3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item An investigation into the use of weathered fly ash (WFA) and coal gasification ash (CGA) as partial replacements for portland cement in concrete(2019) Maboea, Dikeledi MamelloThe cement industry has recognised the need to reduce the output of CO2 emissions in the atmosphere. This investigation considers the use of alternative binders. Three supplementary cementitious materials (SCMs), namely, fly ash (FA), coal gasification ash (CGA), and weathered fly ash (WFA) were used to replace 10%, 15%, and 30% of Portland cement (PC) by mass. Each mix used water/binder (w/b) ratios of 0.50 and 0.60. 100% PC concrete was the primary control and FA concrete the secondary control. Samples were subjected to slump, compressive and tensile strength, durability and shrinkage tests. The compressive strength results of WFA blends at 28-days of testing were observed to be equal to or greater than those of FA blends. At 56-days the compressive strength results of WFA blends measured below those of 28-days. The compressive strength results of 15% CGA blend at 28-days of testing was equal to that of 15% FA with 0.50 w/b and greater than that of 15% FA with 0.60 w/b ratio. The 56-days strength of 30% CGA-0.50 and 30% CGA-0.60 were greater than the corresponding 30% FA blends at 28-days of testing. Indicating an increase in strength with age for CGA blends. Due to the loss of compressive strength at 56-days for WFA, CGA was concluded to be the Sasol ash with the higher potential to be used as a partial replacement of PC in concrete for strength purposes. The durability index tests conducted had varying overall results, CGA blends were less permeable to oxygen, FA blends had the lowest absorption rates and WFA blends were the most resistant to chloride ingress. In conclusion, from the observed results, CGA and WFA can be used as partial replacements of PC in concrete, but further research is required. The research into WFA and CGA as supplementary cementitious materials will assist in gaining knowledge on their impact on the concrete characteristics to allow for greater exploitationItem Exploring the environmental impacts of fly ash on Eskom's business sustainability and sustainable development: a study on Kriel power station in Mpumalanga province of South Africa(2018) Rasimphi, Khuliso JamesFly ash generated at coal fired power stations is associated with various environmental impacts. The aim of this study was to particularly investigate alternative ways in which fly ash generated at Kriel Power Station can be managed effectively to minimize environmental impacts in order to ensure alignment with the notion of sustainable development. The study was primarily focused on exploring the impacts of Kriel Power Station’s fly ash as well as current fly management practices within the context of contemporary principles of environmental management and sustainable development. Quantitative and qualitative research methods were used for data collection. Purposive sampling was used as primary sampling procedure to select fitting sample from the study population. Data from structured questionnaire surveys, semi- structured interviews as well as existing records was used for data collection. This study has found that fly ash utilization is an ideal management practice which is aligned with sustainable development notion as compared to disposal to ash dams. Kriel Power Station’s fly ash was found to consist of various valuable elements which can be used for various industrial production purposes. The findings further suggest that the very same valuable chemical elements found in Kriel Power Station’s fly ash can cause adverse environmental impacts such as water, land and air pollution depending on the management approach. One of the key findings of this research is that fly ash utilization program is currently not well marketed in South Africa; and there is a need for all relevant stakeholders to work together to educate the public on the opportunities presented by fly ash. As part of concluding remarks, this study also suggested some enabling policies which can be established in order to optimize fly ash utilization from the regulator level (national level) to the generator and end user level (institutions). Recommendations on relevant future studies which can potentially be undertaken to explore adverse impacts as well as benefits of fly ash were also made.Item Synthesis and characterisation of carbon nanomaterials using South African coal fly ash and their use in novel nanocomposites(2016) Hintsho, Nomso CharmaineThe synthesis and applications of carbon nanomaterials (CNMs) such as carbon nanofibres (CNFs), carbon nanotubes (CNTs) and carbon nanospheres (CNSs) have attracted a lot of attention due to their unique chemical and physical properties. For the synthesis of CNMs with desired morphology to occur, one needs to consider three components, namely, the catalyst, carbon source and source of power. However, the cost of the catalysts involved in making CNMs is one of the challenging factors. Due to properties such as high aspect ratio, CNM use as fillers in polymer