Iskanje po katalogu digitalne knjižnice

Opis: There is a need to develop new construction materials with improved mechanical performance and durability that are low-priced and have environmental benefits at the same time. This paper focuses on the rheological, mechanical, morphological, and durability properties of synthetic and steel fiber reinforced self-compacting concrete (SCC) containing 5–15% metakaolin (M) by mass as a green replacement for Portland cement. Testing of the fresh mixes included a slump-flow test, density, and porosity tests. Mechanical properties were determined through compression and flexural strength. A rapid chloride penetrability test (RCPT) and the chloride migration coefficient were used to assess the durability of the samples. A scanning electron microscope (SEM) with energy dispersion spectrometry (EDS) was used to study the concrete microstructure and the interfacial transition zone (ITZ). The results show that a combination of metakaolin and hybrid fibers has a negative effect on the flowability of SCC. In contrast, the inclusion of M and hybrid fibers has a positive effect on the compressive and flexural strength of SCC. The fracture of SCC samples without fibers was brittle and sudden, unlike the fiber-reinforced SCC samples, which could still transfer a considerable load with increasing crack mouth opening deflection. Overall, the chloride migration coefficients were reduced by up to 71% compared to the control mix. The chloride reduction is consistent with the resulting compact concrete microstructure, which exhibits a strong bond between fibers and the concrete matrix.
Ključne besede: self-compacting concrete, synthetic and steel fibers, metakaolin, rheology, mechanical properties, chloride penetration, SEM-EDS
Objavljeno v DKUM: 12.03.2025; Ogledov: 0; Prenosov: 3
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Opis: The reuse of decontaminated disposable medical face masks can contribute to reducing the environmental burden of discarded masks. This research is focused on the effect of household and laboratory washing at 50 °C on the quality and functionality of the nonwoven structure of polypropylene medical masks by varying the washing procedure, bath composition, disinfectant agent, and number of washing cycles as a basis for reusability. The barrier properties of the medical mask were analyzed before and after the first and fifth washing cycle indirectly by measuring the contact angle of the liquid droplets with the front and back surface of the mask, further by measuring air permeability and determining antimicrobial resistance. Additional analysis included FTIR, pH of the material surface and aqueous extract, as well as the determination of residual substances—surfactants—in the aqueous extract of washed versus unwashed medical masks, while their aesthetic aspect was examined by measuring their spectral characteristics. The results showed that household washing had a stronger impact on the change of some functional properties, primarily air permeability, than laboratory washing. The addition of the disinfectant agent, didecyldimethylammonium chloride, contributes to the protective ability and supports the idea that washing of medical masks under controlled conditions can preserve barrier properties and enable reusability.
Ključne besede: medical masks, washing, detergent, didecyldimethylammonium chloride, air permeability, antimicrobial activity, residuals
Objavljeno v DKUM: 15.03.2024; Ogledov: 333; Prenosov: 31
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Opis: 4-Vinylbenzyl chloride (VBC) based water-in-oil-in-water emulsions with 85% pore volume and 70% VBC in organic phase were prepared and polymerised by free radical polymerisation. Porous spherical particles of diameters between 50 and 150 m were obtained and their morphological structure and reactivity studied by FTIR spectroscopy, elemental analysis, optical microscopy, scanning electron microscopy and mercury intrusion porosimetry. Strong influence of the suspension stabiliser, namely poly(N-vinylpyrrolidone) (PVP), on the particle form was found. Diameters of spherical polymers particles depend on the PVP concentration, being larger with the lower concentration of PVP. Reactivity of novel supports was demonstrated by the reactions with piperidine, piperazine, tris(hydroxymethyl)methylamine and tris(2-aminoethyl)amine, all yielding corresponding amine derivatives.
Ključne besede: multiple emulsions, polymer supports, 4-vinylbenzyl chloride, solid phase synthesis, solid phase synthesis, high internal phase emulsions
Objavljeno v DKUM: 01.06.2012; Ogledov: 2162; Prenosov: 47
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