The failure behavior of concrete materials is not completely understood because conventional test methods fail to assess the material response independent of the sample size and shape. To study the influence of strength and strain affecting test conditions, four typical concrete sample types were experimentally evaluated in uniaxial compression and analyzed for strength, deformational behavior, crack initiation/propagation, and fracture patterns under varying boundary conditions. Both low friction and conventional compression interfaces were assessed. High-speed video technology was used to monitor macrocracking. Inferential data analysis proved reliably lower strength results for reduced surface friction at the compression interfaces, regardless of sample shape. Reciprocal comparisons revealed statistically significant strength differences between most sample shapes. Crack initiation and propagation was found to differ for dissimilar compression interfaces. The principal stress and strain distributions were analyzed, and the strain domain was found to resemble the experimental results, whereas the stress analysis failed to explain failure for reduced end confinement. Neither stresses nor strains indicated strength reductions due to reduced friction, and therefore, buckling effects were considered. The high-speed video analysis revealed localize buckling phenomena, regardless of end confinement. Slender elements were the result of low friction, and stocky fragments developed under conventional confinement. The critical buckling load increased accordingly. The research showed that current test methods do not reflect the ''true'' compressive strength and that concrete failure is strain driven. Ultimate collapse results from buckling preceded by unstable cracking. Suplemental Files: Additional video files, that supplement the test results presented in Chapter 4, can be accessed through the Florida State University Library System. The high-speed videos were selected to exemplify each specimen type (tall cylinder, small cylinder, column, and cube) under both boundary conditions (conventional and reduced surface friction). 01_TallCylinderConventionalFriction.mp4 - Tall cylinder under conventional friction 02_TallCylinderReducedFriction.mp4 - Tall cylinder under reduced friction 03_SmallCylinderConventionalFriction.mp4 - Small cylinder under conventional friction 04_SmallCylinderReducedFriction.mp4 - Small cylinder under reduced friction 05_ColumnConventionalFriction.mp4 - Column under conventional friction 06_ColumnReducedFriction.mp4 - Column under reduced friction 07_CubeConventionalFriction.mp4 - Cube under conventional friction 08_CubeReducedFriction.mp4 - Cube under reduced friction / A Dissertation submitted to the Department of Civil and Environmental Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Fall Semester, 2012. / September 19, 2012. / compression, concrete, crack, failure, fracture, high-speed video / Includes bibliographical references. / Michelle Rambo-Roddenberry, Professor Co-Directing Dissertation; Wei-Chou Virgil Ping, Professor Co-Directing Dissertation; Peter N. Kalu, University Representative; Kamal Tawfiq, Committee Member.

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Plastic bottles were first used commercially in 1947 but remained relatively expensive until the early 1960s when high-density polyethylene was introduced, with its attractive characteristics such as being strong, lightweight, durable, cheap, and resistance to breakage. Decomposition of plastic bottles or other plastic products can last from 400 to 1000 years; before this process happens, the plastic waste becomes a problem to the environment continuing to clog our waterways, forest, oceans and others natural habitats. As the capacity of landfills decrease and urbanization leads to rapid growth rates in the human population, either in Africa or any part of the world, this concern brought forward the need for this study. The research aimed to present an end-use solution for plastic bottles by investigating the feasibility of utilizing the plastic bottles as reinforcing elements in problematic soils encountered in the construction industry. In South Africa, plastic bottle waste has continued to increase despite efforts by government in the form of new waste legislation and taxes on plastic bottles. Hence, there is a need to find alternative uses for plastic bottle waste. The use of plastic bottle waste shreds as a soil reinforcement material in geotechnical engineering applications can help mitigate the disposal problems associated with plastics. In this study, a series of direct shear tests were conducted to examine the effect of plastic waste shredded pieces on the engineering properties of Cape Flats and Klipheuwel Sand. The shredded plastic bottles that were used for this study were sourced from Kaytech (supplier and manufacturer of Geosynthetics) in South Africa. The research was done to utilize this plastic through the inclusion of shredded plastic bottles as a form of soil reinforcement. The effects of introducing polyethylene shreds cut from used plastic bottles on the settlement parameters were investigated. It was found that presence of plastic shreds improved the shear strength parameters of the sand soil and they tend to improve further with increasing in plastic shred dosage. The cohesion reached its maximum value for both sands at a shred dosage of 30% by dry mass of the soil.

