21. A red Roman column from Emona (Ljubljana, Slovenia)Andreja Maver, Bernarda Županek, Maja Gutman, Dragomir Skaberne, Sabina Dolenec, 2020, original scientific article Abstract: The excavation conducted in 1999 in Ljubljana (Slovenia), in Insula XXVII of the Roman colonia Iulia Emona, un-earthed the remains of a column shaft with an organic core set onto a stone block. The contribution presents this find, its context and likely parallels, the mineralogical-petrographic composition of the stucco, type of the pigments used, as well as the rock of the plinth and its provenance. Of the shaft, only the stucco survives, applied in four mortar layers and painted in red ochre, while its interior surface shows the impressions of reeds. The plinth is a rectangular block made of locally available Lower Jurassic oolitic limestone, presumably from Podpeč. The column may have formed part of a porticus or peristyle, possibly associated with a pool or a bath complex in this part of Late Roman Emona.
Keywords: NUK II Site (Ljubljana, Slovenia), columns, Roman architecture, reed impressions, stucco, limestone, Late Roman period
Published in DiRROS: 04.08.2023; Views: 295; Downloads: 218
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22. Phase development and hydration kinetics of belite-calcium sulfoaluminate cements at different curing temperaturesMaruša Mrak, Nina Daneu, Sabina Dolenec, 2020, original scientific article Abstract: The influence of different curing temperatures on the hydration of belite-calcium sulfoaluminate cement was investigated at 20, 40 and 60 °C. The hydration kinetics and the hydrated phase assemblages were studied by isothermal calorimetry, X-ray powder diffraction, differential thermal analysis and thermogravimetric analysis, as well as field emission scanning electron microscopy. The compressive strength development of the cement pastes was also determined. Results showed that, at early ages, hydration was faster and early compressive strength was higher at elevated temperatures than at ambient temperature. On the other hand, at late ages in cement pastes cured at 60 °C, the amount of ettringite decreased, leading to lower compressive strength, indicating that the degree of hydration was lower at higher temperatures. Moreover, at elevated temperatures prismatic ettringite crystals became smaller due to faster hydration. Other hydration products present were aluminium hydroxide, which is formed together with ettringite from the hydration of calcium sulfoaluminate and gypsum, and C–S–H which precipitates as a main hydration product of belite. Belite hydrated in a lesser amount, especially at 60 °C, when the lowest amount of C–S–H was observed.
Keywords: hydration, cement, temperature, belite, calcium sulfoaluminate, open access, hidratacija, cement, temperatura, belit, kalcijev sulfoaluminat
Published in DiRROS: 04.08.2023; Views: 295; Downloads: 208
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23. The Incorporation of steel slag into belite-sulfoaluminate cement clinkersLea Žibret, Katarina Šter, Maruša Mrak, Mojca Loncnar, Sabina Dolenec, 2021, original scientific article Abstract: The potential use of steel slag from treated steel slag in belite-sulfoaluminate cements was investigated in this study. Cement clinkers with two phase compositions were synthesized, allowing the incorporation of different amounts of steel slag. The phase composition and microstructure of cement clinkers at three different sintering temperatures were studied by X-ray powder diffraction and the Rietveld method, as well as scanning electron microscopy with energy dispersive spectrometry. The results showed that the targeted phase composition of clinkers was achieved at a sintering temperature of 1250%C. However, a higher amount of perovskite instead of ferrite was detected in the clinker with a higher content of Ti-bearing bauxite. Apart from the main phases, such asbelite, calcium sulfoaluminate, and ferrite, several minor phases were identified, including mayenite, perovskite, periclase, and alkali sulfates. In both clinker mixtures, a higher content of MgO in the steelslags resulted in the formation of periclase. Furthermore, the hydration kinetics and compressive strength at 7 and 28 days were studied in two cements prepared from clinkers sintered at 1250%C. As evidenced by the results of isothermal calorimetry, the hydration kinetics were also influenced by the minor clinker phases. Cement with a higher content of calcium sulfoaluminate phase developed a higher compressive strength.
Keywords: cements, BCSA, steel slag, secundary row materials, microstructure, clinker phase
Published in DiRROS: 01.08.2023; Views: 263; Downloads: 123
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24. The influence of calcium sulfate content on the hydration of belite-calcium sulfoaluminate cements with different clinker phase compositionsMaruša Mrak, Frank Winnefeld, Barbara Lothenbach, Sabina Dolenec, 2021, original scientific article Abstract: The influence of different amounts of gypsum on the hydration of a belite-rich and a yeʼelimite-rich belite-calcium sulfoaluminate clinker (BCSA) was investigated. The hydration kinetics, phase assemblages and compressive strength development of cements prepared using yeʼelimite/ calcium sulfate molar ratios of 1, 1.5 and 2 were studied. Besides ettringite and monosulfate, aluminium hydroxide, strätlingite, C-S-H, iron-containing siliceous hydrogarnet and hydrotalcite were present as hydration products. Increasing the amount of gypsum increased the ratio of ettringite to monosulfate formed in the cement paste, lowered the amount of pore solution, delayed the dissolution of belite and ferrite, decreased the formation of strätlingite and, in the case of the yeʼelimite-rich BCSA, led to an increase in compressive strength. Increased amounts of belite in the clinker led to the formation of higher quantities of C-S-H, at the expense of straätlingite and a lower compressive strength, as belite has a lower degree of reaction than yeʼelimite and due to the formation of more C-S-H and stratlingite compared to the more space-filling ettringite. The thermodynamic model established for BCSA cement hydration agrees well with the experimental data. Compressive strength directly correlated with bound water from thermogravimetric analyses and inversely correlated with the porosity calculated from thermodynamic modelling.
