1. Combined effects of metakaolin and hybrid fibers on self-compacting concreteNatalija Bede Odorčić, Gregor Kravanja, 2022, izvirni znanstveni članek 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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2. Morphological, mechanical, and in-vitro bioactivity of gelatine/collagen/hydroxyapatite based scaffolds prepared by unidirectional freeze-castingYasir Beeran Potta Thara, Tomaž Vuherer, Uroš Maver, Vanja Kokol, 2021, izvirni znanstveni članek Opis: The fabrication of biomaterials to be used in segmental bone defects, mimicking the bone's organic-inorganic architecture and mechanical properties to induce osteogenesis, persists as a key challenge. The purpose of this study was to elucidate the effect of a lightweight, morphologically graded, and multiphase self-standing scaffold structure prepared from a combination of gelatine (Gel), collagen type 1 (Col) and/or hydroxyapatite (HAP) nanoparticles by a unidirectional freeze-casting process at different temperatures (−20, −40, −60 °C), followed by carbodiimide induced cross-linking, on their in-vitro mechanical stability and bioactive properties. In addition, the rheological study of differently formulated Gel solutions has been performed to determine the effect of Col and HAP content on their microstructural arrangement, which, together with the freezing kinetic, affects Gel/Col orientation and cross-linking, and, thus, the scaffold's mechanical strength and stability. A bone-like anisotropic, interconnected, and graded porosity (from 120 to a few μm) scaffold structure with up to 30% total porosity and ~61 μm average pores' diameter is obtained by using a higher Col content (Col: Gel = 2:5) and freezing temperature (−20 °C) while forming a few μm thick close-to-parallel lamellae, separated with a 10–100 μm space when prepared at −60 °C. Such a structure influenced in-vitro stability strongly (lower swelling without weight loss), being accompanied with a ~76% increase of compression strength (to 37 kPa) and ~67% decrease of elastic modulus (to 17 kPa) when prepared with HAP and incubated in HBSS for 7 days. On the other hand, a significant reduction of both strength (~78%, to 15 kPa) and elasticity (~95%, to 5 kPa) was noted for a scaffold prepared with HAP at −60 °C, being related to faster degradation and the formation of a highly opened structure on the bottom, required to stimulate the bone ingrowth, while a more closed network structure on the top to adhere with the surrounding soft tissue. None of the scaffolds induced cytotoxicity to human bone-derived osteoblasts, even after 19 days of incubation, but rather improved their viability while promoting cells' adhesions, proliferation, and differentiation, being supported with an increased alkaline phosphatase activity and rod-like CaP formation.
Ključne besede: biomimetic scaffolds, rheology, unidirectional freeze-casting, morphology, compression properties, bioactivity
Objavljeno v DKUM: 10.03.2025; Ogledov: 0; Prenosov: 3
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3. Rheological studies of concentrated guar gumMarija Oblonšek, Sonja Šostar-Turk, Romano Lapasin, 2003, izvirni znanstveni članek Opis: Polymers and surfactants are essential ingredients of the printing paste. Polysaccharides are used commercially to thicken, suspend or stabilise aqueoussystems. Also they are used to produce gels and to act as flocculates, binders, lubricants, to serve as modifiers of film properties, and have a function as adjusters of rheological parameters. Surfactants, on the other hand, perform numerous functions acting as dispersants, wetting agents, emulsifiers and antifoaming agents. The rheological properties of polysaccharide thickeners (guar gums with different substitution levels and different producers) at different concentrations and temperatures and, second,the effects produced by the addition of nonionic surfactants (polyoxyethylene stearyl alcohols with different numbers of EO groups) have been studied under linear and nonlinear shear conditions. Experimental data have been correlated with the different modelsČ flow curves with the Cross, Carreau and Meter-Bird model, and mechanical spectra with the generalized Maxwell model and Friedrich-Braun model. The surface tensions of aqueous systems containing polysaccharide andžor surfactants have been determined overextended concentration ranges in order to detect the CMC conditions and toprovide a better understanding about the polysaccharide-surfactant interactions.
Ključne besede: textile printing, printing pastes, polysaccharides, thickeners, rheology, viscoelasticity, surfactants, guar gum
Objavljeno v DKUM: 01.06.2012; Ogledov: 2589; Prenosov: 90
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4. Rheological study of interactions between non-ionic surfactants and polysaccharide thickeners used in textile printingRebeka Fijan, Sonja Šostar-Turk, Romano Lapasin, 2007, izvirni znanstveni članek Opis: The influence of four non-ionic surfactants (isododecyl and cetyl polyoxyethylene ethers) on aqueous polysaccharide solutions (sodium alginate, guar gum, and sodium carboxymethyl guar), applicable for textile printing pastes, were studied via rheological measurements. Rheology of polysaccharide-surfactant solutions in aqueous matrices is primarily governed by polymer content, which imparts marked shear-thinning and viscoelastic character to the system. Such properties are modulated in moderate but sensible way by changes in surfactant concentration or type. Above 3% surfactants addition to non-substituted guar gum solutions results in a significant impact leading to phase separation and a particular strongly associated phase is formed due to hydrogen bonds between ethylene oxy units from the surfactant and primary hydroxyl groups in guar. A satisfactory fitting of viscosity data is obtained with both the Cross equation and the Roberts-Barnes-Carew model. The experimental results of mechanical spectra can be described quite satisfactory with both the Friedrich-Braun and the generalized Maxwell models.
Ključne besede: textile printing, polysaccharide thickeners, rheology, non-ionic surfactant, polymer-surfactant interactions, viscoelasticity
Objavljeno v DKUM: 01.06.2012; Ogledov: 2016; Prenosov: 93
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