31. Influence of homogenization of alkali-activated slurry on mechanical strengthBarbara Horvat, Mark Češnovar, Katja Traven, Majda Pavlin, Katja Koenig, Vilma Ducman, 2022, published scientific conference contribution Abstract: Alkali-activated materials are promising materials for the construction industry due to the accessibility of the precursors, which are mainly secondary industrial by-products, and their cost- effective and energy-efficient production. Although these materials are not new, some of the parameters in the technological process are not yet fully understood and tested. Therefore, in this paper in the means of mechanical strength, the preparation of alkali-activated pastes by using a three-roll mill homogenization method is discussed. The influence of homogenization of alkali- activated slurry has been evaluated on different waste materials (fly ash, fly ash with metakaolin, slag mixture (electric arc furnace slag and ladle slag), glass wool, waste green ceramics), which are treated with different alkali activators (NaOH, commercial sodium silicate solution, laboratory-produced alkali activators based on waste cathode- ray tube glass) with different curing regimes (60 °C and 70 °C) and different drying methods (drying at room temperature, drying at 105 °C). The viscosity of the slurry before homogenization was higher than after homogenization, the distribution of elements was more uniform and the compressive strength higher in all homogenized alkali activated materials, regardless of other parameters.
Keywords: secondary raw material, alkali activated material, foaming, homogenization, mechanical strength
Published in DiRROS: 21.12.2023; Views: 263; Downloads: 86
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32. Merjeni in izračunani fotobiološki učinki odbite svetlobe na ljudiKatja Malovrh Rebec, 2018, original scientific article Abstract: Pri načrtovanju osvetlitve izračuni le delno napovejo vplive svetlobe na uporabnike prostorov. Svetloba ima namreč poleg dobro poznanih slikovnih učinkov, ki jih možgani interpretirajo na podlagi odzivov čepkov in paličic, tudi neslikovne učinke. Ti ne pripomorejo k orientaciji v prostoru, temveč sporočajo telesu ključne informacije, ki vplivajo na tvorbo hormonov. Vrh te zaznave je v modrem delu spektra vidne svetlobe. Žal delovanja teh fotoreceptorjev še ne opisujemo s parametri, ustaljenimi v praksi projektiranja, zato so vplivi na uporabnike pogosto prezrti. Dodaten izziv pomeni praksa, pri kateri svetlobne učinke preračunavamo v lukse, kar pomeni, da jih množimo s povprečnim človeškim dnevnim vidom. Tak pristop ni primeren za vrednotenje neslikovnih učinkov, ker imajo drugo akcijsko krivuljo. Izmerili smo spektralno sestavo odbitih dnevnih svetlob v modelnem prostoru, ker nas je zanimalo, kakšne razlike nastanejo v slikovni in neslikovni zaznavi, če pobarvamo stene z različnimi barvami. Modra in vijoličasta stena neslikovno stimulirata opazovalca bolj kot slikovno v obeh opazovanih smereh pogleda, oranžna v obeh primerih neslikovno vpliva manj, pri zeleni pa je bila neslikovna zaznava bolj stimulirana od slikovne pri pogledu naprej, pri pogledu v mizo pa je bilo obratno.
Keywords: svetloba, fotobiološki vpliv, spektralna sestava svetlobe, dnevna svetloba
Published in DiRROS: 21.12.2023; Views: 216; Downloads: 76
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33. Pathway toward sustainable winter road maintenance (case study)Katja Malovrh Rebec, Janez Turk, 2023, independent scientific component part or a chapter in a monograph Abstract: Life Cycle Assessment (LCA) method was applied to evaluate the environmental impacts of winter road maintenance managed by an innovative road-weather information system and the impacts of vehicles passing the road during the snowstorm event. A case study refers to 10-hour lasting snowstorm event, considering a specific road section and application of a road-weather information management system to help winter road maintenance agency optimizing activities (salt gritting and/or plowing). Reliable information on the timing of the beginning of the snowstorm event affects (1) the activities of winter road maintenance, (2) the mobility of all vehicles passing the road, and (3) the fuel consumption of the vehicles. Since activities are optimized in case of preventive operation of winter road maintenance, less salt is needed overall. The road remains free of snow cover in case of preventive winter road maintenance operation, meaning that passenger cars and trucks pass the road at normal speed, without undesirable acceleration and braking caused by wheels slipping if snow accumulates on the road. Fuel consumption of vehicles passing salted and snow-free road remains unchanged, while fuel consumption increases in case of snow cover. Reduction of environmental burdens in case of such optimized winter road maintenance operation, is shown in this case study. The overall results of the comparative LCA analysis showed that the use of the road-weather information system in road traffic allows for as much as 25% reduction of environmental footprints. In the scenario where the winter service does not use information system the winter service also uses 40% more salt, which is also related with additional environmental impacts.
