Faculty of Engineering and the Built Environment (ETDs)

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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.
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
Modelling the comminution process in the rotary offset crusher
(University of the Witwatersrand, Johannesburg, 2024) Nghipulile, Titus; Bwalya, M.
There is always a search for size reduction solutions due to the inherent energy inefficiency associated with comminution devices. The rotary offset crusher (ROC) is a new comminution device with a promising performance potential in terms of throughput due to enhanced speed of transportation induced by the centrifugal force of the discs and high frequencies of closure and opening of crushing chamber. The lack of fundamental understanding of the micro- processes that are facilitating both comminution and material transport in this new crusher necessitated a thorough investigation of key factors that drive comminution in this equipment. A combination of experimental and numerical modelling techniques was used to study the effect of key operating variables such as speed of the discs, offset between the vertical axes of the discs, feed size distribution and feed rate. The offset provides some flexibility in the system, but it does not significantly improve the crushing efficiency or the throughput. The speeds of the discs proved to be the key determinants of the degree of breakage achieved in the crusher. Both compressive and shear energies are active, with compressive energy dominating at lower speeds and decreasing with gradual increase in speed while the shear force increases with the increasing speed. Those trends render the device operating at higher speeds to be analogous to a laboratory pulveriser. Feed rates of at least 10 tph and feeds with wide size distributions (including near-vertical exit gap particles) are recommended for future studies in the quest to optimize the throughput of the crusher. Further work is recommended to investigate the effect of crusher profiles on the product quality (size and shape), power draw and throughput. It is anticipated that modifying the crusher profile can further intensify the crushing forces imposed on the particles. Consideration should also be given to increase the opening of the comminution cavity in order to be able to choke feed the crusher and thereby promoting rock-on-rock crushing. It is also recommended that the vibratory motion for the top disc be considered in order to intensify the compressive loads experienced by the particles. Overall, the redesign of this engineering device is necessary to reduce comminution by attrition due to disc-particle contacts and intensify the compressive forces.
Performance evaluation of reduced graphene oxide incorporated dye-sensitized solar cells for stable power generation
(University of the Witwatersrand, Johannesburg, 2024) Ikpesu, Jasper Ejovwokoghene; Iyuke , Sunny E.
Dye-sensitized solar cells (DSSCs) have emerged as a promising alternative to traditional silicon-based solar cells due to their low cost, easy fabrication, and high efficiency in converting sunlight into electricity. However, the performance of (DSSCs) is limited by the charge transfer and recombination processes at the interfaces between the different components of the device. In the recent years, Graphene Oxide (GO) and reduced Graphene Oxide (rGO) have been proposed as potential interfacial components to improve the performance of DSSCs. This research looked at the performance of reduced graphene oxide in dye-sensitized solar cells for sustained power generation. Most dye-sensitized solar cells have benefited from the usage of reduced graphene oxide. This research focuses on the performance of reduced graphene oxide in dye-sensitized solar cells for sustained power generation. Most dye-sensitized solar cells have benefited from the usage of reduced graphene oxide. This is due to its characteristics such as high surface area, superior transparency in the visible region, light absorption, and charge transport. Aerosol Assisted Chemica1 Vapour-Deposition (AACVD) was used to create a fluorine doped tin oxide (FTO) layer. The Hummer's Method was applied to synthesize reduced graphene oxide (rGO). Titanium (IV) oxide – reduced graphene oxide (TiO2-rGO) composite was synthesized at the photoanode via screen printing and spin coating, then inserted in DSSC using roselle dye as a natural dye sensitizer to investigate the cell performance. X-ray diffraction (XRD), ultraviolet diffuse reflectance spectroscopy, scanning electron microscopy/energy dispersive X – ray (SEM/EDX), and profilometry were used to characterize the synthesized/fabricated samples. Using a solar simulator and air mass A.M. 1.5 (100 mw/cm2), current-voltage (I-V) measurements were obtained to determine