31. Magnetic extraction of weathered tire wear particles and polyethylene microplasticsVaibhav Budhiraja, Branka Mušič, Andrej Kržan, 2022, izvirni znanstveni članek Povzetek: Magnetic extraction offers a rapid and low-cost solution to microplastic (MP) separation, in which we magnetize the hydrophobic surface of MPs to separate them from complex environmental matrices using magnets. We synthesized a hydrophobic Fe-silane based nanocomposite (Fe@SiO2/MDOS) to separate MPs from freshwater. Pristine and weathered, polyethylene (PE) and tire wear particles (TWP) of different sizes were used in the study. The weathering of MPs was performed in an accelerated weathering chamber according to ISO 4892-2:2013 standards that mimic natural weathering conditions. The chemical properties and morphology of the Fe@SiO2/MDOS, PE and TWP were confirmed by Fourier transform infrared spectroscopy and Scanning electron microscopy, respectively. The thermal properties of PE and TWP were evaluated by Thermogravimetric analysis. Using 1.00 mg of Fe@SiO2/MDOS nanocomposite, 2.00 mg of pristine and weathered PE were extracted from freshwater; whereas, using the same amount of the nanocomposite, 7.92 mg of pristine TWP and 6.87 mg of weathered TWP were extracted. The retrieval of weathered TWP was 13% less than that of pristine TWP, which can be attributed to the increasing hydrophilicity of weathered TWP. The results reveal that the effectiveness of the magnetic separation technique varies among different polymer types and their sizes; the weathering of MPs also influences the magnetic separation efficiency.
Ključne besede: degradation, magnetic separation, microplastics, polyethylene, tire wear particles, open access
Objavljeno v DiRROS: 03.05.2023; Ogledov: 416; Prenosov: 359
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32. Production and characterization of lightweight aggregates from municipal solid waste incineration fly-ash through single- and double-step pelletization processAlberto Ferraro, Vilma Ducman, Francesco Colangelo, Lidija Korat, Danilo Spasiano, Ilenia Farina, 2023, izvirni znanstveni članek Povzetek: The performance of a cold-bonding pelletization process was investigated for lightweight aggregates (LWAs) production from municipal solid waste incineration (MSWI) fly-ash (FA), by including multiple waste materials in the aggregate mixture. Before pelletization, FA was pre-treated by washing with water, which led to a reduction of chloride (66.79%) and sulphate (25.30%) content. This was further confirmed by XRF and XRD analyses, which showed a reduction of chloride elements and the content of chlorine crystalline phases. The pelletization process was carried out using both single- and double-step methods. For single-step pelletization, all the mixtures contained 80% FA, combined with various compositions of cement (5, 10, and 15%) and granulated blast furnace slag (GBFS) (5, 10, and 15%). For the double-step pelletization 30% of cement and 70% of marble sludge (MS) were added to each of the previous mixtures. The apparent density of all the aggregates varied between 1.60 and 1.87 g cm 3, suggesting their suitability to be classified as LWAs. Aggregates produced from double-step pelletization showed improved characteristics, with water absorption capacity and open porosity generally lower compared to the corresponding aggregates from the single-step pelletization. The best values of compressive (crushing) strength (almost 11 MPa) were observed for double-step pelletization aggregates with initial cement: GBFS mixture of 15%:5%. Results from leaching tests showed an overall significant release of chloride and sulphate. Nevertheless, leaching from double-step pelletization aggregates was reduced by 1.73- 4.02 times for chloride and 1.58-5.67 times for sulphate, further suggesting that better performances are achievable through the addition of an aggregate second layer.
