31. Environmentally friendly protection of European beech against fire and fungal decay using a combination of thermal modification and mineralisationRožle Repič, Andreja Pondelak, Davor Kržišnik, Miha Humar, Nataša Knez, Friderik Knez, Andrijana Sever Škapin, 2024, original scientific article Abstract: The demand for construction timber is continuously increasing, due to its favourable characteristics. However, the adequate protection of wood is key to its successful use, as it is flammable and susceptible to biodegradation. Given that thermal modification enhances the durability of wood, and mineralisation with CaCO3 considerably improves its fire properties, it is worth considering the combined effects of the two methods. European beech (Fagus sylvatica) was selected to determine the effects of a) thermal modification, b) mineralisation through the in-situ formation of CaCO3, and c) a combination of the two procedures, on resistance to decay fungi, reaction to fire and the mechanical properties of the wood. Microscopic analysis and comparisons of the samples before and after exposure to fungi were also conducted. Mineralised wood generally had a slightly alkaline pH value and higher equilibrium moisture content, while thermal modification lowered the equilibrium moisture content. The present study demonstrated the combined effect of thermal modification and mineralisation: the best response to fire as well as resistance to fungi was achieved when the two treatments were combined. Results from the Brinell hardness and three-point bending tests indicate that both modification procedures can slightly impair the mechanical properties of the wood.
Keywords: wood, protection, durability, mechanical properties
Published in DiRROS: 12.07.2023; Views: 351; Downloads: 257
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32. Preparation of façade panels based on alkali-activated waste mineral wool, their characterization and durability aspectsMajda Pavlin, Barbara Horvat, Vilma Ducman, 2022, original scientific article Abstract: Mineral wool is a widely used insulation material and one of the largest components of construction and demolition waste, yet it mainly ends up in landfills. In this work, we explored the potential recycling of waste stone wool in the pilot production of alkali-activated façade panels. The current work shows mechanical properties, SEM-EDS and mercury intrusion porosimetry analyses for three different mix designs used for the preparation of façade panels. They are all composed of waste stone wool and differ in the amount of co-binders (local slag, lime, metakaolin and/or fly ash) selected by the preliminary studies. In this study, co-binders were added to increase early strength and improve the mechanical properties and freeze-thaw resistance. The mechanical properties of each were measured up to 256 days, different durability tests were executed, and, by evaluating the mechanical properties, microstructure and workability of the mortar, the most suitable mix was selected to be used for pilot production. In addition, the leaching test of the selected mixture showed no exceeded toxic trace elements and therefore got classified as non-hazardous waste after its use.
Keywords: alkali activation, waste mineral wool, SEM, XRF, XRD, mechanical strength
Published in DiRROS: 19.06.2023; Views: 334; Downloads: 146
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33. The preparation and characterization of low-temperature foams based on the alkali activation of waste stone woolMajda Pavlin, Barbara Horvat, Mark Češnovar, Vilma Ducman, 2022, original scientific article Abstract: Waste mineral wool represents a huge amount of construction and demolition waste that is still not adequately returned into the value chain but needs to be landfilled. In the present study, waste stone wool (SW) was evaluated for the preparation of alkali-activated foams. For this purpose SW was milled and sieved below 63 μm, then the activator (sodium silicate) and different amounts of foaming agent (hydrogen peroxide, H2O2), varying between 1 wt% and 3 wt%, were added to the slurry and cured in moulds at an elevated temperature (70 ◦ C) for three days. In this way, foamed, highly porous materials were obtained whose density and mechanical properties were influenced by the amount of foaming agent used. The densities obtained ranged between 1.4 and 0.5 g/cm3, with corresponding mechanical properties of between 12.6 and 1.5 MPa and total porosities in the range 37.8–78.6%, respectively. In the most porous samples with the total porosity of 78.6%, a thermal conductivity of 0.092 W/(m∙K) was confirmed. The study confirmed the suitability of waste mineral wool (in our case SW) as a precursor for alkali-activated foams with potential use in the construction sector or other industrial applications.
