3rd International Conference on Technologies & Business Models for Circular Economy Conference Proceedings Editors Sanja Potrč Miloš Bogataj Zdravko Kravanja Zorka Novak Pintarič May 2022 Title 3rd International Conference on Naslov Technologies & Business Models for Circular Economy Subtitle Podnaslov Conference Proceedings Editors Sanja Potrč Uredniki (University of Maribor, Faculty of Chemistry and Chemical Engineering) Miloš Bogataj (University of Maribor, Faculty of Chemistry and Chemical Engineering) Zdravko Kravanja (University of Maribor, Faculty of Chemistry and Chemical Engineering) Zorka Novak Pintarič (University of Maribor, Faculty of Chemistry and Chemical Engineering) Technical editor Jan Perša Tehnični urednik (University of Maribor, University Press) Cover designer Jan Perša Oblikovanje ovitka (University of Maribor, University Press) Graphic material Grafične priloge Authors of proceedings & editors Conference TBMCE, International Conference on Technologies & Business Models Konferenca for Circular Economy Date and location Datum in kraj December 15th, 2020, on-line, Slovenia Organizing Zdravko Kravanja (University of Maribor, Slovenia), Miloš Bogataj Committee (University of Maribor, Slovenia), Zorka Novak Pintarič (University of Organizacijski Maribor, Slovenia), Dragica Marinič (Chamber of Commerce and Industry odbor of Štajerska, Slovenia), Andreja Nemet (University of Maribor, Slovenia), Mojca Slemnik (University of Maribor, Slovenia), Mojca Škerget (University of Maribor, Slovenia), Katja Kocuvan (University of Maribor, Slovenia), Samo Simonič (University of Maribor, Slovenia), Klavdija Zirngast (University of Maribor, Slovenia), Sanja Potrč (University of Maribor, Slovenia), Sabina Premrov (University of Maribor, Slovenia) & Sonja Roj (University of Maribor, Slovenia). International Zdravko Kravanja (University of Maribor, Slovenia), Zorka Novak Scientific Pintarič (University of Maribor, Slovenia), Miloš Bogataj (University of Committee Maribor, Slovenia), Mojca Škerget (University of Maribor, Slovenia), Mednarodni Mariano Martin (University of Salamanca, Spain), Jiří Klemeš (Brno znanstveni University of Technology, Czech Republic), Agustin Valera-Medina odbor (Cardiff University. United Kingdom), Petar Uskoković (University of Beograd, Serbia), Elvis Ahmetović (University of Tuzla, Bosnia and Herzegovina), Stefan Willför (Åbo Akademi University, Finland), Adeniyi Isafiade (University of Cape Town, South Africa), Hon Loong Lam (University of Nottingham, Malaysia), Mario Eden (Auburn University, United States of America), Timothy G. Walmsley, (Waikato University, New Zeeland), Tomaž Katrašnik (University of Ljubljana, Slovenia), Blaž Likozar (National Institute of Chemistry, Slovenia), Primož Oven (University of Ljubljana, Slovenia), Dragica Marinič (Chamber of Commerce and Industry of Štajerska, Slovenia) & Vilma Ducman (Slovenian national building and civil engineering institute, Slovenia). Published by University of Maribor Založnik University Press Slomškov trg 15, 2000 Maribor, Slovenija https://press.um.si, zalozba@um.si Issued by University of Maribor Izdajatelj Faculty of Chemistry and Chemical Engineering Smetanova ulica 17, 2000 Maribor, Slovenija https://www.fkkt.um.si/, fkkt@um.si Publication type Vrsta publikacije E-book Edition Izdaja 1st Available at Dostopno na http://press.um.si/index.php/ump/catalog/book/677 Published at Izdano Maribor, May 2022 This investment is co-financed by the Republic of Slovenia and the European Union Fund for Regional Development” © University of Maribor, University Press / Univerza v Mariboru, Univerzitetna založba Text / besedilo © Authors & Potrč, Bogataj, Kravanja, Novak Pintarič, 2022 This book is published under a Creative Commons 4.0 International licence (CC BY-NC-ND 4.0). This license al ows reusers to copy and distribute the material in any medium or format in unadapted form only, for noncommercial purposes only, and only so long as attribution is given to the creator. Any third-party material in this book is published under the book’s Creative Commons licence unless indicated otherwise in the credit line to the material. If you would like to reuse any third-party material not covered by the book’s Creative Commons licence, you wil need to obtain permission directly from the copyright holder. https://creativecommons.org/licenses/by-nc-nd/4.0/ CIP - Kataložni zapis o publikaciji Univerzitetna knjižnica Maribor 330:502.131.1(082)(0.034.2) INTERNATIONAL Conference on Technologies & Business Models for Circular Economy (3 ; 2021 ; Portorož) 3rd International Conference on Technologies & Business Models for Circular Economy, [September 13th to September 15th 2021, Portorož, Slovenia] [Elektronski vir] : conference proceedings / [editors Sanja Potrč ... [et al.]. - E-zbornik. - Maribor : University of Maribor, University Press, 2022 Način dostopa (URL): https://press.um.si/index.php/ump/catalog/book/677 ISBN 978-961-286-598-6 (pdf) doi: 10.18690/um.fkkt.2.2022 COBISS.SI-ID 109396739 ISBN 978-961-286-598-6 (pdf) DOI https://doi.org/10.18690/um.fkkt.2.2022 Price Cena Free copie For publishe r prof. dr. Zdravko Kačič, Odgovorna oseba založnika Rector of University of Maribor Attribution Potrč, S., Bogataj, M., Kravanja, Z., Novak Pintarič, Z., Citiranje (eds.). (2022). 3rd International Conference on Technologies & Business Models for Circular Economy Maribor: University Press. doi: 10.18690/um.fkkt.2.2022 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY : CONFERENCE PROCEEDINGS S. Potrč, M. Bogataj, Z. Kravanja, Z. Novak Pintarič (eds.) Table of Contents The Development and Assessment of Alkali Activated Paving Blocks Ana Frankovič, Vilma Ducman, Lubica Kriskova, Efthymios Tatsis, 1 Petrica Petrica, Yiannis Pontikes Influence of Homogenization of Alkali-Activated Slurry on Mechanical Strength Barbara Horvat, Mark Češnovar, Katja Traven, Majda Pavlin, Katja König, 11 Vilma Ducman Design of Geothermal Energy Pile Primož Jelušič, Stojan Kravanja, Tomaž Žula 51 Use of Recycled Plastic Waste in Concrete Gregor Kravanja 57 Topology Optimization of Steel-lined Rock Caverns for Underground Storage of Chemical Energy 67 Stojan Kravanja, Primož Jelušič, Tomaž Žula, Zdravko Kravanja Fibre Reinforced Alkali-Activated Rock Wool Majda Pavlin, Barbara Horvat, Vilma Ducman 77 Activity of α-Amylase from P. ostreatus Grown on Waste Substrates Mateja Primožič, Željko Knez, Maja Leitgeb 95 Water-based Electronic Paper as Low-cost Multi-color Screens Martin Rozman 103 The Influence of Different Fibres Quantity on Mechanical and Microstructural Properties of Alkali-activated Foams 113 Katja Traven, Mark Češnovar, Barbara Horvat, Vilma Ducman Analysis of the Possibilities for Energy Recovery in WWTP Rayka K. Vladova, Natasha Vaklieva-Bancheva 127 Sustainability Profit Gained by the Optimized Clamped Beams Tomaž Žula, Stojan Kravanja, Primož Jelušič 137 THE DEVELOPMENT AND ASSESSMENT OF ALKALI ACTIVATED PAVING BLOCKS ANA FRANKOVIČ,1 VILMA DUCMAN,1 LUBICA KRISKOVA,2 EFTHYMIOS TATSIS,2 PETRICA PETRICA,2 YIANNIS PONTIKES2 1 Slovenian National Building and Civil Engineering Institute, Ljubljana, Slovenia ana.frankovic@zag.si, vilma.ducman@zag.si 2 KU Leuven, Department of Materials Engineering, Leuven, Belgium lubica.kriskova@kuleuven.be, efthymios.tatsis@kuleuven.be, petricapetrica1@gmail.com yiannis.pontikes@kuleuven.be Abstract In recent years great attention has been placed by the building sector on alkali-activated technology based on metakaolin, fly ash and ground granulated blast furnace slag (GGBFS), but also on emerging precursors such as by-products from non-ferrous metallurgy. The present work focuses on the development of alkali-activated binders from two slags, one from primary and one from secondary copper production, which were finely milled, blended with GGBFS, and activated with K-based alkali silicate solution with a 1.7 SiO2/K2O molar ratio. The aggregate to paste mass ratio was 2. The mixtures were cast, and cured for a designated time at room temperature and 60% RH. The so-obtained paving blocks were then tested in accordance with European standard for concrete paving blocks. The following properties were measured: splitting tensile strength, abrasion resistance, slip and skid resistance, resistance to freeze-thaw and resistance to freeze-thaw in the presence of de-icing salts. Their properties were compared to those of commercial y available Keywords: concrete paving blocks, and it was found that the performance of Cu slag, the alkali-activated pavers was general y comparable with the alkali activation concrete pavers, while certain properties (e.g., abrasion resistance, process, pavers, freeze-thaw resistance and freeze-thaw resistance in presence of properties, de-icing salts) were considerably better. durability DOI https://doi.org/10.18690/um.fkkt.2.2022.1 ISBN 978-961-286-598-6 2 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. 1 Introduction One of the main objectives of the circular economy is to reduce the overuse of the available raw materials in order to restore ecological balance. This can be achieved by replacing raw materials with industrial waste or by-products. The greatest potential is seen in construction sector which consumes 35-45 % of natural resources [1]. Alkali-activation technology has been recognized as a promising method for the utilization of wastes and industrial by-products which are rich in silica and aluminium. The type of waste and by-products mentioned can therefore be used as a precursor in alkali-activated technology and converted into valuable building and construction materials such as binders, concrete, mortar, paving blocks, and bricks, thereby reducing demand for, and the subsequent environmental impact of, the production of Ordinary Portland Cement (OPC) [2]. In order to produce high quality building products, the composition of the alkali-activated mixture must be properly adjusted. Van De Sande et al. show that the chemical and mineralogical composition of non-ferrous slags used as precursors for alkali-activation play an important role in the mechanical and physical properties of the final product, and that the type of activator affects the kinetics and strength at an early age of the final product [3]. Furthermore, it was shown that using a proper rate of cooling when solidifying the non-ferrous slags led to the formation of a higher content of amorphous phase, and consequently to the formation of a solid alkali-activated binder [4]. One promising final uses for alkali-activated binders with a high residue content is the production of paving blocks. When processing new products, the aim is to develop products which have better, or at least comparable properties, to products already established on the market. The literature shows some cases where alternative materials, such as paving blocks, have been successfully made using alkali-activated technology. For example, Tatarannni et. al. successfully used waste basalt powder as a precursor in an alkali-activated binder for the production of alternative paving blocks [5]. Furthermore, Hossiney et. al. synthesized alkali-activated paving blocks using a high residues content in both the precursor (fly ash and ground granulated blast furnace slags) and the aggregate (recycled asphalt pavements) [6]. A. Frankovič, V. Ducman, L. Kriskova, E. Tatsis, P. Petrica, Y. Pontikes: The Development and Assessment of Alkali Activated Paving Blocks 3. This paper presents an alternative alkali-activated binder developed from non-ferrous metallurgy slag, used in up-scale production of paving blocks, intended for implementation in sustainable urban areas. Since there are no standards available for newly developed alkali-activated products, the performance of the paving blocks developed was evaluated according to standard EN 1338: Concrete paving blocks - Requirements and test methods [7]. 2 Experimental 2.1 Materials Finely milled (approximately 4000 cm2/g Blaine surface area) iron rich mineral formed during/ after secondary Cu production, i.e. Koranel® (Metallo Belgium N.V), was used in the present study. Its chemical composition is given in Table 1; its mineralogical evaluation confirmed the highly amorphous nature of the precursor, which contains 92 % amorphous phase and 8 % of the mineral Hercynite. Table 1: Chemical composition of the materials, in wt% Oxide FeO SiO2 Al2O3 CaO ZnO MgO SO3 Na2O CuO Others Koranel® 51 25 8 3 6 1 <1 <1 <1 3 2.2 Production The paving tiles were produced by blending Koranel® with GGBFS in a 6:1 mass:ratio and activated with a K- based alkali silicate solution (SiO2/K2O molar ratio of 1.7 and water content of 65 wt%), bringing the solution to a powder mass ratio of ~ 0.4. The aggregates and additives were gradually added into the activating solution and the final blend was mixed at high speed for approximately 2 min in a Hobart mixer. The fresh mortars were cast into moulds and cured for a designated time at RT and 60% RH. 4 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. Figure 1: The production process of the alkali activated paving blocks Source: authors from KU Leuven 2.3 Methods The paving blocks developed were tested with respect to their intended use, following the specifications outlined in standard EN 1338: Concrete paving blocks - Requirements and test methods [7]. The testing method for freeze-thaw resistance was adopted according to the standard ASTM C666 / C666M – 15: Standard Test Method for Resistance of Concrete to Rapid Freezing and Thawing [8]. The following parameters were simultaneously determined for both the Koranel®- rich paving blocks developed and for the reference material, a commercial product widely used in urban paving: − slip and skid resistance, − abrasion resistance, − splitting tensile strength, − freeze-thaw resistance, − freeze-thaw resistance in the presence of de-icing salts. A. Frankovič, V. Ducman, L. Kriskova, E. Tatsis, P. Petrica, Y. Pontikes: The Development and Assessment of Alkali Activated Paving Blocks 5. Since the number of samples was limited, some adjustments were made when performing the splitting tensile strength test. As shown in Figure 2, the samples were oriented differently so that two halves could be obtained in order to implement further test methods. Figure 2: Adjustment in the performance of the splitting tensile strength test. Source: own. 3 Results and discussion The test results are shown in Table 2. As can be seen from the results, the slip and skid resistance coefficient (Pendulum Test Value – PTV) is highly dependent on the nature of the surface; it is generally higher on the upper side, while it is very smooth with much lower values on the bottom side, where it had been in contact with the mould. On Rubber 57 under wet conditions, the PTV of the Koranel®-rich samples was 29 at the side which had been in contact with the mould, and 56 at the upper face within the mould. The reference material attained a value of 69. It should be noted that this characteristic could be significantly influenced simply by making a relief of the surface of the mould during the production phase. When determining abrasion resistance, the length of the groove of the Koranel®- rich paving blocks was 17.6 mm, compared to 22.1 mm in the reference material (Figure 3). According to the standard, permissible values for the abrasion resistance of concrete paving blocks have not been specified. From the literature, however, it 6 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. can be seen that natural stone reaches values from 14.8 mm for granite to as high as 27.3 in limestone [9]. Table 2: The performance of alkali activated paving blocks compared to the commercial concrete paving blocks Parameter Unite/conditions Koranel®-rich Reference material Slip and skid resistance (PTV) Rubber 57 – Wet 29/56 69 (Top/bottom) Abrasion resistance mm 17.6 22.1 Splitting tensile strength MPa 9.5 4.0 Freeze-thaw resistance After 300 cycles (-20°C/9°C) Resistant Not resistant Freeze-thaw resistance in After 25 cycles presence of de-icing salts (3% NaCl; - Resistant Not resistant 20°C/20°C) Figure 3: Abrasion resistance of the Koranel® sample (left) and the reference material sample (right) Source: own. As mentioned above, the splitting tensile strength test method was modified. The results obtained showed that the Koranel®-rich paving blocks exhibited a splitting tensile strength of 9.5 MPa, which is higher than that of the reference material, which reached 4 MPa. A. Frankovič, V. Ducman, L. Kriskova, E. Tatsis, P. Petrica, Y. Pontikes: The Development and Assessment of Alkali Activated Paving Blocks 7. Furthermore, freeze-thaw resistance was monitored by measuring the resonant frequency, as shown in Figure 4. The results show that breakage of the internal structure begins in the reference material after about 80 freeze-thaw cycles. After 300 freeze-thaw cycles there was visible deterioration in the reference material, while the Koranel®-rich paving blocks remained unchanged (Figure 5). Figure 4: Resonant frequency after 300 freeze-thaw cycles Source: own. Figure 5: Freeze-thaw resistance after 300 cycles; Koranel®-rich sample (left) and the reference material (right) Source: own. A similar trend was seen when determining the freeze-thaw resistance of the materials in the presence of de-icing salt. The Koranel®-rich paving blocks showed no deterioration after 25 freeze-thaw cycles (freezing at – 20 °C and thawing at 20 °C), while cracks appeared on the surface of the reference material after 20 cycles (Figure 6). 8 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. Figure 6: Results of freeze-thaw resistance tests in the presence of de-icing salts; Koranel®- rich sample after 28 freeze-thaw cycles (left), and the reference material after 20 cycles (right) Source: own. 4 Conclusions Slags generated from the production of various metals were successfully utilized for the production of paving blocks. The performance of blocks obtained in such a way was compared to commercial y available concrete paving blocks, and it was confirmed that the performance of the alkali-activated pavers was on a par with the concrete pavers, with certain properties being notably better: − Koranel®-rich samples were resistant to over 300 freeze-thaw cycles, − Koranel®-rich samples also exhibited resistance to freezing and thawing in the presence of de-icing salts, − the splitting tensile strength of the alkali-activated samples was twice as high as that of the concrete paving blocks, − abrasion resistance was highest in the Koranel®-rich based paving blocks. The technology developed could therefore be successfully implemented in the building sector, providing both the benefit of using waste instead of virgin materials, thus saving resources, and lowering the potential of global warming by replacing cement with alternative binders. Such a solution is completely in alignment with our present-day paradigm of promoting industrial symbiosis and a circular economy. A. Frankovič, V. Ducman, L. Kriskova, E. Tatsis, P. Petrica, Y. Pontikes: The Development and Assessment of Alkali Activated Paving Blocks 9. Acknowledgement “This activity has received funding from EIT RawMaterials, a Knowledge and Innovation Community (KIC) of the European Institute of Innovation and Technology (EIT), a body of the European Union, under Horizon 2020, the EU Framework Programme for Research and Innovation. Project Agreement No. 16365 (RECOVER), project website: https://recover.technology.” References [1] P. Mhatre, V. Gedam, S. Unnikrishnan, S. Verma, Circular Economy in Built Environment – Literature Review and Theory Development, Journal of Building Engineering, https://doi.org/10.1016/j.jobe.2020.101995. [2] Singh, J., & Singh, S. P. (2019). Geopolymerization of solid waste of non-ferrous metal urgy – A review. Journal of Environmental Management, 251, 109571. doi:10.1016/j.jenvman.2019.109571 [3] Van De Sande, J., Peys, A., Hertel, T., Rahier, H., & Pontikes, Y. (2020). Upcycling of non-ferrous metal urgy slags: Identifying the most reactive slag for inorganic polymer construction materials. Resources, Conservation and Recycling, 154, 104627. doi:10.1016/j.resconrec.2019.104627 [4] Pontikes, Y., Machiels, L., Onisei, S., Pandelaers, L., Geysen, D., Jones, P. T., & Blanpain, B. (2013). Slags with a high Al and Fe content as precursors for inorganic polymers. Applied Clay Science, 73, 93–102. doi:10.1016/j.clay.2012.09.020 [5] Tataranni. (2019). Recycled Waste Powders for Alkali-Activated Paving Blocks for Urban Pavements: A Full Laboratory Characterization. Infrastructures, 4(4), 73. doi:10.3390/infrastructures4040073 [6] Hossiney, N., Sepuri, H. K., Krishna Mohan, M., R, A. H., Govindaraju, S., & Chyne, J. (2019). Alkali-activated concrete paver blocks made with recycled asphalt pavement (RAP) aggregates. Case Studies in Construction Materials, e00322. doi:10.1016/j.cscm.2019.e00322 [7] EN 1338: Concrete paving blocks - Requirements and test methods. [8] ASTM C666 / C666M – 15: Standard Test Method for Resistance of Concrete to Rapid Freezing and Thawing. [9] Karaca, Z., Günes Yılmaz, N. & Goktan, R.M. (2012). Considerations on the European Standard EN 14157 Test Methods: Abrasion Resistance of Natural Stones Used for Flooring in Buildings. Rock Mech Rock Eng 45, 103–111. https://doi.org/10.1007/s00603-011-0190-1 10 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. INFLUENCE OF HOMOGENIZATION OF ALKALI-ACTIVATED SLURRY ON MECHANICAL STRENGTH BARBARA HORVAT, MARK ČEŠNOVAR, KATJA TRAVEN, MAJDA PAVLIN, KATJA KÖNIG, VILMA DUCMAN Slovenian National Building and Civil Engineering Institute, Ljubljana, Slovenia barbara.horvat@zag.si, mark.cesnovar@zag.si, katja.traven@zag.si, majda.pavlin@zag.si, ketsi.koenig@gmail.com, vilma.ducman@zag.si 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 Keywords: 70 °C) and different drying methods (drying at room temperature, secondary raw material, drying at 105 °C). The viscosity of the slurry before alkali activated homogenization was higher than after homogenization, the material, distribution of elements was more uniform and the compressive foaming, homogenization, strength higher in all homogenized alkali activated materials, mechanical regardless of other parameters. strength DOI https://doi.org/10.18690/um.fkkt.2.2022.2 ISBN 978-961-286-598-6 12 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. 1 Introduction Alkali activation is a chemically driven process in which aluminosilicate-rich precursors react with alkali media to form a solid binder, making these materials one of the promising alternatives to ordinary Portland cement (Juenger et al., 2011). As aluminosilicates are one of the most common minerals in the earth's crust (Schlesinger, 1991), they are contained in clays, in industrial by-products such as biomass and coal fly ashes, metallurgical slags, red mud and mineral wool waste, which offers the possibility to produce sustainable non-structural materials. The alkali-activated materials produced from these precursors have high mechanical strength, high thermal and chemical resistance and are refractory (Bernal and Provis, 2014). One of the possibilities, due to their thermal stability, are prefabricated lightweight insulation boards (foams). The chemical reaction of the so-called alkali activation begins with the dissolution of the aluminosilicates and ends with solidification. Nowadays, it is more often used in the laboratory than on the construction site, because the process is not wel understood and the technology is not set up in the same way as for ordinary cement concrete mixtures. Nevertheless, some projects, such as E-creteTM, have already shown some of the advantages of using alkali activated materials based on fly ash and slag for pavements: along the freeway in Port Melbourne, precast slabs for VicRoads, which have a much higher strength (55 MPa) than required by governmental legislation (Van Deventer et al., 2012). Therefore, low carbon awareness, a source of precursors and activators with developed technology, and the durable end product for larger-scale production are crucial for production on a larger scale. Numerous articles are published each year, where alkali activation focuses on the phase composition associated with the type of Ca-containing precursor and a sufficient amount of reactive amorphous Al and Si, computer modelling of the Al:Si ratio, the type and amount of activator, knowing that this is the most important factor in producing a material with the desired microstructure and mechanical properties (Vlček et al., 2014). Although some authors also study in detail the precursor preparations (drying, grinding and sieving) (Traven et al., 2019) and curing regimes (Češnovar et al., 2019) there is no real research in the technology of mixing and homogenizing with alkali activation. Size distribution, shape and packing of the precursor particles during mixing play an important role in the rheology of the alkali-activated slurry (Hunger and Brouwers, 2009). The surface tension of the particle- B. Horvat, M. Češnovar, K. Traven, M. Pavlin, K. König, V. Ducman: Influence of Homogenization of Alkali-Activated Slurry on Mechanical Strength 13. fluid interface and the ionic strength of the solution (Provis et al., 2010) is also related to the processability of the slurry. One of the possibilities to solve this problem is the use of chemical admixtures or so-cal ed superplasticisers as used for Portland cement pastes but the results are not yet promising (Criado et al., 2009). Another possibility to achieve better processability of alkali activated slurries is the correct homogenization. This technique offers the possibility of wetting solid particles while the liquid to dry content is not changed, which is important when the activator to precursor ratio is fixed at a calculated value. In most cases, homogenization is done after addition of an activator to the precursor (or vice versa), by manual mixing for 1 to 5 min by hand (with palate knife) (Rajamma et al., 2012), or mechanically with a laboratory mixer (Korat and Ducman, 2017), with an ordinary mixer for cement pastes such as Automix (Samson et al., 2017), Hobart mixer (Nematollahi et al., 2017) or a combination of mixing by hand and with a mixer (Hajimohammadi et al., 2017). However, when homogenization technology is used, there is stil no known relationship with the final mechanical properties of alkali-activated materials. When producing alkali-activated materials on a large scale, preparation of mixtures by manual mixing is impossible due to the longer time required for this process, and manual mixing itself does not provide good and efficient homogenization. This paper tries to clarify how different precursors behave when slurries are mixed manual y and/or with laboratory mixers and when a three-roll homogenizer homogenizes them. The homogenization of alkali activated foams based on electric arc furnace slag and fly ash, which are foamed with Na-perborate or H2O2, is also investigated. In the production of alkali-activated foams, surface agents such as triton, sodium oleate, sodium dodecyl sulfate or others are added to the slurry to stabilize air voids which are formed by a chemical reaction from the foaming agent (Korat and Ducman, 2017). While foaming and surface agents appear in a solid or liquid state, this also affects the viscosity and workability of the slurry. For foams produced by manual or machine homogenization, different combinations of foaming agent (solid, liquid) and surface agent (solid, liquid) are therefore used. 14 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. 