Ključne besede: MSWI fly ash, lightweight aggregate, microtomography, open access
Objavljeno v DiRROS: 03.05.2023; Ogledov: 347; Prenosov: 299
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33. Residual compressive behavior of self-compacting concrete after high temperature exposure - influence of binder materialsMarija Jelčić Rukavina, Ivan Gabrijel, Ivanka Netinger Grubeša, Ana Mladenovič, 2022, izvirni znanstveni članek Povzetek: This paper presents an experimental investigation of the compressive behavior of highstrength self-compacting concrete exposed to temperatures up to 600 C. Ten different concrete compositions were tested, in which part of the cement (by weight) was replaced by three different mineral additives (5–15% metakaolin, 20–40% fly ash and 5–15% limestone). The stress–strain curves, compressive strength, modulus of elasticity and strain at peak stress were evaluated from uniaxial compression tests. Scanning electron microscope micrographs were also taken to evaluate the damage caused by the high temperatures. A sharp decrease in mechanical properties and an increase in peak strain were observed already after 200 C for all mixes tested. The different mineral additives used in this study affected the variations of residual compressive strength by 24% and peak strain by 38%, while the variations of residual modulus elasticity were 14%. Comparing the obtained results with the recommendations for compressive strength given in regulatory code EN 1992-1-2 for high strength concrete, it can be concluded that the strength loss observed in EN 1992-1-2 at temperatures up to 400 C is too conservative. The Popovics model for the relationship between stress and strain provided a good approximation for the experimentally determined stress–strain curves at different temperatures.
Ključne besede: self-compacting concrete, mineral additives, high temperatures, residual mechanical properties, open access
Objavljeno v DiRROS: 28.04.2023; Ogledov: 369; Prenosov: 178
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34. Multiscale femoral neck imaging and multimodal trabeculae quality characterization in an osteoporotic bone sampleEnrico Soldati, Flavy Roseren, Daphne Guenoun, Lucia Mancini, Emilio Catelli, Silvia Prati, Giorgia Sciutto, Jerome Vicente, Stefano Iotti, David Bendahan, Emil Malucelli, Martine Pithioux, 2022, izvirni znanstveni članek Povzetek: Although multiple structural, mechanical, and molecular factors are definitely involved in osteoporosis, the assessment of subregional bone mineral density remains the most commonly used diagnostic index. In this study, we characterized bone quality in the femoral neck of one osteoporotic patients as compared to an age-matched control subject, and so used a multiscale and multimodal approach including X-ray computed microtomography at different spatial resolutions (pixel size: 51.0, 4.95 and 0.9 µm), microindentation and Fourier transform infrared spectroscopy. Our results showed abnormalities in the osteocytes lacunae volume (358.08 ± 165.00 for the osteoporotic sample vs. 287.10 ± 160.00 for the control), whereas a statistical difference was found neither for shape nor for density. The osteoporotic femoral head and great trochanter reported reduced elastic modulus (Es) and hardness (H) compared to the control reference (−48% (p < 0.0001) and −34% (p < 0.0001), respectively for Es and H in the femoral head and −29% (p < 0.01) and −22% (p < 0.05), respectively for Es and H in the great trochanter), whereas the corresponding values in the femoral neck were in the same range. The spectral analysis could distinguish neither subregional differences in the osteoporotic sample nor between the osteoporotic and healthy samples. Although, infrared spectroscopic measurements were comparable among subregions, and so regardless of the bone osteoporotic status, the trabecular mechanical properties were comparable only in the femoral neck. These results illustrate that bone remodeling in osteoporosis is a non-uniform process with different rates in different bone anatomical regions, hence showing the interest of a clear analysis of the bone microarchitecture in the case of patients’ osteoporotic evaluation
Ključne besede: synchrotron X-ray microtomography, bone, trabecular struicture, osteons, osteoporosis, phase-contrast imaging, open access
Objavljeno v DiRROS: 28.04.2023; Ogledov: 398; Prenosov: 188
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35. Tribocorrosion susceptibility and mechanical characteristics of as-received and long-term in-vivo aged nickel-titanium and stainless-steel archwiresJasmina Primožič, Miha Hren, Uroš Mezeg, Andraž Legat, 2022, izvirni znanstveni članek Povzetek: To evaluate the effect of long-term in-vivo aging on orthodontic archwires, we aimed to assess the triboelectrochemical and mechanical characteristics of as-received and in-vivo aged nickel-titanium (NiTi) and stainless-steel (SS) orthodontic archwires. Four consecutive tribocorrosion cycles on six NiTi and six SS archwires, as-received and in-vivo aged, were performed on a reciprocal tribometer. Electrochemical noise and friction coefficient measurements, three-dimensional surface profiling, and hardness measurements were performed. Repassivation times of as-received archwires were longer than of the in-vivo aged; however, were shorter for NiTi. Friction coefficients were higher for NiTi than for SS archwires. Sudden major current drops concomitant with inverse potential shifts and friction coefficients’ fluctuations, were seen for as-received (last cycle) and in-vivo aged (last three cycles) NiTi archwires. More pronounced tribocorrosion damage was observed on in-vivo aged NiTi than on other archwires. Hardness was generally higher inside the wear track of archwires. Long-term in-vivo exposure decreases the corrosion susceptibility of archwires, more evidently for the NiTi ones. Sudden major fluctuations in electrochemical current, potential, and friction coefficient detected for NiTi archwires, might be related to localized residual parts of the oxide layer persisting due to increased surface roughness or to phase transformations of the alloy’s crystal structure.
