21. 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: 302; Prenosov: 140
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22. Report of RILEM TC 267-TRM phase 3 : validation of the R3 reactivity test across a wide range of materialsDiana Londono-Zuluaga, Sabina Dolenec, Maruša Mrak, 2022, izvirni znanstveni članek Povzetek: RILEM TC 267 TRM– “Tests for Reactivity of Supplementary Cementitious Materials” recommends the Rapid Reliable Relevant (R3) test as a method for determining the chemical reactivity of supplementary cementitious materials (SCMs) in Portland cement blends. In this paper, the R3 test was applied to 52 materials from a wide range of conventional and alternative SCMs with the aim to validate such test. An excellent correlation was found between the cumulative heat release and the bound water determined following the R3 test method. Comparison of the R3 test results to mortar compressive strength development showed that all conventional SCMs (e.g. blast furnace slag and fly ashes) followed the same trend, with the notable exception of very reactive calcined kaolinitic clays. It is discussed, through an in-depth statistical regression analysis of the R3 reactivity test results and the 28 days relative compressive strengths, how reactivity threshold values for classification of the chemical reactivity of SCMs could be proposed based on the R3 test results.
Ključne besede: supplementary cementitious materials, reactivity test, heat release, bound water, compressive strength
Objavljeno v DiRROS: 26.04.2023; Ogledov: 254; Prenosov: 146
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23. The effect of rapid weight loss on the handgrip strength of national-level wrestlersCarlo Rossi, Roberto Roklicer, Antonino Bianco, Marko Manojlović, Barbara Gilić, Tatjana Trivic, Patrik Drid, 2021, izvirni znanstveni članek Povzetek: The effects of rapid weight loss (RWL) in combat sports athletes is an area that is not yet fully discovered. Therefore, the goal of this study was to determine the impact of weight loss on HGS (handgrip strength) in Greco-Roman wrestlers.This cross-over study included ten athletes examined for HGS during three time points for each hand. The first measurement – baseline (BL), was performed before we-ight reduction. The second measurement ‒ phase 1 (P1), was taken after high-intensity sports specific training (HISST) combined with RWL. In this phase, participants had to lose 5% of their body mass within three days, after which HISST was carried out (on day 3). The third measurement ‒ phase 2 (P2), was performed seven days after P1, which included HISST with no RWL.When comparing the HGS values, significantly higher values were observed only when P1 was compared with P2 for the left hand (p=0.039). This means that the grip was significantly stronger after RWL was conducted together with HISST.This research could be of great importance to combat sports coaches and athletes as it evaluates the effect of RWL on performance parameters. Therefore, the results of our study could serve to improve the wrestlers’ weight-reduction plan.
Ključne besede: wrestling, wrestlers, weight reduction, handgrip strength, performance
Objavljeno v DiRROS: 02.03.2023; Ogledov: 409; Prenosov: 194
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