Iskanje po repozitoriju

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Povzetek: This research proposes an alternative low-cement multicomponent binder for extrusion-based 3D concrete printing to reduce CO2 emissions associated with high Portland cement content. Due to the extremely low Portland cement content (100 kg/m3), the proposed mixture presents several limitations, making it unsuitable for 3D printing without additional activation. To overcome these limitations, chemical and physico-chemical activation methods were applied to promote rapid early-age structuration, partly associated with accelerated ettringite formation, thereby improving compliance with the printing process requirements. The results demonstrate that both activation methods positively affect Portland cement hydration and improve printing-related properties. The research focuses primarily on the hardened properties of 3D-printed concrete, showing that activation reduces macroscopic porosity and increases density and compressive strength. The applied activation methods also increase overall shrinkage compared to the nonactivated low-cement mixture. However, the absolute shrinkage remains approximately 25–30 % lower than that of a conventional reference mortar with a high Portland cement content. The suitability of the components used in the multicomponent binder was evaluated through pozzolanic activity testing. In contrast, the effects of chemical and physico-chemical activation on binder phase composition were investigated by X-ray diffraction, and the hardened properties of concrete were assessed using X-ray computed tomography, mercury intrusion porosimetry, shrinkage measurements, density, and compressive strength testing. The results demonstrate that chemical and physico-chemical activation enables the effective use of low-cement multicomponent binders in extrusion-based 3D concrete printing, providing a more sustainable alternative to conventional high-cement mixtures.
Ključne besede: 3D-tiskanje betona, večkomponentno vezivo z nizko vsebnostjo cementa, kemična aktivacija, fizikalno-kemična aktivacija, krčenje, 3D concrete printing, low-cement multicomponent binder, chemical activation, physico-chemical activation, shrinkage
Objavljeno v DiRROS: 15.05.2026; Ogledov: 8; Prenosov: 9
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Povzetek: This paper discusses the flexural and tensile strength properties of 3D printed concrete, based on the results of a RILEM TC 304-ADC interlaboratory study on mechanical properties. These properties are determined using different testing techniques, including 3- and 4-point flexural tests, splitting tests, and uniaxial tension tests, on specimens extracted from large 3D printed elements in accordance with a prescribed study plan. The relationship between compressive and flexural or tensile strengths, cast or printed samples, different types of tests, and different loading orientations, are analysed to understand the influence of 3D printing. As expected, the strength can reduce significantly when the main tensile stress is acting perpendicular to the interface between layers. The role of deviations from the standard study procedure, in terms of the time interval between the placing of subsequent layers, or the adoption of a different curing strategy, are also assessed. While the increased time interval significantly impacts the strength in the critical direction, the use of variable curing conditions does not seem to have a clear-cut effect on the strength ratios of the printed to cast specimens. Additionally, the paper looks at the variability in the results for the printed specimens, in order to emphasize the need for multiple replicates for obtaining a proper result. An extensive insight into the aspects affecting the variability is presented in the paper. Finally, with the limited dataset available for specimens tested at a larger scale, it is difficult to arrive at a clear understanding of the role of specimen size (i.e., greater number of layers).
Ključne besede: 3D concrete printing, digital fabrication, flexural strength, tensile strength, interlayer bond strength
Objavljeno v DiRROS: 12.01.2026; Ogledov: 369; Prenosov: 352
Celotno besedilo (7,51 MB)
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Povzetek: : An integrated miniature electrochemical sensor (ES) that offers rapid, sensitive, and selective detection of chemical and biological contaminants in a variety of samples requires temperature control to work accurately. To address this, one approach is to locate temperature sensor (TS) next to the ES components. However, this integration poses a challenge as different firing processes are required for the sensor components and the TS. Commercially available thick-film materials for the realisation of TS are designed for screen printing on alumina and firing in air at 850 °C for 10 minutes. However, a key component of an ES, a carbon-based working electrode, must be fired in an oxygen-lean atmosphere. In this study, we investigated the influence of the firing atmosphere, i.e., air and argon, on the characteristics of thick-film resistors, including thickness, roughness, phase composition, resistivity, and temperature dependence. For the study, we used two commercially available thick-film pastes, NTC2114 and NTC2113, as TS with nominal sheet resistivities of 10 kΩ/sq and 1 kΩ/sq at 25 °C, respectively. Using X-ray powder diffraction analyses, we detected RuO2 and spinel phases in the samples heated at 850 °C in air. However, when the samples were fired in argon, we detect metallic ruthenium and alloys. As a result of these changes, the resistivity of the NTC2114 and NTC2113 increased significantly. However, despite these changes, the relative resistance and the coefficient of temperature sensitivity did not vary significantly, indicating the suitability of these materials as TS. These findings have important implications for the future integration of TS into various screen-printed ES systems, fostering the design and development of systems with enhanced accuracy and reliability in temperature measurements.
