlement and, thus, significantly contribute to the ductility of the cement-based composite material.
Ključne besede: textile-reinforced concrete (TRC), flax textile, natural fibres, finite element, metakaolin, cement-based composites, open access
Objavljeno v DiRROS: 22.05.2023; Ogledov: 407; Prenosov: 191
Celotno besedilo (8,40 MB)
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Povzetek: In light of the forthcoming second generation Eurocodes (EC), the results of conducted systematic in-plane cyclic and compressive tests on three-leaf stone masonry walls are discussed following new requirements and provisions. The new proposal for EC8-3 for existing buildings is based on partial factors safety approach, though it considers different uncertainties in defining input parameters for effective seismic performance-based assessment. Prior to its application, massive calibration effort will be needed since there is no standardized method for shear testing of masonry walls. In this paper, the performance limit states damage, resistance, and displacement capacities from conducted test results were evaluated and assessed through comparison with analytical solutions and imposed limit values, as stated in existing codes. The test results provide a much higher deformation capacity than the limits provided in both existing and new proposal of EC8-3 as well as those in the ASCE code provisions. The reason for this lies in the soft, "ductile" mortar for which the presumed resistance according to code provisions should be significantly higher when considering good quality ashlar three-leaf stone masonry.
Ključne besede: historical masonry, multi-leaf stone masonry, mechanical properties, compression tests, in-plane shear tests, failure mechanisms, drift limits, boundary conditions
Objavljeno v DiRROS: 19.05.2023; Ogledov: 360; Prenosov: 177
Celotno besedilo (4,47 MB)
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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: 309; Prenosov: 125
Celotno besedilo (2,19 MB)
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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: 334; Prenosov: 187
Celotno besedilo (1,42 MB)
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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: 322; Prenosov: 149
Celotno besedilo (1,61 MB)
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