2 Materials and Methods 2.1 Analysis of precursors and their alkali-activated counterparts Fly-ash (FA) (Traven et al., 2020), labelled 10 01 01, from Šoštanj power thermoplant, slag mixture (SM) (Češnovar et al., 2019), labelled 10 09 031, electric arc furnace slag from SIJ Acroni and ladle slag from SIJ Ravne, while glass wool waste (GW) (Horvat et al., 2018), labelled 17 09 041, and green waste ceramics (GWC) (Horvat and Ducman, 2019), labelled 10 12 011, were collected from Termit. The samples of al waste materials were col ected in a way that is representative for landfills. The metakaolin used in experiments (MK; Argeco) (Kramar et al., 2016; Provis et al., 2019) was used in the RILEM project and is not waste material. X-ray fluorescence was performed on melted discs (XRF; Thermo Scientific ARL Perform'X Sequential XRF) prepared with Fluxana(s) (FX-X50-2, lithium tetraborate 50% / lithium metaborate 50%) to lower melting point and with the addition of LiBr(l) (prepared from 50 ml H2O and 7.5 g of LiBr(s) from Acros Organics) to avoid sticking of the melt to the platinum vessel. The measured data were characterized by the UniQuant 5 software. The X-ray powder diffraction (XRD; Empyrean PANalytical X-ray Diffractometer, Cu X-ray source) was solved with the software X'Pert Highscore plus 4.1. The Rietveld refinement was performed using an external standard (a pure Al2O3 crystal) to estimate the amount of amorphous phase and minerals in waste materials. All samples used for XRF and XRD were dried at 70 °C for 24 h (WTB binder), ground with the vibrating disk mill (Siebtechnik) and sieved below 63 µm (SM), 90 µm (FA, GW and WGC). The viscosity of alkali-activated slurries (a mixture of precursor, alkali activator and potential foam stabilizing additives) was measured with the viscometer Haake VT 500 with the detector PK2-1° (measurable viscosity range for this detector is from 0.04 Pa·s to 400 Pa·s) at 25 °C. B. Horvat, M. Češnovar, K. Traven, M. Pavlin, K. König, V. Ducman: Influence of Homogenization of Alkali-Activated Slurry on Mechanical Strength 15. Fourier transform infrared spectroscopy (FTIR; PerkinElmer Spectrum Two) was performed on non-homogenized and homogenized alkali activated fly ash. Scanning electron microscopy (SEM; Jeol JSM-IT500) to investigate surface, shape and microstructure was performed under high vacuum conditions on dried precursors and alkali-activated samples, both sputtered with Au. Energy-dispersive X-ray spectroscopy (EDXS; Oxford Instruments, Link Pentafet) mapping was performed on polished, non-sputtered, alkali-activated samples in low vacuum conditions. All alkali-activated samples for the analysis of SEM were dried in vacuum at 40 °C for 24 h (Kambič, VS 50 S). The surface of a cross-section of polished vacuumed alkali-activated samples was also examined with a digital microscope (Tagarno FHD Trend) and software (Tagarno measuring software). Due to the sensitivity during polishing, especially of foam, the polishing was performed gently by hand. Measurements of bending and compressive strength of alkali activated materials and foam were carried out with compression and bending strength testing machine (ToniTechnik ToniNORM) 1 day after demoulding unless otherwise stated. The geometric density of alkali-activated samples was determined by weighting the sample and dividing its mass by its volume. 2.2 Preparation of precursors, activator and alkali-activated samples All precursors used for alkali activation shown in Fig. 1 were prepared as shown: − FA: used as received; − FA*: FA and MK were used as received. Both precursors were mixed in mass ratio 3:1 respectively; − SM: crushed in the gyratory crusher (Retsch BB50), ground in vibrating disk mill (Siebtechnik), sieved below 63 µm. Afterwards, both slags were mixed in mass ratio 1:1; − GW: drying at 70 °C for 24 h, ground in cement mixer using iron bal s and sieved below 63 µm; 16 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. − WGC: drying at 70 °C for 24 h, ground with a pestle and mortar and sieved below 1 mm. (a) (b) (c) (d) Figure 1: Photograph of precursors’ state used in alkali activation: (a) FA, on the inset, is MK (larger particles fal apart when touched), (b) SM, (c) GW and (d) WGC. On the insets are photographs of the virgin material: (b-up) electric arc slag, (b-down) ladle slag, (c) GW, (d) WGC. Surce: own. For the alkali reaction versatile alkali activators were produced and/or used: − FA: Alkali activator has been produced using ground glass powder (cathode ray tube waste glass) with an average particle size below 90 µm. After boiling for 6 h to 45 h, the prepared suspensions were filtered and the filtrates were analysed for silicon and aluminium content with an inductively coupled plasma optical emission spectrometer (ICP-OES, Varian, Model 715-ES): mass percentage of Na2O 0.02%, the mass percentage of SiO2 2.32%, and mass percentage of Al2O3 0.073%); B. Horvat, M. Češnovar, K. Traven, M. Pavlin, K. König, V. Ducman: Influence of Homogenization of Alkali-Activated Slurry on Mechanical Strength 17. − FA*: Na-water glass “Crystal” (Crystal, 0112, Tennants distribution, with the mass percentage of Na2O 18.8%, and mass percentage of SiO2 37.0%) and NaOH(s) (Donau Chemie Ätznatron Schuppen, EINECS 215-785-5); − SM: Na-water glass “Crystal” (Crystal, 0112, Tennants distribution, with a mass percentage of Na2O 18.8%, and the mass percentage of SiO2 37.0%); − GW: Na-water glass “Termit” (Silvez, mining company Termit, with the mass percentage of Na2O 12.8%, and mass percentage of SiO2 29.2%) and NaOH(s) (Donau Chemie Ätznatron Schuppen, EINECS 215-785-5); − WGC: Na-water glass “Geosil” (Geosil, 344/7, Woelner, with the mass percentage of Na2O 16.9%, and the mass percentage of SiO2 27.5%. Preparation of alkali slurry: − FA: precursor was manually mixed for 1 min with manually premixed alkali activator in mass ratio 3.37:1 respectively; − FA*: precursor was manually mixed for 1 min with manually premixed alkali activators (Na-water glass “Crystal” and NaOH(s)), foaming agent (H2O2, Carlo Erba reagents) and stabilizing agent (Na-dodecyl sulphate, Acros Organics) in mass ratio 2.66:1:0.05:0.04:0.04 respectively. The time of the start of the foaming reaction was estimated from the observation of bubble formation on the surface and volume growth; − SM: precursor was manually mixed with manually premixed alkali activator (Na-water glass “Crystal”), foaming agent (Na-perborate monohydrate(s); Belinka Perkemija d.o.o.) and stabilizing agent (triton(l); X-100 Electrophoresis, Dow Chemical Company) in mass ratio 1.89:1:0.06:0.03 respectively. The time of the start of the foam reaction was estimated from the observation of bubble formation on the surface and volume growth; − GW: precursor was mixed (up to 1000 rpm for 1 min with mixer Tehtnica Železniki, UM-405) with manually premixed alkali activators (Na-water glass “Termit” and NaOH(s)) in the mass ratio 1.28:1:0.05 respectively; − WGC: precursor was mixed (up to 1000 rpm for 1 min with mixer Tehtnica Železniki, UM-405) with alkali activator (Na-water glass “Geosil”) in mass ratio 1.35:1 respectively. 18 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. Half of each slurry was homogenized in a three-roll mill (Exakt 80S) until the slurries did not change their visual texture. All slurries were put into rubber-silicon moulds of size (80x20x20) mm3 and cured (WTB Binder): − FA: at 70 °C for 72 h; − FA*: at 70 °C for 72 h; − SM: at 60 °C for 24 h; − GW: at 60 °C for 24 h; − WGC: at 70 °C for 24 h. Demoulding and drying process before measuring the mechanical strength: − FA: the prisms were demoulded after cooling to room temperature and left at room temperature for an additional 24 h; − FA*: the prisms were demoulded after cooling to room temperature and left at room temperature for an additional 24 h; − SM: the prisms were demoulded after cooling to room temperature and right after the mechanical properties were measured; − GW: the prisms were demoulded after cooling to room temperature and right after the mechanical properties were measured; − WGC: the prisms were demoulded 3 weeks after curing at 70 °C and heat-treated at 105 °C for the additional 24 h (WTB Binder) because they were still not fully solidified. 3 Results and discussion 3.1 Analysis of precursor SEM micrographs of all precursors prepared for alkali activation are shown in Fig. 2 under lower and higher magnification. FA consists of typical spheres (Fig. 2 (a) and (b)) (Kutchko and Kim, 2006), FA* from FA and large aggregates from MK (Fig. 2 (c) and (d)), GW from elongated cylindrical structures (Fig. 2 (g) and (h)), which are also longer than 63 µm (size of the mesh used), while both SM (Fig. 2 (e) B. Horvat, M. Češnovar, K. Traven, M. Pavlin, K. König, V. Ducman: Influence of Homogenization of Alkali-Activated Slurry on Mechanical Strength 19. and (f)) and WGC (Fig. 2 (i) and (j)) come from randomly shaped particles with sharp edges by grinding. (a) (b) (c) (d) (e) (f) 20 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. (g) (h) (i) (j) Figure 2: SEM micrographs of FA [(a) magnification 50x, (b) magnification 500x], FA* [(c) magnification 50x, (d) magnification 500x], SM [(e) magnification 50x, (f) magnification 500x], GW [(g) magnification 50x, (h) magnification 500x] and WGC [(i) magnification 50x, (j) magnification 500x]. Surce: own. The chemical analysis of the precursor is presented in Table 1, with the first row of each precursor showing the mass percentages of elements detected by XRF, and the second row showing the mass percentages of elements in the crystal ine phase determined by Rietveld refinement on XRD patterns, and in the third line, the mass percentages of the elements in the amorphous phase are shown, calculated as the difference between the amount of the mass percentage of an element determined using XRD and the mass percentage of an element in the crystal ine phase. B. Horvat, M. Češnovar, K. Traven, M. Pavlin, K. König, V. Ducman: Influence of Homogenization of Alkali-Activated Slurry on Mechanical Strength 21. Table 1: The first row of each precursor shows the mass percentage of elements measured by XRF, the second row shows the mass percentage of elements in a crystal ine phase determined by Rietveld refinement from XRD, and the third row shows the mass percentage of elements in the amorphous phase. Precursor Elements/m% Na K Cs Mg Ca Sr Ba Al Si XRF 0.89 1.83 0 1.69 8.85 0.05 0.07 12.16 20.91 FA XRD 0 0 0 0.38 1.64 0 0 1.74 4.32 XRF-XRD 0.89 1.83 0 1.31 7.21 0.05 0.07 10.42 16.59 XRF 0.66 1.41 0 1.30 6.72 0.04 0.06 12.50 23.85 FA* XRD 0 0 0 0.39 1.33 0 0.01 1.56 7.12 XRF-XRD 0.66 1.41 0 0.91 5.39 0.04 0.05 10.94 16.73 XRF 0.23 0.17 0 14.28 21.58 0.04 0.03 4.47 9.87 SM XRD 0 0 0 5.43 11.12 0 0.02 1.07 6.03 XRF-XRD 0.23 0.17 0 8.85 10.46 0.04 0.01 3.40 3.84 XRF 12.24 0.29 0 2.22 5.10 0 0.06 1.32 30.73 GW XRD 0 0 0 0.18 0.54 0 0 0 2.61 XRF-XRD 12.24 0.29 0 2.03 4.56 0 0.06 1.31 28.12 XRF 0.25 3.66 0 0.87 2.41 0.02 0.36 12.24 28.76 WGC XRD 0 0 0 0.72 2.41 0 0 4.02 14.81 XRF-XRD 0.25 3.66 0 0.15 0 0.02 0.36 8.22 13.95 The optimum ratio of the amount of substance in the alkaline activated final sample is nNa+K:nAl:nSi=1:1:1.9 (Duxson et al., 2005), which was experimental y proven in our investigations at the WGC, where we only considered elements in the amorphous phase (Horvat and Ducman, 2019). An increased ratio (normalized to the amount of substance Al), where the whole first and second group of the periodic system are taken into account (n1st:n2nd:nAl:nSi), is for precursors: − FA: 0.22:0.61:1:1.53; − FA*: 0.16:0.43:1:1.47; − SM: 0.11:4.97:1:1.09; − GW: 11.05:4.05:1:20.57; − WGC: 0.34:0:1:1.64. If only elements from the first group of the periodic system are considered, for FA, FA* (addition of MK to FA lowered amounts of elements from the first and second group, and lowered ratio Si:Al), SM and GWC addition of Na (element of the first group) and Si is required, which can be both added with Na-water glass and a potential y insufficient amount of Na with NaOH, while in GW too much Na (to avoid efflorescence) is present even without alkali activator, i.e. GW can only be used as an additive to other precursors. 22 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. If elements from the second group are also considered, it is noticeable that FA, FA* and SM contain more amorphous elements from the second group than from the first group. When considering that 1 element from the second group can compensate “wrong” Al charge in the matrix for 2 Al, the normalized amount of substance of Al that can be compensated from both cationic groups present in the precursor is: − FA: 1.44; − FA*: 1.02; − SM: 10.05; − GW: 19.15; − WGC: 0.68. From the above list, it can be concluded that the addition of cations from alkali activators to the precursors FA, FA*, SM and GW lead to efflorescence because the final normalized (normalization to the amount of substance for Al) amount of substance of the cations should have the value 1 (this value is already higher for the precursor without alkali additives alone). The only precursor with a lower substance quantity of the first and second group before the addition of alkali activators is the WGC, which is the only precursor among the selected precursors, with which efflorescence can be avoided if the alkali activators are selected correctly if minerals found in precursors with XRD (Fig. 3) do not dissolve in alkali. − Fig. 3 shows the XRD measurements of all precursors and their Rietveld refinement results (the GOF value of al analyzed samples was below 10 - the value is higher because the precursors are (mostly) waste products and several peaks on the XRD samples could not be determined and are contained in the amount of the amorphous phase). The highest amount of amorphous phase is GW (90%), followed by FA (80%), FA* (70%), WGC (50%) and SM (40%). The higher amount of amorphous phase can lead to a higher amount of aluminosilicate network in the final alkaline activated material. Minerals that are detected with XRD when they do not react with alkali or become unstable at the curing temperature represent aggregates of different Mohs hardness in the final product, i.e. when they have a higher hardness than the alkaline activated sample has higher compressive strength B. Horvat, M. Češnovar, K. Traven, M. Pavlin, K. König, V. Ducman: Influence of Homogenization of Alkali-Activated Slurry on Mechanical Strength 23. (Horvat and Ducman, 2019). The only mineral present in al precursors is quartz, which accounts for a higher mass percentage in al precursors used (Fig. 3). 24 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. (a) (b) (c) (d) B. Horvat, M. Češnovar, K. Traven, M. Pavlin, K. König, V. Ducman: Influence of Homogenization of Alkali-Activated Slurry on Mechanical Strength 25. (e) (f) (g) (h) 26 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. (i) (j) Figure 3: XRD pattern of (a) FA, (c) FA*, (e) SM, (g) GW and (i) GWC. Rietveld refinement of (b) FA, (d) FA*, (f) SM, (h) GW and (j) GWC. Source: own. B. Horvat, M. Češnovar, K. Traven, M. Pavlin, K. König, V. Ducman: Influence of Homogenization of Alkali-Activated Slurry on Mechanical Strength 27. 3.2 Analysis of alkali-activated samples During homogenization of FA slurry gas (white-grey smoke) was produced, while during homogenization of other mixtures slurries became visually just smoother and easier to handle. The compressive and flexural strength of all alkaline activated samples produced from homogenized and non-homogenized slurries are shown in Table 2 together with the viscosity of the slurries and the density of the final products. The viscosity decreases with homogenization from high to measurable high for alkaline activated material from GW, for alkaline activated materials from FA for 55% and from WGC for 60%, for alkaline activated foams from FA* for 15% and from SM for 30%. The compressive strength was increased for al tested samples, i.e. for alkaline activated materials from GW by 25%, from FA by 55% and from WGC by 70%, for alkaline activated foams from FA* by 75% and SM by 50%. The flexural strength was also increased for all samples tested, i.e. for alkaline activated materials from GW by 10%, from FA by 30% and from WGC by 80%, for alkaline activated foams from FA* by 100% and from SM from non-existent to 10% of the value of the flexural strength of alkaline activated material from GW. Table 2: The density of alkali-activated samples, their compressive and bending strengths in the dependence of preparation of alkali slurry, with and without (intact) homogenization. Viscosity Compressive Bending Precursor Preparation Density/ of the slurry of the slurry/ strength/ strength/ Pa·s MPa MPa kg/l Intact 5.03 30.25 7.20 1.71 FA Homogenization 2.23 46.76 9.46 1.77 Intact 0.90 3.23 2.11 0.70 FA* Homogenization 0.75 5.67 4.27 0.84 Intact 1.08 0.92 0 0.64 SM Homogenization 0.76 1.38 1.71 0.64 Intact torque overload 54.91 14.00 1.75 GW Homogenization 41.13 69.87 15.86 1.79 Intact 6.43 11.03 9.05 1.87 WGC Homogenization 2.55 19.00 16.13 1.35 28 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. Mechanical strength of alkali-activated foams increased less if foaming did not start too early because the homogenization did not influence the foaming of the slurry, i.e. final density of alkali-activated foam did not change, the material was just homogenized in its pre-foaming time (SM was foamed with Na-perborate which started to foam approximately 5 min after precursor was mixed with foaming and stabilizing agent, i.e. after 1 min of mixing there were still approximately 4 min for homogenization and moulding), i.e. under the digital microscope, there was no obvious difference in pore size and distribution with and without homogenization (Fig. 4 (e) and (f) respectively). If foaming started during homogenization, gas bubbles were removed from the slurry mechanically and final density of the alkali-activated foam was higher due to homogenization and gas bubble-removal (FA* was foamed with H2O2 which started to react during 1 min time of mixing of the precursor with foaming and stabilizing agent, i.e. homogenization and moulding do influence final properties of the foam). Homogenization during foaming also affected bubble distribution and size, i.e. homogenized sample has smal er, more uniformly sized and more uniformly distributed pores, as it is presented on Fig. 4 (c) and (d), i.e. sample without and with homogenization respectively. Bloating of WGC occurred during drying at 110 °C and was more pronounced when the material was homogenized (Fig. 4 (j)), due to the alkali activation of the whole material, while non-reacted precursors were observed with intact alkali-activated material (light pink and white-yellow particles in Fig. 4 (i); the alkali did not reach the inner volume of the particles of the precursor, which were additional y crushed and dispersed with homogenization). One consequence of the bloating was a decrease in density of almost 30%, which has a negative effect on mechanical strength, i.e. an increase in bending and mechanical strength of homogenized material dried by methods that avoid bloating would result in an even greater increase in mechanical strength. Figure 4: Microphotographs of vacuumed polished alkali-activated samples’ cross-sections performed with a digital microscope at magnification 25 for FA [(a) intact, (b) homogenized], FA* [(c) intact, (d) homogenized], SM [(e) intact, (f) homogenized], GW [(g) intact, (h) homogenized] and WGC [(i) intact, (j) homogenized]. B. Horvat, M. Češnovar, K. Traven, M. Pavlin, K. König, V. Ducman: Influence of Homogenization of Alkali-Activated Slurry on Mechanical Strength 29. 30 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. Figure 4: Microphotographs of vacuumed polished alkali-activated samples’ cross-sections performed with a digital microscope at magnification 25 for FA [(a) intact, (b) homogenized], FA* [(c) intact, (d) homogenized], SM [(e) intact, (f) homogenized], GW [(g) intact, (h) homogenized] and WGC [(i) intact, (j) homogenized] Alkali-activated GW without homogenization showed circular longitudinal pores (Fig. 4 (g)), which are a consequence of manual moulding of slurry that is too viscous (almost as bulk material), whereas these pores are not observed in homogenized alkali-activated GW (Fig. 4 (h)), therefore, the higher mechanical strength of the homogenized sample. FA Alkali-activated without homogenization contains larger black, non-spherical particles that are not present in the homogenized sample (Fig. 4 (a) and (b) respectively). Fig. 5 shows intact alkali-activated FA and Fig. 6 shows homogenized alkali-activated FA. B. Horvat, M. Češnovar, K. Traven, M. Pavlin, K. König, V. Ducman: Influence of Homogenization of Alkali-Activated Slurry on Mechanical Strength 31. (a) (b) (b-Na) (b-K) (b-Ca) (b-Mg) (b-Al) 32 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. (b-Si) (b-O) (b-C) (b-S) (b-Fe) Figure 5: SEM micrograph of intact alkali-activated FA with magnification (a) 30 (intact cross- section after (c-Na) (c-K) (c-Ca) compressive strength test, vacuumed and sputtered with Au, observed at HV), (b) 100 and (c) 50 (cut and polished cross- (c) (c-Mg) (c-Al) (c-Si) section, observed at LV). The EDXS mapping of micrograph (b), (c) is presented on (b- chemical element), (c- chemical element) (c-O) (c-C) (c-S) (c-Fe) respectively. Source: own. B. Horvat, M. Češnovar, K. Traven, M. Pavlin, K. König, V. Ducman: Influence of Homogenization of Alkali-Activated Slurry on Mechanical Strength 33. Figure 6: SEM micrograph of homogenized alkali- activated FA with magnification (a) 30 (intact cross-section (a) (b) after compressive strength test, vacuumed and sputtered with Au, observed at HV) and (b) 100 (cut and polished cross- (b-Na) (b-K) (b-Ca) (b-Mg) (b-Al) section, observed at LV). The EDXS mapping of micrograph (b) is presented on (b- chemical element). (b-Si) (b-O) (b-C) (b-S) (b-Fe) Source: own. 34 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. Fig. 5 (a) and Fig. 6 (a) show that there is no difference in the aluminosilicate network, its polished counterparts in Fig. 5 (b) and Fig. 6 (b) show that homogenization led to the grinding of large fly ash spheres that consist from elements of the second group, which were not reacted according to the EDXS analysis, which is beneficial to the product since this improved the ratio of the first and second group to Al, which means that efflorescence could be avoided or at least minimized. In an intact alkali-activated FA network, incompletely burned organic parts of coal and wood were trapped (Fig. 5 (c)), which were not visible in the homogenized sample. These parts look black to the naked eye under an optical microscope (Fig. 4 (a)) and also under SEM (Fig. 5 (c)), made of C according to EDXS analysis (Fig. 5 (c-C)). From al EDXS mappings of intact and homogenized alkali-activated FA (Fig. 5 and Fig. 6), it can be concluded that the homogenization also led to a better uniformity of all elements in the alkali-activated sample. Fig. 7 shows the FTIR analysis of intact and homogenized alkali-activated FA. C-C bonds are present in the intact sample (bands around 1450 cm-1 and 890 cm-1 belong to the stretching and bending of C-C bonds (Ahmed et al., 2013)), while they have disappeared in the homogenized sample, which proves that the emission of smoke from the slurry during homogenization was the result of the combustion of cel ulose (observed under SEM only in intact alkali-activated FA samples, shown in Fig. 5(c)) from the incomplete combustion of coal and wood. B. Horvat, M. Češnovar, K. Traven, M. Pavlin, K. König, V. Ducman: Influence of Homogenization of Alkali-Activated Slurry on Mechanical Strength 35. Figure 7: Photo FTIR spectra of intact (orange line) and homogenized (green line) FA. Source: own. Fig. 8 shows intact alkali-activated FA* and Fig. 9 shows homogenized alkali-activated FA*: 36 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. Figure 8: SEM micrograph of intact alkali-activated FA* (a) (b) with magnification (a) 30 (intact cross- section after compressive strength test, vacuumed and sputtered with Au, observed at HV) and (b-Na) (b-K) (b-Ca) (b-Mg) (b-Al) (b) 100 (cut and gently polished cross- section, observed at LV). The EDXS mapping of micrograph (b) is presented on (b- chemical element). (b-Si) (b-O) (b-C) (b-S) (b-Fe) Source: own. B. Horvat, M. Češnovar, K. Traven, M. Pavlin, K. König, V. Ducman: Influence of Homogenization of Alkali-Activated Slurry on Mechanical Strength 37. When comparing Fig. 8 (a) and Fig. 9 (a), it becomes clear that the aluminosilicate network shows no visible change, while the pores are more uniform in size and more uniformly distributed after homogenization. The mean value of pore size from SEM micrographs of intact alkali-activated FA* is 240.4 µm (standard deviation 173.7 µm), while the mean value for homogenized alkali-activated FA* is 98.9 (standard deviation 40.4 µm). The value decreased by 60% and the pores are more homogeneously distributed according to the decrease of the standard deviation (4-times) compared to the mean value of the pore diameter (2-times). From the EDXS analysis of alkali-activated FA* polished counterparts (shown in Fig. 8 (b) and Fig. 9 (b)), it is the same as for the alkali-activation of FA (Fig. 5 and Fig. 6), i.e. spheres from elements from the second group did not react and are simply ground after homogenization, which leads to a better element distribution over the entire alkali-activated FA* (Fig. 8 (b-element) and Fig. 9 (b-element)). 