Ključne besede: tribocorrosion, orthodontic archwires, electrochemical noise, open access
Objavljeno v DiRROS: 26.04.2023; Ogledov: 362; Prenosov: 145
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36. Effect of leaching on the composition of hydration phases during chloride exposure of mortarAlisa Machner, Marie Helene Bjørndal, Harald Justnes, Lucija Hanžič, Aljoša Šajna, Yushan Gu, Benoit Bary, Mohsen Ben Haha, Mette R. Geiker, Klaartje De Weerdt, 2022, izvirni znanstveni članek Povzetek: Mortar specimens were exposed to either a 3% NaCl solution or a 3% NaCl+KOH solution for up to 180 days. Exposure to the NaCl solution provoked much more leaching than the NaCl+KOH exposure. Leaching strongly impacted the chloride ingress profiles. The extended leaching led to a maximum total chloride content almost three times higher and a deeper chloride penetration than exposure with limited leaching after 180 days. The higher maximum chloride content seems to be linked to the enhanced binding capacity of the C-S-H and AFm phases upon moderate leaching as determined by SEM-EDS. The total chloride profile appears to be governed by multi-ion transport and the interaction of chloride with the hydration phases. Service life prediction and performance testing both rely on total chloride profiles and therefore ought to take these interactions into account.
Ključne besede: chloride binding, Friedel's salt, Kuzel's salt, ph, GEMS, thermodynamic modelling, open access
Objavljeno v DiRROS: 26.04.2023; Ogledov: 323; Prenosov: 267
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37. Influence of alkalis on the phase development of belite-sulfoaluminate clinkersBarbara Čeplak, Katarina Šter, Maruša Mrak, Luka Škrlep, Mirijam Vrabec, Sabina Dolenec, 2022, izvirni znanstveni članek Povzetek: This paper presents a study on the influence of different amounts of alkalis (K2O and Na2O) on clinker phase formation, microstructure, phase composition and reactivity of belite-sulfoaluminate cement clinker. Using X-ray powder diffraction and scanning electron microscopy with energy dispersive spectrometry, it was found that the amount of C2S and C4AF increases with the incorporation of alkalis, while the amount of C4A3Ś and CŚ decreases. In addition to the major phases, the samples with alkalis also consist of minor phases such as C3A (tricalcium aluminate), KŚ (arcanite), and KC2Ś3 (Ca-langbeinite). The major ions in the major phases were substituted by alkali cations and some other ions (Ca2+, Al3+, Fe3+, S2-, S6+, Si4+). The alkalis also affect the microstructure of the clinker, e.g., the shape of the grains. Consequently, isothermal calorimetry was used to detect differences in hydration kinetics. The clinker with 2 wt. % K2O content was the most reactive, while the sample with 0.5 wt. % Na content was the least reactive. The latter was primarily influenced by the content of the main and minor phases of the clinker.
Ključne besede: BCSA clinker, microstrcuture, reactivity, alkalis, open access
Objavljeno v DiRROS: 06.12.2022; Ogledov: 534; Prenosov: 268
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