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Abstract: 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.
Keywords: alkali-activated materials, biomass ash, sintered aggregates, lightweight aggregates
Published in DiRROS: 06.05.2026; Views: 66; Downloads: 63
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Abstract: This article reviews cold-bonded artificial aggregates (CBAAs) produced from industrial wastes such as bottom ash, fly ash, slags, sludges, and other waste-derived precursors. It provides a detailed examination of the factors influencing their performance and the treatments used to enhance their properties. CBAAs are broadly classified into two groups based on binder type: cement-based aggregates and alkali-activated aggregates (AAAs). Cementbased CBAAs develop their required properties through hydration and pozzolanic reactions. Reported compressive strengths typically range from 1 to 12 MPa, while water absorption ranges from 10 % to 25 %. These properties vary significantly with precursor type, mix proportions, curing conditions, and surface treatments. In AAAs, cement is replaced by an alkaline binder to provide a more environmentally sustainable alternative. The properties of AAAs result from the formation of N-A-S-H or C-A-S-H gels, with commonly reported compressive strengths between 2 and 8 MPa. Performance can be improved by selecting the appropriate precursor type and optimizing the ratio of precursor to alkaline activator. Carbonation further enhances the properties of CBAAs by reducing porosity by up to 30 %, increasing compressive strength by a factor of two to three, and capturing CO₂ through the formation of CaCO₃. Environmental assessments indicate that converting industrial waste into aggregates can lower greenhouse gas emissions and keep leaching parameters within regulatory limits. This review also identifies ongoing challenges, such as precursor variability, energy demand, and scaling production, and outlines future directions to support the commercial deployment of CBAAs.
Keywords: cold bonded artificial aggregate, recycling, properties, perspective
Published in DiRROS: 09.03.2026; Views: 204; Downloads: 154
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Abstract: The Geological Survey of Slovenia (GeoZS), with the assistance of the ENALOS Research and Development (ENALOS), the Slovenian National Building and Civil Engineering Institute (ZAG) and the Katholieke Universiteit Leuven (KUL), has compiled a report documenting the demonstration and application phase of the project. This report contains a technical analysis on the materials produced as well as an economic analysis, and thus more accurately calculates the financial benefits of the technology.
Keywords: odpadni materiali, waste materials, alkalijsko aktivirani materiali, alkali activated material, trajnostni pristop, sustainable approach, jeklarska žlindra, steel slag, rdeče blato, red mud
Published in DiRROS: 15.01.2026; Views: 514; Downloads: 0
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Abstract: Mineral CO2 sequestration is a promising carbon capture and storage approach based on the chemical reaction of CO2 with alkaline materials containing Ca- and Mg-rich (hydr)oxides and silicates. This results in the formation of relatively insoluble and storable carbonates. This study investigates six ashes of different origins and chemical compositions to assess their CO2 sequestration potential and leaching behavior, offering insights into their environmental impact and potential risks. The carbonation experiments were conducted under controlled laboratory conditions and the CO2 sequestration capacity was quantified using a pressure calcimeter, supported by thermogravimetric analysis. Wood ashes and ash from the co-combustion of biomass from a paper mill showed the highest carbonation potential, with CO2 sequestration capacities between 344.8 and 432.3 g CO2 per kg of ash and carbonation efficiencies between 82.4 % and 94.4 %. In addition to the high sequestration capacity of the ashes, carbonation was found to affect the leaching behavior of the ash in the environment by changing its mineralogical composition. The process consistently reduced pH and generally decreased the leaching of certain trace elements, except for Mo, and Cr. Nevertheless, the reduction in the leachability of several elements suggests a partial environmental benefit of carbonation. The findings highlight the dual functionality of the carbonation: it provides a viable route for the permanent binding of CO2 and can enhance the stabilization of industrial residues. However, the persistence of metal leaching indicates that its overall effectiveness in mitigating environmental risks associated with residue disposal or reuse remains material-dependent.
Keywords: enforced carbonation, maximum sequestration capacity, leaching, heavy metals, mineralogy, bio-based ash
Published in DiRROS: 13.01.2026; Views: 305; Downloads: 271
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Abstract: The dataset contains measurements of thermally treated and non-thermally treated alkali-activated aggregates produced from co-incineration biomass ash. It includes data on ash characterization, mechanical performance, thermal behavior, microstructural properties, and the chemical and mineralogical composition of the produced aggregates. This dataset supports the findings presented in the article "Effect of alkali-activation pre-treatment of sintered aggregates from biomass fly ash on microstructural and mineralogical evolution" (https://doi.org/10.1016/j.ceramint.2026.03.041).
Keywords: alkali-activated materials, sintering, lightweight aggregates, thermal treatment
Published in DiRROS: 24.11.2025; Views: 351; Downloads: 209
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