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Use of the modified controlled atmosphere cone calorimeter for the assessment of fire effluents generated by burning wood under different ventilation conditions
Friderik Knez, Matija Uršič, Nataša Knez, Kelly Peeters, Mladen Franko, Primož Zidar, 2021, izvirni znanstveni članek

Povzetek: The ISO 5660-1 cone calorimeter is an affordable, practical, and commonly used solution for the measurement of main fire properties of products and materials. Among its chief drawbacks is its limited ability to reproduce combustion conditions found in real fires. This deficiency is mainly due to its inability to control oxygen availability in order to simulate an underventilated fire. As several toxic or potentially toxic species are formed primarily in oxygen-poor conditions, the controlled atmosphere cone calorimeter (CACC), now defined in ISO 5660-5, is a major improvement when trying to study the toxicity of fire effluents. A proposed additional modification of the CACC via the introduction of chimney sampling ports and oxygen sensors improves the reproducibility and veracity of effluent sampling. This approach allows the implementation of various techniques to sample, collect, and analyze the generated fire effluents. In this study, the experimental set-up was used to capture fire effluents generated by burning wood under different ventilation conditions. A gas chromatograph coupled with mass spectrometer was used to assess and compare the chemical composition of the collected samples. The results obtained with the new experimental set-up proved the ability of the system to reproducibly generate fire effluents under various controlled burning circumstances. It could prove useful as a tool in characterizing the toxicity of fire effluents from various materials on a benchtop scale and ultimately contribute data for the numerical modeling of toxicity of fire effluents in real buildings.
Ključne besede: modified cone calorimeter, controlled atmosphere, wood, fire effluents, open access
Objavljeno v DiRROS: 14.07.2023; Ogledov: 173; Prenosov: 127
.pdf Celotno besedilo (1,67 MB)
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Measurements of bridge dynamic amplification factor using bridge weigh-in-motion data
Jan Kalin, Aleš Žnidarič, Andrej Anžlin, Maja Kreslin, 2022, izvirni znanstveni članek

Povzetek: The dynamic component of bridge traffic loading is commonly taken into account with a Dynamic Amplification Factor (DAF)—the ratio between the dynamic and static load effects on a bridge. In the design codes, this factor is generally more conservative than in reality. Recently a new method of cal- culation of this factor had been developed. Data from 15 different bridges have been analysed since then and this paper presents the results of the analyses. The background for Bridge Weigh-in-Motion is given, and the most recent method for DAF calculation is described. The sites from which the data originated are presented, and the selection of data discussed. The results of the analyses are presented and discussed and some examples of DAF calculations are shown. Data from the considered sites have invariably demonstrated a DAF decrease with increasing axle load. This is a significant result, especially for assessment of existing structures, since it is beneficial to use measured structural param- eters to optimise structural analysis.
Ključne besede: bridge loads, bridge weigh-in-motion, dynamic amplication factor, dynamic analysis, measurement, traffic loading
Objavljeno v DiRROS: 14.07.2023; Ogledov: 147; Prenosov: 97
.pdf Celotno besedilo (2,61 MB)
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Influence of microwaves in the early stage of alkali activation on the mechanical strength of alkali-activated materials
Barbara Horvat, Majda Pavlin, Vilma Ducman, 2023, izvirni znanstveni članek

Povzetek: This study focuses on the influence of microwave irradiation dosimetry on alkali-activated slurry in its early stages. The impact on the chemistry and mineralogy along with the mechanical properties were evaluated by changing the power of microwaves and their duration of exposure. This influenced the dissolution of amorphous content, diffusion, and self-assembly into an aluminosilicate network. The precursors used in this study were metakaolin, a non-waste material commonly used in geopolymerisation technology, and local fly ash and ladle furnace slag as secondary materials. Furthermore, they were chemically and mineralogically analysed, and their mixtures with NaOH and Na-water glass provided the optimal ratio of the amount of elements obtained using the pre-calculation approach. However, the potential extra addition of water was experimentally determined to allow complete wetting of the material and solid workability during moulding. Using Fourier-transform infrared spectroscopy, the influence of water was further investigated in alkali-activated slag and fly ash irradiated with microwaves, which resulted in the highest values of mechanical strength in the dosimetry-mapping part of the analysis. In addition to the time dependence of the expected mechanical strength on the ageing of the alkali- activated material, the synthesised material exhibited a significant dependence on the dose of microwave irra- diation, which was different for every precursor as well as every mixture with different chemistries.
Ključne besede: odpadni material, alkalijska aktivacija, obsevanje z mikrovalovi, mehanska trdnost, waste material, alkali activation, microwave irradiation, mechanical strength
Objavljeno v DiRROS: 12.07.2023; Ogledov: 199; Prenosov: 163
.pdf Celotno besedilo (8,99 MB)
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Pitting corrosion on highly alloyed stainless steels in dilute sulphuric acid containing sodium chloride
Elina Huttunen-Saarivirta, Elisa Isotahdon, Zaiqing Que, M. Lindgren, Ahmad Mardoukhi, Jean-Baptiste Jorcin, Petra Močnik, Tadeja Kosec, Yassine El Ouazari, Sukanya Hägg Mameng, Lena Wegrelius, 2023, izvirni znanstveni članek

