Electronic Theses and Dissertations (PhDs)

Permanent URI for this collectionhttps://hdl.handle.net/10539/38886

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    A bottom-up smart city approach to solid waste management: the case of ICT-enabled waste reclaimers system in two South African cities
    (University of the Witwatersrand, Johannesburg, 2023) Siwawa, Vincent
    This study delves into the realm of waste management in the context of bottom-up smart cities, focusing on the implementation of an innovative ICT-enabled waste reclaimer system in Cape Town and Johannesburg, South Africa. The central inquiry pertains to the pivotal role played by the bottom-up smart city paradigm in addressing waste management challenges and fostering the inclusion of waste reclaimers within the framework of smart cities. The inadequacies inherent in prevailing top-down smart city approaches and techno-centric solutions extends to the lack of mechanisms within the conventional informal recycling system to furnish reliable, immutable, and transparent waste-related data, thereby compromising security. To address these challenges, a novel approach emerges, fusing the capabilities of the Internet of Things (IoT) and blockchain technology into the informal recycling sector. This ICT-enabled waste reclaimer system introduces a comprehensive framework encompassing training initiatives, the provisioning of protective equipment, smartphones to facilitate communication between households and waste reclaimers, measuring instruments, tricycles, and dedicated spaces for sorting and storing recyclable materials. Employing a qualitative research methodology, this study incorporates a blend of document analysis, integrative literature review, and semi-structured interviews with key stakeholders. The selection of case studies, namely BanQu, Kudoti, and Regenize, is underpinned by purposive sampling. An array of research instruments including webinars, photography, participant observations, and transect walks contribute to the rich data collection process. The study draws upon the socio-technical transition theory to sustainability and the Multi-Level Perspective (MLP) as conceptual frameworks to dissect the digital transformation of the informal waste sector through the lens of the ICT-enabled waste reclaimer system. Findings underscore the potential of this innovative system to foster symbiotic connections between waste reclaimers and stakeholders embedded within the recycling value chain. This, in turn, culminates in enhanced working conditions and augmented income for waste reclaimers. Crucially, the ICT-enabled waste reclaimer system offers mechanisms for waste monitoring and tracking, while concurrently introducing incentives and rewards. By generating precise, secure, and reliable data, this system engenders a paradigm shift from a conventional cash- based payment structure to a virtual and electronic payment mechanism. Preliminary evidence showcases a notable threefold increase in recyclable collection by waste reclaimers compared to municipal efforts. In culmination, this study delivers both theoretical and empirical contributions by shedding light on the integration of waste reclaimers and waste management within the context of a bottom-up smart city approach. The study posits a promising trajectory for future research and ushers in new avenues for the development of bottom-up smart cities within the ambit of developing nations.
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    Assessment of the Performance of Corn Cob Ash as a Partial Replacement for Portland Cement in Concrete
    (University of the Witwatersrand, Johannesburg, 2023) Fadele, Oluwadamilola Adepeju; Otieno , Mike
    The production of Portland cement is associated with the release of greenhouse gases especially carbon dioxide which is estimated to be about a ton per every ton of clinker produced contributing to climate change. Several mitigation strategies have been proposed but the most viable remains the use of supplementary cementitious materials as partial replacement for Portland cement. There have been considerable success with the use of some industrial by-products (fly ash and slag) and natural materials (calcined kaolin clay) as supplementary cementitious materials. However, the non-availability of these by-products in countries like Nigeria calls for the investigation of locally available substitutes. Supplementary cementitious materials are either pozzolanic or possess latent hydraulic properties making them choice materials as partial Portland cement replacement. The classification and choice of a material as supplementary cementitious material lies in the understanding of their characteristic properties (chemical composition and mineralogy) and subsequent performance in cementitious systems. The performance of corn cob ash calcined at 700°C and 800°C as partial replacement for Portland cement (PC) compared to Portland cement and fly ash (FA) was studied with the following objectives: to determine the influence of calcination temperature on the reactivity of corn cob ash; investigate the effects of corn cob ash content at varying w/b ratio on the i) hydration reaction of Portland cement; ii) the compressive