38 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. Figure 9: SEM micrograph of homogenized, alkali- activated FA* with (a) (b) magnification (a) 30 (intact cross-section after compressive strength test, vacuumed and sputtered with Au, observed under HV) (b-Na) (b-K) (b-Ca) (b-Mg) (b-Al) and (b) 100 (cut and gently polished cross- section, observed under LV). The EDXS mapping of the micrograph (b) is presented under (b- chemical element). (b-Si) (b-O) (b-C) (b-S) (b-Fe) Source: own. B. Horvat, M. Češnovar, K. Traven, M. Pavlin, K. König, V. Ducman: Influence of Homogenization of Alkali-Activated Slurry on Mechanical Strength 39. Fig. 10 shows intact alkali-activated SM and Fig. 11 shows homogenized alkali-activated SM. The aluminosilicate network before and after homogenization of SM presented in Fig. 10 (a) and Fig. 11 (a) shows no change. The statistics of the measured pores on SEM micrographs show that the mean value of the pore size of intact, alkali-activated SM is 533.8 µm (standard deviation 275.1 µm), while the mean value for homogenized, alkali-activated SM is 444.7 µm (standard deviation 178.4 µm). The value decreased by 15%, and the pores are more homogeneously distributed according to the decrease in standard deviation (1.5 times) compared to the mean value of the pore diameter (1.2 times). When comparing the EDXS results for intact and homogenized SM (Fig. 10 (b-element) and Fig. 11 (b-element) it can be concluded that after homogenization the distribution of the elements in the aluminosilicate network is somewhat more uniform. 40 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. Figure 10: SEM micrograph of intact alkali-activated SM (b) (a) with magnification (a) 30 (intact cross- section after compressive strength test, vacuumed and sputtered with Au, observed at HV) and (b) 100 (cut and gently (b-Na) (b-Ca) (b-Mg) (b-Al) (b-Si) polished cross- section, observed at LV). The EDXS mapping of the micrograph (b) is presented on (b- chemical element). (b-O) (b-C) (b-Mn) (b-Cr) (b-Fe) Source: own. B. Horvat, M. Češnovar, K. Traven, M. Pavlin, K. König, V. Ducman: Influence of Homogenization of Alkali-Activated Slurry on Mechanical Strength 41. Figure 11: SEM micrograph of homogenized alkali- activated SM with (b) magnification (a) 30 (a) (intact cross-section after compressive strength test, vacuumed and sputtered with Au, observed at HV) and (b) 100 (cut and gently (b-Na) (b-Ca) (b-Mg) (b-Al) (b-Si) polished cross- section, observed at LV). The EDXS mapping of the micrograph (b) is presented on (b- chemical element. (b-O) (b-C) (b-Mn) (b-Cr) (b-Fe) Source: own. 42 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. Fig. 12 shows intact alkali-activated GW and Fig. 13 shows homogenized alkali-activated GW. Figure 12: SEM micrograph of intact alkali-activated GW with magnification (a) (a) (b) 30 (intact cross- section after compressive strength test, vacuumed and sputtered with Au, observed at HV) and (b) 100 (cut and (b-Na) (b-Ca) (b-Mg) (b-Al) (b-Si) polished cross- section, observed at LV). The EDXS mapping of micrograph (b) is shown under (b- chemical element). (b-O) (b-C) (b-S) (b-Fe) Source: own. B. Horvat, M. Češnovar, K. Traven, M. Pavlin, K. König, V. Ducman: Influence of Homogenization of Alkali-Activated Slurry on Mechanical Strength 43. The aluminosilicate network of GW with and without homogenization shows no visual difference (Fig. 12 (a) and Fig. 13 (a)), while from the EDXS analysis on the polished samples (Fig. 12 (b-element) and Fig. 13 (b-element)) it can be concluded that homogenization has a great influence on the distribution of the elements, which are somewhat more uniform in the homogenized sample. 44 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. Figure 13: SEM micrograph of homogenized alkali- (b) activated GW with (a) magnification (a) 30 (intact cross-section after compressive strength test, vacuumed and sputtered with Au, observed at HV) and (b-Na) (b-Ca) (b-Mg) (b-Al) (b-Si) (b) 100 (cut and polished cross- section, observed at LV). The EDXS mapping of micrograph (b) is shown under (b- chemical element). (b-O) (b-C) (b-S) (b-Fe) Source: own. B. Horvat, M. Češnovar, K. Traven, M. Pavlin, K. König, V. Ducman: Influence of Homogenization of Alkali-Activated Slurry on Mechanical Strength 45. Fig. 14 shows intact alkali-activated WGC and Fig. 15 homogenized alkali-activated WGC. There is no visual difference in the aluminosilicate network (Fig. 14 (a) and Fig. 15 (a)), while there is a difference in the distribution of the network due to bloating (non-thermal y stable chemicals that change to gas when exposed to higher/high temperatures) after exposure to 105 °C for 24 h. In the intact sample bloating is less pronounced, random and with spherical bubbles, whereas in the homogenized sample is layered and perpendicular to the direction of moulding. From the EDXS analysis (Fig. 14 (b-element) and Fig. 15 (b-element), which was performed on polished samples and is shown in Fig. 14 (b) and Fig. 15 (b) respectively, it can be seen that the precursor itself was wel homogenized, i.e. the distribution of the elements in the entire volume of the alkali-activated material is uniform with and without homogenization (EDXS sees no difference between unreacted and reacted parts of the alkali-activated WGC visible to the naked eye and shown in Fig. 4 (i) and (j)). 46 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. Figure 14: SEM micrograph of intact alkali-activated WGC (a) (b) with magnification (a) 30 (intact cross- section after compressive strength test, vacuumed and sputtered with Au, observed at HV) and (b-Na) (b-K) (b-Al) (b-Si) (b-O) (b) 100 (cut and polished cross- section, observed at LV). The EDXS mapping of the micrograph (b) is presented on (b- chemical element). (b-C) Source: own. B. Horvat, M. Češnovar, K. Traven, M. Pavlin, K. König, V. Ducman: Influence of Homogenization of Alkali-Activated Slurry on Mechanical Strength 47. Figure 15: SEM micrograph of homogenized alkali- activated WGC with magnification (a) 30 (intact cross-section after compressive (a) (b) strength test, vacuumed and sputtered with Au, observed under HV; the direction of moulding is horizontal on the SEM (b-Na) (b-K) (b-Al) (b-Si) (b-O) micrograph) and (b) 100 (cut and polished cross-section observed under LV). The EDXS mapping of micrograph (b) is presented on (b- chemical element). (b-C) Source: own. 48 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. 4 Conclusions The compressive and bending strength of alkali-activated material and alkali-activated foam were higher when the slurry was homogenized in its initial stage of reaction, regardless of other parameters influencing alkali activation, i.e. precursors, alkali activators, the ratio of ingredients, curing regimes and drying procedures. The increase in compressive strength was from 30% to 75%, the increase of bending strength from 10% to more than 100%. However, the homogenization of alkali-activated foam is only possible if the foaming agent has a delayed reaction with the reagents, i.e. when we are dealing with alkali-activated delayed foam, to avoid the increase in density of the foamed product due to the loss of gasses, which should be trapped in the alkali-activated precursor when the mixture is optimal y designed. The viscosity of the slurry was lower after homogenization, or at least it became measurable. The decrease was more than 50% for alkali-activated materials, whereas for alkali-activated foams the decrease in viscosity was just noticeable on an absolute scale. The density of alkali-activated materials did not change when alkali-activated material did not bloat after exposure to high temperatures (which has a negative effect on mechanical strength, as almost solid alkali-activated material turns into solid alkali-activated "foam"), or when alkali-activated foam had a delayed start of foaming. In summary, it can be said that homogenization itself does not affect the alkali-activated reaction, it only affects the distribution of the elements and additionally grinds larger particles, resulting in a more reactive surface and a smaller volume of reagents that must dissolve before the liquid alkali can diffuse. In this way, homogenization helps to ensure that more precursor can react with alkali, which does not have to reach reagents only with "superficial" mixing of the reagents and later by time-limited diffusion in the slurry. Acknowledgements Project No. C3330-17-529032 “Raziskovalci-2.0-ZAG-529032” was granted by Ministry of Education, Science and Sport of the Republic of Slovenia. The investment is co-financed by the Republic of Slovenia, Ministry of Education, Science and Sport and the European Regional Development Fund. The involvement of V. Ducman was supported by the Slovenian Research Agency Programme Group P2-0273. The involvement of K. Traven and K. König was supported by Slovenian Research Agency B. Horvat, M. Češnovar, K. Traven, M. Pavlin, K. König, V. Ducman: Influence of Homogenization of Alkali-Activated Slurry on Mechanical Strength 49. with Project Grant J2 9197. The involvement of M. Češnovar is part of the ERA-MIN FLOW project which has received funding from the Ministry of education, science and sport (acronym: MIZS) under grant agreement No. C 3330-18-252010. M. Pavlin is involved by the support of WOOL2LOOP project that received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 821000. The Metrology Institute of the Republic of Slovenia is acknowledged for the use of XRF. Cooperation with Termit d.d. and Mrs Alenka Sešek Pavlin from Termit d.d.is highly appreciated. References Ahmed, M.H., Byrne, J.A., McLaughlin, J., Ahmed, W., 2013. Study of Human Serum Albumin Adsorption and Conformational Change on DLC and Silicon Doped DLC Using XPS and FTIR Spectroscopy. Journal of Biomaterials and Nanobiotechnology 04, 194–203. https://doi.org/10.4236/jbnb.2013.42024 Bernal, S.A., Provis, J.L., 2014. Durability of Alkali-Activated Materials: Progress and Perspectives. 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Regulating the chemical foaming reaction to control the porosity of geopolymer foams. Materials & Design 120, 255–265. https://doi.org/10.1016/j.matdes.2017.02.026 Horvat, B., Češnovar, M., Pavlin, A., Ducman, V., 2018. Upcycling with alkali activation technology, in: Technologies & Business Models for Circular Economy. Presented at the 1st International Conference on Technologies & Business Models for Circular Economy, Univerzitetna založba Univerze v Mariboru / University of Maribor Press, pp. 261–272. https://doi.org/10.18690/978-961-286-211-4.22 Horvat, B., Ducman, V., 2019. Potential of Green Ceramics Waste for Alkali Activated Foams 30. Hunger, M., Brouwers, H.J.H., 2009. Flow analysis of water–powder mixtures: Application to specific surface area and shape factor. Cement and Concrete Composites 31, 39–59. https://doi.org/10.1016/j.cemconcomp.2008.09.010 Juenger, M.C.G., Winnefeld, F., Provis, J.L., Ideker, J.H., 2011. Advances in alternative cementitious binders. 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Thermomechanical performance of blended metakaolin-GGBS alkali-activated foam concrete. Construction and Building Materials 157, 982–993. https://doi.org/10.1016/j.conbuildmat.2017.09.146 Schlesinger, W.H., 1991. Biogeochemistry: an analysis of global change. Academic Press, San Diego. Traven, K., Češnovar, M., Ducman, V., 2019. Particle size manipulation as an influential parameter in the development of mechanical properties in electric arc furnace slag-based AAM. Ceramics International. https://doi.org/10.1016/j.ceramint.2019.07.296 Traven, K., Črešnovar, M., Škapin, S., Ducman, V., 2020. Evaluation of Fly Ash-based Alkali Activated Foams at Room and Elevated Temperatures, in: 2nd International Conference on : Technologies & Business Models for Circular Economy: Conference Proceedings. Presented at the International Conference on Technologies & Business Models for Circular Economy, University of Maribor, University Press, pp. 23–34. https://doi.org/10.18690/978-961-286-353-1.2 Van Deventer, J.S.J., Provis, J.L., Duxson, P., 2012. Technical and commercial progress in the adoption of geopolymer cement. Minerals Engineering 29, 89–104. https://doi.org/10.1016/j.mineng.2011.09.009 Vlček, J., Drongová, L., Topinková, M., Matějka, V., Kukutschová, J., Vavro, M., Tomková, V., 2014. Identification of phase composition of binders from alkali-activated mixtures of granulated blast furnace slag and fly ash 10. DESIGN OF GEOTHERMAL ENERGY PILE PRIMOŽ JELUŠIČ, STOJAN KRAVANJA, TOMAŽ ŽULA University of Maribor, Faculty of Civil Engineering, Transportation Engineering and Architecture, Maribor, Slovenia primoz.jelusic@um.si, stojan.kravanja@um.si, tomaz.zula@um.si Abstract Sustainable buildings should include energy foundations that exchanges heat energy with the ground. High-rise buildings are often founded on piles because of the large mass of the high-rise building. The article presents the design of an economical y efficient geothermal energy pile. Geothermal energy piles are typical geostructures used for heating/cooling buildings. Geothermal energy piles are exposed to cyclical thermal loads and not only to structural loads like conventional piles. These cyclical loads could increase the settlement of piles, especial y if they are Keywords: installed in fine-grained soil. Today, it is necessary to design geothermal geotechnical structures in such a way that they are economical y energy piles, energy efficient and have a low probability of failure. The proposed foundations, optimization method is illustrated by applying it to a multi-story optimal design, building supported by geothermal energy piles. The example fine-grained soils, presented shows that the load-bearing capacity is fully exploited in high-rise the optimal design solution. buildings DOI https://doi.org/10.18690/um.fkkt.2.2022.3 ISBN 978-961-286-598-6 52 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. 1 Introduction Sustainable buildings should also include energy foundations that exchanges heat energy with the ground. High-rise buildings are often founded on piles because of the large mass of the building. Piles are also used when the magnitude of the load under different parts of the building is uneven, when the construction of a shal ow foundation could damage existing, adjacent buildings, and when the building is not rigid enough and large settlement differences could occur. However, load-bearing piles can also be used to exchange heat energy with the ground. Such piles are cal ed geothermal energy piles or thermal piles. Geothermal energy piles consist of sealed pipe loops that are inserted into the pile and filled with thermal transfer fluid. The thermal fluid, which circulates through a closed loop system, generally contains antifreeze and biocide. When designing geothermal piles, it must be ensured that the soil conditions are suitable to withstand the structural pile loads and that the thermal effect is taken into account. Therefore, the thermal properties of the soil, the average undisturbed soil temperature, the average ambient air temperatures and the geothermal heat flux must be estimated. The most important additional considerations for the design of geothermal piles are the reduction of soil strength properties, radial and axial expansion, thermal y induced axial stresses and the cyclical effect of thermal stresses. This paper presents the design of economical y efficient geothermal energy piles, which are built in fine-grained soils such as clay and silt. Coarse-grained soils such as gravel and sand are less prone to soil shear strength reduction than fine-grained soils. In order to obtain an economical y efficient design of geothermal energy piles, the optimization method was applied (Žula & Kravanja, 2018; Žula & Kravanja, 2020). Figure 1: Geothermal energy piles for high-rise building. Source: P. Jelušič, S. Kravanja, T.Žula: Design of Geothermal Energy Pile 53. 2 Geothermal energy pile design model 2.1 Costs based objective function The most suitable technology for the construction of geothermal piles is the bored pile technology. The objective function COST (EUR) is based on the self-production costs of the geothermal pile produced with the dril ing technology (see Eq. (1)): min: 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 = 𝐶𝐶𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 + 𝐶𝐶𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 + 𝐶𝐶𝑑𝑑𝑟𝑟𝑑𝑑𝑐𝑐,𝑚𝑚𝑚𝑚𝑑𝑑𝑐𝑐 + 𝐶𝐶𝑑𝑑𝑟𝑟𝑑𝑑𝑐𝑐,𝑠𝑠ℎ𝑟𝑟𝑚𝑚𝑑𝑑 + 𝐶𝐶𝑡𝑡ℎ𝑟𝑟𝑑𝑑𝑚𝑚𝑚𝑚𝑑𝑑 (1) where Cdril stands for the cost of ground dril ing, Cconc for the cost of the concrete used for the pile, Crein,main for the main reinforcing steel embedded in the concrete pile, Crein,shear for the shear reinforcing steel and the Cthermal for the cost of the closed pipe loop embedded in the pile. 2.2 Geotechnical constrains Piles for geothermal energy must be able to bear the applied structural load (Jelušič and Žlender, 2020). This load transfer of the structural load to the ground takes place through friction between the ground and the surface of the pile and by end bearing. Five boundary conditions (see Eqs. (2) - (6)) according to the Eurocode standards and recommendations GSHP (GSHP, 2012) ensure the appropriate dimensions of the geothermal piles. The constraints are defined by Eqs. (2) – (6)): 𝐹𝐹𝑑𝑑 ≤ 𝑅𝑅𝑐𝑐,𝑑𝑑 (2) 𝑢𝑢𝑑𝑑𝑐𝑐𝑚𝑚𝑑𝑑 + 𝑢𝑢𝑡𝑡ℎ𝑟𝑟𝑑𝑑𝑚𝑚𝑚𝑚𝑑𝑑 ≤ 𝑢𝑢𝑑𝑑𝑑𝑑𝑚𝑚 (3) 𝐴𝐴𝑚𝑚𝑚𝑚𝑑𝑑𝑐𝑐,𝑑𝑑𝑟𝑟𝑟𝑟 ≤ 𝐴𝐴𝑚𝑚𝑚𝑚𝑑𝑑𝑐𝑐,𝑝𝑝𝑑𝑑𝑐𝑐𝑝𝑝 (4) 𝐴𝐴𝑚𝑚𝑚𝑚𝑑𝑑𝑐𝑐,𝑝𝑝𝑑𝑑𝑐𝑐𝑝𝑝 ≥ 𝐴𝐴𝑚𝑚𝑚𝑚𝑑𝑑𝑐𝑐,𝑚𝑚𝑑𝑑𝑐𝑐 (5) 𝑠𝑠𝑠𝑠ℎ𝑟𝑟𝑚𝑚𝑑𝑑 ≤ 𝑠𝑠𝑠𝑠ℎ𝑟𝑟𝑚𝑚𝑑𝑑,𝑚𝑚𝑚𝑚𝑚𝑚 (6) where Fd (kN) is the design’s vertical-load, Rc,d (kN) is the calculated pile design resistance of the bored reinforced concrete pile, uload (mm) is the settlement caused by the structural load, uthermal (mm) is the settlement caused by thermal effects, ulim (mm) is the al owable settlement of the pile, Amain,req (mm2) is the required main 54 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. reinforcement steel area in the pile, Amain,prov (mm2) is the provided main reinforcement steel area in the critical cross section of the pile, Amain,min (mm2) is the required minimum steel area, sshear (mm) is the link-spacing of shear reinforcement and the sshear,max (mm) is maximum spacing of the shear reinforcement. In order to fulfil al the boundary conditions defined above simultaneously and to achieve the minimum self-production costs of the geothermal energy pile, the optimization method was applied (Kravanja & Grossmann, 1994). In the optimization model, the diameter of the pile D (mm), the length of the pile L (m), the diameter of the main reinforcement bars ∅main (mm), the number of main reinforcement bars nmain (-), the diameter of the links ∅ shear (mm) and the distance between the links sshear (mm) were defined as variables. Assuming that the pile head is free, cooling of the pile leads to additional settlement, while heating causes the pile head to move upwards. Repeated cycles of the thermal effects lead to a deterioration of the shaft friction along the pile with an accumulation of settlements. The additional settlement from the thermal effects uthermal (mm) has been calculated based on the diagram contained in GSHP [16], see Figure 2. The discrete alternatives for each variable are shown in Table 1. 3,5 )m 2,5 ent due m s (mfect 1,5 ettle efalnal sm 0,5 ddtio to ther -0,5 10 15 20 25 30 A Pile Length (m) Figure 2: Additional settlement due to the repeated cycling of the thermal effects. Source: Table 1: Discrete alternatives of the variables. Variable Discrete alternatives D (m) 0.60, 0.70, 0.80, 0.90, 1.00, 1.10, 1.20, 1.30, 1.40, 1.50 L (m) 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 ∅ main (mm) 10, 12, 14, 16, 18, 20, 25, 28, 30 nmain (-) 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40 ∅ shear (mm) 8, 10, 12, 14 sshear (mm) 100, 125, 150, 175, 200, 225, 250 P. Jelušič, S. Kravanja, T.Žula: Design of Geothermal Energy Pile 55. 3 Results The optimization model presented in this article is used to determine the cheapest possible geothermal energy pile and to find an optimal design with the given design parameters. The ground consists of low plasticity clay (CL) at a depth of 0 m to 30 m below ground level. The pile is loaded with a vertical design load Fd = 1481.8 kN. The design data are composed of the undrained shear strength ( cu = 60+5.5∙z, z is the depth below the top of the pile), the drained modulus of elasticity ( Eso = 300∙cu kPa) and the adhesion factor (αsk = 0.5 and αbk = 1.0). The linear increase of the undrained shear strength cu with depth is shown in Figure 3. The geometry and al necessary input data for the optimal pile design are shown in Table 2. The results show that the optimal geothermal energy pile for the given design parameters leads to production costs of about 1952 Є. Undrained shearing strength (kN/m 0 100 200 300 400 0 l 5 cu = 60+5.5∙z leve 10 ound gr 15 (m) 20 elow 25 epth bD 30 Figure 3: Undrained shearing strength of low plasticity clay (CL). Source: Table 2: Optimal design of geothermal energy pile. Parameter Value of parameter D (mm) 800 L (m) 13 ∅ main (mm) 14 nmain (-) 14 ∅ shear (mm) 8 sshear (mm) 150 Fd < Rcd (kN) 1481.8 < 1514.4 (98%) u < ulim (mm) 7.5 < 10 (75%) 56 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. Parameter Value of parameter Amain,req < Amain,prov (mm2) 0 < 2155 Amain,min < Amain,prov (mm2) 2011 < 2155 (93%) sshear < sshear,max (mm) 150 < 168 (89%) COST (€) 1952 4 Conclusion The article presents the cost optimization of a geothermal energy pile. The optimization model integrates the cost objective function of the dril ed geothermal energy concrete pile and the geotechnical constraints that ensured the requirements of the Eurocode specifications and GSHP recommendations. The bearing capacity of the pile and its settlement under the applied load are the most important factors in verifying the pile design. The choice of the design method for pile foundations depends on the type of pile and the instal ation method. A pile design based on structural optimization is much more efficient than a design based on classical structural analysis, because the optimization allows to fully utilize the materials and geometries without resistance reserves. The example presented shows that the load-bearing capacity of the pile is ful y exploited. Acknowledgments This work was supported by the National Research Programmes of Slovenia P2-0268 and P2-0129. References GSHP Association (2012). Thermal pile design, installation and materials standards, Gr. Source Heat Pump Assoc. Milt. Keynes. 82. Jelušič, P., Žlender, B. (2020). Determining optimal designs for conventional and geothermal energy piles. Renew. Energy, 147, 2633–2642, doi:10.1016/j.renene.2018.08.016. Kravanja, Z., Grossmann, I. E.(1994). New developments and capabilities in prosyn—An automated topology and parameter process synthesizer. Comput. Chem. Eng. 1 8, 1097–1114, doi:10.1016/S0098-1354(94)85027-5. Žula, T., Kravanja, S. (2018). Optimization of the sustainability profit generated by the production of beams. In Proceedings of the Technologies & Business Models for Circular Economy; Univerzitetna založba Univerze v Mariboru / University of Maribor Press, pp. 159–165. Žula, T., Kravanja, S. (2020). Sustainability Profit Generated by the Optimization of Continuous Beams. In Proceedings of the 2nd International Conference on : Technologies & Business Models for Circular Economy: Conference Proceedings; University of Maribor, University Press, pp. 133–140. USE OF RECYCLED PLASTIC WASTE IN CONCRETE GREGOR KRAVANJA1, 2 1 University of Maribor, Faculty of Civil Engineering, Transportation Engineering and Architecture, Maribor, Slovenia gregor.kravanja@um.si 2 University of Maribor, Faculty of Chemistry and Chemical Engineering, Maribor, Slovenia gregor.kravanja@um.si Abstract Substantial growth in plastics consumption over the last decades has contributed to an increasing amount of plastic waste being deposited in landfills and in natural environments such as the oceans. The production of new materials from recycled plastics appears to be one of the best solutions for the management of plastic waste. The aim of this paper is to investigate the adequacy Keywords: recycling plastic, of using various recycled plastic waste in concrete. The effects of concrete, waste plastic aggregates or fibers on the physical, mechanical, physical thermal and durability properties of concrete have been properties, mechanical investigated. In addition, several recommendations for future properties, studies are provided. durability DOI https://doi.org/10.18690/um.fkkt.2.2022.4 ISBN 978-961-286-598-6 58 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. 