Povzetek: Stainless steels are widely used in industrial assets and equipment. Despite their good corrosion resistance under a wide range of operating conditions, there is the possibility of pitting corrosion in the presence of chlorides. However, very few studies have identified the safe operating conditions for various high-alloyed stainless steel grades by comparing their pitting susceptibility. In this research, the susceptibility to pitting attack of five stainless steels with austenitic and duplex microstructures was examined in dilute sulphuric acid solution with varying amounts of NaCl at the temperatures of 50, 90 and 130◦C. Based on potentiodynamic polarization scans, none of the test materials underwent pitting corrosion at 50◦C, but differences in susceptibility to pitting attack were clear between the test materials and NaCl concentrations at the temperature of 90◦C, and further tem- perature increase facilitated uniform corrosion. 28-day immersion tests at 90◦ C confirmed the pitting suscepti- bility of duplex grades 1.4662 (PREN 33) and 1.4462 (PREN 35) in the presence of at least 2000 mg/L NaCl, but not the susceptibility of a corresponding austenitic grade 1.4539 (PREN 34). The grades 1.4547 (PREN 43) and 1.4410 (PREN 44) were not susceptible to pitting corrosion under any of the studied conditions. The results from materials microstructural and electrochemical characterization are presented and discussed in this paper.
Ključne besede: stainless steel, austenitic stainless steel, duplex stainless steel, pitting atttack
Objavljeno v DiRROS: 12.07.2023; Ogledov: 170; Prenosov: 187
.pdf Celotno besedilo (42,24 MB)
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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, 2023, izvirni znanstveni članek

Povzetek: 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.
Ključne besede: wood, protection, durability, mechanical properties
Objavljeno v DiRROS: 12.07.2023; Ogledov: 166; Prenosov: 110
.pdf Celotno besedilo (3,26 MB)
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Neogene block rotation inside the dextral fault zone at the Adriatic-European collision zone: reexamination of existing results
Lea Žibret, Gorazd Žibret, 2023, izvirni znanstveni članek

Povzetek: The study focused on the post-Middle-Miocene stress analysis within the dextral strike-slip zone of the Dinaric fault system in the collision zone between the European plate, the Adria microplate and the Pannonian Domain. Block rotations were studied by re-examination of available paleostress data and their spatial distribution. The results are in agreement with the existing block model of the area, indicating CCW rotations within blocks between the main strike-slip faults in which rotation angle increases from W to E. The improved kinematic model, which is proposed in this study, will contribute to the knowledge on the kinematics within the complex collision zones and improve the seismic hazard models.
Ključne besede: collision zone, NW External Dinarides, Southern Alps, paleostress tensor, strike-slip zone, block rotation
Objavljeno v DiRROS: 06.07.2023; Ogledov: 204; Prenosov: 100
.pdf Celotno besedilo (8,47 MB)

Electrochemical cycling behaviour and shape changes of Zn electrodes in mildly acidic aqueous electrolytes containing quaternary ammonium salts
Benedetto Bozzini, Marco Boniardi, Tommaso Caielli, Andrea Casaroli, Elisa Emanuele, Lucia Mancini, Nicola Sodini, Jacopo Strada, 2023, izvirni znanstveni članek

Povzetek: Secondary Zn–based batteries are a valid alternative to Li for stationary storage, but commercial devices are not yet available, chiefly owing to anode shape-change and passivation issues. Mildly acidic aqueous solutions are actively studied, since they seem to limit unstable growth of Zn, with respect to the alkaline ones, customary for primary batteries. Additives can further improve the performance of mildly acidic electrolytes. In this work we focus on the impact of a series of quaternary ammonium salts (TBAB, CTAB, DMDTDAB, BDMPAC, BPPEI, PDADMAC), selected to represent a comprehensive range of molecular functionalities. Electrochemical measurements (cyclic voltammetry, chronopotentiometry and galvanostatic-cycling in split-cells), combined with 2D and 3D imaging techniques (SEM, stereomicroscopy and in situ tomography) were adopted for the assessment Zn behaviour. This multi-technique approach pinpointed TBAB as the single most effective additive for low-current density operation, while at high current densities the additive-free electrolyte allows better cycling performance, coherently with similar results for alkaline electrolytes.
Ključne besede: battery, electrolyte, electrochemical measurements, quaternary Ammomium salt, X-ray computed microtomography, mobility
Objavljeno v DiRROS: 06.07.2023; Ogledov: 221; Prenosov: 88
.pdf Celotno besedilo (2,52 MB)
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Sensor development for corrosion monitoring of stainless steels in H2SO4 solutions
Miha Hren, Tadeja Kosec, Mari Lindgren, Elina Huttunen-Saarivirta, Andraž Legat, 2021, izvirni znanstveni članek