strength of concrete iii) drying shrinkage strain of mortar iv) penetrability of concrete v) microstructure of concrete The laboratory investigation involves using corn cob ash to partially replace Portland cement at two levels of 15% and 30% by mass using two w/b ratios of 0.4 and 0.6 at a water content of 205 kg/m3. The corn cob ashes in binary combination with either Portland cement or fly ash were used to prepare concrete samples which were used for the determination of compressive strength, durability index tests (namely oxygen permeability, water sorptivity and chloride conductivity) to assess the durability of concrete, and microstructural development. The concrete was designed using the South African Cement and Concrete Institute method of mix design. Also, mortar samples made from one part of cement to three parts of sand were prepared for the investigation of drying shrinkage and estimation of strength activity index while paste samples were prepared for determining reactivity of the ashes and effect on Portland cement hydration. iv Reactivity of the ashes was measured using both strength activity index and R3 reactivity test. Strength activity index was estimated from the compressive strength of 50 mm cube mortars at the ages of 28, 56 and 90 days of curing in order to better understand the mechanism of reaction of the ash, while R3 test was performed on model paste using the bound water approach at the age of 7 days. The amorphous content of ash calcined at 700°C and 800°C is 1.9% and 2.4% respectively while the gain in strength of mortar cubes prepared with only Portland cement, Portland cement/fly ash, Portland cement/corn cob ash calcined at 700°C and 800°C between 28 and 90 days are 14%, 24%, 10% and 9% respectively. The surface area of the Portland cement, fly ash, corn cob ash calcined at 700°C and at 800°C is 2.38, 2.224, 3.122 and 2.751 m2/g respectively. The results indicate that the corn cob ashes (CCA) calcined at 700°C (C700) and 800°C (C800) are low reactive materials with limited pozzolanic reactivity while the mechanism of reaction is largely influenced by filler effect due to finer particle size than plain PC. The compressive strength of concrete containing 15% CCA calcined at 700°C and 85% Portland cement ranges between 40 to 58 MPa between 3 and 90 days of curing at w/b ratio of 0.4 compared to 56 to 83 MPa for Portland cement concrete and 48 to 82 MPa for fly ash/Portland cement concrete at the same replacement level. The porosity of concrete containing 15% C700 and C800 at w/b ratio of 0.4 is 9.66 and 6.9% respectively at 28 days of curing compared to 8.37% for PC and 6.52% for fly ash at the same age and replacement level. The presence of CCA affects the heat of hydration of plain PC by prolonging the induction phase by about 12 hours which delayed the evolution of main heat peak. The use of CCA lead to a reduction in strength compared to PC/FA system with compressive strength decreasing with increasing w/b ratio and increasing PC replacement level. CCA has a high potassium oxide content which is highly soluble with a high concentration in the pore solution of concrete. CCA influences volume change leading to a high drying shrinkage strain compared to plain PC and FA. CCA also affects the durability of concrete by increasing the penetrability of concrete which increases with increasing ash content. In terms of the studied properties of cementitious systems, there is no marked difference in the effect of C700 compared to C800 while the effects recorded becomes significant with increasing PC replacement level. In comparison to FA, the effect of CCA on the properties studied was inferior due to the largely crystalline nature resulting in limited pozzolanic activity
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    Prospects of gibbsite-rich laterite as a source of aluminosilicates in geopolymerisation
    (University of the Witwatersrand, Johannesburg, 2024) Gilayeneh, Victor Saye; Nwaubani, Sunday; Otieno, Mike
    Laterite, an iron-rich soil widely found in the tropical and subtropical regions of the world, has shown promise for the development of eco-friendly construction materials through geopolymerisation. However, this material varies greatly in composition based on location, prevailing climate conditions, and even in depth within a given lateritic profile. The top layer of most lateritic profiles is usually low in kaolinite but rich in aluminium or iron hydroxide minerals. Despite these variations, research on the use of laterite in geopolymerisation has predominantly focused on materials rich in kaolinite. Therefore, this study explores the potential of aluminium-rich laterite as a source of aluminosilicates in geopolymerisation. In this study, the reaction kinetics, setting times, flow behaviour, strength development, phase composition, and pore structure of geopolymer derived from aluminous laterite were examined. This study also considered both calcined and uncalcined laterite as well as the influence of calcium minerals, namely calcium carbonate (CaCO3) and Portland cement, which replaced 40% of the laterite. In addition, the influence of the laterite’s properties on the performance of the derived geopolymer was also