Keywords: alkali activation, waste mineral wool, mechanical strength, open access, alkalijska aktivacija, odpadna volna, SEM, XRF, XRD, mehanska trdnost, odprti dostop
Published in DiRROS: 19.06.2023; Views: 270; Downloads: 210
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34. Flame retardant behaviour and physical-mechanical properties of polymer synergistic systems in rigid polyurethane foamsBranka Mušič, Nataša Knez, Janez Bernard, 2022, original scientific article Abstract: In the presented work, the influence of two flame retardants—ammonium polyphosphates and 2,4,6-triamino-1,3,5-triazine on the polyurethane foam (PUR) systems were studied. In this paper, these interactive properties are studied by using the thermal analytical techniques, TGA and DTA, which enable the various thermal transitions and associated volatilization to be studied and enable the connection of the results with thermal and mechanical analysis, as are thermal conductivities, compression and bending behavior, hardness, flammability, and surface morphology. In this way, a greater understanding of what the addition of fire retardants to polyurethane foams means for system flammability itself and, on the other hand, how this addition affects the mechanical properties of PUR may be investigated. It was obtained that retardants significantly increase the fire resistance of the PURs systems while they do not affect the thermal conductivity and only slightly decrease the mechanical properties of the systems. Therefore, the presented systems seem to be applicable as thermal insulation where low heat conductivity coupled with high flame resistance is required.
Keywords: flammability, polyurethane polymer, foams, thermal conductivity, mechanical properties, open access
Published in DiRROS: 08.06.2023; Views: 405; Downloads: 180
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35. Composite beams made of waste wood-particle boards, fastened to solid timber frame by dowel-type fastenersMeta Kržan, Tomaž Pazlar, Boštjan Ber, 2023, original scientific article Abstract: To increase the sustainability of prefabricated timber buildings and constructions, composite timber beams with “box” cross-sections were developed in collaboration with an industry partner. They were constructed from a solid timber frame and from webs made of residual waste wood- particle boards from prefabricated timber buildings production. The developed beams’ design concepts presented in this paper were governed by architectural features of prefabricated timber buildings, geometrical limitations, available production technology, and structural demand related to various possible applications. The paper presents the results of experimental bending tests of six variations of the developed composite timber beams constructed by mechanical fasteners only. The developed design concept of composite timber beams without adhesives is beneficial compared to glued beams in terms of design for deconstruction and lower VOC emissions. The tests were conducted to study the influence of the following parameters on the beams’ mechanical behavior: (i) web material (oriented strand boards (OSBs) vs. cement-particle boards); (ii) the influence of beam timber frame design (flanges and web stiffeners vs. flanges, web stiffeners, and compressive diagonals), and (iii) the influence of stiffener–flange joint design. Besides the beams’ load-bearing capacities, their linear and non-linear stiffness characteristics were the main research interest. While adding compressive timber diagonals did not prove to significantly increase the stiffness of the beams in the case of cement-particle board webs, it increased their load-bearing capacity by enabling the failure of flanges instead of prior webs and stiffener–flange joints failure. For beams with OSB webs, failure of the bottom flange was achieved already with the “basic” timber frame design, but timber diagonals proved beneficial to increase the stiffness characteristics. Finally, mechanical characteristics of the developed beams needed in structural design for their application are provided together with further development guidelines.
Keywords: composite timber beam, box beam, OSB, cement-particle boards, innovative engineered wood product, experimental tests, flexural performance, mechanical fasteners, open access
Published in DiRROS: 29.05.2023; Views: 276; Downloads: 161
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36. In-plane seismic behaviour of ashlar three-leaf stone masonry walls : verifying performance limitsMeta Kržan, Vlatko Bosiljkov, 2021, original scientific article Abstract: In light of the forthcoming second generation Eurocodes (EC), the results of conducted systematic in-plane cyclic and compressive tests on three-leaf stone masonry walls are discussed following new requirements and provisions. The new proposal for EC8-3 for existing buildings is based on partial factors safety approach, though it considers different uncertainties in defining input parameters for effective seismic performance-based assessment. Prior to its application, massive calibration effort will be needed since there is no standardized method for shear testing of masonry walls. In this paper, the performance limit states damage, resistance, and displacement capacities from conducted test results were evaluated and assessed through comparison with analytical solutions and imposed limit values, as stated in existing codes. The test results provide a much higher deformation capacity than the limits provided in both existing and new proposal of EC8-3 as well as those in the ASCE code provisions. The reason for this lies in the soft, "ductile" mortar for which the presumed resistance according to code provisions should be significantly higher when considering good quality ashlar three-leaf stone masonry.