Ključne besede: NTC, thick film, screen printing, temperature sensors
Objavljeno v DiRROS: 23.10.2025; Ogledov: 545; Prenosov: 254
Celotno besedilo (1,39 MB)
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Povzetek: This study investigates the fresh state and hardened state mechanical and durability properties of 3D-printed concrete. The mechanical tests focused on its anisotropic behavior in response to different load orientations. Compressive, flexural, and splitting tensile strengths were evaluated relative to the print layers orientation. Results showed that compressive strength varied significantly, achieving 85% of cast sample strength when the load was applied parallel to the print layers ([u] direction), 71% when the load was applied perpendicular to the print object’s side plane ([v] direction), while only reaching 59% when applied perpendicular to the top plane ([w] direction). Similar trends were observed for flexural strength, with average values reaching 75% of cast sample strength when the load was applied perpendicular to the print layers ([v.u] and [w.u] directions), but decreasing to 53% when the load was applied parallel to print layers ([u.w] direction), underscoring the weaknesses at interlayer interfaces. The splitting tensile strength remained relatively consistent across print orientations, reaching 90% of the cast sample strength. Durability assessment tests revealed that 3D-printed concrete exhibits reduced resistance to environmental factors, particularly at the layer interfaces where the cold joint was formed, which are prone to moisture penetration and crack formation. These findings contribute valuable insights into the mechanical and durability properties of 3D-printed concrete, emphasizing the importance of print orientation and interlayer bonding in its performance. This understanding helps guide the optimal use of 3D-printed elements in real-life applications by aligning load or exposure to environmental factors with the material’s strength and durability characteristics.
Ključne besede: civil engineering, 3D-printing, concrete, additive manufacturing
Objavljeno v DiRROS: 11.02.2025; Ogledov: 3336; Prenosov: 721
Celotno besedilo (6,94 MB)
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Povzetek: The Sitarjevec mine, located near the town of Litija (Central Slovenia), is recognized by the strong yellow colour of its dripstone structures and mine mud deposits. The mine mud, composed predominantly of goethite, accumulates on the ground of the mine shafts as the result of the interaction between percolating underground water, iron ore minerals and microorganisms. Since the accumulation of limonite mine mud is an ongoing process, larger quantities of mud have been deposited in the mine shafts since its closure. These deposits present a real threat of unleashing a mine mud spill on the town of Litija. Such a scenario has already previously occurred. In order to find new potential routes for recycling larger quantities of this mine mud, the present research work was performed to assess the use of mine mud as a pigment in the dye industry. In the first stage, the chemical (XRF) and microstructural (SEM) characteristics of the mine mud were defined together with the identification of its phase composition (XRD), particle size distribution and specific surface area (BET). Furthermore, the pigment was used to colour textile printing paste on a laboratory scale. To define the most appropriate quality of textile prints the rheological response of the various textile printing paste samples was investigated in terms of their plastic viscosity, indicating their suitability for use in textile printing. Test prints wereconducted, and the properties of leaching and fastness in the prints were assessed.
Ključne besede: mine mud, recycling, pigment, printing paste, textile, rheology
Objavljeno v DiRROS: 25.01.2024; Ogledov: 1706; Prenosov: 1140
Celotno besedilo (9,29 MB)
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