Keywords: LCA, okoljski odtisi, cesta, snežne razmere, preventivno delovanje, promet, poraba goriva, varnost, LCA, environmental impacts, road, snow cover, preventive operation, traffic, fuel consumption, safety
Published in DiRROS: 11.12.2023; Views: 188; Downloads: 136
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34. Pozicioniranje in kontrola kakovosti mamogramaZvonko Krajnc, Miljeva Rener, Alenka Rataj, Patricija Rusjan, Gregor Novak, Katja Čebulj, 2004, published scientific conference contribution Abstract: Izhodišča. Pravilno pozicioniranje je predpogoj za zagotavljanje kakovosti mamografskih slik. Zato je pomembno, da dobro poznamo anatomijo in tehnike pozicioniranja, slikanja in razvijanja. Zaključki. Da bi dosegli optimalen prikaz tkiv, rnorarno pravilno nastaviti nosilec kasete in kompresorij ter izkoristiti premakljivost dojk, pomembna pa je tudi pravilna uporaba aparatur.Ob izvajanju mamografije moramo nujno upoštevati kriterije za kontrolo kakovosti. Pri tem nam pomaga pravilnik o pogojih, ki jih morajo izpolnjevati primarni centri za dojke v Republiki Sloveniji, ter evropske smernice. S kontrolo kakovosti bomo u Sloveniji zvišali kvaliteto in s tem prispevali k čirn zgodnejšemu odkrivanju sprememb na dojkah.
Published in DiRROS: 01.12.2023; Views: 242; Downloads: 60
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36. Particle size manipulation as an influential parameter in the development of mechanical properties in electric arc furnace slag-based AAMKatja Traven, Mark Češnovar, Vilma Ducman, 2019, original scientific article Abstract: Alkali-activated materials (AAM) have gained recognition as a promising alternative to technical ceramic and building materials owing to the lower energy demands for production and the potential to use slag as a precursor. In the present study, five sets of slag-based AAM pastes were prepared with different particle sizes (fractions d < 63, 63 < d < 90, and 90 < d < 125 μm in different mass ratios) under the same curing regime and using a fixed precursor to activator (water) mass ratio. Precursors and the hardened AAM are evaluated using BET, XRD, XRF, SEM, FTIR, reactivity of precursors by leaching, and mercury intrusion porosimetry (MIP). Chemical analysis indicated only marginal differences among the different-sized fractions of input materials, whereas the BET surface area and reactivity among the precursors differed significantly-smaller particles had the largest surface area, and thus, higher reactivity. The mineralogical differences between the precursors and hardened AAM were negligible. The results revealed that compressive strength was significantly influenced by particle size, i.e., a threefold increase in strength when the particle size was halved. Microstructural evaluation using MIP confirmed that the porosity was the lowest in AAM with the smallest particle size. The low porosity and high reactivity of the fine fractions led to the highest compressive strength, confirming that manipulation of particle size can significantly influence the mechanical properties.
Keywords: alkalijsko aktivirani materiali, žlindra iz obločne peči, mehanska aktivacija, mehanske lastnosti, poroznost, alkali-activated materials (AAM), electric arc furnace steel slag, mechanical activation, mechanical properties, porosity
Published in DiRROS: 22.11.2023; Views: 293; Downloads: 145
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38. RILEM TC 247-DTA round robin test : mix design and reproducibility of compressive strength of alkaliactivated concretesJohn L. Provis, Kamel Arbi, Susana Bernal, Dali Bondar, Anja Buchwald, Arnaud Castel, Sundararaman Chithiraputhiran, Martin Cyr, Alireza Dehghan, Katja Dombrowski-Daube, Ashish Dubey, Vilma Ducman, Gregor J. G. Gluth, Sreejith Nanukuttan, Karl Peterson, Francisca Puertas, Arie van Riessen, Manuel Torres-Carrasco, Guang Ye, Yibing Zuo, 2019, original scientific article Abstract: The aim of RILEM TC 247-DTA Durability Testing of Alkali-Activated Materials is to identify and validate methodologies for testing the durability of alkali-activated concretes. To underpin the durability testing work of this committee, five alkali-activated concrete mixes were developed based on blast furnace slag, fly ash, and flash-calcined metakaolin. The concretes were designed with different intended performance levels, aiming to assess the capability of test methods to discriminate between concretes on this basis. A total of fifteen laboratories worldwide participated in this round robin test programme, where all concretes were produced with the same mix designs, from single-source aluminosilicate precursors and locally available aggregates. This paper reports the mix designs tested, and the compressive strength results obtained, including critical insight into reasons for the observed variability in strength within and between laboratories.
