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Povzetek: The increasing demand for lightweight construction materials and the depletion of natural aggregates highlight the need for circular solutions based on industrial residues. Co-incineration biomass ash (BA), despite its high availability, carbon content, and variable composition, remains underutilised in high-value applications. This study explores a previously unexamined valorisation route through the production of sintered alkali-activated aggregates using sodium-silicate-assisted pre-treatment. Two BA mixes with different Na2O dosages (7.57 and 5.44 wt% Na2O) were pelletized and thermally treated between 700 and 1200 ◦C. The alkali activation pretreatment simultaneously improved the granulation efficiency, enabled the formation of alkali-activated gel, and supplied Na2O as a flux, significantly influencing the crystalization, melting, and sintering behavior. Comprehensive characterisation using mercury intrusion porosimetry, dilatometry, X-ray diffraction, Fouriertransform infrared spectroscopy, thermogravimetry–differential thermal analysis, and scanning electron microscopy revealed a coherent thermal sequence: from gel deterioration and a macroporosity development below 800 ◦C, to the crystallization of Ca–Mg silicates and the formation of an akermanite-dominated matrix at 800–1000 ◦C, followed by partial melting and sintering in the presence of a liquid phase above 1000 ◦C. A higher alkali content promoted earlier densification and strength development. Aggregates with higher Na2O content (BA1) exhibited an earlier onset and higher intensity of sintering shrinkage, reaching a compressive strength of 4.53 MPa at 1100 ◦C, corresponding to more than a fourfold increase compared to thermally untreated aggregates, whereas the lower-alkali mix (BA2) remained below 0.26 MPa at the same temperature. Open porosity of BA1 aggregates increased to 78.8% after heating to 800 ◦C due to deterioration of the alkali-activated gel, followed by densification accompanied by akermanite-dominated crystallization and pore coalescence, resulting in 73.1% porosity and a bulk density of 1.28 g/cm3 at 1100 ◦C. The results identify BA as a promising precursor for lightweight or dense SAA and demonstrate alkali-activation-assisted thermal treatment to be a technically applicable circular-economy pathway for converting co-incineration BA into value-added construction materials.
Ključne besede: alkali-activated materials, biomass ash, sintered aggregates, lightweight aggregates
Objavljeno v DiRROS: 06.05.2026; Ogledov: 65; Prenosov: 62
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Povzetek: The crystal structure and the pressure-mediated crystal-fluid interaction of mesolite have been re-investigated by a multi-methodological approach, based on single-crystal neutron diffraction and by in-situ single-crystal synchrotron X-ray diffraction, using a diamond anvil cell. The structure refinement based on neutron intensity data collected at 20 K confirms the general model previously reported for mesolite, but largely improves the description of the hydrogen-bond network (with accurate sites location, their libration regime and interactions). Twelve out of the nineteen oxygen sites in the crystal structure of mesolite are involved in H-bonds as donors or as acceptors, reflecting the complex configuration of the H-bonding network. In the high-pressure investigations, four different pressure-transmitting fluids have been employed: the non-penetrating Daphne oil 7575 and the potentially penetrating methanol:ethanol:H2O (1:1:1) mixture, distilled H2O and liquid Ne. The Daphne oil 7575 experiment provided insight into the intrinsic compressional behaviour of mesolite, without any pressure-induced crystal-fluid interaction, yielding an isothermal bulk modulus KV0 = 55.9(7) GPa (βV0 = 0.0179(2) GPa−1). In the aqueous mixtures, H2O molecules have been observed to continuously penetrate into the structural cavities, firstly in the natrolite- and then in the scolecite-type sheets, in the pressure range 0.8–1.9 GPa. By comparing the results of this study to the literature data, there is an apparent correlation between the pressure at which the adsorption process occurs and the H2O concentration of the pressure-transmitting medium: a higher H2O fraction allows the over-hydration of the scolecite-type sheets at lower pressures. When compressed in liquid Ne, atoms of neon appear to be able to penetrate into the natrolite-type sheets, interacting with the extra-framework population via weak van der Waals forces.
