1. Ultravisokozmogljivi beton z bazaltnimi vlakni ter samočistilnimi in luminiscenčnimi površinamiAndrej Ivanič, Ahmad Rizwan Mumtaz, Natalija Bede Odorčić, Núria Garro, Samo Lubej, Antonio Comite, Marcello Pagliero, Nikolina Škrilec, Gregor Kravanja, 2026, original scientific article Abstract: Raziskava obravnava razvoj ultravisokozmogljivega betona (UHPC), zasnovanega na optimizirani cementni matriki z nizkim vodovezivnim razmerjem, doseženim z metodo mokrega zgoščanja delcev. V mešanico je bil dodan 1 vol.% bazaltnih vlaken, ki so bistveno izboljšala duktilnost materiala, zmanjšala njegovo krhkost ter učinkovito premoščala nastale razpoke. Analiza SEM-EDS je potrdila homogeno razporeditev vlaken in njihovo dobro vez s hidratacijsko matrico. Razvita mešanica je dosegla tlačno trdnost 138,5 MPa in upogibno trdnost 12,5 MPa, kar kljub delni nadomestitvi cementa z metakaolinom potrjuje zelo visoko mehansko zmogljivost UHPC. Za pridobitev dodatnih multifunkcionalnih lastnosti, kot sta izrazita vodoodbojnost in luminiscenčno emitiranje svetlobe, je bila uporabljena dvoslojna biomimetična površinska obdelava na osnovi nanodelcev SiO2 in luminiscenčnega prahu. Preizkusi omočenja so pokazali stabilno superhidrofobnost s kontaktnimi koti do 154,9°, luminiscenčni sloj pa je omogočil oddajanje vidne zelene svetlobe pri približno 520 nm. Rezultati potrjujejo, da sinergija optimizirane UHPC-matrice, bazaltnih vlaken in funkcionalnih površinskih slojev pomembno razširja uporabnost betona, zlasti pri trajnostno zasnovanih elementih, kjer sta nadzor razpok in zaščita pred vodo ključnega pomena, hkrati pa je zagotovljena pasivna nočna vidljivost brez zunanjega vira energije.
Keywords: ultravisokozmogljivi beton, UHPC, bazaltna vlakna, metakaolin, metoda mokrega zgoščanja delcev, superhidrofobnost, luminiscenca
Published in DiRROS: 24.04.2026; Views: 115; Downloads: 114
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2. Alkali-activated materials from diverse solid precursors : structural, mechanical and radiological propertiesNataša Mladenović Nikolić, Marija Ivanović, Snežana B. Nenadović, Jelena Potočnik, Sabina Dolenec, Dušan Bučevac, Aleksandar Kandić, Ljiljana Kljajević, 2026, original scientific article Abstract: This study investigates the gel characteristics of alkali-activated materials (AAMs) synthesized using wood ash (WA), and metakaolin (MK) as solid precursors. The research explores the influence of precursor type and sodium hydroxide (NaOH) concentrations in the alkali activator solution on the resulting physicochemical, microstructural, mechanical, and radiological properties of gels. The alkaline activators were prepared by mixing sodium hydroxide solutions (6 M and 12 M) with a sodium silicate (water glass) solution at a volume ratio of 1.5. The physicochemical characteristics of raw materials and AAMs were thoroughly analyzed using X-ray fluorescence (XRF), Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM) with EDS elemental mapping. FTIR analysis confirmed the formation of an amorphous gels geopolymer network. XRD revealed the presence of characteristic crystalline phases (quartz, calcite) within an amorphous matrix. Mechanical properties, such as compressive strength, depended on precursor type and alkali molarity: metakaolin (12 M) reached ~14 MPa, while wood ash showed ~4 MPa (6 M) and ~0.5 MPa (12 M) due to high CaO, low Si and Al, and unfavorable SiO2/Al2O3 (5.71) and Na2O/Al2O3 (3.19) ratios. Furthermore, this research estimates radiological doses by quantifying radionuclide content via gamma-spectrometry. Alkali activation significantly reduced radiological haz- ard parameters, with radium equivalent activity (Raeq) decreasing to 238.0 Bq/kg and the external hazard index (Hex) to 0.643 for A12MK, while the annual effective dose rate for A12WA was only 0.265 nSv/y-all values remaining well below the recommended safety limit of 370 Bq/kg (≤1 mSv/y). The decrease in activity concentration index (Iγ), Raeq, and Hex with increasing NaOH concentration indicates effective radionuclide immobilization within the geopolymer matrix, confirming the suitability of these alkali-activated materials for safe use in construction from a radiation protection perspective.