the performance of the cells. Tin oxide thin films doped with fluorine (F:SnO2) were successfully deposited on a glass substrate using the AACVD process at various doping percentages and the optical properties of the FTO and substrate layers were investigated using absorbance spectra. A low absorption value of 12% F: SnO2 resulted in a higher transmittance of 90% were achieved. This shows that the optical and electrical properties of the DSSC were altered by fluorine doped tin oxide. The results of the developed spin coated TiO –rGO Nano composites revealed that the Hall Effect increases with thin-film thickness iv while mobility increases with carrier concentration. The optical absorption results of TiO2–rGO nanocomposites demonstrate that as dopant amount increases, the band gap energy falls from 3.6 eV to 1.4 eV. The findings indicate that there is a strong interaction between Titanium dioxide (TiO2) and reduced Graphene Oxide (rGO), which could result in better visible light absorption and consequently improve light harvesting efficiency when utilized in a dye sensitized solar cell. Open circuit voltage (0.53 V), short circuit photocurrent (0.12 mA/cm2), fill factor (0.02), and photoelectric conversion efficiency (11.52%) were the simulation results for the cell parameters obtained for the DSSC manufactured using reduced graphene oxide. Meanwhile, the open circuit voltage (0.56 V), short circuit photocurrent (0.63 mA/cm2), fill factor (0.03), and photoelectric conversion efficiency (4.70%) of the DSSC without reduced graphene oxide were obtained. The power conversion efficiency of the dye-sensitized solar cell with graphene oxide was 6.82 % greater than that of the cell without graphene oxide. A four-week stability test was also performed on the DSSC fabricated with reduced graphene oxide to measure the extent of electrolyte deterioration. After the first 24 days, the short circuit current value reduced by 39% from its original value of 0.1190 mA/cm2. Under white light irradiation, the efficiency value of the DSSCs was found to be stable for the first 12 days before gradually decreasing to 24% of its initial value. The improved performance of DSSCs with reduced graphene oxide may be ascribed to an increase in electron transport efficiency and visible light absorption. When reduced graphene oxide was used, the performance improved due to increased light absorption, a wider range of absorption wavelengths, faster electron transport, and suppression of charge recombination. Based on this research, comparing the absorbance and transmittance of fluorine- doped tin oxide (F: SnO2) at 4%, 8%, and 12% with regard to wavelengths (ℷ) at 230 nm and 1100 nm; It shows that at 12% (F: SnO2), the lowest absorbance yields better transmittance, and increasing the cell's efficiency by 11.52%. The power conversion efficiency (PCE) of DSSCs demonstrates that DSSCs fabricated with reduced graphene oxide improved cell performance and outdoor stability. Which confirm that the TiO2 - rGO is a good material for solar application.
Development and Application of activated carbons from Avocado waste: Resource recovery for sustainable applications
(University of the Witwatersrand, Johannesburg, 2023) Mohale, Lehlohonolo; Mulopo, Jean
This research sought to produce activated carbons that could be used for hydrogen storage. The effect of hydrothermal pretreatment of the char, the effect of varying the activation ratio of KOH as the activation agent and the effect of activation temperature in producing these activated carbons were evaluated. Hydrothermal pretreatment of the char enhanced the properties of the resulting activated carbons. The best performing activated carbon was produced from the hydrochar pretreated at 200℃. It was observed that activation improved with increased activation agent concentration and activation temperature, to a point, and the best activated carbon was produced at 1:3 activation ratio and 800℃ activation temperature. This activated carbon had the highest total pore and micropore volumes of 1.45cm3/g and 1.16 cm3/g, respectively. The highest surface area of 2529.8m2/g was obtained, which is relatively higher than previously reported surface areas obtained from activated carbons created from coal or biomass. The porosity and the high surface area show well developed activated carbons that have desirable gas adsorption performance. The activated carbons had oxygen containing functional groups that aid in hydrogen sorption, the highest hydrogen sorption at 77K and 1 bar was 352 cm3/g, which supports the use of the produced activated carbons in the hydrogen economy. These activated carbons enable the circular economy. Well developed micropores were observed in the activated carbons produced through this work and their gravimetric capacity meets the DOE targets for hydrogen storage.
