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Povzetek: Alkali-activated binders are an environmentally friendly alternative to Portland cement, particularly when locally-available raw materials are used. It is well known that alkali activation with a sodium silicate activator generates a hardened binder with higher compressive strength than a binder hardened with sodium hydroxide. As the alkali-silicate activators are produced through energy extensive processes, and their use can significantly increase the carbon footprint of the final products, it is of great significance to develop alternative alkaline activators based on locally-available waste materials. This article assesses the potential to apply waste bottle glass and waste cathode-ray tube (CRT) glass to synthesise alternative alkali activators by the hydrothermal method. Inductively coupled plasma-optical emission spectrometry (ICP-OES) was used to determine silicon and aluminium content in the alternative activators. The influence of dissolution process parameters (time, temperature, particle size) on the concentrations of silicon and aluminium in the alternative activators was investigated. The alternative activators with silicon concentration up to 19 g/L and aluminium concentration up to 0.9 g/L were prepared at T = 120 °C and boiling time 24 h. The alternative alkali activators and, for comparison, also commercial sodium silicate were used in the alkali activation of fly ash powder. The formed pastes were cured at 70 °C for 72 h. Mechanical strength measurements indicated that alkali activation of fly ash with the optimal alternative activator yielded hardened paste with compressive strength of 33 MPa. However, the compressive strength of hardened paste prepared from fly ash and commercial sodium silicate reached 70 MPa. Part of this difference can be ascribed to the lower density of hardened pastes prepared with alternative activators.
Ključne besede: alkali -activated materials, alternative alkali activators, waste bottle glass, waste cathode -ray tube glass, fly ash, hydrothermal method
Objavljeno v DiRROS: 25.01.2024; Ogledov: 170; Prenosov: 113
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Povzetek: Fly ash and phosphogypsum were used as Naturally Occurring Radioactive Materials (NORM) by-products for the synthesis of belite-sulfoaluminate clinkers. The influence of raw mixture composition and firing temperature was investigated. Clinkers and cements were examined by X-ray powder diffraction and scanning electron microscopy with energy dispersive X-ray spectroscopy. The compressive strength of the cements was determined after 28 days. Clinker phases identified included ye’elimite, ß-phase of belite, ternesite and gehlenite, while the main hydration product of the cement pastes was ettringite. The results showed that belite-sulfoaluminate cements can be fabricated with a compressive strength of 45.9 N/mm2 by firing the raw mixture (70 wt.% marl, 10 wt.% bauxite and 20 wt.% phosphogypsum) at a temperature of 1320°C/1h.
Ključne besede: clinker, microstructure, fly ash, gypsum, calcium sulphoaluminate
Objavljeno v DiRROS: 27.10.2023; Ogledov: 367; Prenosov: 140
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Povzetek: Huge quantities of fly ash and bottom ash are generated from thermal power plants and it presents great concern for country, mainly due to the environmental effects. In this study, fly ashes and bottom ash were characterized from technical and radiological aspects. Health effect due to the activity of radionuclides 226Ra, 232Th and 40K was estimated via radium equivalent activity (Raeq), external hazards index (Hex), the external absorbed dose rate (D) and annual effective dose rate (EDR). The specific surface area (40.25 m2 g−1), particle density (1.88 g cm−3) and LOI (23.49%) were typical for bottom ash. Siliceous fly ash contained 32% reactive silica. The annual effective dose rate for all ashes is ≤ 0.2 mSv y−1. Both, fly ash and bottom ash present potential secondary raw materials to be used for building purposes as result of their technological and radiological assessment.
Ključne besede: fly ash, bottom ash, gamma spectrometry, building materials
Objavljeno v DiRROS: 22.05.2023; Ogledov: 285; Prenosov: 137
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Povzetek: The performance of a cold-bonding pelletization process was investigated for lightweight aggregates (LWAs) production from municipal solid waste incineration (MSWI) fly-ash (FA), by including multiple waste materials in the aggregate mixture. Before pelletization, FA was pre-treated by washing with water, which led to a reduction of chloride (66.79%) and sulphate (25.30%) content. This was further confirmed by XRF and XRD analyses, which showed a reduction of chloride elements and the content of chlorine crystalline phases. The pelletization process was carried out using both single- and double-step methods. For single-step pelletization, all the mixtures contained 80% FA, combined with various compositions of cement (5, 10, and 15%) and granulated blast furnace slag (GBFS) (5, 10, and 15%). For the double-step pelletization 30% of cement and 70% of marble sludge (MS) were added to each of the previous mixtures. The apparent density of all the aggregates varied between 1.60 and 1.87 g cm 3, suggesting their suitability to be classified as LWAs. Aggregates produced from double-step pelletization showed improved characteristics, with water absorption capacity and open porosity generally lower compared to the corresponding aggregates from the single-step pelletization. The best values of compressive (crushing) strength (almost 11 MPa) were observed for double-step pelletization aggregates with initial cement: GBFS mixture of 15%:5%. Results from leaching tests showed an overall significant release of chloride and sulphate. Nevertheless, leaching from double-step pelletization aggregates was reduced by 1.73- 4.02 times for chloride and 1.58-5.67 times for sulphate, further suggesting that better performances are achievable through the addition of an aggregate second layer.
Ključne besede: MSWI fly ash, lightweight aggregate, microtomography, open access
Objavljeno v DiRROS: 03.05.2023; Ogledov: 342; Prenosov: 292
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