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Query: "author" (Andreja Pondelak) .

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1.
Lastnosti lesa iz rudnika Sitarjevec
Miha Humar, Boštjan Lesar, Davor Kržišnik, Andreja Pondelak, Andrijana Sever Škapin, Angela Balzano, José Gonçalves, 2024, original scientific article

Abstract: Rudarska tradicija v Litiji, segajoča v staro železno dobo, je vključevala intenzivno uporabo lesa v rudnikih, še posebej za podporo in zaščito rovov. Rudnik Sitarjevec je bil znova odprt za turizem leta 2017, in v letu 2021 so odprli glavni rov. Les ostaja ključen material v rudnikih, čeprav so ga v preteklosti nadomeščali z drugimi materiali. Uporabljeni les je izpostavljen razkroju zaradi visoke vlažnosti in gliv, kot je bela hišna goba. Ta gliva lahko povzroči razgradnjo lesa in je pogosta v vlažnih okoljih rudnikov. Obstoj gliv je pomemben, saj lahko vplivajo na obiskovalce rudnika. Visoka relativna zračna vlažnost (96,6 %) in stalna temperatura (10,1 °C) v rudniku ustvarjata razmere, ki so ugodne za rast gliv, vendar pa relativno nizka temperatura ni omejujoč dejavnik za razgradnjo lesa. Koncentracija glivnih spor v rudniku je visoka in je razložena z razširjenostjo gliv v samem rudniku. Poleg tega smo opazili, da je v lesu veliko anorganskih onesnaževal ter veliko kristalov.
Keywords: razkroj, bela hišna goba, težke kovine, kristali, spore
Published in DiRROS: 21.06.2024; Views: 255; Downloads: 76
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3.
Effect of sucrose concentration on streptococcus mutans adhesion to dental material surfaces
Anamarija Zore, Franc Rojko, Nives Matijaković Mlinarić, Jona Veber, Aleksander Učakar, Roman Štukelj, Andreja Pondelak, Andrijana Sever Škapin, Klemen Bohinc, 2024, original scientific article

Abstract: Enamel demineralization, known as dental caries, is instigated by the bacterium Streptococcus mutans, which generates acid during carbohydrate metabolism. Among carbohydrates, sucrose is the most cariogenic and capable of biofilm formation. This study aimed to explore and comprehend Streptococcus mutans’ adherence to two prevalent dental material surfaces, i.e., a cobalt–chromium(Co-Cr) alloy and a resin-based composite, under the influence of various sucrose concentrations. To understand bacterial adhesion, the surfaces were characterized using profilometry, tensiometry, and surface charge measurements. Bacterial adhesion was evaluated using scanning electron microscopy and crystal violet dye methods. Results revealed that the composite surface exhibited greater rough-ness compared with the Co-Cr alloy surface. Both surfaces displayed hydrophilic properties and a negative surface charge. Bacterial adhesion experiments indicated lower bacterial adherence to the Co-Cr alloy than to the composite surface before the addition of sucrose. However, the introduction of sucrose resulted in biofilm development on both surfaces, showcasing a similar increase in bacterial adhesion, with the highest levels being observed at a 5% sucrose concentration in the bacterial suspension. In conclusion, the findings suggest sucrose-rich foods could facilitate bacterial adaptation despite less favorable surface characteristics, thereby promoting biofilm formation.
Keywords: bacterial adhesion, streptococcus mutans, dental material surfaces, sucrose concentration
Published in DiRROS: 31.01.2024; Views: 331; Downloads: 138
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4.
Flexible polymer connections for clt structures
Boris Azinović, Andreja Pondelak, Jaka Gašper Pečnik, Václav Sebera, 2020, published scientific conference contribution

