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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: 146; Prenosov: 100
Celotno besedilo (4,77 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: 3581; Prenosov: 756
Celotno besedilo (6,94 MB)
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Povzetek: Marine ostracods of the family Bairdiidae Sars, 1888 have an evolutionary history starting from the Ordovician with an explosive diversification of ornate forms during the Triassic. Representatives of the family are notoriously homeomorphic, which makes their taxonomy a major challenge of modern ostracodology. Their classification has thus been problematic since the 1970s. Here we present the first CT-scan investigation of recent and fossil ornate Bairdiidae valves in order to characterize and evaluate the taxonomic significance of unexploited characters, such as pores and pore canals. Thanks to 3D tomography, we explore the distribution of pores at the surface and the pathway of pore ca- nals within the valve wall of the recent genus Triebelina van den Bold, 1946 and the Triassic genera Nodobairdia Kollmann, 1963 and Mirabairdia Kollmann, 1963. In Triebelina indopacifica van den Bold, 1946, we describe an unexpected system of double pore canals, so far unknown in ostracods. We confirm that pore systems in Triebelina have largely intramural positions. In the Triassic Bairdiidae (Nodobairdia mammilata Kollmann, 1963 and Mirabairdia pernodosa Kollmann, 1963), we recognize simple unrimmed and massively nodular pores as well as marginal pores. Lateral normal pores of the Triassic specimens appear to be mostly in intra-solum positions. Although still exploratory and at the limits of the tomographic resolution, these observations provide new evidence to reject the formerly proposed synonymy of Triassic genera with Triebelina, which obstructed the establishment of a phylogenetic classification.
Ključne besede: ostracods, ornate Bairdiidae, morphology, normal pore canals, CT-scan, 3D analysis
Objavljeno v DiRROS: 08.03.2024; Ogledov: 1845; Prenosov: 1395
Celotno besedilo (10,78 MB)
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Povzetek: In recent years many researchers have been involved in studies in the field of pre-treatment of various raw materials. Temperature treatment of materials results in several advantages, which have been already recognised and successfully applied in various fields of applications. Where at the same time, the practices has been adopted also in the field of 3D printing. Enhanced strength and stiffness, assuring desirable performance criteria of the 3D printed models, reflect the most important characteristics. 3D printing binder jetting technology is based on the application of liquid binders onto powdered material, where gypsum powders have been commercially used as a base raw material. As natural raw materials can be replaced by other materials, such as recycled industrial by products, the aim of this research work was to evaluate the potential usage of three synthetic gypsum powders from different industrial processes for 3D printing. The investigation covered (a) mineralogical and microstructural characteristics of gypsums from different origin and (b) the effect of pre-treatment of gypsum powders at different temperatures (up to 500 °C). On the basis of the results, the most promising temperature regime for each different waste gypsum powder treatment, reflecting in the most optimal setting time, was defined. Synthetic gypsums were characterized by X-ray diffraction (QXRD), scanning electron microscopy (SEM) and differential thermal analysis (TG/DTA). The results showed that all three synthetic gypsums (calcium sulfate dihydrate, CaSO 4∙2H2O) thermally degrade into calcium sulfate anhydrite (CaSO 4) via an intermediate calcium sulfate hemihydrate (CaSO 4∙ ½H2 O, bassanite) phase. Microstructural and mineralogical differences were observed when temperature treated gypsums from different origins were compared. The detailed knowledge of gypsum powder properties at different temperature regime is important parameter for the assurance of 3D printing key parameters such as flowability, roughness and wettability, especially for determination of saturation levels and setting time. After all, these parameters define final mechanical properties of 3D printed structures. By using such approach, the understanding of material compatibility for 3D printing technology can be defined and improved if necessary.
Ključne besede: 3D print, additive manufacturing, gypsum, temperature
Objavljeno v DiRROS: 25.01.2024; Ogledov: 1708; Prenosov: 1172
Celotno besedilo (9,29 MB)
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Povzetek: This experimental study aimed to develop a fiber-reinforced lightweight mineral wool-based alkali activated mortar. The lightweight mineral wool-based alkali activated mortars were produced using premade foam and reinforced by polypropylene (PP) fibers. They were assessed in terms of fresh and hardened-state properties. Fresh-state properties were investigated by mini-slump tests. Hardened-state characteristics were assessed by ultrasonic pulse velocity, dry density, compressive and flexural strengths, drying shrinkage, efflorescence, water absorption, and permeable porosity. For the first time, the resistance of the synthesized lightweight mineral wool-based alkali activated mortars against harsh conditions (carbonation, freeze and thaw, and high temperature) were evaluated. The porous structures of the developed lightweight alkali activated mortars were also analyzed using an X-ray micro-computed tomography (CT) technique. Lightweight mix compositions with densities in a range of 770%1510 kg/m3, compressive strengths of 1%9 MPa, and flexural strengths of 2.6%8 MPa were developed. Increases in both density and strength after carbonation were also recorded, while a decrease of strength was noticed after exposure to freeze/thaw and high temperatures of up to 500 %C.
Ključne besede: alkali activation, mineral wool, mortars
Objavljeno v DiRROS: 24.10.2023; Ogledov: 1690; Prenosov: 939
Celotno besedilo (10,47 MB)
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