Keywords: wood ash, metakaolin, alkali-activated materials, radionuclides
Published in DiRROS: 24.03.2026; Views: 196; Downloads: 160
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3. Enhancing densification of metakaolin-based geopolymers via the cold sintering processAbdullah Jabr, Srečo D. Škapin, Sara Tominc, Nina Daneu, Jakob Koenig, Vilma Ducman, Lidija Korat Bensa, Raúl Bermejo, Matjaž Spreitzer, 2025, original scientific article Abstract: Clay-based materials typically require high-temperature processing (>900 ◦C), resulting in high energy consumption. This study explores cold sintering of metakaolin (MK) powders to achieve high mechanical strength at significantly lower processing temperatures. By applying uniaxial pressure of 400 MPa and heating to only 240 ◦ C in the presence of 15 mol/L NaOH solution, successful densification of structurally sound and dense samples with an average density of 2.16 g/cm³ and a biaxial flexural strength of ~35 MPa was achieved. This strength surpasses that of conventionally sintered MK (1470 ◦C) by ~30 %. Densification was found to be governed by synergistic mechanisms involving MK exfoliation, conformal sintering around aggregates, and the precipitation of an amorphous sodium aluminosilicate hydrate phase. Crack formation was avoided through process optimization and verified using X-ray micro-computed tomography. These findings offer new insights into the chemo- mechanical mechanisms of cold sintering and demonstrate its potential as an efficient route for producing structural materials.
Keywords: cold sintering, metakaolin, geopolymer, delaminations, exfoliation
Published in DiRROS: 15.10.2025; Views: 534; Downloads: 273
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4. Rapid immobilisation of chemical reactions in alkali-activated materials using solely microwave irradiationAnže Tesovnik, Barbara Horvat, 2024, original scientific article Abstract: Efflorescence, a time-dependent and water-driven phenomenon, is a major concern inalkali-activated materials (AAMs), impacting their practical use and preservation in a time-frozen state for post-characterisation. Although a method for stopping chemical reactions in conventional cements exists, it is time-consuming and not chemical-free. Therefore, this study explored the effects of low-power microwave-induced dehydration on efflorescence, mechanical performance, and structural integrity in AAMs, to create an alternative and more “user-friendly” dehydration method. For this purpose, several mixtures based on secondary raw (slag, fly ash, glass wool, and rock wool) and non-waste (metakaolin) materials were activated with a commercial Na-silicate solution in ratios that promoted or prevented efflorescence. Characterisation techniques, including Fourier-transform infrared spectroscopy and X-ray diffraction, showed that microwave dehydration effectively removed water without altering crystallinity, while mercury intrusion porosimetry and compressive strength tests confirmed increased porosity. In addition to being an efficient, time-saving, and solvent-free manner of stopping the reactions in AAMs, microwave irradiation emerged as an innovative, chemical-free method for evaluating curing finalisation and engineering foams in a stage when all other existing methods fail. However, the artificially provoked efflorescence in aged dehydrated AAMs connected the slipperiness of AAM with the instant extraction of Na, which raised the need for further research into alternative alkali replacements to evaluate the practical use of AAM.
Keywords: materials chemistry, alkali-activated materials, geopolymers, slag, fly ash, rock wool, glass wool, metakaolin, microwave irradiation, dehydration, stopping chemical reactions, efflorescence
Published in DiRROS: 23.12.2024; Views: 1335; Downloads: 853
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5. Dehydration with microwave irradiationAnže Tesovnik, Barbara Horvat, 2024, complete scientific database of research data Abstract: The dataset supports the results shown in the tables and figures in the article entitled “Rapid immobilisation of chemical reactions in alkali-activated materials using solely microwave irradiation” (doi: https://doi.org/10.3390/min14121219). It contains measurements of mechanical and structural evaluation, as well as chemical and mineralogical analysis.
