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Abstract: Two synthesis pathways (one- and two-part) in alkali-activated binders were compared using ground granulated blast furnace slag (GGBFS), mineral wool (MW) activated using dry and liquid alkali activators with similar Na2O/SiO2 modulus. The effect of activator type on reaction kinetics, strength development, setting times, and durability shows that one-part synthesis does not only improve early strength, but also provide better durability properties. While the highest compressive strength (56 MPa, 90 days) was achieved for the one-part mix (DM), the reaction products (presence of Mg–Al layered double hydroxide and C–S–H-like phases) observed for both mortar mixes were similar. The DM mortars showed better resistance to sulfate attack than two-part mix (WM) mortars and sets faster. The results highlight the significance of the one-part pathways in the synthesis of alkali-activated materials.
Keywords: recycling, alkali activated material, mineral wool
Published in DiRROS: 11.03.2024; Views: 106; Downloads: 76
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Abstract: Mineral wool, i.e. rock and glass wool, represents considerable challenge after its functional-time runs out due to its small density leading to large volume consumption during transport and in landfills where it usually ends. Because rock wool is mineralogically and chemically a promising precursor material for alkali-activation, it was milled from few centimetres-decimeters long fibres to micron-sized fibres. Since fibres in alkali-activated materials generally show an increase in mechanical strength, especially the bending strength, 1 m% of additional fibres (basalt, cellulose (2 types), glass, polypropylene, polyvinyl alcohol and steel fibres) was used in the alkali mixture, that was curred at 40 °C for 3 days. Time dependence of the mechanical strengths of alkali- activated materials with and without additional fibres was followed. Maximal increase of compressive and bending strength after 28 days was reached with polypropylene fibres, i.e. it was 20% and 30% higher than compressive and bending strength of alkali- activated material without additional fibres respectively.
Keywords: secondary raw material, alkali activated material, foaming, homogenization, mechanical strength
Published in DiRROS: 21.12.2023; Views: 233; Downloads: 79
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Abstract: As part of the WOOL2LOOP project, the Slovenian National Building and Civil Engineering Institute (ZAG), in collaboration with Termit d.d. were responsible for the production of façade panels. An initial mix design was developed at ZAG, where alkali-activated façade panels were produced, primarily from stone wool waste, while production took place at Termit. The mix design was changed twice during the pilot production, before a final product with suitable durability was developed. A compressive strength of up to 60 MPa and bending strength of approximately 20 MPa was achieved. The mechanical properties, however, varied, due to the unevenly milled batches of the milled mineral wool. Milling on a larger scale is very challenging, and it is difficult to obtain consistent quality of the milled material. Once the correct curing process had been found, however, the panels produced showed good performance. Moreover, the results from leaching tests showed that the elevated concentrations of certain elements (Cr, As and Mo) did not exceed the legal limits for non- hazardous waste.
Keywords: waste mineral wool, alkali activated material, façade panels, pilot production, circular economy
Published in DiRROS: 28.11.2023; Views: 270; Downloads: 101
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Abstract: The production of alkali-activated materials with excellent mechanical performance requires the use of waterglass, which has a significant carbon footprint. Such materials can have a lower carbon footprint if we replace water glass with alternative activators sourced from waste. In this study, we assessed the suitability of locally available amorphous waste materials (stone wool, glass wool, bottle glass and cathode-ray tube glass) as a source for the preparation of alternative alkali activators. We quantified the amount of silicon and aluminium dissolved in the activator solutions via inductively coupled plasma-optical emission spectrometry. The alternative activators were then used to produce alkali-activated fly ash and slag. The compressive strength values of alkali-activated fly ash specimens upon the addition of NaOH, water glass and the most promising alternative activator were 38.98 MPa, 31.34 MPa and 40.37 MPa, respectively. The compressive strength of slag specimens activated with alternative activators with the highest concentration of dissolved silicon (21 g/L) was, however, 70% higher than the compressive strength of slag specimens activated with only 10 M sodium hydroxide. The compressive strength of slag specimens with the addition of the most promising alternative activator was significantly lower (3.5 MPa) than the compressive strength of those that had been activated by commercial water glass (34.3 MPa).
Keywords: alkalijsko aktivirani materiali, alternativni aktivatorji, lastnosti, alkali activated materials/geopolimers, alternative activators, properties
Published in DiRROS: 22.08.2023; Views: 221; Downloads: 151
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Abstract: This study focuses on the influence of microwave irradiation dosimetry on alkali-activated slurry in its early stages. The impact on the chemistry and mineralogy along with the mechanical properties were evaluated by changing the power of microwaves and their duration of exposure. This influenced the dissolution of amorphous content, diffusion, and self-assembly into an aluminosilicate network. The precursors used in this study were metakaolin, a non-waste material commonly used in geopolymerisation technology, and local fly ash and ladle furnace slag as secondary materials. Furthermore, they were chemically and mineralogically analysed, and their mixtures with NaOH and Na-water glass provided the optimal ratio of the amount of elements obtained using the pre-calculation approach. However, the potential extra addition of water was experimentally determined to allow complete wetting of the material and solid workability during moulding. Using Fourier-transform infrared spectroscopy, the influence of water was further investigated in alkali-activated slag and fly ash irradiated with microwaves, which resulted in the highest values of mechanical strength in the dosimetry-mapping part of the analysis. In addition to the time dependence of the expected mechanical strength on the ageing of the alkali- activated material, the synthesised material exhibited a significant dependence on the dose of microwave irra- diation, which was different for every precursor as well as every mixture with different chemistries.
Keywords: odpadni material, alkalijska aktivacija, obsevanje z mikrovalovi, mehanska trdnost, waste material, alkali activation, microwave irradiation, mechanical strength
Published in DiRROS: 12.07.2023; Views: 360; Downloads: 271
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