School of Civil & Environmental Engineering (ETDs)
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Item 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, VincentThis 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.Item 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 , MikeThe 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 activityItem Developing of a parametrically resonw1t vibrating screen, modelling, simulation and dynamic testing(University of the Witwatersrand, Johannesburg, 2023-07) Mohanlal, Mishal; Li, KuinianA novel coupled spring pendulum vibrating screen is proposed with the goal of developing efficient screening using parametric resonance. A simple spring pendulum is initially studied to provide the basis of the dissertation. The theoretical model of the proposed vibrating screen is developed using Lagrangian mechanics which includes damping and generalized forces. Two derivations of the vibrating screen are proposed, the first being a 4DOF (degree of freedom) system and the second being a 3DOF system. The 3DOF system is found to present better numerical stability and is thus utilized for the study. It is shown that the 3DOF system is comparable to the simple spring pendulum for the case where initial conditions are applied to similar coordinates. The proposed vibrating screen presents motion which is not indicative of traditional vibrating screens. It is found that a system where attributes are sized for parametric resonance requires far smaller excitation forces to achieve higher accelerations and displacements compared to traditional vibrating screens. The proposed vibrating screen is an unfeasible design due to the large displacements; high foundation loads and limitations on mechanical components. Discrete element method (DEM) simulations of the proposed vibrating screen are performed to study the efficiency with varying inclinations of the mesh deck. The results are compared to a linear motion vibrating screen. The proposed screen requires far less energy compared to traditional vibrating screens and achieves higher efficiencies with larger deck inclinations. The derived differential equations are verified by experimental testing using free vibrations. The numerical simulations and experimental tests present a good correlation. Signal processing is implemented to compare the natural frequencies from the experimental testing and numerical simulations, the results present a good correlation.Item A Comparative Study of the Efficiencies of Vertical Bracing Practices(University of the Witwatersrand, Johannesburg, 2023-11) Saunders, Shawn Wayne Valintino; Elvin, AlexThe efficiencies of cross sections and configurations applied to vertical bracing are investigated by evaluating reference configurations (RCs), composed of cross braced circular hollow section (CHS) members, against comparative configurations (CCs), consisting of cross-braced Angle members, and single-CHS members. The metrics used to evaluate efficiencies were mass, raw materials costs, and fabrication and erection costs. CCs were found to be more efficient than RCs for most analysed cases, metric and configuration dependent. The following results were found: i. Mass metric a. Crossed-Angle more efficient in 79% of analysed cases. b. Single CHS more efficient in 87% of analysed cases. ii. Raw materials costs metric a. Crossed-Angle more efficient in 92% of analysed cases b. Single CHS more efficient in 88% of analysed cases iii. Fabrication and erection costs metric a. Crossed-Angle more efficient in 90.4% of analysed cases b. Single CHS more efficient in 88.5% of analysed cases Inversions of the efficiency parameter findings, with RCs more efficient than CCs, were observed when: i. RC CHS member slenderness ratios were less than 80-90. ii. CC design loads were greater than 225 kN, 1200 kN and 1500 kN for mass, raw materials and total cost efficiency metrics, respectively