Keywords: belite-calcium sulfoaluminate cement, gypsum, hydration, thermodynamic modelling
Published in DiRROS: 28.07.2023; Views: 288; Downloads: 219
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25. Microstructural characteristics of belite–sulfoaluminate cement clinkers with bottom ashLea Žibret, Andrej Ipavec, Sabina Dolenec, 2022, original scientific article Abstract: The incorporation mechanism of impurities derived from raw materials into a belite-sulfoaluminate cement clinker with bottom ash was investigated in two raw mixtures. Alkalis lowered the sintering temperature by 50 °C. Ti stabilized β belite and prevented the formation of γ-belite. Sodalite solid solution showed an incomplete substitution of Si by Al. At a higher Ti content ferrite solid solution trended towards perovskite composition. Although calcium sulfoaluminate only fully developted at 1300 °C, the clinkers sintered at 1200 °C were the most reactive, as the presence of anhydrite at 1200 °C accelerated early hydration. Clinker reactivity decreased with an increase in sintering temperature.
Keywords: BSCA clinker, belite, calcium sulfoaluminate, secondary raw materials, microstructure, reactivity
Published in DiRROS: 03.07.2023; Views: 400; Downloads: 190
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26. Quantitative in situ X-ray diffraction analysis of early hydration of belite-calcium sulfoaluminate cement at various defined temperaturesMaruša Mrak, Christian L. Lengauer, Sabina Dolenec, 2021, original scientific article Abstract: The influence of temperature on the early hydration of belite-calcium sulfoaluminate cements with two different calcium sulfate to calcium sulfoaluminate molar ratios was investigated. The phase composition and phase assemblage development of cements prepared using molar ratios of 1 and 2.5 were studied at 25, 40 and 60 ◦C by in situ X-ray powder diffraction. The Rietveld refinement method was used for quantification. The degree of hydration after 24 h was highest at ambient temperatures, but early hydration was significantly accelerated at elevated temperatures. These differences were more noticeable when we increased the temperature from 25 ◦C to 40 ◦C, than it was increased from 40 ◦C to 60 ◦C. The amount of calcium sulfate added controls the amount of the precipitated ettringite, namely, the amount of ettringite increased in the cement with a higher molar ratio. The results showed that temperature also affects full width at half maximum of ettringite peaks, which indicates a decrease in crystallite size of ettringite at elevated temperatures due to faster precipitation of ettringite. When using a calcium sulfate to calcium sulfoaluminate molar ratio of 1, higher d-values of ettringite peaks were observed at elevated temperatures, suggesting that more ions were released from the cement clinker at elevated temperatures, allowing a higher ion uptake in the ettringite structure. At a molar ratio of 2.5, less clinker is available in the cement, therefore these differences were not observed.
Keywords: in situ X-ray diffraction, hydration, temperature, cement, rietveld analysis
Published in DiRROS: 26.06.2023; Views: 331; Downloads: 193
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27. Technical and radiological characterisation of fly ash and bottom ash from thermal power plantEmilija Fidanchevski, Biljana Angjusheva, Vojo Jovanov, Pece Murtanovski, Ljubica Vladiceska, Nikolina Stamatovska Aluloska, Jelena Krneta Nikolić, Andrej Ipavec, Katarina Šter, Maruša Mrak, Sabina Dolenec, 2021, original scientific article Abstract: Huge quantities of fly ash and bottom ash are generated from thermal power plants and it presents great concern for country, mainly due to the environmental effects. In this study, fly ashes and bottom ash were characterized from technical and radiological aspects. Health effect due to the activity of radionuclides 226Ra, 232Th and 40K was estimated via radium equivalent activity (Raeq), external hazards index (Hex), the external absorbed dose rate (D) and annual effective dose rate (EDR). The specific surface area (40.25 m2 g−1), particle density (1.88 g cm−3) and LOI (23.49%) were typical for bottom ash. Siliceous fly ash contained 32% reactive silica. The annual effective dose rate for all ashes is ≤ 0.2 mSv y−1. Both, fly ash and bottom ash present potential secondary raw materials to be used for building purposes as result of their technological and radiological assessment.