1 Introduction The world is on the edge of a global plastic calamity and our collective action over the next decade wil determine the future of our planet. If current trends in production and waste management continue, around 12,000 million tonnes of plastic waste will end up in landfills or in natural environments such as the oceans by 2050 (Geyer et al., 2017). The UN Environment Programme estimated that for every square mile of ocean, there are 46,000 pieces of floating plastic (Silverman, 2007). The production of new materials by recycling plastic waste seems to be one of the best solutions for the disposal of plastic waste. Concrete is the most widely used material and is available at low cost. The main raw materials consist of cement, water, and aggregates. Approximately 65-80% of the concrete volume is taken up by aggregates, which strongly influence the general workability, durability, permeability, and strength of concrete. The use of recycled plastics as fine aggregates can eliminate large amounts of waste material while solving problems associated with aggregate mining, waste disposal and lack of aggregates on construction sites (Almeshal et al., 2020). The use of a lightweight plastic aggregate as an alternative to natural aggregates usual y reduces the weight of concrete and offers many advantages, such as lower costs, enhanced thermal insulation performance and better handling. Overal , the use of waste material in concrete production is considered to be environmental y and economical y beneficial (Faraj et al., 2020). The aim of this paper is to investigate the appropriateness of using recycled plastics in concrete mixes. The influence of the commonly used recycled plastic aggregates or fibers on the physical, mechanical, thermal and durability properties of concrete has been extensively investigated. Furthermore, several recommendations for future studies are provided. 2 Different types of waste polymers in concrete Generally, plastic is incorporated into concrete in the form of plastic aggregates as an alternative to natural aggregates or as a fiber that is intended to reinforce the concrete. The most commonly used recycled plastics in concrete are (PP) plastic particles (Faraj et al., 2019), PP fibers (Madhavi et al., 2014), high-density G. Kravanja: Use of Recycled Plastic Waste in Concrete 59. polyethylene (HDPE) particles (Badache et al., 2018), polyvinyl chloride (PVC) pipe (Gupta, 2013), polyethylene terephthalate (PET) plastics fibers, particles and bags PET (Sulyman et al., 2016), expanded polystyrene (EPS) foams (Dissanayake et al., 2017), high impact polystyrene (PHIS) granules (Olofinnade et al., 2020), high toughness poly-propylene (PPHT) fibers (Ikai et al., 2010), polyethylene (PE) granules (Chen et al., 2019), and shredded recycled plastic waste (Jain et al., 2020). The properties of the most commonly used plastic waste polymers in concrete, such as tensile strength (σ), modulus of elasticity (E) and thermal conductivity (λ), are shown in Table 1. Al types of plastic waste have much lower young moduli and thermal conductivities than those of concrete mixes. Table 1: Properties of commonly used waste plastic polymers in concrete materials (Jacob-Vail ancourt and Sorel i, 2018). Material σ/MPa E/GPa λ /(W/m.K) PET 55–80 2.1–3.1 0.15 PVC 50–60 2.7–3.0 0.17–0.21 PS 30–55 3.1–3.3 0.105 PP 25–40 1.3–1.8 0.12 PE 18–30 0.6–1.4 0.33–0.52 Natural aggregate / 70 2.29–2.78 Cement* / 36–40 1 *cement paste with w/c = 0.5 3 Properties of concrete containing plastic waste The effects of the addition of plastics on the properties of concrete in the green state, the mechanical properties in the cured state, durability and thermal properties are discussed in this section. 3.1 Physical properties Workability, which determines the concrete homogeneity, is the most important property of concrete in the green state. The slump test is normal y applied to the measured workability. The addition of waste material can greatly influence workability. (Guendouz et al., 2016). Increasing the substitution level of fine plastic aggregates decreases slump and consequently the workability of concrete (Batayneh et al., 2007). In order to prevent poor mixture consistency and to increase workability, the use of superplasticizers is therefore recommended (Faroug et al., 60 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. 1999). The incorporation of plastic waste reduces the density of the concrete. The use of lightweight plastic paving concrete has many advantages. For example, the risk of earthquakes is greatly reduced because the force of earthquake depends linearly on dead building weight (Akçaözoğlu et al., 2010). 3.2 Mechanical properties Compressive and flexural strength are the most important properties that verify the behavior of concrete (Fig. 1) Among them, splitting tensile strength, pulse velocity, triaxial strength and elastic modules are frequently investigated. The quality of concrete depends on the compressive strength. The results of the 28-day compressive strength of concrete with plastic waste are shown in Fig. 2. An increase in the volume fraction of plastics by up to 40% reduced the compressive strength (Fig. 2a). However, the addition of a limited amount of plastic to the concrete can lead to smal improvements in mechanical properties (Fig. 2b). Similarly, the flexural strength of concrete, which was evaluated by the three-point loading of the four-point loading test, decreased with increasing the volume fraction of plastics. The addition of a smal percentage of plastics can improve the ability to resist failure in bending (Fig. 3b). The factors that can negatively affect the compressive and flexural strength of concrete containing plastic waste are: hydrophobic nature of the plastics, which can cause a cement hydration reaction, low strength between the cement paste and the surface of plastic waste aggregates, high porosity, reduced modulus of elasticity and deterioration of the plastic aggregates (Gu and Ozbakkaloglu, 2016). Figure 1: Compressive and flexural strength are influenced to a great extent by the addition/replacement of various forms of plastics. Source: own. G. Kravanja: Use of Recycled Plastic Waste in Concrete 61. Figure 2: Variation of compressive strength of concrete with varying plastic content: PP medium aggregates (Faraj et al., 2019), PP fine aggregates 1 and 2 (Yang et al., 2015), PET fine aggregates 1 end 2 (Hama and Hilal, 2017), HIPS fine aggregates(Chunchu and Putta, 2019), PET plastic bags (Safi et al., 2013), PP fibers (Aslani et al., 2019), PET waste and PF contents (Al-Hadithi and Hilal, 2016). Source: own. Figure 3: Variation of flexural strength of concrete with different plastic content:: PP medium aggregates 1 and 2 (Faraj et al., 2019), PP fine aggregates (Yang et al., 2015), PET plastic bags (Safi et al., 2013), PP fibers (Aslani et al., 2019), PET waste 1, 2, 3 (Gesoglu et al., 2017). Source: own. 62 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. 3.3 Durability The durability performance of concrete is usual y assessed on the basis of water absorption properties, air and water permeability, chloride migration, carbonization, shrinkage, and freezing/thawing resistance. Water absorption increases as the exchange ratio of sand to plastic waste aggregates increases (Coppola et al., 2018). This indicates that mixing natural aggregates and plastics leads to more porous concrete. The water and air permeability increases with the content of plastic waste in the concrete. More voids in the concrete matrix lead to greater chloride ion penetration and higher carbonation of the cement-like composite (Silva et al., 2013). During the carbonization process, calcium hydroxide Ca(OH)2 reacts with carbon dioxide (CO2) from the atmosphere and has a negative effect on the mechanics of concrete. In case of shrinkage, plastic waste has a higher drying shrinkage compared to conventional concrete. In general, the shrinkage stress of plastic-containing cement paste decreases (Bendimerad et al., 2016). The freeze and thawing resistance of concrete containing waste plastics meets al the standards for safe usage. In some cases, increasing plastic waste content in concrete even enhance frost resistance and durability (Kan and Demirboğa, 2009). 3.4 Fire resistance and thermal properties Fire resistance is an important property of concrete that ensures general building safety. The fire resistance of concrete is characterized by the cement paste and the aggregate. When exposed to fire, concrete heats up 50 times slower than steel. However, replacing natural aggregates with waste plastic aggregates can create holes in the concrete at 400 °C to 600 °C, which reduce its flexural strength and produce toxic smoke (Sayadi et al., 2016). The thermal conductivity of concrete containing plastic waste decreased considerably. The recycling of plastics in concrete leads to improved thermal insulation properties and higher energy efficiency of buildings (Dweik et al., 2008). G. Kravanja: Use of Recycled Plastic Waste in Concrete 63. 4 Conclusions Plastics can easily be used in concrete in certain proportions. The following conclusions are: − the workability of concrete containing recycled plastic is reduced. To increase the workability of concrete in the green phase, superplasticizers should be used, − the inclusion of plastic in concrete does not effectively improve the mechanical properties of concrete. The strength of concrete should be balanced with reactive materials such as silica fume, metakaolin and iron slag to create an additional pozzolanic reaction, − the durability of concrete containing plastic waste is severely impaired. Water absorption increases as the exchange ratio of sand to plastic waste aggregates increases, − More voids in the concrete matrix leads to more chloride ion penetration and higher carbonation, − replacing natural aggregates with plastic waste aggregates can create holes in concrete at 400 °C to 600 °C, which impairs the bending strength, − freeze and thawing resistance of concrete containing waste plastics meets all the standards for safe usage. In order to make concrete containing recycled waste more attractive and better accepted by the construction industry, future studies should focus on economic efficiency, social acceptance, material properties such as adhesion, triaxial failure, abrasion and impact resistance, rheological properties, thixotropy, durability properties such as sulfate resistance and general long-term resistance to environmental exposure. The outcomes of this paper show that the use of recyclable plastics in concrete leads to more sustainable building materials in the construction industry. Acknowledgments I would like to acknowledge the Slovenian Research Agency (ARRS) for financing research in the frame of Programme P2-0046 (Separation processes and production design). 64 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. References Akçaözoğlu, S., Atiş, C.D., Akçaözoğlu, K., 2010. An investigation on the use of shredded waste PET bottles as aggregate in lightweight concrete. Waste management 30(2), 285-290. Al-Hadithi, A.I., Hilal, N.N., 2016. The possibility of enhancing some properties of self-compacting concrete by adding waste plastic fibers. Journal of Building Engineering 8, 20-28. Almeshal, I., Tayeh, B.A., Alyousef, R., Alabduljabbar, H., Mohamed, A.M., Alaskar, A., 2020. Use of recycled plastic as fine aggregate in cementitious composites: A review. 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Construction and Building Materials 201, 691-701. Chunchu, B.R.K., Putta, J., 2019. Rheological and strength behavior of binary blended SCC replacing partial fine aggregate with plastic E-waste as high impact polystyrene. Buildings 9(2), 50. Coppola, B., Courard, L., Michel, F., Incarnato, L., Scarfato, P., Di Maio, L., 2018. Hygro-thermal and durability properties of a lightweight mortar made with foamed plastic waste aggregates. Construction and Building Materials 170, 200-206. Dissanayake, D., Jayasinghe, C., Jayasinghe, M., 2017. A comparative embodied energy analysis of a house with recycled expanded polystyrene (EPS) based foam concrete wal panels. Energy and Buildings 135, 85-94. Dweik, H.S., Ziara, M.M., Hadidoun, M.S., 2008. Enhancing concrete strength and thermal insulation using thermoset plastic waste. International Journal of Polymeric Materials 57(7), 635-656. Faraj, R.H., Ali, H.F.H., Sherwani, A.F.H., Hassan, B.R., Karim, H., 2020. Use of recycled plastic in self-compacting concrete: A comprehensive review on fresh and mechanical properties. Journal of Building Engineering, 101283. Faraj, R.H., Sherwani, A.F.H., Daraei, A., 2019. Mechanical, fracture and durability properties of self-compacting high strength concrete containing recycled polypropylene plastic particles. Journal of Building Engineering 25, 100808. Faroug, F., Szwabowski, J., Wild, S., 1999. Influence of superplasticizers on workability of concrete. Journal of materials in civil engineering 11(2), 151-157. Gesoglu, M., Güneyisi, E., Hansu, O., Etli, S., Alhassan, M., 2017. Mechanical and fracture characteristics of self-compacting concretes containing different percentage of plastic waste powder. Construction and Building Materials 140, 562-569. Geyer, R., Jambeck, J.R., Law, K.L., 2017. Production, use, and fate of al plastics ever made. Science advances 3(7), e1700782. Gu, L., Ozbakkaloglu, T., 2016. Use of recycled plastics in concrete: A critical review. Waste Management 51, 19-42. Guendouz, M., Debieb, F., Boukendakdji, O., Kadri, E., Bentchikou, M., Soualhi, H., 2016. Use of plastic waste in sand concrete. J. Mater. Environ. Sci 7(2), 382-389. Gupta, P.K., 2013. Confinement of concrete columns with unplasticized Poly-vinyl chloride tubes. International Journal of Advanced Structural Engineering 5(1), 19. G. Kravanja: Use of Recycled Plastic Waste in Concrete 65. Hama, S.M., Hilal, N.N., 2017. Fresh properties of self-compacting concrete with plastic waste as partial replacement of sand. International Journal of Sustainable Built Environment 6(2), 299-308. Ikai, S., Reichert, J., Rodrigues, A., Zampieri, V., 2010. Asbestos-free technology with new high toughness polypropylene (PP) fibers in air-cured Hatschek process. Construction and building materials 24(2), 171-180. Jain, A., Siddique, S., Gupta, T., Sharma, R.K., Chaudhary, S., 2020. Utilization of shredded waste plastic bags to improve impact and abrasion resistance of concrete. Environment, Development and Sustainability 22(1), 337-362. Kan, A., Demirboğa, R., 2009. A new technique of processing for waste-expanded polystyrene foams as aggregates. Journal of materials processing technology 209(6), 2994-3000. Madhavi, T.C., Raju, L.S., Mathur, D., 2014. Polypropylene fiber reinforced concrete-a review. International journal of emerging technology and advanced engineering 4(4), 114-119. Olofinnade, O., Chandra, S., Chakraborty, P., 2020. Recycling of high impact polystyrene and low-density polyethylene plastic wastes in lightweight based concrete for sustainable construction. Materials Today: Proceedings. Safi, B., Saidi, M., Aboutaleb, D., Maal em, M., 2013. The use of plastic waste as fine aggregate in the self-compacting mortars: Effect on physical and mechanical properties. Construction and Building Materials 43, 436-442. 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Construction and Building Materials 84, 444-453. 66 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. TOPOLOGY OPTIMIZATION OF STEEL-LINED ROCK CAVERNS FOR UNDERGROUND STORAGE OF CHEMICAL ENERGY STOJAN KRAVANJA,1 PRIMOŽ JELUŠIČ,1 TOMAŽ ŽULA,1 ZDRAVKO KRAVANJA2 1 University of Maribor, Faculty of Civil Engineering, Transportation Engineering and Architecture, Maribor, Slovenia stojan.kravanja@um.si, primoz.jelusic@um.si, tomaz.zula@um.si 2 University of Maribor, Faculty of Chemistry and Chemical Engineering, Maribor, Slovenia zdravko.kravanja@um.si Abstract The paper presents the topology optimization of lined rock caverns designed for underground storage of chemical energy. This type of storage can store a high amount of hydrogen, methane, natural gas, carbon dioxide or other substances. The caverns are made of concrete shells and lined with thin steel sheets to seal the content. Optimization is performed by the mixed-integer non-linear programming (MINLP) approach. The MINLP computer program GAMS/Dicopt is used. The model includes Keywords: the cost objective function, which is subjected to geomechanical underground and design constraints. In this attempt, the topology calculation is storage, included in the discrete optimization of the underground storage. topology optimization, A numerical example at the end of the paper shows the overall cost discrete MINLP optimization of an underground gas storage optimization, facility. The optimal discrete design with the optimal number of mixed-integer non-linear caverns of the storage is explicitly determined. Additional programming, investment savings are achieved. MINLP DOI https://doi.org/10.18690/um.fkkt.2.2022.5 ISBN 978-961-286-598-6 68 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. 1 Introduction This paper deals with the topology optimization of lined rock caverns (LRC) designed for underground storage of chemical energy. This type of storage can store a high amount of hydrogen, methane, natural gas, carbon dioxide or other substances. The LRC caverns consist of 2 meters or more thick, cylindrical y shaped concrete wal s and are lined with 12-15 mm thin steel sheets. They are up to 100 m high, are built with diameters of up to 30 m or more and are bored to a depth of 300 m. Because the LRCs contain the gas under high pressure (between 3 and 30 MPa), they have to be bored into a rock with high strength (limestone, dolomite, granite, gneiss). The concrete wal s of the caverns transfer the internal pressure onto the rock mass, while the steel lining seal the gas content. The surrounding rock mass carry the gas pressure, see (Sofregaz US Inc., 1999), (Brandshaug et al., 2001), (Chung et al., 2003) and (Glamheden & Curtis, 2006). In the near past, some investigations have been carried out in the field of optimization of underground gas storages. For example, the optimization of a single gas cavern with non-linear programming (NLP) was introduced by (Kravanja & Žlender, 2010), the optimization of any number of caverns in the UGS was later presented by (Žlender & Kravanja, 2011), while the optimization in different rock environments was reported by (Kravanja & Žlender, 2012) and (Jelušič et al., 2019). The latter reference introduced a prediction of the minimal investment costs using an adaptive network based fuzzy inference system (ANFIS) for the UGSs with capacities from 10 to 100 million m3 of natural gas. The optimization of the discrete dimensions of the caverns was performed by (Kravanja & Žula, 2018) using mixed-integer non-linear programming (MINLP). Underground gas storage facilities (UGS) are usual y constructed from one to four LRCs. The correct determination of the number of LRCs built is very important as it has a strong impact on the investment costs. Therefore, we perform the topology optimization of the UGS with the calculation of the optimal number of LRCs. The topology logical constraints are inserted into the optimization model. In this way, the optimal discrete design of the storage facility with the optimal number of caverns is explicitly determined. S. Kravanja, P. Jelušič, T. Žula, Z. Kravanja: Topology Optimization of Steel-lined Rock Caverns for Underground Storage of Chemical Energy 69. 2 MINLP problem formulation The optimization problem of the lined rock cavern is non-linear, continuous and discrete. Mixed-integer non-linear programming (MINLP) is thus applied. The general MINLP optimization problem is formulated as follows: min z= f (x, y) subjected to: gk (x, y) ≤ 0 k ∈ K x ∈ X = {x ∈ Rn: xLO ≤ x ≤ xUP} y ∈ Y ={0,1} m where x is a vector of continuous variables and y is a vector of discrete (binary 0-1) variables. The function f(x, y) is the objective function, which is subjected to the (in)equality constraints gk(x, y). At least one function must be non-linear. All functions must be continuous and differentiable. 3 MINLP optimization model According to the above MINLP formulation, the MINLP optimization model of the UGS is being developed. The model comprises the cost objective function of the system, which is subjected to geomechanical, design and logical constraints. The model input data (constants) and variables are also defined. While the geomechanical constraints assure sufficient strength of the surrounding rock, they also prevent the uplift of the rock above the cavern, they prevent rock col apse between caverns and they limit the large deformations of the concrete wal and steel lining. The design constraints define the relationships between the dimensions of the LRC, internal gas pressure and the rock. They also represent the upper and lower bounds of the variables. The logical constraints define the relationships between discrete (binary 0-1) variables and determine the system topology (number of caverns) and the discrete dimensions of the structure. Since the model is simple and contains only some main constraints, it is suitable for use in the preliminary design phase. 70 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. The design variables (x) represent the number of caverns NOCAV, the inner diameter of the cavern DCAV [m], the depth of the cavern DEPTH [m], the height of the cavern tube HCAV [m], the thickness of the concrete cavern wal TWALL [m] and the gas pressure PGAS [MPa], see Fig. 1. These variables are explicitly rounded on whole discrete values during the optimization process. Figure 1: Vertical cross-section of lined rock cavern. Sourece: own. The objective function includes the investment costs of the UGS system COST S [€]. It is defined by Eq. (1). COSTS = FIX + f(x)· NOCAV (1) The equation defines the fixed costs FIX and the dimension-dependent costs f(x) of a cavern, multiplied by the number of caverns NOCAV. While the fixed costs include the upper-ground and underground works, the dimension-dependent costs represent the excavation and protection of the cavern and its tunnel, as wel as the costs for the drainage system, concrete, reinforcement and steel lining of the cavern. S. Kravanja, P. Jelušič, T. Žula, Z. Kravanja: Topology Optimization of Steel-lined Rock Caverns for Underground Storage of Chemical Energy 71. Topology logical constraints define the objective variable NOCAV - the number of caverns built in a UGS facility, see Eqs. (2)-(4). The variable NOCAV is calculated as the sum of the binary variables yNOCAVi, i∈ I, see Eq. (3). Eq. (4) defines only one possible vector of binary variables, which is assigned for each topology (number of caverns). For example, the minimal topology with a single cavern is defined in this way by the vector of binary variables y NOCAV = {1,0,0,0,0,…,0} and not by y NOCAV = {0,1,0,0,0,…,0} or others. NOCAV LO ≤ NOCAV ≤ NOCAV UP (2) NOCAV = ∑i yNOCAVi (3) yNOCAVi- 1 ≥ yNOCAVi (4) Discrete dimensions are determined by Eqs. (5)-(7). For example, the height of the cavern tube HCAV is calculated as a scalar product between a vector of the discrete value alternatives q HCAV and a vector of the binary variables y HCAV, see Eq. (6). Only one discrete value is then selected for the variable, since the sum of j, j∈ J, binary variables is equal one, see Eq. (7). All design variables are determined in this way. HCAV LO ≤ HCAV ≤ HCAV UP (5) HCAV = ∑i qHCAVj · yHCAVj (6) ∑i qHCAVj = 1 (7) 4 Numerical example The simultaneous topology, discrete dimension and cost optimization of the underground gas storage in Senovo, Slovenia, is presented. The UGS in Senovo is planned to store 22.24 million m3 of natural gas. Note that the primary project comprised four lined rock caverns, which were to be included in the UGS - to store 5.56 million m3 of natural gas each. This design (with the specified number of four caverns) was optimized with MINLP by (Kravanja and Žula, 2018) and achieved the optimal result of 72.88 million EUR., see Fig. 2, which represented 47.7 % of the savings compared to the design obtained with the classical method (FEM). 72 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. Figure 2: Optimized lined rock caverns of the UGS (Nocav = 4). Sourece: own. The topology, discrete dimension and cost optimization of the Senovo UGS is performed using a new MINLP optimization model, which includes topology logical constraints and some other modifications. The cost items and prices defined in the cost objective function are the same as those used in the project and in our previous optimizations, see Table 1. The model is written in GAMS, the General Algebraic Modelling System by (Brooke et al., 1988). Four different topologies have been defined that determine 1, 2, 3 or 4 caverns. The LRC superstructure also includes 200 different rounded dimension alternatives for the inner diameter of the cavern, 2000 alternatives for the depth of the cavern, 2000 alternatives for the height of the cavern tube, 30 alternatives for the thickness of the concrete cavern wal and 200 discrete alternatives for the internal gas pressure. The overal combinatorics of the discrete problem is high: a total 4434 binary variables of the alternatives yield 1.92·1013 different LRC structural alternatives. One of them is optimal. This discrete MINLP optimization is performed with the program GAMS/DICOPT, which was developed by (Grossmann & Viswanathan, 2002). Note that comprehensive MINLP problems we usual y optimize with the computer synthesizer MipSyn by (Kravanja, 2010). The optimal result represents the minimal total investment costs of the UGS of 57.62 million EUR. The optimal topology with S. Kravanja, P. Jelušič, T. Žula, Z. Kravanja: Topology Optimization of Steel-lined Rock Caverns for Underground Storage of Chemical Energy 73. 2 caverns is obtained. Fig. 3 shows the vertical cross-section of the optimized lined rock caverns. The figure shows the calculated “optimal” discrete variables (dimensions and the internal gas pressure). Note that this optimal result shows an additional 21 % of the net savings compared to the previous optimized design with fixed topology. Table 1: Cost items and prices. Cost item Price Upper ground works 2 982 500 EUR Underground works 2 798 025 EUR Price of the tunnel excavation 2 440 EUR/m1 Price of the tunnel protection 1 340 EUR/m1 Price of the cavern excavation 100 EUR/m3 Price of the cavern protection 90 EUR/m2 Price of the cavern drainage 60 EUR/m2 Price of the cavern wal concrete 190 EUR/m3 Price of the wal reinforcement 2 000 EUR/t Price of the steel lining 920 EUR/m2 61.19 0 r 17. 