Ključne besede: zeolite, mesolite, single-crystal neutron diffraction, high pressure, compressibility, cristal-fluid interaction
Objavljeno v DiRROS: 10.04.2026; Ogledov: 163; Prenosov: 53
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Povzetek: This study explores the properties of supplementary cementitious materials (SCMs) obtained from the under-calcining thermal reactivation of construction and demolition waste fines (CDW) and of pure hydrated cement pastes (HCPs) derived from different commercial cements (CEM I, CEM II, CEM III, and CEM IV, classified according to EN 197–1). Samples were thermally treated at 350 ◦C (low-energy activation) and 600 ◦C (high-reactivity optimization) to increase pozzolanic and/or hydraulic behavior without inducing CO₂ release from calcination. Phase transformations were analyzed by X-ray Powder Diffraction with Rietveld refinement, thermal behavior by TGA/DTA, and morphological evolution by SEM, while reactivity and hydration kinetics were assessed using isothermal calorimetry. Results indicate pronounced differences in thermal response among the HCPs and CDW, governed by their specific phase assemblages and initial SCM content (limestone, slag, and pozzolans). At the selected under-calcining high-reactivity temperature (600 ◦C), γ-C₂S formation is favored. Thermal reactivation of slag-rich cement (CEM III) yielded the most reactive circular SCM, combining both high hydraulic (260 J/g - EN 196–11) and pozzolanic (329 J/g - ASTM C1897–20) performances with reduced carbon impacts.
Ključne besede: secondary scms, thermal reactivation, hydrated cement, clinker minerals
Objavljeno v DiRROS: 09.04.2026; Ogledov: 129; Prenosov: 103
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Povzetek: This study investigates the thermal behaviour of two opaque and one transparent thin intumescent coating at material level (coating only) and system level (coating applied at real scale on timber), and their effects on timber in fire. Micro-scale tests were conducted to examine the underlying mechanisms of intumescence and degradation for each coating individually, while bench-scale tests demonstrated how these behaviours translate to larger scales. Critical temperature and heat flux thresholds were identified at which the coatings begin to insulate the timber through the formation of the intumescent char layer, as well as those marking degradation of the layer and the reduction of its insulating efficacy. The findings highlight that coating type and thickness, heating conditions and exposure duration influence mass retention, swelling pattern, and the integrity of the intumescent char layer. Overall, the transparent coating exhibited lower durability than the opaque ones. It was also shown that, due to the similar temperature ranges of timber pyrolysis and coating swelling, timber degradation occurs close to the coated surface during the transient swelling process, resulting in a heated region of 15- 20 mm with negligible mechanical properties by the end of swelling. Therefore, intumescent coatings provide insulation progressively rather than immediately.
Ključne besede: mass timber, thin intumescent coatings, swelling, fire testing, charring, fire safety
Objavljeno v DiRROS: 08.04.2026; Ogledov: 99; Prenosov: 91
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Povzetek: A new type of slate-mimicking roofing tile based on the alkali-activation of an Fe-rich slag has been developed. The main scientific contribution lies in the targeted valorisation of Fe-rich slag for thin, slate-like roofing elements that must satisfy strict roofing-specific requirements, including a limited thickness, low permeability, freeze–thaw resistance, dimensional stability, and high surface quality. Achieving the required properties and optical appearance necessitated a double-layer setup, where a fibre layer primarily provided the required mechanical properties, while a surface layer ensured the desired optical appearance. The microstructure of the produced roofing tiles was analysed using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS) and Hg-porosimetry (MIP), and was compared to reference products on the market. A life cycle assessment (LCA) indicates that the current laboratory-scale production cannot yet compete with established market solutions; however, projected improvements in curing energy efficiency at industrial scale suggest strong potential for environmental competitiveness. Hence these roofing tiles could become an environmentally friendly alternative to current roofing materials. Additionally, a demonstration roof was installed to monitor the long-term performance of the roofing tiles over several years under real seasonal exposure.
Ključne besede: slag, roofing tiles, slate like tiles, performance
Objavljeno v DiRROS: 07.04.2026; Ogledov: 165; Prenosov: 108
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