examined. The flow behaviour of the paste was found to be influenced by the viscosity of the activating solution, while the setting times and heat of reaction varied according to the type of laterite and the presence of calcium carbonate or Portland cement, which reduced the setting times and accelerated the rate of heat liberation within the first hour of the isothermal calorimetry test. The geopolymer mix based on calcined laterite displayed the highest amount of heat liberated, while its uncalcined laterite counterpart showed the lowest. All mixes within the calcined laterite series exhibited higher compressive strength than those in the uncalcined series, but only the calcined laterite mixes containing calcium minerals achieved structural strength. The uncalcined laterite mixes experienced strength regressions, with samples of the uncalcined laterite mix containing calcium carbonate developing cracks and subsequently disintegrating. The phase assemblage, porosity and pore structure were also influenced by the type of laterite and the presence of calcium carbonate or Portland cement. However, the presence of calcium carbonate also led to severe efflorescence and subflorescence, which negatively impacted the porosity and structural integrity. Also, the dissolution of gibbsite initiated the development of unstable phases in the uncalcined laterite mixes within the geopolymer and hybrid categories. Conversely, in the absence of activators, especially sodium hydroxide, as demonstrated in the binary mix containing uncalcined laterite, the dissolution of gibbsite is inhibited, resulting in the formation of stable phases.
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    A decision support framework for grading of civil engineering contractors and evaluation of infrastructure project performance
    (University of the Witwatersrand, Johannesburg, 2024) Chiloane-Nwabueze, Salome
    The construction sector plays a key role in the economic development of a country. The management of this sector is thus crucial in maximising the performance of the sector and the economy. The South African construction sector performance has some level of inefficiencies that could be improved to enhance the sector’s performance outputs. Therefore, the study aimed to develop a framework for grading civil engineering contractors and the evaluation of project performance. To achieve this, the study reviewed the literature on relevant key concepts and CIDB processes and systems. The government of South Africa has mandated the registration and grading of contractors to the Construction Industry Development Board (CIDB). The CIDB grade is a license for trading with the government. It certifies contractors who are graded as capable of delivering projects up to a pre-determined contract value in each class of work. Currently, the grading system is based on two key determinants, which are the contractor’s track record (i.e., completed projects) and available capital. Presently, a contractor grade does not denote the contractors’ capabilities. However, contractor grading and performance evaluation should be a multi-criteria decision-making process. A questionnaire was developed and distributed to the key participants in the industry to establish whether there is a need for enhancing the current registration, grading, and performance evaluation of contractors in the construction sector and to establish relevant criteria. Of the 149 respondents, the results of the study have revealed that most of the respondents (88.6%) agree that enhancing the current construction sector entry requirements could assist in improving contractors’ capabilities. Moreover, 90.6% of the respondents have indicated that enhancing the current construction sector entry requirements will assist in improving the performance outputs of the construction sector. A multicriteria decision-making methodology using the Analytical Hierarchy Process (AHP) based on seven main criteria with seventeen sub-criteria was carried out for iii grading of contractors and performance evaluation of contractors. Thereafter, using the results obtained from the AHP, an enhanced framework was developed for registering, grading, and evaluating the performance of contractors. Relevant scenarios and CIDB grading scenarios were applied to test and validate the developed framework. The construction sector entry requirements have been proposed by the study based on the literature reviewed and results of the state of practice survey to improve the sector performance. One way of improving the sector’s performance is through entry regulation. Organisations and some countries worldwide have some form of entry regulation to manage the construction sector. To minimise business failure and poor performance, new entrants need to have at least a recognised technical qualification in the aspiring field of work. This will ensure that new entrants have the relevant knowledge of the field in which they aspire to enter. Having entry regulations and improved grading and performance evaluation systems may assist in improving the sector’s performance. Proposals on the enhancements that may be considered by the CIDB are made which may assist in improving the industry’s performance.
