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1123. Temperature pre-treatment of gypsum for powder based 3D printing technologyVesna Zalar Serjun, Lidija Korat, 2021, objavljeni znanstveni prispevek na konferenci 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: 313; Prenosov: 171
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1125. LCA and LCC assessment of UHPFRC application for railway steel bridge strengtheningIrina Stipanović, Sandra Škarić Palić, Aljoša Šajna, Martín-Sanz Henar, Eleni Chatzi, 2021, objavljeni znanstveni prispevek na konferenci Povzetek: Most of the existing railway steel bridges are nowadays older than 70 years, experiencing serious aging and overload problems. Therefore they either need to be replaced or strengthened to fulfil the increased requirements. The main idea of strengthening existing steel bridges is considering the possibility of adding load bearing deck above the main girders without replacing them. In this particular case study, the original steel structure of the 9m long railway bridge was dismantled and transported to the laboratory for the experimental assessment and development of the new rehabilitation method. Based on the assessment results, a strengthening slab was designed using Ultra High Performance Fibre Reinforced Concrete (UHPFRC) formula. In the life cycle analysis, using LCC and LCA models, the comparison of the application of UHPFRC cast in-situ deck is compared to the bridge replacement solution, which was actually selected method by the owner. The executed solution used also a temporary bridge in order to enable continuous traffic, which has caused very high construction costs. In order to compare different options, we have additionally analysed a solution without a temporary bridge, which created three life cycle scenarios. Most important steps during the construction, exploitation and end-of-life stage have been taken into account and integrated into the LCA and LCC models. Finally the environmental, economy and societal impacts of three solutions were compared over the period of 60 years. The rehabilitation option with UHPFRC deck has shown by far the lowest direct and environmental cost while the user delay costs only after the period of 50 years are not the most convenient for users. Superior characteristics of UHPFRC enabled the optimization of the load bearing deck and by that a very low total used quantity of material resulting in minimum direct and indirect costs.
Ključne besede: railway steel bridge, UHPFRC, strengthening, LCA, LCC model
Objavljeno v DiRROS: 25.01.2024; Ogledov: 230; Prenosov: 160
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1128. Experimental carbonation study for durability assessment of novel cementitious materialsSebastijan Robič, Aljoša Šajna, Lucija Hanžič, Alisa Machner, Marie Helene Bjørndal, Klaartje De Weerdt, Yushan Gu, Benoit Bary, Rosamaria Lample, 2021, objavljeni znanstveni prispevek na konferenci Povzetek: The design process of concrete structures is carried out using standards and guidelines, while the durability predictions of concrete structures is supported only with exposure classes and experience-based requirements. To improve durability predictions of the carbonation resistance of concrete, a numerical model is being developed within the Horizon 2020 project EnDurCrete, coupling the rate of carbonation, and the drying rate. To verify the numerical model, an accelerated carbonation study was carried out. Experiments were conducted on mortars incorporating a novel CEM II/C (S-LL) cement, developed within the EnDurCrete project, and a commercially available reference cementCEM II/A-S. EnDurCrete mortars (EnM) and reference mortars (RefM) were prepared with water-cement ratios of 0.6 and 0.5 (denoted with label extensions -06 and -05). Visual assessments and thermogravimetric analysis (TGA) were used to measure the carbonation rates, which were found to be ~1.0 mm day-0.5 in EnM-06 and ~0.6 mm day-0.5 in RefM-06, while in EnM-05 and RefM-05 the values were ~0.7 and ~0.2 mm day-0.5 respectively. Additionally, TGA shows that the initial portlandite (CH) content is ~1.5 wt% in EnM-06 as opposed to ~3.0 wt% in RefM-06. The difference in the initial CH content in the two hydrated binders might explain the difference in their carbonation rate. During the moisture transport experiments a gravimetric method was used to determine mass changes as specimens underwent drying and resaturation with and without CO2 present. The drying led to a decrease in mass, but in the presence of CO2 this mass loss was compensated by the mass gain due to uptake of CO2 during carbonation. The resaturation experiments indicate an increase in the suction porosity in the carbonated samples compared to the non-carbonated samples.
Ključne besede: concrete, absorption of water, carbonation, durability assessment, model verification
Objavljeno v DiRROS: 25.01.2024; Ogledov: 260; Prenosov: 172
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1130. Mud from the Sitarjevec mine as a pigment for textile printingDarja Rant, Mateja Štefančič, Vesna Zalar Serjun, Mateja Golež, 2021, objavljeni znanstveni prispevek na konferenci 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: 263; Prenosov: 147
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