Abstract: This paper explores the possibility of using flexible polymer adhesives to dissipate energy in CLT buildings during earthquakes. In the first series of tests, pull-off tests of various polyurethane (PUR) adhesives were performed. The connection was tested in pull-pull configuration using monotonic, tension-only loading. The tests have shown that the adhesive can resist large deformations already in tension loading and with small thicknesses of the bond-line. Based on the pull-off test results, one adhesive has been selected for further testing. Monotonic lap-shear tests were performed with the selected adhesive and thick bond-line (3 mm and 6 mm). The results show, that the standard method for lap-shear testing (EN 205) needs to be adapted for thick glue-line. It was found that the strength of 3 mm glue-line is higher than 6mm one, which is in agreement with adhesion theory. The flexible PUR adhesives could potentially be used in CLT structures for anchoring the CLT wall with “flexible” glued-in rods or as a “flexible” vertical shear connection between the CLT walls. Such systems have a potential to dissipate energy in seismic areas.
Keywords: CLT connections, flexible adhesive, polyurethane, energy dissipation, pull-off, lap-shear
Published in DiRROS: 19.01.2024; Views: 313; Downloads: 147
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5.
The role of relative humidity on crystallization of calcium carbonate from calcium acetoacetate precursor
Andreja Pondelak, Francesca Rosi, Celeste Maurich, Costanza Miliani, Srečo D. Škapin, Andrijana Sever Škapin, 2019, original scientific article

Abstract: Calcium acetoacetate, Ca(OAcAc)2, was exposed 7, 30 and 365 days to different values of relative humidity (33%, 48%, 75% and 96%) at 40 °C in order to study its transformation to CaCO3. The resulting Ca(OAcAc)2 decomposition and the time dependence of the phase transformations were monitored and critically evaluated by Fourier transform infrared spectroscopy, field emission scanning electron microscopy and X-ray powder diffraction. The impact of relative humidity on CaCO3 polymorph formation was thoroughly assessed. In all of the conditions used and for all ageing periods, the formed crystal structure is found to be vaterite. At the lowest relative humidity (33%), the amorphous CaCO3 remains more or less almost untransformed even after one year of exposure. It is proposed that the reason for the stability of amorphous CaCO3 is due to the limited amount of physisorbed water on the surfaces of the particles, which is considered the driving force for its transformation. However, the carbonation process is faster in the case of the highest humidity (96%). The findings are not only important for better solutions in the field of cultural heritage, but also shed new light on the fundamental mechanism of CaCO3 crystallization.
Keywords: calcium acetoacetate, relative humidity, carbonation, amorphous carbonate, vaterite, mechanism
Published in DiRROS: 22.11.2023; Views: 521; Downloads: 216
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6.
Efficiency of novel photocatalytic coating and consolidants for protection of valuable mineral substrates
Andreja Pondelak, Sabina Dolenec, Jonjaua Ranogajec, Luka Škrlep, Snezana B. Vučetić, Vilma Ducman, Andrijana Sever Škapin, 2019, original scientific article

Abstract: In the process of protection and consolidation of valuable materials, the efficiency is the crucial property that needs to be considered. TiO2/ZnAl layered double hydroxide (LDH) coating and silicate- and carbonate-based consolidants were synthesized and proposed to be used for protection and consolidation of four porous mineral substrates: brick, stone, render and mortar. The photocatalytic efficiency of TiO2/ZnAl LDH coating, as well as consolidation efficiency of two consolidants, both applied on model substrates, were studied. The photocatalytic coating showed significant activity and performed well after the durability tests involving rinsing and freezing/thawing procedures. After treatment with both consolidants, a serious enhancement of consolidation of the used substrates was found. On the other hand, the application of TiO2/ZnAl LDH, as well as consolidants, caused negligible changes in the water vapour permeability values and in appearance of the porous mineral substrates, indicating a high level of compatibility.
Keywords: photocatalytic coating, consolidant, protection, conservation, porous substrate, cultural heritage
Published in DiRROS: 21.11.2023; Views: 382; Downloads: 235
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7.
Strižna trdnost spojev z ribjim klejem lepljenega lesa ovrednotena z metodo ABES
Matic Sitar, Andreja Pondelak, Samo Grbec, Milan Šernek, 2023, original scientific article

