1. Laboratory testing of old bridge girders : preliminary resultsMaja Kreslin, Mirko Kosič, Aljoša Šajna, Andrej Anžlin, Doron Hekič, Vladimir Požonec, Petra Triller, 2025, objavljeni znanstveni prispevek na konferenci Povzetek: This paper presents key results on the laboratory testing of old girders removed from a flood-damaged bridge located near Ljubljana, Slovenia. The structure was widened in 1989 to accommodate pedestrians and cyclists by integrating prefabricated prestressed reinforced concrete T-girders. To assess the structural behaviour of the bridge, six girders were subjected to a rigorous testing program involving bending and shear tests in a laboratory setting. The tests were performed on girders with static lengths of 12.20 meters and 9.90 meters. The program aimed to evaluate the structural performance of the girders. Preliminary results indicate satisfactory structural behaviour of the prestressed T-girders under the applied loads, with insights into their performance under both bending and shear stresses. This study contributes valuable data for assessing the long-term behaviour of bridges. The outcomes are particularly relevant for optimising resource allocation in bridge rehabilitation projects and ensuring safety and functionality in transportation networks.
Ključne besede: laboratory testing, prestressed girders, assessment, load test, operational modal analysis, damage, acoustic emission
Objavljeno v DiRROS: 22.01.2026; Ogledov: 421; Prenosov: 264
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2. Mechanical properties of 3D printed concrete : a RILEM 304‑ADC interlaboratory study – flexural and tensile strengthRob Wolfs, Jelle Versteege, Manu Santhanam, Shantanu Bhattacherjee, Freek Bos, Annika Robens-Radermacher, Shravan Muthukrishnan, Costantino Menna, Katarina Šter, Aljoša Šajna, 2025, izvirni znanstveni članek 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: 488; Prenosov: 852
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3. Investigating the synergistic impact of freeze-thaw cycles and deicing salts on the properties of cementitious composites incorporating natural fibers and fly ashIldikó Merta, Vesna Zalar Serjun, Alenka Mauko Pranjić, Aljoša Šajna, Mateja Štefančič, Bojan Poletanovic, Farshad Ameri, Ana Mladenović, 2025, izvirni znanstveni članek Povzetek: In cold climates, concrete structures confront durability challenges due to harsh conditions. This study evaluates the effects of incorporating natural fibers, such as hemp and flax fibers (at 1 vol%), and partially replacing cement with fly ash (at 25 and 50 wt%) on the properties of cementitious composites subjected to accelerated aging under freeze-thaw cycles and deicing salts. Findings reveal that natural fibers enhance the freeze-thaw resistance, reducing deterioration (scaling) to 5-8% after 56 cycles. When mortars were subjected to accelerated freeze-thaw cycles, the compressive strength of plain mortar significantly decreased (up to 57%). However, adding natural fibers to the matrix substantially reduced its compressive strength loss. In the case of flexural strength, plain mortars experienced 33% loss, while hemp, flax, and polypropylene fiber mortars showed only 13%, 23%, and 10% losses, respectively. Furthermore, mortars experience a notable enhancement in their energy absorption capacity when reinforced with natural fibers, particularly with hemp fibers (up to 348% higher than plain mortar). Under harsh conditions, hemp and flax-reinforced mortars, with 25wt% fly ash replacement, lose the compressive strength significantly however still demonstrate an alternative to synthetic fibers in terms of flexural strength. Even with 25wt% of fly ash, mortars with natural fiber reinforcement display significantly superior energy absorption capacities compared to plain mortars (up to 48%).
Ključne besede: cementitious composites, natural fibers, freeze-thaw cycles, mechanical properties, mass loss, fly ash
Objavljeno v DiRROS: 23.12.2024; Ogledov: 1695; Prenosov: 730
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4. Environmental life cycle assessment of railway bridge materials using UHPFRCKarmen Fifer Bizjak, Aljoša Šajna, Katja Slanc, Friderik Knez, 2016, izvirni znanstveni članek Povzetek: The railway infrastructure is a very important component of the world’s total transportation network. Investment in its construction and maintenance is significant on a global scale. Previously published life cycle assessment (LCA) studies performed on road and rail systems very seldom included infrastructures in detail, mainly choosing to focus on vehicle manufacturing and fuel consumption. This article presents results from an environmental study for railway steel bridge materials for the demonstration case of the Buna Bridge in Croatia. The goal of these analyses was to compare two different types of remediation works for railway bridges with different materials and construction types. In the first part, the environmental impact of the classical concrete bridge construction was calculated, whereas in the second one, an alternative new solution, namely, the strengthening of the old steel bridge with ultra-high-performance fibre-reinforced concrete (UHPFRC) deck, was studied. The results of the LCA show that the new solution with UHPFRC deck gives much better environmental performance. Up to now, results of LCA of railway open lines, railway bridges and tunnels have been published, but detailed analyses of the new solution with UHPFRC deck above the old bridge have not previously been performed.
Ključne besede: railway, materials, ife cycle assessment, bridge, environmental
Objavljeno v DiRROS: 23.08.2024; Ogledov: 1175; Prenosov: 943
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5. Pitna voda v Mestni občini Ljubljana : pot od vodnega vira do kozarcaTadeja Kosec, Nina Gartner, Brigita Jamnik, Viviana Golja, Alenka Labovič, Lucija Smojver, Sabina Dolenec, Aljoša Šajna, Monika Novak Babič, Nina Gunde-Cimerman, Tinkara Kopar, 2019, strokovna monografija Ključne besede: centralni vodovodni sistem Ljubljana (CVS), pitna voda, materiali v stiku s pitno vodo, vzdrževanje sistemov, preskušanje, kovinski materiali, organski materiali, cementni materiali, mikrobiološki vpliv, certificiranje proizvodov, vodno gospodarstvo, oskrba z vodo
Objavljeno v DiRROS: 08.03.2024; Ogledov: 1683; Prenosov: 972
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6. Construction materials for a sustainable future : proceedings of the 2nd International Conference CoMS 2020/212021, zbornik recenziranih znanstvenih prispevkov na mednarodni ali tuji konferenci Povzetek: Zbornik pokriva številne, predvsem tehnične teme, ki so pomembne za trajnostni razvoj gradbenega sektorja, kot ključnega dejavnika pri doseganju ciljev EU za obvladovanje podnebnih sprememb in za prehod v brezogljično družbo. Vsebinsko naslavlja inovacije v gradbenih materialih in tehnologijah, vključno s komponentami za zdravo in udobno bivanje, ter interakcije med materiali in okoljem. Poleg energetske učinkovitosti stavb je v njem zajeto področje širšega razumevanja trajnostnega načrtovanja, gradnje in vzdrževanja stavb ter monitoring, ocenjevanje in modeliranje stavb. Vključuje pa tudi vsebine, ki se nanašajo na krožno gospodarstvo, kot je recikliranje materialov in komponent ter koncepti sanacij stavb, ter na digitalizacijo in avtomatizacijo področja.
Ključne besede: trajnostno gradbeništvo, trajnostna gradnja, gradbeni materiali, tehnologije, energetska učinkovitost, zborniki, elektronske knjige
Objavljeno v DiRROS: 25.01.2024; Ogledov: 2238; Prenosov: 1029
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7. 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: 1605; Prenosov: 1194
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8. 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: 1652; Prenosov: 1212
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