31. Effects of the temperature on the pore evolution during sintering of the belite-sulfoaluminate cement clinker using x-ray computed microtomographySabina Dolenec, Lidija Korat, Maruša Mrak, Andrej Ipavec, Lea Žibret, 2020, izvirni znanstveni članek Povzetek: In this paper, the effects of the sintering temperature on the pore evolution of the belite-sulfoaluminate cement clinker were evaluated. Belite-sulfoaluminate cement clinker with a targeted composition of 65 w/% b-belite, 20 w/% calcium sulfoaluminate and 10 w/% ferrite was sintered at three different temperatures: 1200 °C, 1250 °C and 1300 °C. To quantitatively evaluate the pore evolution during sintering, a 3D microstructure reconstruction by micro-CT was used. From the data, the pore volume frac- tion and pore number were extracted and compared, and the pore size distribution with the sintering temperature was obtained as well. Additionally, the pore shape and distribution were displayed in 3D based on actual microstructure data. Clinker samples were also characterized by Hg-intrusion porosimetry and gas sorption. The changes in the pore evolution occurred to a larger extent when sintering at 1300 °C. Apart from a significant porosity decrease, pore coarsening was evident at this temperature, reducing their connectivity and shrinkage of the clinker. Simultaneously, the bulk and apparent densities increased with the temperature due to densification, while the BET surface area of the studied clinkers decreased, indicating the rounding of pores and particle coalescence with an increasing grain growth.
Ključne besede: klinker, belit-sulfoaluminat, razvoj por, sintranje
Objavljeno v DiRROS: 04.08.2023; Ogledov: 319; Prenosov: 138
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32. A red Roman column from Emona (Ljubljana, Slovenia)Andreja Maver, Bernarda Županek, Maja Gutman, Dragomir Skaberne, Sabina Dolenec, 2020, izvirni znanstveni članek Povzetek: 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.
Ključne besede: NUK II Site (Ljubljana, Slovenia), columns, Roman architecture, reed impressions, stucco, limestone, Late Roman period
Objavljeno v DiRROS: 04.08.2023; Ogledov: 295; Prenosov: 218
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33. Phase development and hydration kinetics of belite-calcium sulfoaluminate cements at different curing temperaturesMaruša Mrak, Nina Daneu, Sabina Dolenec, 2020, izvirni znanstveni članek Povzetek: 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.
Ključne besede: hydration, cement, temperature, belite, calcium sulfoaluminate, open access, hidratacija, cement, temperatura, belit, kalcijev sulfoaluminat
Objavljeno v DiRROS: 04.08.2023; Ogledov: 293; Prenosov: 208
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34. The Incorporation of steel slag into belite-sulfoaluminate cement clinkersLea Žibret, Katarina Šter, Maruša Mrak, Mojca Loncnar, Sabina Dolenec, 2021, izvirni znanstveni članek Povzetek: 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.
Ključne besede: cements, BCSA, steel slag, secundary row materials, microstructure, clinker phase
Objavljeno v DiRROS: 01.08.2023; Ogledov: 262; Prenosov: 123
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35. The role of electricity mix and production efficiency improvements on greenhouse gas (GHG) emissions of building components and future refurbishment measuresTajda Potrč Obrecht, Sabina Jordan, Andraž Legat, Alexander Passer, 2021, izvirni znanstveni članek Povzetek: Purpose: An estimation of the environmental impact of buildings by means of a life cycle assessment (LCA) raises uncertainty related to the parameters that are subject to major changes over longer time spans. The main aim of the present study is to evaluate the influence of modifications in the electricity mix and the production efficiency in the chosen reference year on the embodied impacts (i.e., greenhouse gas (GHG) emissions) of building materials and components and the possible impact of this on future refurbishment measures.
Methods: A new LCA methodological approach was developed and implemented that can have a significant impact on the way in which existing buildings are assessed at the end of their service lives. The electricity mixes of different reference years were collected and assessed, and the main datasets and sub-datasets were modified according to the predefined substitution criteria. The influence of the electricity-mix modification and production efficiency were illustrated on a selected existing reference building, built in 1970. The relative contribution of the electricity mix to the embodied impact of the production phase was calculated for four different electricity mixes, with this comprising the electricity mix from 1970, the current electricity mix and two possible future electricity-mix scenarios for 2050. The residual value of the building was also estimated.
