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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: 363; Prenosov: 283
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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: 399; Prenosov: 291
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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: 364; Prenosov: 262
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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: 407; Prenosov: 179
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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: 314; Prenosov: 190
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