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Abstract: The study investigates alkali-activated fly ash (FA) composites reinforced with keratin-based fibres from Chesapeake Bay Retrievers. To increase reactivity, the FA was milled and sieved below 125 μm, while the fibres were incorporated at two mass ratios (1 m% and 5 m%) relative to the FA as part of the preliminary study. Mechanical tests on 3-day-old composites showed that the addition of 1 m% fibres improved performance significantly, increasing the compressive strength by almost 50% (to ~70 MPa) and bending strength by over 30%. In contrast, the addition of 5 m% fibres resulted in a “hairy”, low-binder structure with reduced geometric density and compressive strength. Nevertheless, the fibre- rich composite displayed a unique cushioning effect that restored shape under cyclic pressure, suggesting potential for non-structural applications such as pathways or insulation. The results demonstrated that small additions of keratin fibres can improve the performance of AAM, but excessive fibre content compromises its strength.
Keywords: alkali-activated materials, fly ash, keratin-based fibres, Chesapeake Bay Retriever, circular economy
Published in DiRROS: 15.05.2026; Views: 39; Downloads: 28
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Abstract: This study deals with the mechanical and microstructural characterization of geopolymers synthesized from locally available fly ash. A low calcium fly ash was activated using a sodium silicate solution. Samples were characterized by means of flexural and compressive tests, Fourier Transform Infrared (FTIR) spectroscopy, X-ray powder diffraction (XRD), and scanning electron microscopy(SEM). Porosity and pore size distributions were identified using mercury intrusion porosimetry and gas sorption. The compressive strength of the produced geopolymers, which is in the range of 1.6 to 53.3 N/mm2, is strongly related to the water content as well as SiO2/Na2O mass ratio of an alkali activator. The compressive strength significantly increased with decreases in the water content and increased silicon concentration used for the synthesis of geopolymers.
Keywords: geopolymers, fly ash, microstructure, mechanical properties
Published in DiRROS: 05.09.2025; Views: 781; Downloads: 371
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Abstract: 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%).
Keywords: cementitious composites, natural fibers, freeze-thaw cycles, mechanical properties, mass loss, fly ash
Published in DiRROS: 23.12.2024; Views: 1632; Downloads: 673
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Abstract: Aggregates made from fly ash have been developed by means of the cold-bonding process, with the addition of Portland cement as a binder at (10, 20, and 30) % of mass fractions, and by pouring the mixtures into moulds. After curing for 28 d the samples were processed into aggregate by crushing and sieving. An aggregate containing a weight percentage of 10 % of cement was additionally produced by pelletization on a granulating plate. The density, water-adsorption capacity, porosity, compressive strengths, and frost resistance of the samples were determined. The aggregates prepared by both routes were then used to make concrete samples, whose properties were then compared to those of conventional concrete made using limestone aggregate. The compressive strength of the concrete made with the granulated aggregate reached 16.0 MPa after 28 d, whereas that of the concrete made with crushed aggregate amounted to 24.1 MPa, and that of the conventional concrete was 34.6 MPa.
Keywords: fly ash, lightweight aggregates, density, compressive strength, frost resistance
Published in DiRROS: 14.08.2024; Views: 1227; Downloads: 749
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Abstract: Human activities have caused an enormous rise of the CO2 concentration in the Earth’s atmosphere over the past 200 years. In order to alleviate this problem, the threats to and the concerns of the international community need to be converted into economic opportunities for national economies, which shall develop and utilize technological opportunities rather than simply accepting international obligations to reduce CO2 emissions. In the article we analyze technological possibilities in the Slovenian context as possible opportunities for promoting sustainable development based on regional, renewable resources. Beginning with an analysis of the amine process for CO2 concentration and its possibilities, we continue with CO2 chemistry examples, like the precipitation of calcium carbonate from Ca++ sources like lime or fly ash. Through the concept of product engineering we emphasize the need for a stepwise realization from the laboratory to a pilot plant and then to the industrial scale. The growth of biomass through forestry or algae production can provide an additional CO2 sink. However, for an efficient technical solution and implementation a close working relationship between biologists and engineers is required.
Keywords: CO2 minimization, technological opportunities, amine concentration, CO2 chemistry, forestry, algae production, fly ash CO2 absorption
Published in DiRROS: 05.08.2024; Views: 1019; Downloads: 893
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