Keywords: measurments, alkali-activated materials, geopolymers, slag, fly ash, rock wool, glass wool, metakaolin, microwave irradiation, dehydration, stopping of chemical reactions, efflorescence
Published in DiRROS: 12.08.2024; Views: 1660; Downloads: 11768
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6. Adsorption efficiency of cadmium (II) by different alkali-activated materialsNataša Mladenović Nikolić, Ljiljana Kljajević, Snežana B. Nenadović, Jelena Potočnik, Sanja Knežević, Sabina Dolenec, Katarina Trivunac, 2024, original scientific article Abstract: The objective of this study was to demonstrate the potential utilization of fly ash (FA), wood ash (WA), and metakaolin (MK) in developing new alkali-activated materials (AAMs) for the removal of cadmium ions from waste water. The synthesis of AAMs involved the dissolution of solid precursors, FA, WA, and MK, by a liquid activator (Na2SiO3 and NaOH). In concentrated solutions of the activator, the formation of an aluminosilicate gel structure occurred. DRIFT spectroscopy of the AAMs indicated main vibration bands between 1036 cm−1 and 996 cm−1, corresponding to Si-O-Si/Si-O-Al bands. Shifting vibration bands were seen at 1028 cm−1 to 1021 cm−1, indicating that the Si-O-Si/Si-O-Al bond is elongating, and the bond angle is decreasing. Based on the X-ray diffraction results, alkali-activated samples consist of an amorphous phase and residual mineral phases. The characteristic “hump” of an amorphous phase in the range from 20 to 40◦ 2θ was observed in FA and in all AWAFA samples. By the XRD patterns of the AAMs obtained by the activation of a solid three-component system, a new crystalline phase, gehlenite, was identified. The efficiency of AAMs in removing cadmium ions from aqueous solutions was tested under various conditions. The highest values of adsorption capacity, 64.76 mg/g (AWAFA6), 67.02 mg/g (AWAFAMK6), and 72.84 mg/gmg/g (AWAMK6), were obtained for materials activated with a 6 M NaOH solution in the alkali activator. The Langmuir adsorption isotherm and pseudo-second kinetic order provided the best fit for all investigated AAMs.
Keywords: fly ash, metakaolin, wood ash, adsorption kinetics, cadmium (II)
Published in DiRROS: 23.05.2024; Views: 2607; Downloads: 1038
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7. Influence of ammonium polyphosphates and 2,4,6-triamino-1,3,5-triazine on the mechanical-physical properties of polyurethane and alkali-activated materialsBranka Mušič, Barbara Horvat, 2024, published scientific conference contribution Abstract: In building constructions, the tendency towards an ever-better material directs us to composite materials. In this work, we prepared an organic-organic and organic-inorganic composite material by incorporating fire retardants, ammonium polyphosphates, and 2,4,6-triamino-1,3,5-triazine, into a polyurethane network and an aluminosilicate network (ASN) of alkali-activated material. Polyurethane foams (PUR) are well-known materials that, due to their properties, such as low weight-to-strength ratio, low electrical and thermal conductivity, flexibility, and relatively simple preparation process, are used in various industries, also in the construction industry, e.g., for thermal insulation of windows and doors or fixing and sealing joinery. Opposite, the ASN of alkali-activated metakaolin, successfully paves the way for new applications, such as high-temperature protection. In this paper, these interactive properties of prepared composites are studied using thermal testing and mechanical analysis. It was found that inhibitors significantly increase the fire resistance of PUR systems while they slightly reduce the mechanical properties. Incorporating polymer flame retardant into ASN in building products, such as façade panels , can decrease the mechanical properties but can offer the non-flammable building envelope not get heated from burning surroundings, i.e., not becoming a convection heat source, but rather represent a fire-distinguisher for flammable materials.
Keywords: flame retardants, polyurethane, alkali activated material, metakaolin, microwave irradiation, mechanical strength
Published in DiRROS: 12.03.2024; Views: 4365; Downloads: 1039
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8. Waste rubber incorporated in the alkali-activated metakaolin’s aluminosilicate network enhanced by microwave irradiationBarbara Horvat, Branka Mušič, 2024, published scientific conference contribution Abstract: Building materials represent the possibility of prolonging the life of waste materials. The key is to ensure that the products are suitable for their function. So we activated metakaolin with the alkaline Na-silicate solution in the ratio that ensures the prevention of efflorescence and high mechanical strength (Horvat and Ducman, 2019). As the waste material (to be incorporated in the aluminosilicate network (ASN) of the alkali-activated metakaolin) ground waste rubber from electric cables was used in the preselected mass ratios. Its inclusion in products, like paving stones, can reduce stiffness, improve durability, dampen vibrations, and reduce road noise. The mechanical strengths of test samples with rubber present on the active surface or slightly below were higher compared to samples where rubber was encapsulated throughout the volume. Compressive strength was higher when samples were irradiated with low powers of microwaves while irradiation with higher powers led to the foaming of alkali-activated slurry. The encapsulation quality of the ground rubber was evaluated by SEM while the chemical influence on ASN was determined by EDS, FTIR, and XRD. Slipperiness change on the active surface of pavement stones proved that the addition of the ground rubber enhanced the walking safety of the product.