Results and discussion: In the case presented, the relative share of the electricity mix GHG emission towards the total value was as high as 20% for separate building components. If this electricity mix is replaced with an electricity mix having greater environmental emissions, the relative contribution of the electricity mix to the total emissions can be even higher. When, by contrast, the modified electricity mix is almost decarbonized, the relative contribution to the total emissions may well be reduced to a point where it becomes negligible. The modification of the electricity mix can also influence the residual value of a building. In the observed case, the differences due to different electricity mixes were in the range of 10%.
Conclusions: It was found that those parameters that are subject to a major change during the reference service period of the building should be treated dynamically in order to obtain reliable results. Future research is foreseen to provide additional knowledge concerning the influence of dynamic parameters on both the use phase and the end-of-life phase of buildings, and these findings will also be important when planning future refurbishment measures.
Ključne besede: global warming potential (GWP), production phase, electricity mix, production efciency, residual value, refurbishment, building components, life cycle assessment (LCA)
Objavljeno v DiRROS: 31.07.2023; Ogledov: 386; Prenosov: 196
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36. An LCA methodolody for assessing the environmental impacts of building components before and after refurbishmentTajda Potrč Obrecht, Sabina Jordan, Andraž Legat, Marcella Ruschi Mendes Saade, Alexander Passer, 2021, izvirni znanstveni članek Povzetek: Refurbishment is one of the most important measures for reducing the environmental impacts of the construction sector in the near future. According to the life cycle assessment (LCA) methodology for buildings, the environmental impacts of refurbishment measures should be assessed within the whole life cycle of the building and reflected in separate modules. However, in practice, refurbishment is often treated as the beginning of a new building life cycle. This leads to difficulties in correctly assessing the environmental impacts for the components that are reused or recycled after the refurbishment. The division of a building’s life cycle into two separate life cycles indicates that the environmental impacts must be divided between the life cycle before and the life cycle after the refurbishment for a correct assessment of the environmental impacts and a calculation of the residual value. We propose a newly developed methodology for calculating the environmental impacts and the residual value of refurbishment measures that also involves a division between life cycles. The new methodology is a combi-nation of already exiting methodologies that are innovatively combined and consists of four sequential steps. In the first step, the input, output and reuse flows between the life cycles before and after the refurbishment are defined. In the second step, the environmental impacts are assessed using the chosen allocation approach (i.e., the cut-off, cut-off with module D, avoided-burden, 50:50 and the product environmental footprint (PEF)). In the third step, a maintenance scenario is implemented according to the selected reference-service-life (RSL) database. In the fourth step, the residual value is estimated. The methodology was tested on selected building components. A sensitivity analysis for different allocation approaches and RSL databases was performed to show how the choice of these parameters can influence the results. The differences between the selected allocation approaches emerge if materials with recycled content are used or if the materials are being recycled or reused at the end of their life cycle. The developed methodology reliably estimates the environmental impacts as well as the residual value of the life cycle before and after the refurbishment. We expect that this research will stimulate practitioners to avoid the negligence of previous environmental flows, bringing scientific consistency to future assessments of refurbishment measures.
Ključne besede: Life cycle assessment (LCA), refurbishment, allocation approaches, residual value, reference service life (RSL)
Objavljeno v DiRROS: 28.07.2023; Ogledov: 335; Prenosov: 214
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37. 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, izvirni znanstveni članek Povzetek: 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.
Ključne besede: belite-calcium sulfoaluminate cement, gypsum, hydration, thermodynamic modelling
Objavljeno v DiRROS: 28.07.2023; Ogledov: 288; Prenosov: 219
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38. Microstructural characteristics of belite–sulfoaluminate cement clinkers with bottom ashLea Žibret, Andrej Ipavec, Sabina Dolenec, 2022, izvirni znanstveni članek Povzetek: 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.
Ključne besede: BSCA clinker, belite, calcium sulfoaluminate, secondary raw materials, microstructure, reactivity
Objavljeno v DiRROS: 03.07.2023; Ogledov: 400; Prenosov: 190
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39. 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, izvirni znanstveni članek Povzetek: 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.
Ključne besede: in situ X-ray diffraction, hydration, temperature, cement, rietveld analysis
Objavljeno v DiRROS: 26.06.2023; Ogledov: 330; Prenosov: 193
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40. 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, izvirni znanstveni članek Povzetek: 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.
Ključne besede: fly ash, bottom ash, gamma spectrometry, building materials
Objavljeno v DiRROS: 22.05.2023; Ogledov: 285; Prenosov: 137
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