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    The theory and practice of community participation in provision of urban structure
    (University of the Witwatersrand, Johannesburg, 1993) Abbott, John; McCutcheon, Robert
    The thesis develops a new approach to community participation, for application to infrastructure provision projects in developing countries, based upon social surveys and case studies of negotiations in five South African communities. Existing approaches to community participation are analysed and shown to be unsuitable for infrastructure provision. The thesis compares the characteristics of infrastructure projects with those of other types of development projects and demonstrates how these characteristics can be used to situate a given project within a project environment defined in terms of two variables: the openness of government to community involvement in decision-making, and project complexity. Social surveys carried out in Soweto and KwaThandeka showed the centrality of infrastructure to social change in South Africa. Existing urban management systems were unable to cope with the stresses placed upon them. Four facets of urban management were identified as being under stress: institutional capacity, legitimacy, affordability, and user convenience. These stresses change the nature of infrastructure provision from the supply of end products into a complex process. Central to this process are: an increased number of actors influencing decisions, the enhanced role of technical professionals, and the social implications of different levels of service. The case-study of KwaThandeka included a study of the negotiation process with the provincial administration. This research led to the development of a performance specification for comparing social, economic and technical measures of value. A new conceptual framework for community participation was derived, based upon the different actors involved in the decision-making process and the different needs of each of those actors. Three case studies from Natal identified different implementation strategies for community participation. Communities were found to have three distinct needs: involvement in the political process; involvement in technical decision-making; and representation as consumers of services. An analytical tool was developed to assist project managers in understanding the relationships between actors in a project. The thesis shows how technical project management can be integrated into the participation process. The success of community participation can be evaluated by assessing the degree of consensus achieved between actors, and the intensity of community involvement.
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    Comparative study of five country-specific labour-intensive infrastructure development programmes : implications for South Africa
    (University of the Witwatersrand, Johannesburg, 2010) Quainoo, Harry Akyen; McCutcheon, R.T.
    Unemployment and abject poverty in South Africa are widespread, persistent and disproportionately high. These problems are aggravated by inadequate capacity at all tiers of government and huge infrastructure backlogs in rural South Africa. Employment-intensive means of infrastructure delivery have been successfully implemented in several sub-Saharan African countries and elsewhere to generate employment and reduce poverty. It should be possible to replicate similar large-scale national programmes in South Africa. But South Africa has failed. Both prior to and since 1994, several supposedly employment-intensive programmes have been implemented in South Africa with poor results. In an endeavour to contribute to future South African policy and good practices regarding employment, this thesis describes and analyses in detail five major Sub-Saharan programmes and reaches conclusions regarding their achievements and shortcomings. Lessons derived bridge the knowledge gap between the large-scale programmes embarked upon in the sub-Saharan countries in the mid-1980s and the year 2007; these lessons should be applied to future endeavours in South Africa to generate significant employment per unit of expenditure and contribute to poverty alleviation. A major conclusion reached was that the success of employment-intensive infrastructure development programmes depends to a large extent on fundamental factors such as appropriate and implementable policy, government commitment, adequate and sustainable funding, adequate capacity and good preparation. Specifically, the thesis demonstrated that prior to implementation a sufficient timeframe is required for programme preparation in order to make significant contribution towards poverty reduction. Equally, national programme expansion requires a strategic balance between centralisation and decentralisation. In particular, for programme extension and decentralisation, due regard must be given to training and capability building and available resources. Deriving from the thesis’ major conclusions, the author developed three crucially important frameworks for anti-poverty infrastructure development programmes, namely; a four-phased model for evaluating the chances of success of infrastructure programmes, a five-phased result-oriented guidelines for testing the workability of infrastructure development policies, and a practical guideline for monitoring and evaluating employment-creation programmes that maximises the benefits thereof and pre-empts institutional memory loss through systematic knowledge management.