Abstract: V prispevku smo s pomočjo sistema za avtomatizirano vrednotenje zlepljenosti (ABES) ugotavljali razvoj strižne trdnosti ribjega kleja pri lepljenju lesa. Uporabili smo bukov (Fagus sylvatica L.) furnir, ki smo ga lepili pri konstantnem tlaku 12 barov, medtem ko smo spreminjali temperaturo in čas stiskanja. Temperatura je znašala med25 °C in 100 °C, z intervalom 25 °C, čas stiskanja pa od 1 minute do 60 minut. Dosežena maksimalna strižna trdnost je znašala okoli 10 N/mm², dosegli smo jo pri vseh štirih proučevanih temperaturah stiskanja. Na podlagi rezultatov študije smo ugotovili, da strižna trdnost ribjega kleja pri različnih temperaturah segrevanja neenakomerno narašča. Pri višjih temperaturah segrevanja hitreje dosežemo maksimalne strižne trdnosti. Strižne trdnosti spoja lepila iz ribjega kleja smo ugotavljali tudi po standardih EN 204 in EN 205.
Keywords: wood
Published in DiRROS: 14.11.2023; Views: 443; Downloads: 227
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8.
Improving the flame retardancy of wood using an eco-friendly mineralisation process
Andreja Pondelak, Andrijana Sever Škapin, Nataša Knez, Friderik Knez, Tomaž Pazlar, 2021, original scientific article

Abstract: A novel environmentally friendly method for in situ formation of CaCO3 deep inside a wood’s structure is presented. The method is based on vacuum-pressure impregnation using a one-component treatment medium – a water solution of calcium acetoacetate - and a single stage process to significantly improve the fire retardancy of the treated material.
Keywords: mineralisation, flame retardancy, calcium acetoacetate, calcium carbonate, wood
Published in DiRROS: 31.07.2023; Views: 492; Downloads: 335
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9.
Environmentally friendly protection of European beech against fire and fungal decay using a combination of thermal modification and mineralisation
Rožle 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: 469; Downloads: 336
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10.
Combining mineralisation and thermal modification to improve the fungal durability of selected wood species
Rožle Repič, Andreja Pondelak, Davor Kržišnik, Miha Humar, Andrijana Sever Škapin, 2022, original scientific article

Abstract: The development of non-biocidal and environmentally friendly systems to protect wood against biological decay has become a high priority in recent years. In the present study the impact of an innovative modification procedure, combining two environmentally friendly modification methods: thermal modification and mineralisation, using an aqueous solution of calcium acetoacetate as a precursor, on the fungal durability of wood was evaluated. European beechwood (Fagus sylvatica) and Norway sprucewood (Picea abies) were selected as model wood species. Wood samples were treated using either a single or combination of both methods and exposed to four different fungi: Gloeophyllum trabeum, Rhodonia placenta, Trametes versicolor and Pleurotus ostreatus. The effect of the different modifications on moisture content, dynamic vapour sorption, contact angle and pH value was also evaluated. Overall, the highest durability against Rhodonia placenta, Trametes versicolor and Pleurotus ostreatus was achieved through thermal modification in both wood species, while the combination of mineralisation and thermal modification has a synergistic effect against degradation by Gloeophyllum trabeum. In the case of beechwood the mass loss decreased from 41% for native to 6% for combined modified samples. We proved that the effectiveness of different treatment against fungal decay of wood were in strong dependence of their moisture content, dynamic vapour sorption, contact angle and pH values. The role of fungi on the morphology of the wood and on crystal structure of formed carbonate was investigated using SEM-EDS analysis.
Keywords: thermal modification, wood mineralization, fungal durability, environmentally friendly modification methods
Published in DiRROS: 20.06.2023; Views: 497; Downloads: 487
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