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Povzetek: Supplementary cementitious materials can affect the porosity of concrete, pore solution pH and chloride binding, all of which influence the type and magnitude of corrosion damage. Advanced corrosion monitoring techniques are needed to follow the development of corrosion on steel embedded in concrete across space and over time. In this study, coupled multi-electrode arrays (CMEAs) were used to characterise corrosion processes in OPC and three blended cements. Cyclic wetting with chlorides was undertaken to initiate corrosion. The results showed three distinct types of corrosion: localised corrosion (CEM I), localised corrosion that expanded over time (CEM II), and a combination of localised and general corrosion (CEM III and CEM IV). Cathodic locations were also monitored successfully, and the corrosion behaviour was related to total porosity and pH of the pore solution. MicroCT was used to quantify the volume of corroded material, which agreed well with results calculated from the CMEA measurements.
Ključne besede: blended cements, coupled multi-electrode array, corrosion of steel in concrete, supplementary cementitious materials, open access
Objavljeno v DiRROS: 29.05.2023; Ogledov: 459; Prenosov: 279
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Povzetek: In this study we compare the leaching behavior and the antibacterial and cytotoxic properties of 100% slag or stone wool derived alkali activated materials. The antibacterial activity was measured as the inhibiting capacity against two Gram- negative bacterial strains, Escherichia coli and Pseudomonas aeruginosa and one Gram-positive bacterial strain: Enterococcus faecalis. The cytotoxicity properties were tested on mouse embryonic fibroblast NIH-3T3 cell-line. It was proved that the high quality of the 3D aluminosilicate network of the consolidated materials obtained from powders of CaO or MgO-rich slags or stone wool, opportunely activated with NaO and/or Na-silicate, was capable of stabilizing heavy metal cations. The concentrations of leachate heavy cations were lower than the European law limit when tested in water. The effect of additives in the composites, basal fibers or nanocellulose, did not reduce the chemical stability and slightly influenced the compressive strength. Weight loss in water increased by 20% with basalt fibers addition, while it remained almost constant when nanocellulose was added. All the consolidated materials, cement-like in appearance, exhibited limited antibacterial properties (viability from 50 to 80% depending on the bacterial colony and the amount of sample) and absence of cytotoxicity, envisaging good acceptance from part of the final consumer and zero ecological impact. CaO-rich formulations can replace ordinary Portland cement (showing bacterial viability at 100%) with a certain capability for preventing the reproduction of the E. coli and S. aureus bacteria with health and environmental protection results.
Ključne besede: antibacterial properties, cytotoxicity, alkali-activated materials, slag, stone wool, waste utilization, social acceptance
Objavljeno v DiRROS: 22.05.2023; Ogledov: 490; Prenosov: 308
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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: 476; Prenosov: 222
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Povzetek: Since recycled technologies usage is mandatory for environmental safety, and in this regard, it is important to examine new materials that can be used in construction and are primarily produced from fly ash. In addition to characteristics such as hardness and compressive strength, the given materials must also be radiologically and environmentally safe. The main concept of engineered geopolymer gel composites based on fly ash residues is focused on developing binder materials via gel formation processes that can replace ordinary cement materials. This study is unique in researching the potential use of fly ash from the Nikola Tesla thermal power plant in Serbia, where the hybrid geopolymeric materials synthesized from fly ash are experimentally examined with the addition 1 wt% and 2 wt% of polyvinyl alcohol (PVA). This paper aims to investigate the structural, morphological, mechanical, and radiological properties of hybrid materials with the addition of PVA and without additive in the period of ageing for 28 days at room temperature. The phase composition was investigated using X-ray powder diffraction (XRPD) analysis, while morphological characteristics of these materials were examined using scanning electron microscopy and energy dispersive X-ray analysis (SEM-EDS). Vibrational spectra of obtained samples are investigated using diffuse reflectance infrared Fourier transform (DRIFT) and Fourier transform infrared (FTIR) techniques. The hardness and compressive strength are also examined, indicating that the 1 wt% addition in geopolymeric matrix results in the best mechanical properties. Radiological measurements of investigated all geopolymer samples show decreasing activity concentrations of radionuclides for 50% compared to fly ash.
Ključne besede: geopolymer gel, inorganic binders, hybrid materials, fly ash, radiological properties, strength, open access
Objavljeno v DiRROS: 12.05.2023; Ogledov: 435; Prenosov: 235
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Povzetek: Flotation wastes are becoming a valuable secondary raw material and source of many metals and semimetals worldwide with the possibilities of industrial recycling. The flotation tailings contain oxide and sulfide minerals that have not been sufficiently stabilized and form acidic mine waters, which in turn contaminate groundwater, rivers, and reservoi6sediments. An effective way to recycle these mine wastes is to recover the metals through leaching. While the focus is on acid bioleaching by iron- and sulfur-oxidizing bacteria, alkaline leaching, and the removal of iron- containing surface coatings on sulfide minerals contribute significantly to the overall environmental efficiency of leaching. For this study, static and percolate bioleaching of copper from flotation waste at the Bor copper mine in Serbia was investigated in alkaline and then acidic environments. The aim of the study was to verify the effect of alkaline pH and nutrient stimulation on the bioleaching process and element extraction. A sample was taken from a mine waste site, which was characterized by XRF analyses. The concentration of leached copper was increased when copper oxide minerals dissolved during alkaline bioleaching. The highest copper yield during alkaline bioleaching was achieved after 9 days and reached 67%. The addition of nutrients in acidic medium enhanced the degradation of sulfide minerals and increased Cu recovery to 74%, while Fe and Ag recoveries were not significantly affected. Combined bioleaching with alkaline media and iron- and sulfur-oxidizing bacteria in acidic media should be a good reference for ecological Cu recovery from copper oxide and sulfide wastes.
Ključne besede: copper, alkaline, acidic bioleaching, secondary raw materials, open access
Objavljeno v DiRROS: 05.05.2023; Ogledov: 469; Prenosov: 229
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