Iskanje po repozitoriju

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Povzetek: The European Union’s shift towards a circular economy emphasizes the substitution of virgin materials with recycled alternatives, particularly in the construction sector, which can accommodate large volumes of industrial by-products. Ashes from coal, biomass, paper sludge, and co-combustion processes are abundant secondary materials whose variable chemical and mineralogical compositions necessitate careful assessment to enable safe and effective reuse.This study investigates the hydration behaviour and early carbonation potential of ashes of different origin. The ashes were characterized using X-ray fluorescence, X-ray diffraction, and scanning electron microscopy coupled with energy-dispersive spectroscopy. Hydraulic reactivity was evaluated by preparing ash pastes at a 1:1 water-to-ash ratio and monitoring hydration product formation over time using XRD. Carbonation of co-combustion ash was studied under controlled CO₂ conditions (2 % CO₂, 50 % RH, 20 °C ± 1 °C) at different moisture contents (0 wt.%, 10 wt.%, 20 wt.%, and 40 wt.%) and early curing times (0 hours, 1 hours, 4 hours, and 24 hours).Results indicate distinct differences among the ashes. Paper sludge ash exhibited the most extensive formation of calcium aluminate hydrates, coal and co-combustion ashes showed moderate hydration, while biomass ash produced only minor secondary phases. Carbonation of co-combustion ash proceeded concurrently with hydration, with lime depletion and calcite formation enhanced by higher moisture and longer curing. These coupled processes influenced both the kinetics and composition of hydration products. The findings demonstrate the potential of diverse combustion ashes for valorisation in construction materials and provide insight into their reactivity under early-age hydration and carbonation conditions, supporting circular economy initiatives.
Ključne besede: circular economy, ashes from combustion, hydraulic activity, carbonation, phase composition, amorphous phase
Objavljeno v DiRROS: 14.01.2026; Ogledov: 161; Prenosov: 87
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Povzetek: The content of leftover cement paste is a crucial parameter for determining recycled aggregates quality. Various methods assess this, including wet techniques (acid dissolution, chemical degradation, water absorption), physical approaches (freeze-thaw cycles, mechanical shredding, oven-dried density, thermal disaggregation), and spectroscopic or microscopy analyses. However, these methods often lack accuracy, are time-consuming, or depend on operator skill. A novel X-ray Powder Diffraction and Rietveld quantitative phase analysis approach is introduced to improve measurements precision. Results are compared with multi-scale analyses (microscopy, Xray computed tomography, mechanical testing) on recycled aggregate concrete specimens. Findings highlight a strong correlation between leftover cement paste content and key concrete properties, including microstructure, hydration products, and mechanical performance. This study confirms that leftover cement paste content is a decisive factor in recycled concrete aggregate properties, and that the proposed method offers a rapid and reliable approach to control this parameter.
Ključne besede: recycled concrete aggregate, leftover cement paste, CDW, X-ray diffraction, microstructure
Objavljeno v DiRROS: 27.08.2025; Ogledov: 465; Prenosov: 279
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Povzetek: In cold climates, concrete structures confront durability challenges due to harsh conditions. This study evaluates the effects of incorporating natural fibers, such as hemp and flax fibers (at 1 vol%), and partially replacing cement with fly ash (at 25 and 50 wt%) on the properties of cementitious composites subjected to accelerated aging under freeze-thaw cycles and deicing salts. Findings reveal that natural fibers enhance the freeze-thaw resistance, reducing deterioration (scaling) to 5-8% after 56 cycles. When mortars were subjected to accelerated freeze-thaw cycles, the compressive strength of plain mortar significantly decreased (up to 57%). However, adding natural fibers to the matrix substantially reduced its compressive strength loss. In the case of flexural strength, plain mortars experienced 33% loss, while hemp, flax, and polypropylene fiber mortars showed only 13%, 23%, and 10% losses, respectively. Furthermore, mortars experience a notable enhancement in their energy absorption capacity when reinforced with natural fibers, particularly with hemp fibers (up to 348% higher than plain mortar). Under harsh conditions, hemp and flax-reinforced mortars, with 25wt% fly ash replacement, lose the compressive strength significantly however still demonstrate an alternative to synthetic fibers in terms of flexural strength. Even with 25wt% of fly ash, mortars with natural fiber reinforcement display significantly superior energy absorption capacities compared to plain mortars (up to 48%).
Ključne besede: cementitious composites, natural fibers, freeze-thaw cycles, mechanical properties, mass loss, fly ash
Objavljeno v DiRROS: 23.12.2024; Ogledov: 1381; Prenosov: 527
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Povzetek: The EU prioritizes transitioning to a circular economy, aiming to boost sustainable resource management through policies promoting recycling and reuse, benefiting both the environment and the economy. Many successful case studies demonstrate using various incineration waste by-products (ashes) as substitutes for natural materials, yielding environmental advantages and showcasing sustainable resource management practices. While extensive literature covers ash characterization and applications, the direct links between the properties of the main components, the amorphous phase, and research findings remain elusive. Analysis predominantly centers on microstructural phase development, influencing mechanical, physical, and chemical properties and guiding research interpretations. Existing standards for ash use primarily address coal-derived fly ash, with SIST EN 13282-2 allowing alternative sources like circulating fluidized bed and paper sludge incineration residues. Yet, beyond this standard, no regulations mandate using different ash types. Nonetheless, the applicability of ashes for the geotechnical composite materials has already been confirmed in the field since numerous geotechnical projects have been carried out in Slovenia. Such composites have been recognized as beneficial practices, and the majority of them also possess legal permission for usage according to the Slovenian Technical Approvals. Given the varying value and complexity of ashes, detailed characterization before use is crucial. Assessing the recycling potential of different ashes requires a precise definition of basic properties such as microstructure, minerals, and chemical composition. Emphasis should be placed on characterizing the hydraulic properties and gaining detailed insights into the amorphous phase, ensuring informed decision-making regarding their recycling processes.
Ključne besede: waste by-products from incineration processes, ashes, recycling, amorphous phase, (latent) hydraulic properties, hydration
Objavljeno v DiRROS: 22.07.2024; Ogledov: 979; Prenosov: 689
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Povzetek: The Sitarjevec mine, located near the town of Litija (Central Slovenia), is recognized by the strong yellow colour of its dripstone structures and mine mud deposits. The mine mud, composed predominantly of goethite, accumulates on the ground of the mine shafts as the result of the interaction between percolating underground water, iron ore minerals and microorganisms. Since the accumulation of limonite mine mud is an ongoing process, larger quantities of mud have been deposited in the mine shafts since its closure. These deposits present a real threat of unleashing a mine mud spill on the town of Litija. Such a scenario has already previously occurred. In order to find new potential routes for recycling larger quantities of this mine mud, the present research work was performed to assess the use of mine mud as a pigment in the dye industry. In the first stage, the chemical (XRF) and microstructural (SEM) characteristics of the mine mud were defined together with the identification of its phase composition (XRD), particle size distribution and specific surface area (BET). Furthermore, the pigment was used to colour textile printing paste on a laboratory scale. To define the most appropriate quality of textile prints the rheological response of the various textile printing paste samples was investigated in terms of their plastic viscosity, indicating their suitability for use in textile printing. Test prints wereconducted, and the properties of leaching and fastness in the prints were assessed.
Ključne besede: mine mud, recycling, pigment, printing paste, textile, rheology
Objavljeno v DiRROS: 25.01.2024; Ogledov: 1426; Prenosov: 903
Celotno besedilo (9,29 MB)
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