Povzetek: Equipment made of different stainless steels is often used in the hydrometallurgical processing industry. In this study, an electrical resistance sensor was developed for monitoring corrosion in acidic solutions at high temperature. Two types of stainless steel were used as the electrode materials, namely grade 316L stainless steel (EN 1.4404) and grade 2507 duplex stainless steel (EN 1.4410). The materials and sensors were exposed to a 10% H2SO4 solution containing 5000 mg/L of NaCl at various temperatures. Results from the sensors were verified using electrochemical techniques and postexposure examination. Results showed that the microstructure played an important role in the interpretation of corrosion rates, highlighting the importance of using an appropriate stainless steel for the production of sensors. Electrochemical tests and postexposure examination both showed that the grade 2507 had a significantly lower corrosion rate compared to the grade 316L. Under industrial‑process conditions, the results for the grade 2507 sensor were promising with respect to sensor durability and performance, despite the extremely harsh operating environment.
Ključne besede: stainless steel, hydrometallurgical industry, sulphuric acid, electrical resistance sensor, corrosion
Objavljeno v DiRROS: 05.07.2023; Ogledov: 186; Prenosov: 127
.pdf Celotno besedilo (5,12 MB)
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Experimental carbonation study for a durability assessment of novel cementitious materials
Lucija Hanžič, Sebastijan Robič, Alisa Machner, Marie Helene Bjørndal, Klaartje De Weerdt, Yushan Gu, Benoit Bary, Rosa Maria Lample Carreras, Aljoša Šajna, 2021, izvirni znanstveni članek

Povzetek: Durability predictions of concrete structures are derived from experience-based require- ments and descriptive exposure classes. To support durability predictions, a numerical model related to the carbonation resistance of concrete was developed. The model couples the rate of carbonation with the drying rate. This paper presents the accelerated carbonation and moisture transport exper- iments performed to calibrate and verify the numerical model. They were conducted on mortars with a water-cement ratio of either 0.6 or 0.5, incorporating either a novel cement CEM II/C (S-LL) (EnM group) or commercially available CEM II/A-S cement (RefM group). The carbonation rate was determined by visual assessment and thermogravimetric analysis (TGA). Moisture transport experi- ments, consisting of drying and resaturation, utilized the gravimetric method. Higher carbonation rates expressed in mm/day−0.5 were found in the EnM group than in the RefM group. However, the TGA showed that the initial portlandite (CH) content was lower in the EnM than in the RefM, which could explain the difference in carbonation rates. The resaturation experiments indicate an increase in the suction porosity in the carbonated specimens compared to the non-carbonated specimens. The study concludes that low clinker content causes lower resistance to carbonation, since less CH is available in the surface layers; thus, the carbonation front progresses more rapidly towards the core.
Ključne besede: mortar, absorption of water, carbonation, durability assessment, model verification
Objavljeno v DiRROS: 05.07.2023; Ogledov: 160; Prenosov: 109
.pdf Celotno besedilo (4,84 MB)
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Characterizing steel corrosion in different alkali-activated mortars
Nina Gartner, Miha Hren, Tadeja Kosec, Andraž Legat, 2021, izvirni znanstveni članek

Povzetek: Alkali-activated materials (AAMs) present a promising potential alternative to ordinary Portland cement (OPC). The service life of reinforced concrete structures depends greatly on the corrosion resistance of the steel used for reinforcement. Due to the wide range and diverse properties of AAMs, the corrosion processes of steel in these materials is still relatively unknown. Three different alkali-activated mortar mixes, based on fly ash, slag, or metakaolin, were prepared for this research. An ordinary carbon-steel reinforcing bar was installed in each of the mortar mixes. In order to study the corrosion properties of steel in the selected mortars, the specimens were exposed to a saline solution in wet/dry cycles for 17 weeks, and periodic electrochemical impedance spectroscopy (EIS) measurements were performed. The propagation of corrosion damage on the embedded steel bars was followed using X-ray computed microtomography (XCT). Periodic EIS measurements of the AAMs showed different impedance response in individual AAMs. Moreover, these impedance responses also changed over the time of exposure. Interpretation of the results was based on visual and numerical analysis of the corrosion damages obtained by XCT, which confirmed corrosion damage of varying type and extent on steel bars embedded in the tested AAMs.
Ključne besede: corrosion, alkali-activated mortars, steel reinforcement, electrochemical impedance spectroscopy, X-ray computed microtomography, visual analysis
Objavljeno v DiRROS: 05.07.2023; Ogledov: 204; Prenosov: 112
.pdf Celotno besedilo (7,00 MB)
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