Keywords: alkali-activated materials (AAM), mechanical properties, test method, Rilem TC, durability
Published in DiRROS: 14.09.2023; Views: 244; Downloads: 143
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39. The potential of ladle slag and electric arc furnace slag use in synthesizing alkali activated materials; the influence of curing on mechanical propertiesMark Češnovar, Katja Traven, Barbara Horvat, Vilma Ducman, 2019, original scientific article Abstract: Alkali activation is studied as a potential technology to produce a group of high performance building materials from industrial residues such as metallurgical slag. Namely, slags containing aluminate and silicate form a useful solid material when activated by an alkaline solution. The alkali-activated (AA) slag-based materials are promising alternative products for civil engineering sector and industrial purposes. In the present study the locally available electric arc furnace steel slag (Slag A) and the ladle furnace basic slag (Slag R) from different metallurgical industries in Slovenia were selected for alkali activation because of promising amorphous Al/Si rich content. Different mixtures of selected precursors were prepared in the Slag A/Slag R ratios 1/0, 3/1, 1/1, 1/3 and 0/1 and further activated with potassium silicate using an activator to slag ratio of 1:2 in order to select the optimal composition with respect to their mechanical properties. Bending strength of investigated samples ranged between 4 and 18 MPa, whereas compressive strength varied between 30 and 60 MPa. The optimal mixture (Slag A/Slag R = 1/1) was further used to study strength development under the influence of different curing temperatures at room temperature (R. T.), and in a heat-chamber at 50, 70 and 90 °C, and the effects of curing time for 1, 3, 7 and 28 days was furthermore studied. The influence of curing time at room temperature on the mechanical strength at an early age was found to be nearly linear. Further, it was shown that specimens cured at 70 °C for 3 days attained almost identical (bending/compressive) strength to those cured at room temperature for 28 days. Additionally, microstructure evaluation of input materials and samples cured under different conditions was performed by means of XRD, FTIR, SEM and mercury intrusion porosimetry (MIP).
Keywords: alkali activation, slag, influence of curing regime, FTIR
Published in DiRROS: 13.09.2023; Views: 269; Downloads: 153
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40. Evaluation of locally available amorphous waste materials as a source for alternative alkali activatorsKatja Koenig, Katja Traven, Majda Pavlin, Vilma Ducman, 2021, original scientific article Abstract: The production of alkali-activated materials with excellent mechanical performance requires the use of waterglass, which has a significant carbon footprint. Such materials can have a lower carbon footprint if we replace water glass with alternative activators sourced from waste. In this study, we assessed the suitability of locally available amorphous waste materials (stone wool, glass wool, bottle glass and cathode-ray tube glass) as a source for the preparation of alternative alkali activators. We quantified the amount of silicon and aluminium dissolved in the activator solutions via inductively coupled plasma-optical emission spectrometry. The alternative activators were then used to produce alkali-activated fly ash and slag. The compressive strength values of alkali-activated fly ash specimens upon the addition of NaOH, water glass and the most promising alternative activator were 38.98 MPa, 31.34 MPa and 40.37 MPa, respectively. The compressive strength of slag specimens activated with alternative activators with the highest concentration of dissolved silicon (21 g/L) was, however, 70% higher than the compressive strength of slag specimens activated with only 10 M sodium hydroxide. The compressive strength of slag specimens with the addition of the most promising alternative activator was significantly lower (3.5 MPa) than the compressive strength of those that had been activated by commercial water glass (34.3 MPa).
Keywords: alkalijsko aktivirani materiali, alternativni aktivatorji, lastnosti, alkali activated materials/geopolimers, alternative activators, properties
Published in DiRROS: 22.08.2023; Views: 243; Downloads: 160
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