Keywords: fly ash, bottom ash, gamma spectrometry, building materials
Published in DiRROS: 22.05.2023; Views: 285; Downloads: 137
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28. Impact of metakaolin on mechanical performance of flax textile-reinforced cement-based compositesFilip Majstorović, Václav Sebera, Maruša Mrak, Sabina Dolenec, Marco Wolf, Laetitia Sarah Jennifer Marrot, 2022, original scientific article Abstract: This study presents research on the effect of Portland cement (PC) replacement with metakaolin on the mechanical behavior of flax textile-reinforced cementitious matrices (TRCM). The composition of cementitious matrices and in-situ flax fibres was determined using X-ray diffraction and thermogravimetric analysis, while the reinforcement efficiency of the textile and mechanical behavior of TRCMs was investigated by three-point bending tests and finite element analysis. High amounts of PC replacement with metakaolin provided a calcium hydroxide-free environment, more suitable for the natural fibres, to avoid their degradation and embrittlement and, thus, significantly contribute to the ductility of the cement-based composite material.
Keywords: textile-reinforced concrete (TRC), flax textile, natural fibres, finite element, metakaolin, cement-based composites, open access
Published in DiRROS: 22.05.2023; Views: 372; Downloads: 175
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29. Radiological and physico-chemical characterization of red mud as an Al-containing precursor in inorganic binders for the building industryLjiljana Kljajević, Miljana Mirković, Sabina Dolenec, Katarina Šter, Mustafa Hadžalić, Ivana Vukanac, Miloš Nenadović, 2021, original scientific article Abstract: The potential re-use of red mud in the building and construction industry has been the subject of research of many scientists. The presented research is a contribution to the potential solution of this environmental issue through the synthesis of potential construction materials based on red mud. A promising way of recycling these secondary raw materials is the synthesis of alkali-activated binders or alkali activated materials. Alkali-activated materials or inorganic binders based on red mud are a new class of materials obtained by activation of inorganic precursors mainly constituted by silica, alumina and low content of calcium oxide. Since red mud contains radioactive elements like 226Ra and 232Th, this may be a problem for its further utilization. The content of naturally occurring radionuclides in manufactured material products with potential application in the building and construction industry is important from the standpoint of radiation protection. Gamma radiation of the primordial radionuclides, 40K and members of the uranium and thorium series, increases the external gamma dose rate. However, more and more precedence is being given to limiting the radiological dose originating from building materials on the population these days. The aim of this research was to investigate the possible influence of alkali activation-polymerization processes on the natural radioactivity of alkali activated materials synthesized by red mud (BOKSIT a. d. Milići, Zvornik, Bosnia and Herzegovina) and their structural properties. This research confirmed that during the polymerization process the natural radioactivity was reduced, and that the process of alkali activation of raw materials has an influence on natural radioactivity of synthesized materials.
Keywords: red mud, inorganic binder, DRIFT, natural radioactivity, gamma index, building industry
Published in DiRROS: 12.05.2023; Views: 367; Downloads: 111
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30. Potential usage of hybrid polymers binders based on fly ash with the addition of PVA with satisfying mechanical and radiological propertiesMiljana Mirković, Ljiljana Kljajević, Sabina Dolenec, Miloš Nenadović, Vladimir Pavlović, Milica Rajačić, Snežana B. Nenadović, 2021, original scientific article Abstract: Since recycled technologies usage is mandatory for environmental safety, and in this regard, it is important to examine new materials that can be used in construction and are primarily produced from fly ash. In addition to characteristics such as hardness and compressive strength, the given materials must also be radiologically and environmentally safe. The main concept of engineered geopolymer gel composites based on fly ash residues is focused on developing binder materials via gel formation processes that can replace ordinary cement materials. This study is unique in researching the potential use of fly ash from the Nikola Tesla thermal power plant in Serbia, where the hybrid geopolymeric materials synthesized from fly ash are experimentally examined with the addition 1 wt% and 2 wt% of polyvinyl alcohol (PVA). This paper aims to investigate the structural, morphological, mechanical, and radiological properties of hybrid materials with the addition of PVA and without additive in the period of ageing for 28 days at room temperature. The phase composition was investigated using X-ray powder diffraction (XRPD) analysis, while morphological characteristics of these materials were examined using scanning electron microscopy and energy dispersive X-ray analysis (SEM-EDS). Vibrational spectra of obtained samples are investigated using diffuse reflectance infrared Fourier transform (DRIFT) and Fourier transform infrared (FTIR) techniques. The hardness and compressive strength are also examined, indicating that the 1 wt% addition in geopolymeric matrix results in the best mechanical properties. Radiological measurements of investigated all geopolymer samples show decreasing activity concentrations of radionuclides for 50% compared to fly ash.
Keywords: geopolymer gel, inorganic binders, hybrid materials, fly ash, radiological properties, strength, open access
Published in DiRROS: 12.05.2023; Views: 294; Downloads: 135
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