Keywords: secondary raw material, alkali activated material, waste rubber, metakaolin, encapsulation of organic in inorganic material, microwave irradiation, mechanical strength
Published in DiRROS: 12.03.2024; Views: 3416; Downloads: 1174
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9. Thermal insulation and flammability of composite waste polyurethane foam encapsulated in geopolymer for sustainable building envelopeBarbara Horvat, Nataša Knez, Uroš Hribar, Jakob Koenig, Branka Mušič, 2024, original scientific article Abstract: Polyurethane foam (PUR) is a lightweight, thermally insulating, widely used, and highly flammable material that has after its use an adverse effect on the environment, i.e., PUR disposal is considered hazardous. Its flammability can be mitigated using various fire retardants, but they do not change the hazardous nature of waste PUR. Therefore, in the current study, waste PUR with and without flame retardants based on N and P was incorporated into a geopolymer, the alkali-activated material (AAM) based solely on metakaolin, to evaluate the potential recycling route of waste PUR while taking into account its flammability, so it can enter safely into the circular economy through the building industry. To enhance the mechanical properties of the composite, a fresh mixture was irradiated with microwaves. However, the irradiation of geopolymer containing PUR negatively influenced mechanical performance, which led to the evaluation of the behaviour of the complex dielectric constant of PUR and fire retardants. Materials and composites were evaluated regarding their chemistry, mineralogy, microstructure, and porosity to connect the structure with extrinsic properties like geometrical density, thermal conductivity, and fire properties. Nonetheless, positive influences of PUR being encapsulated in the geopolymer were lowered density (from 1.8 to 1.6 kg/l) and improved thermal insulation ability (from 940 to 860 mW/(m·K)) of the composites: with the inclusion of <5 % of PUR, thermal insulation improved by nearly 10 %. However, the contribution of PUR to the composite originated from its skeleton, which has more than 15 times bigger geometrical density (0.81 kg/l) compared to the density of the skeleton (0.047 kg/l). This offers an open field for further advancements of thermal properties, but would also lead to a decrease of the compressive strength, which was already lowered from 90 MPa for 30 % with <5 % of added grated PUR. Furthermore, the flammable nature of PUR and its other drawbacks can be controlled by permanent embedding in the noncombustible structure of geopolymer, making the envelope of sustainable buildings green and safer. Overall, including grated waste PUR in geopolymer represents a promising, easy, cost-effective recycling path with low energy consumption, where the composite cannot develop fire on a scale of pure PUR, even in the worst-case scenario, but only if the composite is designed in a way, that flammable materials cannot join flames during their combustion. This paper gives prospects to other flammable waste materials to be safely used in the circular economy, and to porous materials to shape properties of the composite by their intrinsic and/or extrinsic properties.
Keywords: waste polyurethane foam, polymeric flame retardants, alkali activated material, metakaolin, microwave irradiation, thermal-fire behaviour, mechanical strength
Published in DiRROS: 01.03.2024; Views: 3488; Downloads: 1955
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10. PUR in geopolymerBarbara Horvat, Nataša Knez, Uroš Hribar, Jakob Koenig, Branka Mušič, 2024, complete scientific database of research data Abstract: The dataset supports the results shown in the tables and figures in the article entitled “Thermal insulation and flammability of composite waste polyurethane foam encapsulated in geopolymer for sustainable building envelope” (doi: 10.1016/j.jclepro.2024.141387). It contains measurements of fire-behaviour characteristics, thermal conductivity, the behaviour of the material in the electromagnetic field in relation to the frequency, mechanical and structural evaluation, as well as chemical and mineralogical analysis.
Keywords: measurements, waste polyurethane foam, polymeric flame retardants, alkali activated material, metakaolin, microwave irradiation, thermal-fire behaviour, mechanical strength
Published in DiRROS: 20.02.2024; Views: 7391; Downloads: 678
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