17.5 2 2 55. 89. r 0 17. 2.0 30.0 2.0 34.0 Figure 3: Optimized lined rock caverns of the UGS (Nocav = 2). Sourece: own. 74 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. 5 Conclusions The paper discusses the simultaneous topology, discrete dimension and cost optimization of the lined rock caverns of underground storage of chemical energy. The optimization is performed by the mixed-integer non-linear programming, MINLP. The MINLP optimization model is developed into which the topology logical constraints are inserted. The numerical example at the end of the paper shows the advantages of the presented simultaneous optimization approach, tested on the case of the underground gas storage Senovo, Slovenia. A new optimal topology of two caverns is found. Significant additional investment savings are achieved. The result achieved represents the trade-off between the storage capacity and the investment costs of construction. In a future study, the operating costs of the underground storage facility, including filling and emptying of the storage, will be investigated. The proposed approach is also attractive for the optimization of underground storage facilities for hydrogen or methane. Acknowledgments The authors are grateful for the support of funds from the Slovenian Research Agency (research programes P2-0129, P2-0268 and P2-0032). References Brandshaug, T., Christianson, M., Damjanac, B. (2001).Technical review of the lined rock cavern (LRC) - concept and design methodology: mechanical response of rock mass. US Department of Energy. Brooke, A., Kendrick, D., Meeraus, A. (1988). GAMS - A User's Guide. Scientific Press, Redwood City, CA. Chung, I.M., Cho, W., Heo, J.H. (2003). Stochastic hydraulic safety factor for gas containment in underground storage caverns. J Hydrol, 284, 77-91. Glamheden, R., Curtis, P. (2006). Excavation of a cavern for high-pressure storage of natural gas. Tunnel ing and Underground Space Technology, 21(1), 56-67. Grossmann, I.E., Viswanathan, J. (2002). DICOPT - Discrete and Continuous Optimizer. Engineering Design Research Center (EDRC) at Carnegie Mel on University, Pittsburgh, PA. Jelušič, P., Kravanja, S., Žlender, B. (2019). Optimal cost and design of an underground gas storage by ANFIS, Journal of natural gas science and engineering, 61, 142-157. doi: 10.1016/j.jngse.2018.11.003 Kravanja, S., Žlender, B. (2010). Optimal design of underground gas storage. In: WIT Transactions on the Built Environment, 112, 389-399. doi.org/10.2495/HPSM100361 Kravanja, S., Žlender, B. (2012). Optimization of the underground gas storage in different rock environments. In: WIT Transactions on the Built Environment, 125, 15-26. doi.org/10.2495/OP120021 Kravanja, S., Žula, T. (2018). MINLP optimization of the underground lined rock. In: Conference proceedings, International Conference on Technologies & Business Models for Circular S. Kravanja, P. Jelušič, T. Žula, Z. Kravanja: Topology Optimization of Steel-lined Rock Caverns for Underground Storage of Chemical Energy 75. Economy, 1, 2018, Portorož. 1st ed. Maribor: University of Maribor Press, 149-157. http://press.um.si/index.php/ump/catalog/view/367/345/590-2. Kravanja, Z. (2010). Challenges in sustainable integrated process synthesis and the capabilities of an MINLP process synthesizer MipSyn. Comput Chem Eng, 34(11), 1831-1848. doi:10.1016/j.compchemeng.2010.04.017 Sofregaz US Inc. (1999). Commercial potential of natural gas storage in lined rock caverns (LRC). US Department of Energy, Federal Energy Technology Center. Žlender, B., Kravanja, S. (2011). Cost optimization of the underground gas storage. Eng Struct, 33, 2554-2562. doi.org/10.1016/j.engstruct.2011.05.001 76 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. FIBRE REINFORCED ALKALI- ACTIVATED ROCK WOOL MAJDA PAVLIN, BARBARA HORVAT, VILMA DUCMAN Slovenian National Building and Civil Engineering Institute, Ljubljana, Slovenia majda.pavlin@zag.si, barbara.horvat@zag.si, vilma.ducman@zag.si Abstract Mineral wool, i.e. rock and glass wool, represents considerable chal enge after its functional-time runs out due to its small density leading to large volume consumption during transport and in landfills where it usually ends. Because rock wool is mineralogically and chemical y a promising precursor material for alkali-activation, it was milled from few centimetres-decimeters long fibres to micron-sized fibres. Since fibres in alkali-activated materials generally show an increase in mechanical strength, especial y the bending strength, 1 m% of additional fibres (basalt, cellulose (2 types), glass, polypropylene, polyvinyl alcohol and steel fibres) was used in the alkali mixture, that was curred at 40 °C for Keywords: 3 days. Time dependence of the mechanical strengths of alkali- waste mineral wool, activated materials with and without additional fibres was fibre, fol owed. Maximal increase of compressive and bending strength alkali-activated after 28 days was reached with polypropylene fibres, i.e. it was 20% material, mechanical and 30% higher than compressive and bending strength of alkali- strength, activated material without additional fibres respectively. upcycling DOI https://doi.org/10.18690/um.fkkt.2.2022.6 ISBN 978-961-286-598-6 78 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. 1 Introduction Mineral wool (rock/stone, glass and slag wool) is a material consisting of fibres and shots, where shots did not fiberize before solidification. The less the shots mineral wool contains, the better it's quality (Brane Sirok et al., 2008). Newer production technologies add on fibres’ surface different organic resins as the binder to modify mineral wool’s compressive, bending and tensile strengths (Kowatsch, 2010). Yearly global production of the mineral wool is increasing with the average annual rate of 1.8% since 2013 and has reached 19M tonnes in 2019 (“The Global Mineral Wool Market Started to Slow Down - Global Trade Magazine,” n.d.), while the yearly amount of mineral wool’s waste in Austria is 20-30K tonnes (Sattler et al., 2020). When predicted that mineral wool waste is approximately linked to the number of inhabitants, mineral wool waste in al EU countries together is then 1M-1.5M tonnes yearly. Therefore it is crucial to solve the problem of waste mineral wool disposal due to its large volume consumption during transport and in landfills. One way for use of the waste mineral wool is using it as a precursor in alkali activation, where milled mineral wool reacts with alkali and forms aluminosilicate matrix, in which not-reacted fibres get completely immobilized (Horvat et al., 2018). Alkali activation idea was 1st reported in a patent in 1895, whereas the precursor was proposed blast-furnace slag and as activator the caustic soda with slaked lime (Whiting, 1895). But only in last decade researchers started to test also some other precursors than metakaolin, slag and fly-ash, i.e. refractory materials, foundry sand and other foundry wastes (Horvat et al., 2019), waste green ceramics (Horvat and Ducman, 2019) and last years also waste mineral wools where glass wool had higher compressive strength than rock wool (Yliniemi et al., 2016). All these materials can be used in alkali activation because they contain big enough amount of amorphous Al and Si, which are present in the matrix in the tetrahedron formation with O-bridges. To compensate electric charge of Al in the tetrahedron, elements of the 1st and 2nd group are needed, i.e. the positive ions either come from the precursor if it contains them in the amorphous phase, or from the alkali activator (Horvat and Ducman, 2019). M. Pavlin, B. Horvat, V. Ducman: Fibre Reinforced Alkali-Activated Rock Wool 79. In many materials, additional mechanical reinforcement is achieved with the addition of fibres made from different materials and of different sizes and shapes, i.e. in polymer composites (Navin Chand, 2008), metal and ceramic matrix composites (Eckold, 1994), civil engineering composites (Harris, 2005), syntactic foams (Sydney H. Goodman and Hanna Dodiuk-Kenig, 2014) etc. The purpose of presented work is to evaluate the effect of several different fibres (basalt, cellulose, glass, polypropylene, polyvinyl alcohol and steel fibres) on mechanical strengths in alkali activated pulverized waste rock wool. 2 Materials and Methods 2.1 Analysis of precursor, additives and alkali-activated materials Rock wool waste (RW) (Horvat et al., 2018), labelled 17 09 041, was collected from Termit. RW was 1st manually cleaned of all large impurities, cut into smaller pieces, and milled in a concrete mixer by using steel balls (27 pieces, 47.5 mm in diameter), every kilogram of RW for 2.5 hours (coarse RW). The milled sample was dried at 105 °C for 24 hours and sieved below 63 µm. The residue was ground in the homogenizer (powder mixer shaker, Turbola T2F) in 2 l plastic container with steel balls (50 pieces of diameter 9.8 mm) and sieved below 63 µm (fine RW). The particle size of coarse and fine RW was measured by particle size and shape analyzer (Microtrac MRB, SYNC). Fibres were used from previous projects: basalt (B), cellulose (fibres (CF) and fibres squeezed into thin cubes (CC)), glass (G), polypropylene (PP), polyvinyl alcohol (PVA) and steel fibres (S). Chemical analysis of RW was performed using X-ray fluorescence (XRF; Thermo Scientific ARL Perform'X Sequential XRF) on melted discs of the mixture of ignited RW powder (sieved below 63 µm) and Fluxana(s) (FX-X50-2, lithium tetraborate 50% / lithium metaborate 50% is used to lower melting point) with the addition of a few drops of LiBr(l) (prepared from 50 ml H2O and 7.5 g of LiBr(s) from Acros Organics, which is used to avoid sticking of the melt to the platinum vessel). Obtained data were characterized by software UniQuant 5. 80 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. Mineralogical characterization of RW powder (sieved below 63 µm) was performed with X-ray powder diffraction (XRD; Empyrean PANalytical X-ray Diffractometer, Cu X-ray source) and software X'Pert Highscore plus 4.1. Rietveld refinement with an external standard (a pure Al2O3 crystal) was used to estimate the amount of amorphous phase and minerals. Scanning electron microscope (SEM; Jeol JSM-IT500) under low vacuum conditions was used to investigate surface, shape, size and microstructure of non-sputtered RW, fibres and/or alkali-activated materials. Bending and compressive strength of alkali-activated fibreless and fibre reinforced samples were measured with compression and bending strength testing machine (ToniTechnik ToniNORM) at age 3 and 28 days. Alkali-activated samples’ geometric density was determined by weighting the sample and dividing its mass by its volume. 2.2 Preparation of alkali-activated samples RW as precursor and fibres used as additional reinforcement in alkali-activated synthesis are shown in Fig. 1. RW that was used in alkali-activation was prepared in the same manner as for XRF and XRD analysis, i.e. milled and sieved below 63 µm, while dry fibres were used as received. (a) (b) M. Pavlin, B. Horvat, V. Ducman: Fibre Reinforced Alkali-Activated Rock Wool 81. (c) (d) (e) (f) (g) (h) Figure 1: Photograph of (a) mil ed and sieved RW (on the inset is original RW), and fibres: (b) basalt, (c) cel ulose fibres, (d) cel ulose cubes, (e) glass fibres, (f) polypropylene fibres, (g) polyvinyl alcohol fibres, and (h) steel fibres. Source: own. As alkali-activator, only Na-water glass (Silvez, mining company Termit, with the mass percentage of Na2O 12.8%, and mass percentage of SiO2 29.2%) was used. Alkali slurry was prepared in mass ratio RW : Na-water glass : fibre = 100 : 95 : 0/1, moulded into rubber-silicon moulds measuring (80x20x20) mm3 and cured in drying chamber (WTB Binder) at 40 °C for 3 days. 82 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. 3 Results and discussion 3.1 Analysis of precursor SEM micrographs of RW that was not milled (original RW), that was milled (coarse RW), and that was milled for so long that it could be sieved below 63 µm (fine RW) are presented in Fig. 2 (a, b, c respectively). Particle size analysis of coarse and fine RW is presented in Fig. 3. (a) (b) (c) (d) M. Pavlin, B. Horvat, V. Ducman: Fibre Reinforced Alkali-Activated Rock Wool 83. (e) (f) Figure 2: SEM micrographs of not milled RW [(a) magnification 50x, (b) magnification 250x], mil ed RW [(c) magnification 50x, (d) magnification 250x], mil ed and sieved below 63 µm RW [(e) magnification 50x, (f) magnification 250x]. Source: own. RW, even if milled and sieved below 63 µm, keeps an elongated cylindrical shape (Fig. 2). With 1st step milling long thin fibres are broken into smaller pieces (Fig. 2 (a) to (c)), while “stones” stay intact until the sample is mil ed so long that it can be fully sieved below 63 µm (Fig. 2 (c) to (e)). The milling effect can be seen also in Fig. 3, where red line represents material after 1st step milling and the blue line represents material that was milled and sieved under 63 µm. Both prepared samples are fine-grained, i.e. more than 50% of all material is smaller from 75 µm: 50% of coarse RW grains are below or equal to 52 µm, while 50% of fine RW grains are smaller or equal to 31 µm. Coefficient of uniformity for coarse RW is 6.7, while for fine RW is 4.8. Coefficient of curvature on the other hand is for coarse RW 0.8, while for fine RW is a bit higher than 1.0. For the well-graded material coefficient of uniformity should be bigger from 1, and the coefficient of curvature between 1 and 3, meaning that only fine RW is well graded. Therefore in alkali-activation, only RW that was milled and sieved below 63 µm was used as a precursor. 84 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. (a) (b) Figure 3: (a) Particle size distribution, (b) cumulative particle size distribution of coarse RW (red line), and fine RW (blue line). Source: own. All fibres used in alkali-activation to gain higher bending and compressive strength are presented in Fig. 4. Natural fibres are from cellulose (Fig. 4 (c) to (f), CC and CF), while al the rest are completely artificial (B, G, PP, PVA and S). Several of them are found ordered in larger groups: B, G and PVA; without any specific order is CF, PP, and also S (which is present in alkali-activated synthesis just as few fibres due to its higher density); while CC is squeezed into thin cubes with random orientation of cellulose fibres. (a) (b) M. Pavlin, B. Horvat, V. Ducman: Fibre Reinforced Alkali-Activated Rock Wool 85. (c) (d) (e) (f) (g) (h) 86 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. (i) (j) (k) (l) (m) (n) Figure 4: SEM micrographs of fibers at 50x (left) and 250x (right) magnification: B [(a), (b)], CC [(c, (d)], CF [(e), (f)], G [(g), (h)], PP [(i), (j)], PVA [(k), (l)], and S [(m), (n)]. Source: own. M. Pavlin, B. Horvat, V. Ducman: Fibre Reinforced Alkali-Activated Rock Wool 87. XRF chemical analysis of RW is presented in 1st row in Table 1, XRD mineralogical analysis is in its 2nd row of Table 1, wherein crystal ine phase only smal amount of quartz was present (determined by Rietveld refinement), and in the 3rd line of Table 1 elements’ mass percentages in the amorphous phase are calculated as the difference between the XRF and XRD results. Table 1: Chemical (XRF) and mineralogical (XRD) analysis of RW. Precursor Elements/m% Na K Cs Mg Ca Sr Ba Al Si XRF 1.5 0.2 0 6.3 11.6 0 0 8.6 18.9 RW XRD 0 0 0 0 0 0 0 0 0.1 XRF-XRD 1.5 0.2 0 6.3 11.6 0 0 8.6 18.8 According to the literature (Duxson et al., 2005) for reaching the highest compressive strength most promising ratio Na, Al and Si present in AAM is 1:1:1.9. In our previous work (Horvat and Ducman, 2019) this model was tested and upgraded to be able to compare the amorphous amount of whole 1st and 2nd group to Al and Si, to predict also potential future efflorescence. For used RW ratio of the amount of substance between (1st : 2nd : Al : Si) is (0.2: 1.7 : 1 : 2.1). If no element from the 2nd group participates in the reaction, efflorescence can be avoided by the addition of elements from 1st group with NaOH without changing the amount of Si, or with Na-water glass were the amount of Si rises and could compromise the final mechanical strength as a side effect. 3.2 Analysis of alkali-activated samples The compressive and bending strength of 3 and 28 days old alkali-activated RW with and without fibres is presented in Table 2 and Fig. 5. Mechanical strengths of all alkali-activated samples with and without fibres increase with time while their density decreases due to the evaporation of water, i.e. shrinking has a smal er effect than the mass loss. At the same time, chemical reactions (besides physical evaporation of water) are stil going on and creating strong chemical bonds in the matrix. These bonds more than just compensate the negative effects of the evaporation that result in crack formation in the matrix (which can be seen on micrographs of alkali-activated materials presented on Fig. 6). 88 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. Table 2: Compressive and bending strengths of alkali-activated samples with their geometrical densities after 3 and 28 days (presented on one decimal). Compressive strength/ Bending strength/ Density/ Fibre MPa MPa kg/l 3 days 28 days 3 days 28 days 3 days 28 days / 21.3 38.6 7.3 11.3 1.7 1.6 B 26.2 32.9 7.8 13.0 1.8 1.6 CC 21.1 30.0 7.7 12.0 1.7 1.6 CF 21.5 38.8 6.1 12.4 1.7 1.7 G 18.1 41.3 5.4 17.9 1.8 1.6 PP 27.4 40.1 9.5 12.2 1.8 1.6 PVA 25.5 43.8 9.1 14.5 1.7 1.6 S 24.6 39.9 7.9 12.7 1.7 1.7 (a) (b) Figure 5: (a) Bending and (b) compressive strength of alkali activated RW with and without fibres. Source: own. All fibres used in alkali-activation of RW increased the bending strengths of 28-days old material, while for compressive strengths this is true only for G, PP, PVA and S, while other fibres either decreased its value (B, CC) or had no influence (CF). Highest reached BS after 28 days had a sample with G fibres (17.9 MPa was BS, while CS reached 41.3 MPa), while highest CS after 28 days had sample with PVA fibres (43.8 MPa was CS, while BS reached 14.5 MPa), i.e. CS and BS for samples containing G fibres was 10% and 60% higher than values for reference respectively, while CS and BS for samples containing PVA fibres was 20% and 30% bigger from alkali-activated RW without additional fibres. M. Pavlin, B. Horvat, V. Ducman: Fibre Reinforced Alkali-Activated Rock Wool 89. SEM micrographs of alkali-activated samples with and without fibres are presented on Fig. 6. Matrix of alkali-activated RW did not change with the addition of fibres, because none reacted with alkali and did not change the chemical reaction. All samples had spherical pores (organic resin present on RW reacts with alkali and releases gasses, which get trapped into the matrix when matrix gets too viscose for the bubble to be able to travel out from the slurry with the difference of densities; Fig. 6 (a)) and 1-dimensional cracks which are a consequence of physical evaporation of water while drying (Fig. 6 with magnification 250). (a) (b) (c) (d) 90 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. (e) (f) (g) (h) (i) (j) M. Pavlin, B. Horvat, V. Ducman: Fibre Reinforced Alkali-Activated Rock Wool 91. (k) (l) (m) (n) (o) (p) Figure 6: SEM micrographs of alkali-activated RW at 50x (left) and 250x (right) magnification without additional fibres [(a), (b)], and with additional fibres: B [(c, (d)], CC [(e), (f)], CF [(g), (h)], G [(i), (j)], PP [(k), (l)], PVA [(m), (n)], and S [(o), (p)]. Source: own. 92 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. To determine the optimal amount of added fibres further investigation is needed, where focus would be also on the number of fibres (through density and mass), their geometry (approximate diameter and length) and their whole surface area present in the alkali-activated material. 4 Conclusions The results show that the addition of fibres is beneficial for bending strength, while compressive strength increased only with the addition of glass, polypropylene, polyvinyl alcohol and steel fibres, while other fibres left the compressive strength either intact, or even lowered it. Most promising among all samples, that increased both mechanical strengths, was a sample with added polyvinyl alcohol fibres (bending strength increased for 20%, while compressive strength for 30%), while addition of glass fibres resulted in overall biggest increase of bending strength (60%). Acknowledgements Project No. C3330-17-529032 “Raziskovalci-2.0-ZAG-529032” was granted by Ministry of Education, Science and Sport of the Republic of Slovenia. The investment is co-financed by the Republic of Slovenia, Ministry of Education, Science and Sport and the European Regional Development Fund. WOOL2LOOP project received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 821000. Slovenian Research Agency supported Programme Group P2-0273. The Metrology Institute of the Republic of Slovenia is acknowledged for the use of XRF. Cooperation with Termit d.d. and Mrs Alenka Sešek Pavlin from Termit d.d.is highly appreciated. References Brane Sirok, Bogdan Blagojevic, Peter Bullen, 2008. Mineral Wool Production and Properties. Woodhead Publishing. Duxson, P., Provis, J.L., Lukey, G.C., Mal icoat, S.W., Kriven, W.M., van Deventer, J.S.J., 2005. Understanding the relationship between geopolymer composition, microstructure and mechanical properties. Colloids and Surfaces A: Physicochemical and Engineering Aspects 269, 47–58. https://doi.org/10.1016/j.colsurfa.2005.06.060 Eckold, G., 1994. Design and manufacture of composite structures. Woodhead, Cambridge. Harris, B., 2005. Fatigue in Composites: Science and Technology of the Fatigue Response of Fibre-Reinforced Plastics 870. Horvat, B., Češnovar, M., Pavlin, A., Ducman, V., 2018. Upcycling with alkali activation technology, in: Technologies & Business Models for Circular Economy. Presented at the 1st International Conference on Technologies & Business Models for Circular Economy, Univerzitetna založba Univerze v Mariboru / University of Maribor Press, pp. 261–272. https://doi.org/10.18690/978-961-286-211-4.22 M. Pavlin, B. Horvat, V. Ducman: Fibre Reinforced Alkali-Activated Rock Wool 93. Horvat, B., Ducman, V., 2019. Potential of Green Ceramics Waste for Alkali Activated Foams 30. Horvat, B., Pavlin, A.S., Ducman, V., 2019. Foundry wastes as potential precursor in alkali activation technology, in: Technologies & Business Models for Circular Economy. Presented at the 2nd International Conference on Technologies & Business Models for Circular Economy, Univerzitetna založba Univerze v Mariboru / University of Maribor Press. Kowatsch, S., 2010. Mineral Wool Insulation Binders, in: Pilato, L. (Ed.), Phenolic Resins: A Century of Progress. Springer Berlin Heidelberg, Berlin, Heidelberg, pp. 209–242. https://doi.org/10.1007/978-3-642-04714-5_10 Navin Chand, 2008. Tribology of Natural Fiber Polymer Composites. Woodhead Publishing. Sattler, T., Pomberger, R., Schimek, J., Vol precht, D., 2020. MINERAL WOOL WASTE IN AUSTRIA, ASSOCIATED HEALTH ASPECTS AND RECYCLING OPTIONS. Detritus 174–180. https://doi.org/10.31025/2611-4135/2020.13904 Sydney H. Goodman, Hanna Dodiuk-Kenig, 2014. Handbook of Thermoset Plastics, Third. ed. William Andrew. The Global Mineral Wool Market Started to Slow Down - Global Trade Magazine [WWW Document], n.d. URL https://www.globaltrademag.com/the-global-mineral-wool-market-started-to-slow-down/ (accessed 12.19.20). Whiting, J., 1895. Manufacture of Cement. 544706. Yliniemi, J., Kinnunen, P., Karinkanta, P., Illikainen, M., 2016. Utilization of Mineral Wools as Alkali-Activated Material Precursor. Materials 9, 312. https://doi.org/10.3390/ma9050312 94 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. ACTIVITY OF α--AMYLASE FROM P. OSTREATUS GROWN ON WASTE SUBSTRATES MATEJA PRIMOŽIČ,1 ŽELJKO KNEZ,1, 2 MAJA LEITGEB1, 2 1 University of Maribor, Faculty of Chemistry and Chemical Engineering, Laboratory for Separation Processes and Product Design, Maribor, Slovenia mateja.primozic@um.si, zeljko.knez@um.si, mateja.leitger@um.si 2 University of Maribor, Faculty of Medicine, Maribor, Slovenia zeljko.knez@um.si, mateja.leitger@um.si Abstract Forest and agricultural waste can be a major development and ecological opportunity. Therefore, it is reasonable to use biological waste further to produce energy and for the manufacture of certain products with high added value, such as, for example, the cultivation of fungi and, consequently, the production of biocatalysts with high market value. In addition, the use of agriculture waste for Oyster mushroom ( Pleurotus ostreatus) growth can be integrated to waste management and the development of the bioeconomy. The cultivation of P. ostreatus using waste plant biomass from agriculture (straw, grass, courgettes, cucumbers, peaches, apricots, pears, and peppers) was Keywords: performed in order to obtain the highest increase in biomass P. ostratus, production of the cultivated mushroom and as a potential source α-amylase, of α-amylase, with high catalytic activity. The highest α-amylase activity, agriculture activities were achieved when pears or apricots were used as a waste, substrate for P. ostreatus cultivation. cultivation DOI https://doi.org/10.18690/um.fkkt.2.2022.7 ISBN 978-961-286-598-6 96 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. 