Investigating operational parameters that would affect the performance of a laboratory impact crusher
(University of the Witwatersrand, Johannesburg, 2022) Ndlovu, Mangaliso Nhlakanipho; Bwalya, Mulenga; Chipise, Liberty; Chimwani, Ngonidzashe
Impact crushers are widely used in the mining and construction industries to crush and size various types of materials. However, their performance can be affected by several operational parameters, including the rotor speed, rotor position, number of rotors and relative direction of rotors. The aim of this study is to investigate the impact of these parameters through a numerical model, Discrete Element Method (DEM). A Laboratory scale impact crusher was simulated using various configurations while also making use of a range of materials with known breakage data to predict expected grinding rates in the crusher. The Discrete Element Method (DEM) algorithm is a computational approach utilized to solve complex problems that involve numerous interacting bodies. In this technique, the dissipative forces (such as normal, tangential or frictional forces) at contact points are simulated using a spring-slider-dashpot model. While the movement of particles is computed using Newton's laws of motion. During simulations, the information about contact events are captured and saved in output files, which can later be used for various purposes. The energy spectra, a record of energy involved in every contact event of one such output that is utilised to predict the breakage of particles of different materials provided their breakage characteristics are known. Using the DEM simulation various equipment configurations of a laboratory impact crusher were conducted. The results showed that the rotor speed, number of rotors, rotor direction and rotor position significantly influenced the number of impacts and energy spectrum produced by the crusher. The crusher operation configuration significantly affected the energy spectra obtained. Additionally, the comparison of the crushing characteristics of the double rotor impact crusher to those of the single rotor impact crusher revealed differences in their performance that can be attributed to their design and operating parameters. - 3 - [OFFICIAL] The findings of this study provide valuable insights into the design and operation of impact crushers, and can be used to improve their efficiency and productivity when processing a variety of materials with different operational parameters.
Determinants of Professional Service Output Quality in the South African Construction Industry
(University of the Witwatersrand, Johannesburg, 2024) Govender, Neil; Laryea, Samuel; Watermeyer, Ron
The debate regarding the relationship between fees and the quality of professional services in the construction industry has persisted since the 1980s. In the South African context, members of professional industry bodies have strongly suggested that the declining quality of professional service outputs (PSOs) in the construction industry is due to low fees. While various studies in the construction literature have asserted that low or “discounted” fees are one of the main factors influencing the quality of PSOs, other studies have rejected this assertion. However, a comprehensive investigation into the major built environment professions, aimed at identifying and evaluating various factors influencing PSO quality, as well as understanding how and to what extent quality is specifically influenced by fees, is notably absent from the construction literature. To address this gap, a three-stage research design was employed. This design included an industry-wide survey with 604 participants, a survey of nine industry experts averaging 38 years of experience, and case studies conducted with seven built environment consulting companies. The data analysis involved a combination of content analysis, descriptive analysis, and thematic analysis. The study revealed nuances in the key factors influencing PSO quality across various built environment professions. While fees were identified as a key factor influencing PSO quality, other key factors, such as the time required to produce PSOs, experience, available information, and project briefs, were also identified. This highlights the need for project stakeholders to effectively manage professional fees in conjunction with these other key factors to ensure the quality of PSOs is not diminished. The findings of this study provide both clients and professionals with the knowledge to navigate the complex interplay between fees and PSO quality, ultimately fostering more successful and efficient projects.