Keywords: historical masonry, multi-leaf stone masonry, mechanical properties, compression tests, in-plane shear tests, failure mechanisms, drift limits, boundary conditions
Published in DiRROS: 19.05.2023; Views: 332; Downloads: 169
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37. Improved synthetic route of incorporation of nanosilicon species into phenol-formaldehyde resin and preparation of novel ZnAl-layered double-hydroxide hybrid phenol-formaldehyde resinAna Dremelj, Romana Cerc Korošec, Andreja Pondelak, Branka Mušič, 2022, original scientific article Abstract: Hybrid phenol-formaldehyde (PF) resins represent one of the most important niche groups of binding systems for composites. New industrial needs, environmental requirements, and price fluctuations have led to further research on materials with enhanced mechanical and thermal properties. The preparation of novel hybrid materials can be achieved by inclusion of various elements or functional groups in the organic polymer phenolic framework. Herein, we report the synthesis and characterization of a PF-based hybrid material with different nanoscale silicone species and ZnAl-layered double hydroxide (LDH). The main goals of this study were to improve the synthetic pathways of hybrid resin, as well as to prepare granulated composite materials and test samples and determine their characterization. Added inorganic species increased the glass-transition temperature by a minimum of 8 °C, which was determined using differential scanning calorimetry (DSC). Rheological properties (melting viscosity and flow distance) of the hybrid resin were measured. The homogeneity of distribution of added species across the organic matrix was evaluated with scanning electron microscopy (SEM). With synthesized new hybrid-binding systems, we prepared different granulated composite materials and evaluated them with the measurements of rheological properties (flow curing characteristics). Tensile strength of samples, prepared from granulated composite material, improved by more than 5%.
Keywords: phenol-formaldehyde hybrid resins, nano-SiO2, ZnAl-LDH, composites, glass-transition temperature, mechanical properties
Published in DiRROS: 03.05.2023; Views: 398; Downloads: 177
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38. Residual compressive behavior of self-compacting concrete after high temperature exposure - influence of binder materialsMarija Jelčić Rukavina, Ivan Gabrijel, Ivanka Netinger Grubeša, Ana Mladenovič, 2022, original scientific article Abstract: This paper presents an experimental investigation of the compressive behavior of highstrength self-compacting concrete exposed to temperatures up to 600 C. Ten different concrete compositions were tested, in which part of the cement (by weight) was replaced by three different mineral additives (5–15% metakaolin, 20–40% fly ash and 5–15% limestone). The stress–strain curves, compressive strength, modulus of elasticity and strain at peak stress were evaluated from uniaxial compression tests. Scanning electron microscope micrographs were also taken to evaluate the damage caused by the high temperatures. A sharp decrease in mechanical properties and an increase in peak strain were observed already after 200 C for all mixes tested. The different mineral additives used in this study affected the variations of residual compressive strength by 24% and peak strain by 38%, while the variations of residual modulus elasticity were 14%. Comparing the obtained results with the recommendations for compressive strength given in regulatory code EN 1992-1-2 for high strength concrete, it can be concluded that the strength loss observed in EN 1992-1-2 at temperatures up to 400 C is too conservative. The Popovics model for the relationship between stress and strain provided a good approximation for the experimentally determined stress–strain curves at different temperatures.
Keywords: self-compacting concrete, mineral additives, high temperatures, residual mechanical properties, open access
Published in DiRROS: 28.04.2023; Views: 378; Downloads: 185
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39. Current trends on mechanical, corrosion resistance, and antibacterial properties of metallic materials : editorialMarjetka Conradi, Aleksandra Kocijan, 2022, preface, editorial, afterword Keywords: steel, corrosion resistance, mechanical properties, antibacterial properties
Published in DiRROS: 22.06.2022; Views: 519; Downloads: 140
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