1 Introduction One of the economical y interesting medical mushrooms is P. ostreatus, which is easily cultivated by beginners, as it has an extremely strong undergrowth. The genus Pleurotus includes groups of edible ligninolytic fungi with medicinal properties and important biotechnological and environmental applications. One of the most important aspects of Pleurotus fungi is related to the use of their ligninolytic system for various applications, such as the biological conversion of agricultural waste into useful animal feed and other food products, and the use of their ligninolytic enzymes for biodegradation of organic pollutants, xenobiotics and industrial contaminants. The cultivation of P. ostreatus is important for the production of lignocel ulosic and other enzymes. Mushrooms are grown on different nutrient bases, i.e. substrates in which the undergrowth or mycelium develops. These substances, however, contain polymeric organic compounds that are difficult to decompose. In order to consume organic matter, mushrooms must first eliminate certain enzymes that decompose this substrate. The prevalence of mushroom enzymes has long been known and exploited for use in the food industry and in many other industries. Mushrooms respond to their habitat through controlled gene expression and secretion of specific enzymes. The enzymes split the molecules into smaller units, and mushrooms mycelium absorbs these reduced organic molecules as nutrients directly through the cel walls. The conversion of substrates into mushroom biomass is mediated by the secretion of a variety of hydrolytic and oxidative enzymes. In nature, P. ostreatus grows on waste wood, but it is also possible to grow it on agrarian waste to produce enzymes to stimulate oxidation reactions (laccase, manganese peroxidase, lignin peroxidase) and hydrolysis (amylase, cellulase, xylanase, tanase)(da Luz et al., 2012). The cultivation of P. ostreatus, Pleurotus eryngi , Pleurotus pulmonarius, Agrocybe Aegerita and Volvariel a volvacea was performed on three types of agricultural waste (wheat straw, cotton waste, and peanut shells) (Philippoussis et al., 2001). High growth rates of al studied mushroom cultures on the agricultural waste were detected. Waste of coffee leaves, eucalyptus bark, with or without the addition of rice bran, was used as the substrate for P. ostreatus cultivation. The lignocellulolytic enzyme activity increased with time after inoculation and the substrate composition affected the enzyme activity (da Luz et al., 2012). The production of lignocel ulolytic enzymes such as laccase, manganese peroxidase, endoglucanase, exoglucanase and 3-glucosidase was successfully performed by degradation of Chrysanthemum and Rosa residues using P. ostreatus (Quevedo-Hidalgo et al., 2015). Rashad et al. M. Primožič, Ž. Knez, M. Leitgeb: Activity of α-Amylase from P. ostreatus Grown on Waste Substrates 97. (Rashad et al., 2009) studied the enzymatic activity of amylase, cellulase, invertase, polygalacturonase and pectinase from P. ostreatus cultivated on citrus wastes and papaya. A higher activity of amylase was observed in the unsupplemented lemon pulp and papaya waste. Further, the ability of P. ostreatus and Pleurotus sajor-caju fungi to produce laccase and carboxymethylcel ulase enzymes on a variety of agricultural wastes in the solid-state fermentation process (SSF) was studied. Enzymatic activity was highest on substrates that contained bran, had high nitrogen content and low C/N ratio (Kurt & Buyukalaca, 2010). Belšak-Šel et al. (Belšak-Šel et al., 2015) studied the increase in laccase production from P. ostreatus by optimizing the culture medium. The level of laccase activity produced by P. Ostreatus in the SSF process in wheat bran was significantly influenced by lignocel ulose biomass and glucose content. Production of enzymes with SSF offers the advantage of reducing production costs and increasing the rate of mycelium growth. Additional, P. ostreatus, as wel as other mushrooms ( Lentinula edodes, G. frondosa, Cantharel us cibarius and Agaricus bisporus) are rich in B vitamins (Solomko & Eliseeva, 1988), organic acids, β - lipids, proteins and micronutrients (e.g. selenium or chromium)(Dikeman et al., 2005; Valentão et al., 2005). Amylases are important in many industrial processes and are one of the most widely used enzymes required for the preparation of fermented foods and now in the light of biotechnology they are considered useful for biopharmaceutical applications. They are useful tools in medicinal and clinical applications (Afzaljavan & Mobini-Dehkordi, 2013). α- Amylases can be obtained from plants, animals and microorganisms. However, enzymes from fungal and bacterial sources have dominated applications in industrial sectors (de Souza & de Oliveira Magalhães, 2010). Therefore, P. ostreatus was cultivated on waste vegetable biomass from agriculture (straw, grass, courgettes, cucumbers, peaches, apricots, pears, and peppers) in combination with wheat bran to maximize mushroom growth as a potential source of α-amylase. 98 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. 2 Methods 2.1 P. ostreatus cultivation P. ostreatus was cultivated on substrate containing waste vegetable biomass from agriculture and wheat bran in volumetric ratio 1:1 in the presence of growth media from yeast extract and peptone. The P. ostreatus was cultivated for 8 days at 27 °C. 2.2 Extraction of enzymes from P. ostreatus The extraction of P. ostreatus mycelium was performed using 0.05 M sodium citrate buffer as a solvent and for 90 min by shaking at 200 rpm. The obtained extract was centrifuged 20 min at 5000 rpm. Supernatant was used for the determination of α- amylase activity. 2.3 Determination of total protein concentration and α-amylase activity The total protein concentration was assayed by the Bradford method (Bradford, 1976) and activity of α-amylase was defined spectrophotometrical y at 595 nm. The activity was expressed as the change in absorbance at 595 nm per minute per solid of α-amylase (Čolnik et al., 2016). 3 Results 3.1 Mycelium growth of P. ostreatus P. ostreatus was cultivated on waste vegetable biomass from agriculture (straw, grass, courgettes, cucumbers, peaches, apricots, pears, and peppers) in combination with wheat bran to maximize mushroom growth. The increase in mycelium growth of P. ostreatus after 8 days of cultivation on different substrates was pursued (Figure 1). M. Primožič, Ž. Knez, M. Leitgeb: Activity of α-Amylase from P. ostreatus Grown on Waste Substrates 99. Figure 1: Influence of substrates on mycelium growth of P. ostreatus Source: own. As can be seen from Figure 1, the highest increase in mycelium growth of P. ostreatus after 8 days of cultivation on different substrates was detected when apricot as a substrate was used. Significant increase in mycelium growth of P. ostreatus was also detected when straw, peaches, pears, and peppers were used as a substrate. As can be seen from Figure 1, the highest increase in mycelium growth of P. ostreatus after 8 days of cultivation on different substrates was detected when apricot as a substrate was used. Significant increase in mycelium growth of P. ostreatus was also detected when straw, peaches, pears, and peppers were used as a substrate. Figure 2: Influence of substrates on total protein concentration and specific activity of α- amylase Source: own. 100 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. 4 Conclusion The P. ostreatus fungus was successful y grown on waste vegetable biomass from agriculture (straw, grass, courgettes, cucumbers, peaches, apricots, pears, and peppers) in combination with wheat bran. With increase in the time of cultivation of P. ostreatus on selected media, an increase in biomass growth was detected. The most suitable substrate, among those tested, for α-amylase production was composed from pear and wheat bran. Thus, waste vegetable biomass are suitable substrates for the cultivation of P. ostreatus for the purpose of α-amylase production. Due to bioconversion of nutrient-rich waste and by-product to value-added products, the environmental burdens imposed by these wastes are al eviated, and consequently, the regional and international economy can be boosted. Acknowledgement The authors acknowledge the financial support from the Slovenian Research Agency (research core funding No. P2-0046 - “Separation Processes and Product Design”). References Afzaljavan, F., & Mobini-Dehkordi, M. (2013). Application of alpha-amylase in biotechnology. LAP LAMBERT Academic Publishing. https://www.morebooks.de/store/gb/book/application- of-alpha-amylase-in- biotechnology/isbn/978-3-659-40419-1 Belšak-Šel, N., Gregori, A., Leitgeb, M., Klinara, D., & Čelan, Š. (2015). Effect of Solid State Fermentation Medium Optimization on Pleurotus ostreatus Laccase Production. Acta Chimica Slovenica, 62(4), 932–939. https://doi.org/10.17344/acsi.2015.1764 Bradford, M. (1976). Rapid and Sensitive Method for Quantitation of Microgram Quantities of Protein Utilizing Principle of Protein-Dye Binding. Analytical Biochemistry, 72(1–2), 248–254. https://doi.org/10.1006/abio.1976.9999 Čolnik, M., Primožič, M., Knez, Ž., & Leitgeb, M. (2016). Use of Non-Conventional Cell Disruption Method for Extraction of Proteins from Black Yeasts. Frontiers in Bioengineering and Biotechnology, 4, 33. https://doi.org/10.3389/fbioe.2016.00033 da Luz, J. M. R., Nunes, M. D., Paes, S. A., Torres, D. P., de Cássia Soares da Silva, M., & Kasuya, M. C. M. (2012). Lignocellulolytic enzyme production of Pleurotus ostreatus growth in agroindustrial wastes. Brazilian Journal of Microbiology, 43(4), 1508–1515. https://doi.org/10.1590/S1517-838220120004000035 de Souza, P. M., & de Oliveira Magalhães, P. (2010). Application of microbial α-amylase in industry – A review. Brazilian Journal of Microbiology, 41(4), 850–861. https://doi.org/10.1590/S1517-83822010000400004 Dikeman, C. L., Bauer, L. L., Flickinger, E. A., & Fahey, G. C. (2005). Effects of stage of maturity and cooking on the chemical composition of select mushroom varieties. Journal of Agricultural and Food Chemistry, 53(4), 1130–1138. https://doi.org/10.1021/jf048541l M. Primožič, Ž. Knez, M. Leitgeb: Activity of α-Amylase from P. ostreatus Grown on Waste Substrates 101. Kurt, S., & Buyukalaca, S. (2010). Yield performances and changes in enzyme activities of Pleurotus spp. (P. ostreatus and P. sajor-caju) cultivated on different agricultural wastes. Bioresource Technology, 101(9), 3164–3169. https://doi.org/10.1016/j.biortech.2009.12.011 Philippoussis, A., Zervakis, G., & Diamantopoulou, P. (2001). Bioconversion of agricultural lignocellulosic wastes through the cultivation of the edible mushrooms Agrocybe aegerita, Volvariella volvacea and Pleurotus spp. World Journal of Microbiology and Biotechnology, 17(2), 191–200. https://doi.org/10.1023/A:1016685530312 Quevedo-Hidalgo, B., Narváez-Rincón, P. C., Pedroza-Rodríguez, A. M., & Velásquez-Lozano, M. E. (2015). Production of lignocellulolytic enzymes from floriculture residues using Pleurotus ostreatus. Universitas Scientiarum, 20(1), 117–127. https://doi.org/10.11144/Javeriana.SC20-1.eple Rashad, M. M., Abdou, H. M., Mahmoud, A. E., & Nooman, M. U. (2009). Nutritional analysis and enzyme activities of Pleurotus ostreatus cultivated on Citrus limonium and Carica papaya wastes. Australian Journal of Basic and Applied Sciences, 3(4), 3352–3360. Solomko, E. F., & Eliseeva, G. S. (1988). [Biosynthesis of vitamins B by the fungus Pleurotus ostreatus in a submerged culture]. Prikladnaia Biokhimiia I Mikrobiologiia, 24(2), 164–169. Valentão, P., Andrade, P. B., Rangel, J., Ribeiro, B., Silva, B. M., Baptista, P., & Seabra, R. M. (2005). Effect of the conservation procedure on the contents of phenolic compounds and organic acids in chanterelle (Cantharellus cibarius) mushroom. Journal of Agricultural and Food Chemistry, 53(12), 4925–4931. https://doi.org/10.1021/jf0580263 102 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. WATER-BASED ELECTRONIC PAPER AS LOW-COST MULTI-COLOR SCREENS MARTIN ROZMAN 1 University of Maribor, Faculty of Chemistry and Chemical Engineering, Laboratory for Physical Chemistry and Chemical Thermodynamics, Maribor, Slovenia martin0rozman@gmail.com Abstract Electronic paper devices also known as electrochromic devices are known for their ability to change color with option to remain in certain color state even after the electrical power has been lifted. Traditional devices such as electrochromic windows used mechanisms like electrophoresis or intercalation and use special materials such as water-less electrolyte, and transparent conductive materials (TCM). As such, these devices can sometimes be relatively difficult to assemble, especially in developing countries, where such materials are harder to come by. Recently, certain improvements have been made by using alternative electrode positioning, that they do not require TCM. Presented here is a novel type of electronic paper that is recyclable, can be Keywords: pH indicator, constructed as a monochrome or multi-color device and can be electronic paper, scaled accordingly to desired screen size. Presented electronic stainless steel, paper, is a semi-open electrochemical device, which uses pH alternative electrode indicator dyes and water-salt solution, combined with easily positioning, obtained sheet steel. water electrolyte DOI https://doi.org/10.18690/um.fkkt.2.2022.8 ISBN 978-961-286-598-6 104 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. 1 Introduction Electrochromism is the phenomena, where a device can change coloration under applied electric current or potential, with additional ability to sustain newly adopted color even after the power source has been disconnected. As such, electrochromic devices (ECDs) that exhibit such qualities are known as electrochromic devices and are in principle much different compared to more traditional fast responding liquid crystal displays (LCDs) or light emitting diodes (LEDs). (Kim and Song) (Krasnov) Due to their unique behavior, they can be used in much more different applications compared to more conventional screen technologies such as smart windows and electronic paper. First electrochromic devices showed up at start of 1960s, (Kumamoto et al.) (Platt) where they had relatively limited use due high potentials requirements and slow response time. Vast improvement was shown with introduction of novel materials such as tungsten trioxide (WO3) and new sol-gel synthesis developed first by Hersh and coworkers (Hersh et al.) which promised development of novel devices and its widespread use. Shortly after, al -polymer devices were developed, which utilized polymer based transparent conductive electrodes (TCE) using poly(3,4-ethylenedioxythiophene) (PEDOT) and other polymers. (Pei et al.) (Kobayashi et al.) Due to certain materials cost, namely TCE materials, adoption of these devices was quite slow, and once the battery technology developed enough to support high potential demand of LCDs, making ECDs less interesting. Recently, several attempts have been made to avoid use of TCE, which could substantially reduce production cost of different devices, from solar cells, as well as ECDs. (Rozman et al. "Novel Geometric Approach for Photosensor Construction Based on Dye-Sensitization of Tio2 Nanoparticles on Stainless Steel") (Rozman et al. "Flexible Electrochromic Tape Using Steel Foil with Wo3 Thin Film") In a paper of Lukšič et al it was shown that it is possible to construct a device, that does not require TCE. (Rozman et al. "An Inverted Sandwich Electrochromic Device Architecture Does Not Require Optical y Transparent Electrodes") In addition, presented device utilized salt-based water electrolyte, combined with pH dye that uses electrolysis as a color changing mechanism, thus avoiding the use organic solvents. By combining different pH dyes it could be possible to find a combination of coloration responses, where al the dyes share the same basic color that can be interpreted as bleached state, while the tinted state of each individual assembled cel is proportional to used pH dye. Due to already established lists of known responses for individual pH, it is easy to find a dye with appropriate M. Rozman: Water-based Electronic Paper as Low-cost Multi-color Screens 105. coloration response, (Khan et al.) (Van der Schueren and De Clerck) but finding the right combination of dyes to assemble such device might still be difficult. This is due to the reason, that selected pH dyes should not interact with electrolyte electrodes or each other since this could severely affect the longevity of the device. Here, we present a method on how to assemble a multi-color electrochromic device, which incorporates several electrochemical semi-cel s with added dye, where semi-cel s share the same electrolyte. In addition, assembled device utilizes so-called “inverted geometry”, with which it is possible to avoid using TCE. 2 Materials and methods 2.1 Materials Technical materials such as stainless steel foil type AISI 316 (TBJ Industrieteile GmbH, Germany) tissue paper (Paloma multi fun, Slovenia), insulation tape (Tesa, Germany) and microscope slide glass (IsoLab GmbH, HE-2400, Germany) have been obtained from different suppliers. Chemicals such as sodium acetate (99.9%) and ammonium sulphate (99.9%), ethanol (99.8%) along with pH dyes methyl red (99.9%), bromothymol blue (99.9%), α-naphtophtalein (99.9%) were obtained from Sigma-Aldrich. 2.2 Device assembly Before device assembly different pH dye solutions as wel as electrolytes were prepared. Two different electrolytes were prepared using sodium acetate and ammonium nitrate, both dissolved in separate measuring flask with concentration of 2.5 M. For completed 4-pixel device 2.5 M sodium acetate was used, while for individual pixel device assembled under instructions from literature (Rozman et al. "An Inverted Sandwich Electrochromic Device Architecture Does Not Require Optical y Transparent Electrodes") that used methyl red dye, 2.5 M ammonium sulphate was used. Next, pH dyes were prepared by dissolving of 0.1 g of selected dye in 20 mL of ethanol each in separate beaker and stirred until the dye was dissolved. The same mass was used for al selected dyes: Bromothymol blue (BM), Methyl red (MR) and α-Naphtophtalein (AN). Each solution was then placed in its own measuring flask. For each individual dye, a paper patch measuring 5 mm by 25 mm was cut using scissors. Each patch was then soaked with the individual pH dye 106 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. and let 20 minutes to dry on air. One additional patch has been made that was first soaked in bromothymol blue and was then additional y sprinkled with dropper using α-Naphtophtalein. This 4th patch was done to be used so the device could demonstrate 4-pixel operation and was not characterized in details. After dyed paper preparation, four electrodes were cut using scissors, measuring 5 mm by 25 mm each, and they were adhered on one side with insulation tape. Each electrode was wrapped on the end of the electrode with dyed paper in such way, that an area of 5 mm by 5 mm was covered. Next, a counter electrode that measured 25 mm by 10 mm was cut. Following counter electrode preparation, working electrodes with wrapped paper were positioned on counter electrode and were then soaked with 2.5 M sodium acetate using dropper. The entire device was encapsulated into two pieces of glass measuring 35 mm x 35 mm, with excess liquid removed using paper towels. Constructed 4-pixel device measured 10 mm x 10 mm and used „inverted geometry“ assembly approach. Fig. 1: Assembled water-based ECD in various coloration states. The initial color state after completed assembly is presented in lower right corner. Surce: own. M. Rozman: Water-based Electronic Paper as Low-cost Multi-color Screens 107. 2.3 Characterization methods Device testing was done using variable power supply PS-302A (Voltrcraft GmbH, Germany), while electrochemical measurements were done using Autolab PGSTAT128N (Metrohm, Swtzerland) on 5 mm x 5mm devices, that represented individual pixels. Spectrophotometric measurements were done using Cary 50 (Agilent, USA) with fiber probe attachment for specular reflectance measurement. 3 Results 3.1 Cyclic voltammetry Voltametric measurements were first done to determine behavior of stainless steel electrodes in different electrolytes. 10 cycles were done in potential window between -4 and +4 V, with starting point at 0 V with reference connected directly on counter electrode terminal. It was determined that. In fig. 2 it can be observed that both electrolytes have inertial potential window between -2 and + 2 V, suggesting that the main reaction is electrolysis of water, where on positively charged anode the water splits into oxygen and hydronium ion (3𝐻𝐻2𝐶𝐶  2𝐻𝐻3𝐶𝐶+ + ½ 𝐶𝐶2 + 2𝑒𝑒−) where on negatively charged cathode, the water splits into hydroxyl ion and hydrogen (2𝐻𝐻2𝐶𝐶 + 2𝑒𝑒−  2𝐶𝐶𝐻𝐻− + 𝐻𝐻2). The cathodic and anodic peaks for both Fig. 2a and 2b that are visible between +/-1.5 V and 2.5 V are belonging to gas reduction, either oxygen reduction or hydrogen oxidation, respectively. Only post-measurement inspection after 10 cycles showed that ammonium sulphate is more corrosive, which could be related to sulphate anions, which are more aggressive towards stainless steel compared to acetate anions. Despite having more artefacts, that were recorded during voltammetry in Fig 2a, that were due to gas build-up, the 2.5 M sodium acetate proved superior to 2.5 M ammonium sulphate. Additionally, 2.5 M ammonium sulphate had almost too high conductivity, resulting in increased current consumption while having no coloration response advantage. This can be observed as a signal cut-off below – 3 V and above + 3 V, in Fig. 3b, where potentiostat/galvanostat instrument was limited to maximum 40 mA/cm2 to prevent excessive heating of tested device. 108 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. Fig. 2: Cyclic voltammetry of assembled 5 mm x 5mm device using 2.5 M sodium acetate (fig. 2a) and 2.5 M ammonium sulphate (fig. 2b) with AISI 316 stainless steel electrodes. Presented are 1st (black label) and 10th (red label) cycle. Surce: own. 3.2 Chronoamperometry Chronoamperometry (Fig. 3) was performed with positive pulse of + 3.5 V and negative pulse of -3.5 V both lasting for 30 s and between ach with 30 s waiting period. Potential polarity was altered after each pulse. This experiment was done to determine the conductivity and performance on two different devices, 2.5 M sodium acetate with bromothymol blue (black label) and 2.5 M ammonium sulphate with methyl red (red label) respectively. During 5 cycles of assembled device, it was observed that both devices have adequate coloration response, with no indications that any of the dyes would be affected due to electrolysis After completing 5 cycles, it was determined that sodium acetate is less corrosive to stainless steel and was thus used as a preferred electrolyte. Fig. 3: Chronoamperometry of assembled 5 mm x 5mm devices. Presented are 2.5 M sodium acetate (black label) and 2.5 M ammonium sulphate (red label) 5 mm x 5 mm devices. Surce: own. M. Rozman: Water-based Electronic Paper as Low-cost Multi-color Screens 109. 3.3 UV-Vis reflectance spectrophotometry UV-Vis measurements of individual pixels of assembled 4-pixel device were done to determine change of coloration. The UV-Vis measurements were performed on an assembled 4-pixel device, with spectrums recorded for three pixels that had individual color, using Bromothymol blue, Methyl red, and α-Naphtophtalein. Since the constructed device used 2.5 M sodium acetate, the pixel dyed with methyl red performed less ideal y, due to Methyl red low pH required for coloration change of around 4.6, while sodium acetate has relatively high measuring around 8-9. (Rozman et al. "An Inverted Sandwich Electrochromic Device Architecture Does Not Require Optical y Transparent Electrodes") Nevertheless, device was successful in obtaining al required color changes, which can be seen in Fig. 4. Both Bromothymol blue and α-Naphtophtalein are yel ow in acidic media, and colored in basic media, while Methyl red has reverse response with yel ow coloration in basic media and red coloration in basic media. Main coloration difference can be observed at around 600 nm for Bromothymol blue, 650 nm for α-Naphtophtalein, while for Methyl red the main difference between both states can be visible in area between 400 to 500 nm. Fig. 5: UV-Vis spectrums of 4-pixel ECD device for various dyes: Bromothymol blue (fig. 4a), Methyl red (Fig. 4b), and α-Naphtophtalein (Fig 4c). For each label, appropriate visible color is used. Surce: own. 110 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. 4 Conclusions It is possible to construct water based ECDs, that can have different coloration and could be potential y used as actual screens, and that despite marginal change in UV-Vis spectrum, coloration change of Methyl red was observable with naked eye. Results are suggesting that both Bromothymol blue and α-Naphtophtalein are most suitable for future use in development of water based multicolor screen, while Methyl red should be replaced with more suitable pH dye. In addition, such devices, could be made with relatively simple tooling and using traditional electrical engineering to connect several such devices into functional screens. Despite their relatively slow response, they could still be used in roles, where reaction time is less important, but large screen surface is desired. Such devices could be used for advertisement boards or other displays where low cost and simple development are a priority. Acknowledgments M. Rozman wish to thank Slovenian research agency programs P2-0046, and P1-0403. M. Rozman would also like to thank N. Cetin for support during sample preparation. References Hersh, H. N. et al. "Mechanism of Electrochromism in Wo3." Applied Physics Let ers, vol. 27, no. 12, 1975, pp. 646-648, doi:10.1063/1.88346. Khan, Muhammad Imran et al. "A Review on Ph Sensitive Materials for Sensors and Detection Methods." Microsystem Technologies, vol. 23, no. 10, 2017, pp. 4391-4404, doi:10.1007/s00542-017-3495-5. Kim, Kyeong-Hyeon and Jang-Kun Song. "Technical Evolution of Liquid Crystal Displays." NPG Asia Materials, vol. 1, no. 1, 2009, pp. 29-36, doi:10.1038/asiamat.2009.3. Kobayashi, Tetsuhiko et al. "Electrochemical Reactions Concerned with Electrochromism of Polyaniline Film-Coated Electrodes." Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, vol. 177, no. 1, 1984, pp. 281-291, doi:https://doi.org/10.1016/0022-0728(84)80229-6. Krasnov, Alexey N. "Electroluminescent Displays: History and Lessons Learned." Displays, vol. 24, no. 2, 2003, pp. 73-79, doi:https://doi.org/10.1016/S0141-9382(03)00015-5. Kumamoto, J. et al. "Electrochromism (Stark Effect) in Solids Due to Isolated Absorbing Centers." The Journal of Chemical Physics, vol. 36, no. 11, 1962, pp. 2893-2896, doi:10.1063/1.1732398. Pei, Qibing et al. "Electrochromic and Highly Stable Poly(3,4-Ethylenedioxythiophene) Switches between Opaque Blue-Black and Transparent Sky Blue." Polymer, vol. 35, no. 7, 1994, pp. 1347-1351, doi:https://doi.org/10.1016/0032-3861(94)90332-8. Platt, John R. "Electrochromism, a Possible Change of Color Producible in Dyes by an Electric Field." The Journal of Chemical Physics, vol. 34, no. 3, 1961, pp. 862-863, doi:10.1063/1.1731686. M. Rozman: Water-based Electronic Paper as Low-cost Multi-color Screens 111. Rozman, Martin et al. "An Inverted Sandwich Electrochromic Device Architecture Does Not Require Optical y Transparent Electrodes." Advanced Materials Technologies, vol. 4, no. 9, 2019, p. 1900389, doi:https://doi.org/10.1002/admt.201900389. Rozman, Martin et al. "Novel Geometric Approach for Photosensor Construction Based on Dye-Sensitization of Tio2 Nanoparticles on Stainless Steel." Sensors and Actuators A: Physical, vol. 295, 2019, pp. 51-58, doi:https://doi.org/10.1016/j.sna.2019.05.034. Rozman, Martin et al. "Flexible Electrochromic Tape Using Steel Foil with Wo3 Thin Film." Electrochimica Acta, vol. 330, 2020, p. 135329, doi:https://doi.org/10.1016/j.electacta.2019.135329. Van der Schueren, Lien and Karen De Clerck. "Coloration and Application of Ph-Sensitive Dyes on Textile Materials." Coloration Technology, vol. 128, no. 2, 2012, pp. 82-90, doi:https://doi.org/10.1111/j.1478-4408.2011.00361.x. 112 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. THE INFLUENCE OF DIFFERENT FIBRES QUANTITY ON MECHANICAL AND MICROSTRUCTURAL PROPERTIES OF ALKALI-ACTIVATED FOAMS KATJA TRAVEN,1 MARK ČEŠNOVAR,1, 2 BARBARA HORVAT,1 VILMA DUCMAN1 1 Slovenian National Building and Civil Engineering Institute, Ljubljana, Slovenia katja.traven@zag.si, mark.cesnovar@zag.si, barbara.horvat@zag.si, vilma.ducman@zag.si 2 International Postgraduate School Jožef Stefan, Ljubljana, Slovenia mark.cesnovar@zag.si Abstract Alkali activated foams (AAFs) were produced using electric arc furnace steel slag (EAF) and ladle furnace basic slag (LS), obtained from two metallurgical companies in Slovenia. They were activated with a mixture of sodium water glass (Na2SiO3) and solid NaOH and foamed with hydrogen peroxide (H2O2). Pores were stabilized with the addition of Triton as a surfactant. Four types of fibres were added to the studied mixture (polypropylene (PP), polyvinyl-alcohol (PVA), basalt (B), and glass wool (GW)) in five different quantities: 0.5, 1.0, 1.25, 1.5 and 2.0 vol % in order to additionally stabilize the structure and thus improve its mechanical properties. The results of mechanical properties showed, that compressive strength was increased in all 20 specimens, partially due to the increased density as wel as to the fibre addition. Flexural strength on the other hand was the most Keywords: improved in the samples where PP and PVA fibres were added. alkali activated materials, The samples with the addition of B and GW fibres on the other lightweight hand showed only small or no improvement in flexural strength in foams, comparison to the referenced sample. Additionally, the fibres, porosity, microstructure of used fibres and selected foams was also mechanical investigated by the means of SEM analysis. properties DOI https://doi.org/10.18690/um.fkkt.2.2022.9 ISBN 978-961-286-598-6 114 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. 1 Introduction Alkali activated foams (AAFs) present a promising material to be used as an insulating and/or acoustic insulation material in the building and construction area. They are produced from different aluminosilicate sources (i.e. slags, fly-ashes, calcined clays) mixed with alkali activator (different water glasses, NaOH, KOH) and foaming agent (such as H2O2, metal powders) (Ducman & Korat, 2016). The main advantage of AAFs production is in the lower processing temperatures (up to 100 °C) required to achieve properties similar to traditional foamed glass or ceramics, both of which are produced at highly elevated temperatures (above 900 °C). Furthermore, given their low density, good thermal properties, fire resistance and applicable mechanical properties, AAFs offer an environmental y friendly alternative to ordinary insulation materials such as aerated cement concrete, mineral wool or EPS (Abdollahnejad et al., 2017). The resulting porous hardened structure contains air voids and could thus be very fragile, therefore the additional stabilization of the structure by the addition of different types of fibres represents one possible way to improve mechanical properties (Mastali et al., 2018). The main tendency found in the literature is the use of locally available fibres from natural bio-resources such as hemp (Li et al., 2004), bamboo (Chen et al., 2018), wood (Lin et al., 1994), cotton (Alomayri et al., 2013), sisal (Almeida et al. , 2018) and others due to their renewable and recyclable nature. The second and also very important feature of the fibres used for the AAFs production is their stability with sustainability in a highly alkaline environment when exposed to high temperatures (Abdulkareem et al., 2019). For example, cellulose-based bio fibres usually decompose at temperatures around 360 °C, therefore such foams would not be applicable in the field where high-temperature resistance is required. Hence, some studies in the field of alkali-activated materials’ reinforcement are focused also on the use of steel ( Rashad, 2020), basalt (Mastali et al. , 2018), or glass fibres (Puertas et al., 2006), all of which should survive elevated temperatures. Good performance was achieved also with the use of synthetic fibres such as polypropylene (Wang & Tan, 2011) or polyvinyl alcohol (Nguyen et al., 2020). K. Traven, M. Češnovar, B. Horvat, V. Ducman: The Influence of Different Fibres Quantity on Mechanical and Microstructural Properties of Alkali-activated Foams 115. In the present study, the influence of different amounts (0.5, 1.0, 1.25, 1.5 and 2.0 vol %) of polypropylene (PP), polyvinyl-alcohol (PVA), basalt (B), and glass wool (GW) fibres on mechanical properties was investigated. Further, also the microstructural incorporation of these fibres into a foamed alkali-activated matrix was assessed by means of SEM analysis. 2 Experimental 2.1 Materials and AAFs preparation Electric arc furnace steel slag (EAF, designated as Slag A) and ladle furnace basic slag (LS, designated as Slag R), obtained from two metallurgical companies in Slovenia were used as precursors with Slag A/Slag R ratio equals 1, as already discussed in our previous study (Češnovar et al. , 2019). Slags were activated with the mixture of 31.5 mass % of Na2SiO3 Crystal 0112, 54.2 % aqueous solution with SiO2/Na2O = 1.97, produced by Tennants distribution, Ltd. and 0.5 mass % of solid NaOH produced by Donau Chemie and foamed with 2.5 mass % of H2O2 (30 % aqueous solution, produced by Belinka, Slovenia). Pores were stabilized with the addition of 1.5 mass % of Triton (designated as T; Triton X-100, produced by Merck, Germany) as a surfactant. Four types of fibres were separately added to the studied mixture (polypropylene (PP), polyvinyl-alcohol (PVA), basalt (B), and glass wool (GW)) in five different quantities: 0.5, 1.0, 1.25, 1.5 and 2.0 vol %. For reference also non fibred foam was produced (designated as blank). The list of prepared mixtures with the corresponding designations is shown in Table 1. The fresh foamed pastes were poured into 20 × 20 × 80 mm3 moulds and cured at 70 °C for 3 days. Mechanical strengths were determined 3 days after curing at a temperature of 70 °C. 116 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. Table 1: Compositions of different AFFs prepared for the investigation; where PP = polypropylene, PVA = polyvinyl alcohol, B = basalt, and GW = glass wool fibres. Sample designation Slag A + Slag Na2SiO3 NaOH H2O2 T Fibres R [g] [g] [g] [g] [g] [g] Blank 192 96 1.5 7.5 4.5 / 0.5 vol % 0.53 1.0 vol % 1.06 PP 1.25 vol % 192 96 1.5 7.5 4.5 1.32 1.5 vol % 1.59 2.0 vol % 2.12 0.5 vol % 0.42 1.0 vol % 0.84 PVA 1.25 vol % 192 96 1.5 7.5 4.5 1.01 1.5 vol % 1.26 2.0 vol % 1.68 0.5 vol % 0.32 1.0 vol % 0.66 B 1.25 vol % 192 96 1.5 7.5 4.5 0.82 1.5 vol % 0.98 2.0 vol % 1.32 0.5 vol % 0.32 1.0 vol % 0.66 GW 1.25 vol % 192 96 1.5 7.5 4.5 0.82 1.5 vol % 0.98 2.0 vol % 1.32 2.2 Fibres For this study, four different types of fibres were used as shown in Fig. 1. They are al of elongated shapes and comprised of different sizes (approximately 11, 12, 7 and 1 cm in length for PP, PVA, B and GW, respectively) and with theoretical densities (0.94, 1.19, 2.9 and 2.9 g/cm3 for PP, PVA, B and GW, respectively) therefore different volumetric percentage (designated as vol %) of each fibre type was added to the mixture. Fibres were added to the activator solution and mixed to obtain as homogenous fibre distribution as possible. K. Traven, M. Češnovar, B. Horvat, V. Ducman: The Influence of Different Fibres Quantity on Mechanical and Microstructural Properties of Alkali-activated Foams 117. a) b) c) d) e) f) g) h) Figure 1: Macro and micro images of polypropylene (a, b), polyvinyl alcohol (c, d) basalt (e, f) and glass wool (g, h) fibres. Source: own. 118 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. 2.3 Characterization methods and instruments The densities of al AAFs were determined by weighing the individual foams and dividing the thus determined weights by the corresponding dimensions of the specimens (i.e. so-cal ed geometrical density). Flexural strengths (σFS) and compressive strengths (σCS) were determined at an age of 3 days by means of a Toninorm test equipment (Toni Technik, Germany), using a force application rate of 0.005 kN/s and calculated according to equations (1) and (2). σ 3Fl FS = (1) 2bd2 F – force l – length between support span b – width of sample d – thickness of sample σ F CS = (2) A F – force A – area The relative densities (rel. ρ), as well as relative flexural and compressive strengths, were calculated, using the following equation (3). (ρ0 – ρx) rel. ρ = (3) ρ0 ρ0 – density of the blank sample ρx – density of the studied fibres reinforced sample K. Traven, M. Češnovar, B. Horvat, V. Ducman: The Influence of Different Fibres Quantity on Mechanical and Microstructural Properties of Alkali-activated Foams 119. Microstructural analysis of the fibres, as wel as hardened AAFs, was performed by a JSM IT500, JEOL (Japan) with a tungsten filament cathode. Prior to SEM scanning, the samples were vacuum-dried and sputter-coated with gold. 3 Results and discussion 3.1 Mechanical properties The absolute densities and mechanical properties of the produced AAFs are given in Table 2. Additionally, graphical presentations of the relative (with regard to the measurements of blank foam sample) densities and flexural as well as compressive strengths are shown in Fig. 2. It can be observed, that foam with no added fibres exhibit a relatively low density of 0.39 g/cm3 and is thus also very fragile with compressive strength of only 0.21 MPa and flexural strength below detection limit. With the addition of fibres the densities are increased in most cases (with the exceptions in specimens 1.25 vol % PVA, 1.25 vol % B, 1.25 vol % GW, and 0.5 vol % B) and are in the range between 0.35 and 0.55 g/cm3. As expected the foams with the highest density – specimens 1.0 vol % PP, 2.0 vol % PP and 1.0 vol. % PVA, exhibit also the highest compressive strengths (1.24, 1.31 and 1.20 MPa, respectively). These three specimens also showed the best development of flexural strength (0.62, 0.54 and 0.41 MPa, respectively) which could partially be assigned to the density gain and partially to the reinforcement as a consequence of fibres addition. From Fig. 2 could also be observed that al specimens regardless of the fibres type addition showed better compressive strengths. Interestingly, only 26 % density gain for specimen 2.0 vol % PP resulted in 3.3-times higher compressive strength. Further, specimens with PP and PVA addition also exhibit improved flexural strength. The samples with the addition of B and GW fibres on the other hand showed only smal or no improvement in flexural strength in comparison to the referenced sample (specimen with no added fibres). Additionally, from this study, some logical correlation between fibres quantity and mechanical strength improvement was not proved, since the maximum flexural strength was reached with the addition of 1.0 vol % of PP and 2.0 vol % of PVA fibres. 120 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. Table 2: A list of the absolute densities (ρ), flexural strengths (σFS), and compressive strengths (σCS) of al samples (n. d. = below detection limit). ρ [g/cm3] σFS [MPa] σCS [MPa] Blank 0.39 n. d. 0.21 0.5 vol % 0.44 0.15 0.57 1.0 vol % 0.55 0.62 1.24 PP 1.25 vol % 0.43 0.43 0.52 1.5 vol % 0.42 0.34 0.41 2.0 vol % 0.49 0.54 1.31 0.5 vol % 0.39 0.02 0.50 1.0 vol % 0.50 0.41 1.20 PVA 1.25 vol % 0.38 0.09 0.34 1.5 vol % 0.41 0.13 0.36 2.0 vol % 0.45 0.47 0.71 0.5 vol % 0.38 n. d. 0.39 1.0 vol % 0.48 n. d. 0.75 B 1.25 vol % 0.35 0.02 0.30 1.5 vol % 0.40 n. d. 0.29 2.0 vol % 0.43 0.04 0.26 0.5 vol % 0.40 0.01 0.71 1.0 vol % 0.47 n. d. 0.85 GW 1.25 vol % 0.35 0.01 0.41 1.5 vol % 0.40 n. d. 0.39 2.0 vol % 0.45 0.03 0.58 Figure 2: Graphical representation of the relative (with regard to the blank sample) densities (ρ), flexural strengths (σFS), and compressive strengths (σCS). Source: own. K. Traven, M. Češnovar, B. Horvat, V. Ducman: The Influence of Different Fibres Quantity on Mechanical and Microstructural Properties of Alkali-activated Foams 121. 3.2 Microstructural evaluation The microstructures of AAFs with different fibres (in al cases the quantity of 2 vol %) and at different magnifications are presented in Figs. 3–6. SEM micrographs of PP fibre-reinforced AAFs are presented in Fig. 3. Fig. 3a shows the evenly distributed PP fibres in the alkali-activated matrix whereas Figs. 3b and 3c show a more detailed view of the boundary between the fibre and the matrix. a) b) c) Figure 3: SEM micrographs of polypropylene reinforced AAFs (2 vol %) at different magnifications: a) PP distribution in the matrix; b) and c) boundary between a PP fibre and the matrix. Source: own. Similarly, also the distribution of PVA fibres is uniform in the matrix as shown in Fig. 4a and the boundary between the fibre and the matrix is presented in Fig. 4b. Additionally, as observed in Fig. 4c, PVA fibres seem to be less resistant to the highly alkaline environment and/or foaming agent in the fresh alkali-activated slurry, 122 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. therefore damages on the fibres may occur as shown in Fig. 4c. However, these damages could also contribute to the better adhesion of the fibres to the matrix resulting in better mechanical properties. After al , specimen 1.0 vol % PVA reaches one of the highest compressive and flexural strengths among studied ones. a) b) c) Figure 4: SEM micrographs of polyvinyl alcohol reinforced AAFs (2 vol %) at different magnifications: a) PVA distribution in the matrix; b) boundary between a PVA fibre and the matrix; c) damaged PVA fibres. Source: own. Fig. 5a shows the distribution of B fibres in the alkali-activated matrix. Their distribution is also quite uniform. Due to the chemical composition of the basalt fibres (alumino-silicate composition, similar to precursors) these fibres could also react with the alkaline activator and the spots seen on Fig. 5c could be a consequence of these reaction. Similar observations on SEM micrographs of B fibres after K. Traven, M. Češnovar, B. Horvat, V. Ducman: The Influence of Different Fibres Quantity on Mechanical and Microstructural Properties of Alkali-activated Foams 123. exposure to NaOH solution were detected also by Elshafie & Whittleston (Elshafie & Whittleston, 2016). However, probably due to the more fragile nature of the B fibre, the reinforcement was not as successful as in the case of PP and PVA fibres. a) b) c) Figure 5: SEM micrographs of basalt reinforced AAFs (2 vol %) at different magnifications: a) B distribution in the matrix; b) and c) boundary between a B fibre and the matrix. Source: own. GW fibres are the smal est among the studied ones, therefore they are barely observed in the alkali-activated matrix as shown in Fig. 6a. Regarding to their chemical composition they are comparable to the B fibres. The advantage of such smal er fibres could be firstly in their better incorporation into the alkali-activated matrix (Figs. 6b and 6c) especially in cell and void boundaries and secondly, due to their glassy phase the dissolution in alkalis is also possible. But for the flexural strength improvement probably much higher concentrations should de added. 124 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. a) b) c) Figure 6: SEM micrographs of glass wool reinforced AAFs (2 vol %) at different magnifications: a) GW distribution in the matrix; b) and c) boundary between a GW fibre and the matrix. Source: own. 4 Conclusions With the aim of the mechanical properties improvement, four types of fibres (polypropylene (PP), polyvinyl-alcohol (PVA), basalt (B), and glass wool (GW)) in five different quantities (0.5, 1.0, 1.25, 1.5 and 2.0 vol %) were added to the selected alkali-activated foamed mixture. The results of mechanical properties showed, that compressive strength was increased in all 20 specimens, partially due to the increased density, which is a consequence of fibre addition. Flexural strength on the other hand was the most improved in the samples where PP and PVA fibres were added. The samples with the addition of B and GW fibres showed only smal or no improvement in flexural strength in comparison to the referenced sample (specimen K. Traven, M. Češnovar, B. Horvat, V. Ducman: The Influence of Different Fibres Quantity on Mechanical and Microstructural Properties of Alkali-activated Foams 125. with no added fibres). However, some logical correlation between fibres quantity and mechanical strength improvement was not proved in this study. The best performance in terms of mechanical properties was achieved in the case of the specimen where 2.0 vol % of PP fibres was added. SEM micrographs revealed, that in most cases the fibres are uniformly distributed. In the case of PVA fibres also some damaged fibres were observed which could contribute to better adhesion and therefore improved mechanical properties. Acknowledgements Development of AAFs is part of the ERA-MIN FLOW project which has been financed by the Ministry of education, science, and sport (acronym: MIZS) under grant agreement No. C 3330-18-252010. Project No. C3330-17-529032 “Raziskovalci-2.0-ZAG-529032” was granted by Ministry of Education, Science and Sport of the Republic of Slovenia. The investment is co-financed by the Republic of Slovenia, Ministry of Education, Science and Sport and the European Regional Development Fund. 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Chen, H., Zhang, W., Wang, X., Wang, H., Wu, Y., Zhong, T., and Fei B. 2018. "Effect of Alkali Treatment on Wettability and Thermal Stability of Individual Bamboo Fibres." Journal of Wood Science 64, no. 4: 398-405. https://dx.doi.org/10.1007/s10086-018-1713-0. Elshafie, S., and Whittleston, G. 2016. "Evaluating the efficiency of basalt and glass fibres on resisting the alkaline, acid and thermal environments." American Journal of Materials Science 6(1): 19-34. doi:10.5923/j.materials.20160601.02. Češnovar, M., Traven, K., Horvat, B., and Ducman V. 2019. "The Potential of Ladle Slag and Electric Arc Furnace Slag Use in Synthesizing Alkali Activated Materials; the Influence of Curing on Mechanical Properties." Materials 12, no. 7: 1-18. https://dx.doi.org/https://doi.org/10.3390/ma12071173. Ducman, V., and Korat, L. 2016. "Characterization of Geopolymer Fly-Ash Based Foams Obtained with the Addition of Al Powder or H2O2 as Foaming Agents." 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ANALYSIS OF THE POSSIBILITIES FOR ENERGY RECOVERY IN WWTP RAYKA K. VLADOVA, NATASHA VAKLIEVA-BANCHEVA Institute of Chemical Engineering, Bulgarian Academy of Sciences, Akad. G. Bontchev, Sofia, Bulgaria r.vladova@iche.bas.bg Abstract In recent years, there has been increasing talk of improving energy efficiency and the ability to reduce greenhouse gases in wastewater treatment plants. This necessitates exploring the possibilities for reducing energy costs and the possibilities for obtaining energy from wastewater. In the present study, an analysis of the energy consumed at different stages of wastewater treatment in a municipal WWTP in the Republic of Bulgaria is made, and the Keywords: average monthly consumption of electricity required for the anaerobic treatment of one cubic meter of wastewater is estimated. Based on wastewater treatment, the col ected and analyzed data, an assessment was made of the cost analysis, possibilities for energy recovery from dry matter from sludge, by energy combustion and anaerobic digestion. The obtained results allow efficiency, energy recovery, for the reconstruction of a facility and the use of the hitherto circular unused energy potential contained in the sludge. economy. DOI https://doi.org/10.18690/um.fkkt.2.2022.10 ISBN 978-961-286-598-6 128 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. 1 Introduction Wastewater treatment plants are facilities designed to meet certain standards regarding the quality of treated water. In recent years, new stricter requirements have been imposed on the quality of discharged water, as wel as the mandatory biological treatment of wastewater in agglomerates over 2000 inhabitants for the countries of the European Union and removal of nutrients nitrogen and phosphorus in wastewater treatment from settlements with more 10,000 population equivalents (Council Directive No. 91/271/CEE) implies higher costs in their treatment. One of the main operating costs in the WWTP is the energy consumption both in the wastewater treatment and the need for electricity in the dewatering of sludge. This necessitates the need to assess the energy efficiency of these facilities of national importance and to study the possibilities for reducing the consumed energy, as wel as the possibilities for restoring such. Global y, WWTPs consume between 3-5 % of energy (McCarty et al., 2011), making them one of the largest energy consumers managed by municipalities. Different wastewater treatment technologies have different energy costs. WWTP energy consumption depends on the degree of wastewater pol ution, the location of the installation, the equipment, as well as the aeration processes. To estimate the energy consumption in different treatment plants Longo et al. 2016 offer key energy efficiency indicators (KPIs) using data available at each treatment plant. Fraia et al. 2018 define an indicator that connects the energy consumption in a treatment plant with the input quantities of BOD. The study defines different performance classes, linking the indicators of specific energy consumption with the parameters for the efficiency of pol utant removal. One of the ways to reduce energy consumption is to optimize the work and improve the energy efficiency of production systems, as wel as the search for opportunities for energy production. Reducing energy consumption in wastewater treatment processes would improve their energy efficiency and, last but not least, lead to a reduction in carbon emissions. The optimization of energy costs could be considered in two directions: − replacement of the available equipment with more modern one, whose energy consumption should be minimal; R. K. Vladova, N. Vaklieva-Bancheva: Analysis of the Possibilities for Energy Recovery in WWTP 129. − the possibilities to recover energy from waste products obtained as a result of wastewater treatment. A study of each phase of the technological scheme of a municipal wastewater treatment plant (Panepinto et al. 2016) offers a multi-stage methodology for assessing the energy aspects of wastewater treatment. The energy balance made makes it possible to make some suggestions for optimizing the work processes in the plant. Indicators for the total energy consumption per m3 are calculated in relation to the amount of pollutants removed. Possibilities for reducing energy consumption are also being explored by Chae K. & Kang J. 2013, offering a methodology for assessing energy independence through appropriate renewable energy technologies using different types of photovoltaics. The aim of the present study is to analyze the electricity consumed at the individual stages of treatment, as wel as to analyze the average monthly consumption of electricity required for the treatment of one cubic meter of wastewater. The paper analyzes the possibilities for energy recovery from dry sludge using different technologies. 2 Methodology The main stages of wastewater treatment are mechanical treatment, biological treatment and the last stage related to sludge treatment. Each of these stages has a different energy consumption, depending on the amount of treated water, the technology used, as wel as the degree of pol ution. The quality of treated wastewater is characterized by key indicators, such as the amount of removed organic pollutants, removed suspended solids, chemical and biological oxygen demand, as wel as the content of nitrogen and phosphorus, al of which must meet certain standards. The availability of these data, as well as the assessment of total electricity consumption, helps to develop energy performance indicators for wastewater treatment (Longo et al. 2016). Data for the calculation of these indicators are available at each treatment plant. They are related to the total electricity consumption in relation to the volume of treated wastewater (𝐾𝐾𝐾𝐾𝐾𝐾𝑉𝑉), the electricity consumption in relation to the population equivalent (𝐾𝐾𝐾𝐾𝐾𝐾RE), as wel as the amount of consumed electricity for 130 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. the removed COD (𝐾𝐾𝐾𝐾𝐾𝐾𝐶𝐶𝐶𝐶𝐶𝐶). The most commonly used indicator expresses energy consumption in relation to the amount of treated water. 