Investigating aspects of rapid urbanisation and densification in Sub-Saharan Africa and the effect on the physical morphology of selected suburbs in Johannesburg
(University of the Witwatersrand, Johannesburg, 2024) Dörmann, Kirsten; Jenkins, Paul
This study examines the transformation of the South African version of the bungalow from a free-standing house into a courtyard form of building – seen as a bungalow ‘compound’– due to the significant change in occupancy. It focuses on two lower-income inner-city neighbourhoods of Johannesburg, Yeoville and Rosettenville. Both were created at the beginning of the 20th century, on either side of the city’s mining belt. After the political changes in 1990, these neighbourhoods have been almost completely re-populated with immense socio- cultural changes – and intensely densified. This radical change has, however, been kept hidden behind the boundary walls of the private properties. There has been little attention and very limited evidence concerning the alterations to the properties despite them being widespread. The research brings a new understanding of the ‘transformed house on the plot’ and its life forms as part of wider city-making processes. Although based on a typological approach to reading the change of the domestic spaces over time, this is analysed in-depth vis-à-vis social, economic, juridical, and political entanglements and highlights the need for transdisciplinary knowledge transfers. The study examines the bungalow compounds through innovative design research, applied via a Case Study approach, to a particularly complex category of ‘as built’ documentation. It investigates the outcome as a form of re-description of a part of the transforming African city – rather than the standard sterile service instrument of spatial administration. In this context, the pattern book and the notion of type are revisited to develop an alternate catalogue of properties based on more than thirty detailed case studies. Methodologically, the research considers the bungalow compound as an epistemic object that can manifest as a problem space across multiple themes, scales, and contexts. In doing so, the study addresses the misconception of architecture as a finished product and appropriates essential incompleteness as a device to locate relevant knowledge(s). It considers the inevitable lack of complete evidence as an opportunity to understand the documentation of these emerging dynamic ‘house worlds’ as readings of what is and what could be.
Project Reality - Imagining the symbiotic relationship between virtual reality and the human narrative
(University of the Witwatersrand, Johannesburg, 2024) Peneda, Michael
With virtual reality technology being ever more integrated in our daily lives, through the accessibility to technology such as smartphones, personal computers, the internet, and social media. The potential possibilities for exploration, education, historical preservation, spatial exploration and how we define reality are endless. With the Newtown precinct having historical, educational, and recreational facilities within the heart of Johannesburg yet not functioning as a true representation of a cultural precinct. It provides the perfect catalyst for a virtual reality centre that enables the public to access this technology and explore its vast potential whilst reviving and transforming Newtown into a functional cultural precinct. Whilst being supported by the surrounding public infrastructure as well as creating a new pillar to support the precinct. This virtual reality centre provides the ability for users to explore both the virtual realm and the physical, while being able to easily transition from one to the other. With new ways of engaging with spatial exploration, immersive education, and new representations of historical narratives. With the building functioning as an amalgamation of new representations of classical typologies such as museums, exhibition spaces, galleries, research development and education facilities. By housing the functionalities of these typologies within the centre yet representing them in new ways with unique ways of engaging with them.
A Review of the Stope Support System at Impala Bafokeng North Shaft Owing to Stope Closure at Shallow Mining Depths
(University of the Witwatersrand, Johannesburg, 2024) Walsh, Trevor; Stacey, Thomas
Impala Bafokeng’s North Shaft is a shallow platinum mine on the western limb of the Bushveld Igneous Complex. Shallow mines experience very little horizontal stress which leads to a support issue of the tensile zone. North Shaft relies heavily on mine pole support due to the requirements for a stiff support system. Elongate support failure in the deeper parts of the mine have occurred due to a change in the loading environment. The support failure has resulted in inadequate support resistance in the back areas and some large falls of ground. In this research report the Hybrid Section stope closure rate was measured. The closure does not appear to be linked to a detachment of a hangingwall parting. The ground penetrating radar scans and borehole data correlate with the observations. The falls of ground are structure related and occur in the back areas of the panel after the elongate support had failed. The footwall material is weaker than the hangingwall material and the pillar punches into the footwall. The footwall fractures and tensile cracks in the panel footwall indicate that the stresses are forced to move horizontally due to the footwall 4 parting plane. The footwall thrusts into the panel causing the high closure observed. The combination of a shorter panel length and pencil sticks would provide adequate support for the high closure rates observed.

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