nanocomposites has been on the forefront to improve the mechanical strength of polymer materials such as polyesters. Due to their hydrophobic nature, the interaction between the filler and matrix tends to be problematic. In this study, we investigated the use of a waste material, coal fly ash as a catalyst for the synthesis of CNMs using the chemical vapour deposition method. The use of CO2 and C2H2 as carbon sources, either independently or together, was also employed. A comparison of two different ashes was also investigated. Lastly, the use of these synthesized and acid treated CNMs as fillers was examined. The catalysts and synthesized CNMs were characterised using SEM, TEM, EDS, laser Raman spectroscopy, XRD, BET, TGA and Mössbauer spectroscopy. The mechanical properties were investigated by testing the tensile, flexural and impact properties. The synthesis of CNMs using fly ash as a catalyst without pre-treatment or impregnating with other metals was achieved. Optimum yields and uniform morphology was obtained at 650 oC, at a flow rate of 100 ml/min using H2 as a carrier gas and C2H2 as a carbon source. Mössbauer spectroscopy revealed that cementite (Fe3C) was the compound responsible for CNF formation. Further, CNMs were formed over fly ash as a catalyst, using CO2 as a sole carbon source, an additive and a carbon source before reacting with C2H2. Duvha was Page | iii found to be a better fly ash catalyst compared to Grootvlei and an optimum loading was achieved at 0.25%. Treating the CNFs with HCl/HNO3 resulted in the highest tensile, flexural and impact strengths. This studyItem Fly ash catalysed synthesis of CNFs for use in a photocatalytic CNF-TiO2 hybrid(2016) Moya, Arthur NdumisoThis study has explored the CVD synthesis of carbon nanofibres (CNFs) using Eskom’s waste coal fly ash as a catalyst with acetylene and hydrogen as the carbon source and carrier gas, respectively. In the process, a possible growth mechanism for these carbon nanofibres was sought. CNFs were successfully synthesised from fly ash and were found to have an average diameter of 22±7 nm. The growth mechanism of these CNFs was studied using EDS, TEM and laser Raman spectroscopy. It was observed that CNFs grew via root growth on spherical particles of fly ash and by tip growth on irregular-shaped metal oxide agglomerates. Both of these were found, through EDS analysis, to be Fe-rich. CNFs were functionalised between 2-12 h under reflux at 110 °C using a 3:1 (v/v) combination of HNO3 and H2SO4 in order to introduce functional groups onto their surfaces to act as anchors for hydrophilic reactants. The functionalisation of these CNFs was studied using TEM, laser Raman spectroscopy, ATR-FTIR spectroscopy, PXRD, BET, XRF and TGA. ATR-FTIR spectroscopy showed that some carbonyl functional groups were present on the surfaces of these CNFs after functionalisation. The functionalised CNFs (fCNFs) were then treated using a simple hydrothermal method to deposit 10% (m/m) of TiO2 nanoparticles onto their surface. This hydrothermal method employed the drop-wise addition of TiCl4 to a cold water-fCNFs mixture, which was then refluxed at 115 °C for 2-12 h. Laser Raman spectroscopy confirmed the presence of both TiO2 (phase pure anatase) and CNFs. ATR-FTIR spectroscopy provisionally revealed the presence of covalent Ti-O-C bonds. Studies where the duration of exposure to TiCl4 and the functionalisation time of CNFs were examined showed that the particle size and agglomeration of the TiO2 nanoparticles did not affect the surface area of the CNF-TiO2 hybrids significantly. However, CNF-TiO2 hybrids which were shown by TGA to have high fly ash content were observed to have low surface areas. fCNFs functionalised at 2 h had the highest surface area, at all fixed durations of exposure to TiCl4 by comparison with fCNFs which had been functionalised for longer periods.Item Purification of coal fly ash leach solution by solvent extraction(2016) Rushwaya, Mutumwa JepsonThe solvent extraction of iron and titanium from solution generated by the two-step sulphuric acid leaching of coal fly ash by Primene JMT was investigated. The influence of hydrogen ion concentration, Primene JMT concentration, aqueous to organic volume phase ratio and temperature on the extraction of iron and titanium was determined by the use of Design of Experiments. Hydrogen ion concentration and the interaction between the aqueous to organic volume phase ratio with Primene JMT concentration had a significant effect on the extraction of iron while temperature did not. Hydrogen ion concentration and temperature did not have a significant effect on the extraction of titanium, while the interaction between Primene JMT concentration and aqueous to organic volume phase ratio had a significant effect. Extraction improvement tests showed that at a hydrogen ion concentration of 0.28M, 88% iron and 99% extraction of titanium from coal-fly ash leach solution could be achieved. Construction of a McCabe-Thiele diagram showed that a four-stage solvent extraction system with Primene JMT could reduce the iron and titanium concentration in the coal fly ash leach solutions to below 0.05g/L