𝐾𝐾𝐾𝐾𝐾𝐾𝑉𝑉 = 𝐸𝐸𝐸𝐸 �𝑘𝑘𝑘𝑘ℎ� (1) 𝑉𝑉 𝑚𝑚3 𝐾𝐾𝐾𝐾𝐾𝐾𝑃𝑃𝐸𝐸 = 𝐸𝐸𝐸𝐸 � 𝑘𝑘𝑘𝑘ℎ � (2) 𝑃𝑃𝐸𝐸 𝑃𝑃𝐸𝐸 𝑦𝑦𝑟𝑟𝑚𝑚𝑑𝑑 𝐾𝐾𝐾𝐾𝐾𝐾𝐶𝐶𝐶𝐶𝐶𝐶 = 𝐸𝐸𝐸𝐸 � 𝑘𝑘𝑘𝑘ℎ � (3) 𝐶𝐶𝐶𝐶𝐶𝐶 𝑑𝑑𝑟𝑟𝑚𝑚𝑐𝑐𝑝𝑝𝑟𝑟𝑑𝑑 𝑘𝑘𝑘𝑘 𝑑𝑑𝑟𝑟𝑚𝑚𝑐𝑐𝑝𝑝𝑟𝑟𝑑𝑑 𝐶𝐶𝐶𝐶𝐶𝐶 Based on this scientific development, an assessment was made of the energy efficiency at each stage in the object of study. The obtained results are summarized in fig. 1. Data on energy consumption for a period of one year relative to the volume of treated water are used. The data are based on daily records made in a municipal WWTP designed for 70,000 population equivalents, with average daily capacity of 13,400 m3. The average amount of energy required for the treatment of one m3 of wastewater after the calculations is 0.188 kWh/m3. Energy consumption 5% 11% Мechanical treatment Biological treatment 84% Sludge treatment Figure 1: Energy consumption at different stages of treatment Source: own. As can be seen from Fig. 1 with the highest energy costs is the stage of biological treatment. At this stage, the wastewater enters bio pools (2 pieces), where denitrification is performed with the help of activated sludge. The activated sludge method used includes oxygen-free nitrogen removal zones. Each bio-pool has three corridors - the first is for pre-denitrification, without aeration, and the other two are aerated, also the free phosphorus is removed in the facility. Passing through the bio- R. K. Vladova, N. Vaklieva-Bancheva: Analysis of the Possibilities for Energy Recovery in WWTP 131. pool, the activated sludge is separated from the treated water into secondary radial precipitators. The wastewater treated in this way is discharged into a water intake, and the activated sludge is returned to the process as recirculated by a pump station for recycling sludge. After aerobic stabilization in the bioreactor and the associated facilities for compaction and dewatering of the sludge in a sludge compactor, the excess activated sludge is removed to drying fields for natural dewatering without the use of special equipment. The reason for the higher energy consumption at this stage is due to the removal of both organic pollutants and the biogenic elements nitrogen and phosphorus. 3 Technologies for energy recovery in WWTP The analysis of the energy consumption in the WWTP inevitably leads to the study of the possibilities for energy recovery. Over the last decade, the perception of WWTPs has changed and wastewater is considered an energy resource for energy recovery. The energy contained in organic pollutants could be transformed into electrical and thermal, through appropriate technologies. The main source of organic energy in the WWTP is generated as a waste product as a result of wastewater treatment and these are sludge. In many countries, energy recovery technology uses the combustion of sludge as a result of which energy is released. This process is performed at a high temperature to eliminate harmful gas emissions. The amount of energy obtained as a result of combustion depends on the content of organic matter. The moisture content of the sludge as wel as the drying methods, in which the treatment costs increase, also have a significant influence. The advantages of this technology is that in addition to energy production, the amount of sludge that must be disposed of is reduced. Another possibility is the recovery of energy is through the production of biogas. This technology is one of the most common and is suitable for medium and large treatment plants, where anaerobic wastewater treatment is performed using anaerobic microorganisms at temperatures typical of mesophilic microorganisms 33-37 ° C. As a result of their activity, organic substances are decomposed into biogas, containing mainly methane 55-65%, carbon dioxide 30-40%, water and others. The use of the obtained biogas as recovered energy also has some chal enges due to the presence of many impurities that must be removed before the biogas can be used. 132 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. Another disadvantage of this technology is its not very high energy value (Appels et al., 2008). All this would require additional capital expenditures. The sludge from the municipal treatment plants is also used for fertilization of agricultural lands, after preliminary analysis, for the presence of harmful substances. Unfortunately, there are many countries that do not use sludge, and dispose of it without further processing. In Bulgaria, a large part of this waste product is deposited about 90%, the rest is used for land reclamation and biogas production after anaerobic digestion. In order to determine the unused energy potential contained in the sewage sludge in this work is have made an analysis of the possibilities for energy recovery, through the two most common technologies, combustion and energy production from biogas. 3.1 Data The data for this study summarize the operation of the WWTP and the amount of sludge produced for a period of six years after the reconstruction of the WWTP. The records are summarized for each of the years studied. Table 1 presents the total content of generated sludge in the facility, as wel as the amount of dry sludge for the respective year. It is necessary to mention that in the studied WWTP the sludge is deposited in drying fields without additional energy being used for its dehydration, renewable solar energy is used for drying. The dry matter content varies in the range of 24-50% in different years, and the average for the study period is about 36%. This would require minimal amounts of energy in cases where the sludge incineration method is applied. The present study does not consider the amount of energy required to be used in cases of high moisture content to meet the combustion requirement. Table 1: Quantities of landfiled sludge. year dry basis/t total/t 2014 252.52 979.6 2015 292.56 953 2016 260.46 712.54 2017 219.87 705.48 2018 210.09 388.98 2019 134.39 480.34 R. K. Vladova, N. Vaklieva-Bancheva: Analysis of the Possibilities for Energy Recovery in WWTP 133. 4 Results For the purposes of the study, is used data from Vipin Singh et al. 2020, which explores the energy potential of sludge through combustion and anaerobic digestion. The paper describes that the average potential for energy recovery by incineration of sewage sludge is in the range of about 555-1068 kWh / ton of dry sludge, while the potential for energy generation as a result of biogas production is significantly lower from 315-608 kWh / ton dry sludge. Based on these data, for the purposes of the analysis, the lowest energy values were used for the production of energy from dry matter in both technologies. After the calculations and the analysis of the data, results are presented for the amount of energy that could be recovered through sludge incineration technology. Fig. 2. The average amount of energy recovered in one year would be ~ 126,715 kWh. Energy (kWh) recovery by incineration of sewage sludge 180000 160000 140000 120000 100000 80000 60000 40000 20000 1 2014 2015 2016 2017 2018 2019 Figure 2: Energy recovery potential of sludge using incineration plants Source: own. Or the amount of energy that can be recovered by burning one ton of dry sludge is 92.5 kWh. 134 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. Presented results for the amount of energy that could be recovered as a result of biogas production are shown in fig. 3. The average amount of recovered energy for one year in the production of biogas is ~ 71 920 kWh or 52.5 kWh of energy per ton of dry matter. Energy (kWh) through the production of biogas 100000 90000 80000 70000 60000 50000 40000 30000 20000 1 2014 2015 2016 2017 2018 2019 Figure 3: Energy potential of sludge using biogas production Source: own. It should be mentioned that these are the minimum amounts of energy that could be recovered. It is also important to say that two methane tanks and a gas holder have been built on the territory of the respective treatment plant, which have not been put into operation at this time. This would reduce the investment costs for reconstruction, and thus the choice of appropriate energy recovery technology. 5 Conclusions In this study, an analysis was made of the energy consumption as wel as the average amount of energy required for the treatment of one m3 of wastewater. Possibilities for energy recovery using sludge as a renewable energy resource were analyzed. The data used for the analysis are based on real records from the WWTP after main reconstruction, in which the removal of nitrogen and phosphorus is carried out. The study provides an opportunity to assess the benefits of modernization and choice of technology for energy recovery from wastewater. The minimum amounts of energy R. K. Vladova, N. Vaklieva-Bancheva: Analysis of the Possibilities for Energy Recovery in WWTP 135. that can be recovered from one ton of dry organic matter by combustion and anaerobic digestion are 92.5 kWh, respectively and 52.5 kWh. The choice of which of these technologies would be more suitable for the respective site is a choice of management decision, which must take into account an analysis of investment costs. Acknowledgments This work has been supported by the Bulgarian Ministry of Education and Science under the National Research Programme “Young scientists and postdoctoral students” approved by DCM # 577 /17.08.2018. This work was realized thanks to the data provided by the WWTP in Kyustendil, Republic of Bulgaria. References Appels L., Baeyens J., Degreve J., Dewil R. (2008). Principles and potential of the anaerobic digestion of waste-activated sludge. Progress in energy and combustion science, 34(6), 755-781. doi: 10.1016/j.pecs.2008.06.002 Council Directive No. 91/271/CEE, 21 May 1991, regarding urban wastewater treatment. Chae K., Kang J. (2013). Estimating the energy independence of a municipal wastewater treatment plant incorporating green energy resources. Energy Conversion and Management, 75, 664-672, doi: 10.1016/j.enconman.2013.08.028 Fraia, S. Di., Massarotti, N., Vanoli L. (2018). A novel energy assessment of urban wastewater treatment plants. Energy Conversion and Management. 163, 304-313, doi:10.1016/j.enconman.2018.02.058 Longo S, d’Antoni B.M., Bongards M., Chaparro A., Cronrath A., Fatone F., Lema M.J., Mauricio-Iglesiasa M., Soarese A., Hospido A.( 2016). Monitoring and diagnosis of energy consumption in wastewater treatment plants. A state of the art and proposals for improvement. A ppl Energy, 179, 1251–1268. doi: 10.1016/j.apenergy.2016.07.043 McCarty, P.L., Bae, J., Kim, J. (2011). Domestic wastewater treatment as a net energy producerdcan this be achieved? Environ. Sci. Technol. 45, 7100-7106. doi: 10.1021/es2014264 Panepinto D., Fiore S., Zappone M., Genon G., Meucci L. (2016). Evaluation of the energy efficiency of a large wastewater treatment plant in Italy. Appl Energy,161, 404-411. doi: 10.1016/j.apenergy.2015.10.027 Vipin, S., Phuleria C. H., Chandel K. M. (2020). Estimation of energy recovery potential of sewage sludge in India: Waste to watt approach. Journal of Cleaner Production, 276, 122538, doi: 10.1016/j.jclepro.2020.122538 136 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. SUSTAINABILITY PROFIT GAINED BY THE OPTIMIZED CLAMPED BEAMS TOMAŽ ŽULA, STOJAN KRAVANJA, PRIMOŽ JELUŠIČ University of Maribor, Faculty of Civil Engineering, Transportation Engineering and Architecture, Maribor, Slovenia tomaz.zula@um.si, stojan.kravanja@um.si, primoz.jelusic@um.si Abstract The paper presents the optimization of the sustainability profit achieved by the production of clamped beams in civil engineering. It proposes to design a range of beams using three different material alternatives: structural steel, reinforced concrete and glulam. For this reason, three optimization models of beams are developed for the three materials. In addition, two different objectives are defined for each material alternative: for the economic profit and for the sustainability profit (which includes the eco costs of global warming). The proposed objectives are subject to the design, resistance and deflection constraints of the clamped beam, which are determined in accordance with the Keywords: specifications of Eurocodes 2, 3 and 5. The mixed-integer non- sustainability profit, linear programming (MINLP) approach is used to find most GHG emissions, advantageous material alternative of the beams. GAMS /Dicopt is optimization, used. The numerical example presented at the end of the paper mixed-integer non-linear clearly shows that reinforced concrete beams have the highest programming, economic and sustainability profit. MINLP DOI https://doi.org/10.18690/um.fkkt.2.2022.11 ISBN 978-961-286-598-6 138 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. 1 Introduction The paper deals with the optimization of the sustainability profit achieved by the production of clamped beams in the area of civil engineering. In this case, the sustainability profit is a sum of the economic profit and eco costs of global warming. It is assumed that a number of beams are designed using 3 different material alternatives: glulam, structural steel and reinforced concrete. The objective of this paper is to find the optimal design of the clamped beam subjected to the highest sustainability and economic profit, performed by mixed- integer non-linear programing approach. In the areas of sustainability and optimization, various optimization methods and different goals have been proposed. For example, Zaforteza et al. (2009) reported the optimization of CO2 emissions and production costs of concrete constructions using simulated annealing (SA). Camp and Huq (2013) proposed the calculation of optimal concrete frames with a hybrid big bang-big crunch algorithm (BB-BC), where the objective was to minimize the total cost or CO2 emissions. Alonso and Berdasco (2015) presented the carbon footprint calculations of some wood products. Li et al. (2017) introduced a topology optimization of welded box girders with minimal greenhouse gas emissions, where an improved ground structure method (IGSM) was applied. 2 MINLP model formulation Since the problem of clamped beam is the non-linear discrete-continuous optimization problem, the MINLP is used for the solution and can be formulated as follows: min sep= f (x, y) subjected to: ms (x, y) ≤ 0 s ∈ S x ∈ X = {x ∈ Rn: xLO ≤ x ≤ xUP} y ∈ Y ={0,1} m T. Žula, S. Kravanja, P. Jelušič: Sustainability Profit Gained by the Optimized Clamped Beams 139. where x are the continuous variables and y are the discrete (0, 1) variables. Function sep is the objective function for the economic profit and for the sustainability profit (which includes eco costs of global warming). ms (x, y) represents the design, resistance and deformation constraints. 3 Numerical example The example shows the optimization of 800 equal clamped beams. Each beam is 8.0 meters long, subjected to the combined effect of the dead-weight, the permanent load of 9.0 kN/m (g) and the imposed variable load of 12.0 kN/m (q), see Fig. 1. It is proposed to make each clamped beam from three different material alternatives: glulam, structural steel and reinforced concrete. At this point, the comparison and competitiveness between these 3 beam materials has been investigated for different material and dimensional variants and for 2 different objectives, i.e. for the optimization of sustainability and economic profit. For extensive and time-consuming optimization problems, we usual y use the program MipSyn (Kravanja, 2010). Since the optimization problem of the clamped beam is a single discrete non-linear problem, Dicopt (Grossmann, 2002) was chosen for the application. 6 different optimization models for the clamped beam (CLAMBOPT) were modeled as a combination between 3 various materials (wood, steel and concrete) and 2 various objective functions. GAMS (General Algebraic Model ing System), (Brooke et al., 1988), was employed for modeling and input/output interpretations. Each model consists of the input data (scalars), variables, and the objective function, which is subjected to the design, loading and dimensionig (in)equality constraints. These constraints were defined in accordance with the Eurocode standards: Eurocode 2 (2004) for concrete, Eurocode 3 (2005) for steel and Eurocode 5 (2004) for wood. The clamped beams were tested for bending moment, shear force and lateral torsional buckling. Vertical deflections were also checked. 140 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. g + q L=8.0 m Figure 1: Clamped beam. reinforced concrete timber steel h h h tw As ft b b b Figure 2: Cross sections of the clamped beam. The clamped girder super-structure contains of 3 different materials. The glulam girder super-structure comprises 131 rounded dimensional variations for the section height and 101 different rounded dimensional variation for the section width. The steel girder super-structure comprises eight different dimensional variations of standard steel plate thicknesses for flanges and webs separately, 1051 rounded dimensional variations for flange width and 1301 rounded dimensional variations for web height and three different steel grades. In addition, thirteen standard steel reinforcing bars, seven different concrete grades 101 rounded dimension variants for the section width (rounding up to whole centimeters) and 131 rounded dimension variants for the section height are involved in the concrete girder superstructure. The specified material and dimension variants (binary variables) result in 13 231 design variants for the wooden beam, 262 531 392 different design variants for the steel beam and 1 204 021 different design variants for the concrete beam. T. Žula, S. Kravanja, P. Jelušič: Sustainability Profit Gained by the Optimized Clamped Beams 141. 2 different objective functions were proposed for 2 different defined criteria. The 1st criterion of optimization comprises the maximization of the economic profit ( P EP [€]) of 800 identical beam structures. The economic profit is calculated as the sum of the self-manufacturing material, labor cost, sel ing price and overhead cost. The objective function was defined separately for 3 different materials, see Eq. (1). N is a number of clamped beams ( N = 800), C SP [€] is the sales price of a clamped beam, C MP j [€/kg] stands for the material unit prices of ( j∈ J: glulam, protection and impregnation paint for the wood beam; structural steel, gas consumption, electrodes and anticorrosion-resistant paint for the steel beam; and formwork slab-panels, concrete and steel reinforcing bars for the concrete beam). ρj [kg/m3] is the corresponding unit mass and Vj [m3] is the volume. While C LC i stands for the labor cost per hour [€/h], ti [h] is the time required for ( i∈ I: painting and impregnating of the glulam; welding, cutting and painting the steel beam; and curing, vibrating and placing the concrete, placing and cutting the reinforcement, and paneling the concrete beam), and f O is an indirect overhead cost factor ( f O = 2). For more details on the cost factors used in the economic objective function, see (Jelušič, 2017) and (Kravanja, 2017). max P EP= N∙ � C SP − C MP j∙ ρ ∙ V j j − C LC i∙ ti∙ f O� (1) The 2nd criterion is to maximize the sustainability profit ( P SP [€]), which is calculated for 800 beams as the sum of the economic profit and the eco costs of global warming caused by the beam production (EVR, 2018). The objective function was defined separately for 3 materials, see Eq. (2). C W (€/kg CO2 eq.) is a price of global warming, 0.116 €/kg CO2 eq. (EVR, 2018), ρm [kg/m3] and Vm [m3] are the corresponding units of mass and volume respectively, and f CO2 m is the emission factor of the carbon footprint ( m ∈ M; for the glulam beam, steel and reinforced concrete beam, respectively). The carbon footprint emission factor used in the study is 0.11–0.16 kg CO2 equivalent/kg for concrete, 2.43 kg CO2 equivalent/kg for steel reinforcing bars, 0.69 kg CO2 equivalent/kg for glulam and 1.72 kg CO2 equivalent/kg for steel. max P SP= P EP+ N∙�- C W∙ f ∙ ρ ∙V CO2 m m m� (2) 142 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. Table 1: Results of the clamped beam optimizations. Reinforced Laminated Criterion Concrete timber Steel C 50/60 GL24h S 235 Economic profit (€) 624,968 292,227 94,211 1.* b (cm) 32.0 41.0 27.9 h (cm) 45.0 41.0 41.9 Sustainability profit (€) 540,531 252,734 27,761 2.* b (cm) 32.0 41.0 27.9 h (cm) 45.0 41.0 43.9 * 1. Economic profit; 2. Sustainability profit Table 1 shows the optimization results for 2 different objective functions and 3 different materials. The results show that concrete beams have the highest economic and sustainability profit, while steel beams have the worst performance for all criteria. 4 Conclusion The paper presents the optimization of the sustainability profit achived by the production of clamped beams in the area of civil engineering. The optimal solutions are calculated based on 2 different objective functions, i.e. economic profit and sustainability profit. The optimizations of the beam alternatives are performed by the MINLP approach. The numerical example clearly shows that reinforced concrete girders have the highest economic and sustainability profit, while steel girders have the worst performance on all criteria. Acknowledgments This work was supported by the National Research Programmes of Slovenia P2-0268 and P2-0129. References Alonso, C.M., Berdasco, L. (2015). Carbon footprint of sawn timber products of Castanea sativa Mil. in the north of Spain. Journal of Cleaner Production, 102, 127-135. doi.org/10.1016/j.jclepro.2015.05.004 Brooke, A., Kendrick, D., Meeraus, A. (1988). GAMS - A User's Guide, Scientific Press, Redwood City, CA. Camp, C.V., Huq, F. (2013). CO2 and cost optimization of reinforced concrete frames using a big bang-big crunch algorithm. Engineering Structures, 48, 363-372. doi.org/10.1016/j.engstruct.2012.09.004 Eurocode 2. (2004). Design of concrete structures. European Committee for Standardization, Brussels. T. Žula, S. Kravanja, P. Jelušič: Sustainability Profit Gained by the Optimized Clamped Beams 143. Eurocode 3. (2005). Design of steel structures. European Committee for Standardization, Brussels. Eurocode 5. (2004). Design of timber structures. European Committee for Standardization, Brussels. Grossmann, I.E., Viswanathan, J. (2002). DICOPT - Discrete and Continuous Optimizer. Engineering Design Research Center (EDRC) at Carnegie Mel on University, Pittsburgh, PA. Jelušič, P., Kravanja, S. (2017). Optimal design of timber-concrete composite floors based on the multi-parametric MINLP optimization. Composite structures, 179, 285-293. doi.org/10.1016/j.compstruct.2017.07.062 Kravanja, S., Žula, T., Klanšek, U. (2017). Multi-parametric MINLP optimization study of a composite I beam floor system. Engineering structures, 130, 316-335. doi.org/10.1016%2Fj.engstruct.2016.09.012 Kravanja, Z. (2010). Challenges in sustainable integrated process synthesis and the capabilities of an MINLP process synthesizer MipSyn. Comput. Chem. Eng. 34(11), 1831-1848. doi.org/10.1016/j.compchemeng.2010.04.017 Li, B. Hong, J., Liu, Z. (2017). A novel topology optimization method of welded box-beam structures motivated by low-carbon manufacturing concerns. Journal of Cleaner Production, 142, 2792-2803. doi.org/10.1016/j.jclepro.2016.10.189 The Model of the Eco-costs / Value Ratio (EVR). (2018). Delft University of Technology, www.ecocostsvalue.com/. Accessed on: 23 Mar 2018. Zaforteza, I.P., Yepes, V., Hospitaler, A., Vidosa, F.G. (2009). CO2-optimization of reinforced concrete frames by simulated annealing. Engineering Structures, 31, 1501-1508. doi.org/10.1016/j.engstruct.2009.02.034 144 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS. 3RD INTERNATIONAL CONFERENCE ON TECHNOLOGIES & BUSINESS MODELS FOR CIRCULAR ECONOMY: CONFERENCE PROCEEDINGS SANJA POTRČ, MILOŠ BOGATAJ, ZDRAVKO KRAVANJA, ZORKA NOVAK PINTARIČ (EDS.) University of Maribor, Faculty of Chemistry and Chemical Engineering, Maribor, Slovenia sanja.potrc@um.si, milos.bogataj@um.si, zdravko.kravanja@um.si, zorka.novak@um.si Abstract The 3rd International Conference on Technologies & Business Models for Circular Economy (TBMCE) was organized by the Faculty of Chemistry and Chemical Engineering, University of Maribor in collaboration with the Strategic Research and Innovation Partnership - Networks for the Transition into Circular Economy (SRIP- Circular Economy). The conference was held virtually on December 15, 2020. TBMCE 2020 was devoted to presentations of circular economy concepts, technologies and methodologies that contribute to the shift of business entities and Keywords: society as a whole to a more responsible, circular management of circular resources. The conference program included panel discussions, economy, plenary and keynote sessions, oral and poster presentations on the sustainable development, following topics: Sustainable energy, Biomass and alternative raw processes and materials, Circular business models, Secondary raw materials and technologies, functional materials, ICT in Circular Economy, Processes and circular business models, technologies. The event was under the patronage of Ministry of research and Economic Development and Technology. development DOI https://doi.org/10.18690/um.fkkt.2.2022 ISBN 978-961-286-598-6 Document Outline 3.2 Analysis of alkali-activated samples 2.2 Fibres 4 Conclusions 2 MINLP model formulation 3 Numerical example ,max-,P-EP.=N∙,,C-SP.−,C-MPj.∙,ρ-j.∙,V-j.−,C-LCi.∙,t-i.∙,f-O... (1) ,max-,P-SP.=,P-EP.+N∙,,-C-W.,∙f-CO2m.∙,ρ-m.,∙V-m... (2) 4 Conclusion