The combination of MFI zeolite nano-sheets with competitive adsorption of water (H2O) in hydrocracking of long-chain paraffins presents a promising opportunity to produce diesel with high yield and with high cetane number. Thus, in wet hydrocracking of a long-chain paraffin (n-hexadecane (n-C16)) over MFI nano-sheets, it was investigated whether catalytic activity increased with increasing number of Brønsted acid (H + ) sites (decreasing silicon-to-aluminium (Si/Al) ratio), while secondary cracking remained completely suppressed. Also, it was investigated whether more Al atoms could be incorporated into the framework of MFI nano-sheets by modifying the new synthesis method. It was demonstrated that the new synthesis method, which utilizes C22H45–N + (CH3)2–C6H12–N + (CH3)2–C6H13 (C22-6-6) as structure-directing agent (SDA), could be extended to various Si/Al ratios in the range 25 – 100. The nano-sheets exhibited extra-framework Al (EFAl) species. Nano-sheets with Si/Al = 75 exhibited an oddly large amount of EFAl species compared to the other nano-sheets. For nano-sheets with Si/Al = 75, a high fraction of the EFAl species may have formed during calcination of the ammonium form and may encompass flexible Al species with predominantly Al in octahedral coordination (AlVI). Nano-sheets were loaded with 0.9 wt% platinum (Pt) via incipient wetness impregnation (IWI). Pt/nano-sheets with Si/Al = 25, 50 and 100 exhibited similar and high Pt dispersion (γPt). In contrast, Pt/nano-sheets with Si/Al = 75 exhibited a very low γPt, which was probably a result of the abundance, nature and/or location of EFAl species present in the support. In dry hydrocracking of n-C16, the catalytic activity increased with decreasing Si/Al ratio, strongly suggesting that the number of H+ sites increased with decreasing Si/Al ratio. Nano-sheets with Si/Al = 75 most likely contained AlVI species associated with Brønsted acidity, supporting the presence of flexible AlVI species. In wet hydrocracking of n-C16, at a constant and sufficiently high γPt, the activity increased with increasing number of H+ sites (decreasing Si/Al ratio), while secondary cracking remained completely suppressed. Pt/nano-sheets with Si/Al = 75 displayed a lower activity than 2 Pt/nano-sheets with Si/Al = 100, which may be a result of the very low γPt of Pt/nano-sheets with Si/Al = 75, underlining the importance of high γPt. For Pt/nano-sheets with Si/Al = 25, 50 and 100, H2O favoured linear cracking products at low cracking yields. In contrast, for Pt/nano-sheets with Si/Al = 75, H2O favoured branched cracking products, which may be a result of Pt sites on the external surface of the support being too far from the H+ sites inside the micropores. The new synthesis method could be extended to a modified SDA, namely C22H45–N + (CH3)2–C6H12–N + (CH3)2–C3H7 (C22-6-3), at various Si/Al ratios in the range 25 – 100. Replacing the terminal –C6H13 group in C22-6-6 with –C3H7 resulted in an increase in the framework Al (FAl) content of MFI nano-sheets with Si/Al ≥ 50, with the increase being the most pronounced for nano-sheets with Si/Al = 50. This was due to the increased occupancy of the zeolite framework by the hydrophilic region of C22-6-3 in comparison to the hydrophilic region of C22-6-6 under the given set of synthesis conditions, since –C3H7 was less bulky than –C6H13. Calcined nano-sheets were loaded with 1 wt% Pt via competitive ion exchange (CIE). In dry and wet hydrocracking of n-C16, the activity increased with decreasing Si/Al ratio and in wet hydrocracking, secondary cracking was not completely suppressed up to high conversions. This was probably due to the presence of additional H+ sites generated after SDA removal. H2O favoured linear cracking products at low cracking yields. Sodium (Na+ ) ion-exchanged nano-sheets were loaded with 1 wt% Pt via CIE. The average Pt size (dPt) of the Pt/Na+ nano-sheets were larger than the dPt of the Pt/calcined nano-sheets, which may be a result of the nature and/or location of EFAl species present in the Na+ supports. In dry and wet hydrocracking of n-C16, differences in activity were observed and in wet hydrocracking, secondary cracking was not completely suppressed up to high conversions. This was probably due to insufficient intimacy between H+ sites and Pt sites such that the rate was controlled by diffusion of olefinic intermediates from H+ sites to Pt sites and vice versa. H2O favoured linear cracking products at low cracking yields.

Shells find applications in many engineering disciplines (Zingoni 1997), with containment shells of revolution being among the most important (Zingoni 2001, 2015). Searching for the most efficient geometrical forms remains one of the most important goals of shell research. Associated with that is the need to develop appropriate analytical tools for novel shell forms. Complete toroidal shells are not widely used shells of revolution owing to their geometries and associated complexities in the theory of the shells. They can offer certain structural and functional advantages over conventional shells and are mainly used for fluid containment. Toroids have also been proposed for nuclear fusion reactors, rocket fuel tanks, medical hyperbaric treatment units and applications in aerospace and underwater fields. Any desired cross-sectional forms of the shells can be developed theoretically, suggesting the possibility of adopting toroidal shells in many engineering applications if the behaviour of the shells can be understood and quantified. The design analysis of thin-walled structures is mostly based on strength and stiffness considerations. Based on linear elastic theory, Zingoni, Enoma & Govender (2015) presented an elegant theoretical solution for the non-shallow bending of an elliptic toroid, while Enoma and Zingoni (2017) have investigated toroidal shells having the same type of multi-shell cross-section as was first proposed by Zingoni (2001) for novel sludge digester shells. On the basis of classical elastic shell theory and numerical modelling, this thesis attempts to provide a framework upon which complete toroidal shells of any cross-sectional profile can be analysed, and investigates the state of stress and buckling of selected toroidal shell forms including unconventional ones under axisymmetric pressure loading, i.e. when each of the shells is used as a pressure vessel and a storage tank. Following the general strategy developed for shells of revolution by Zingoni (1997) over the past 20 years, reasonably accurate results for shell stresses are derived by combining the membrane solution with an approximate solution of the bending-theory equations for toroidal shells, instead of attempting to solve the exact differential equations, which is extremely difficult. The developed formulations are applied to various cross-sectional types of toroidal vessels under both uniform pressure and hydrostatic pressure loading, and the accuracy of the formulation is verified in each of the cases through numerical examples with finite-element analysis. For the buckling considerations, governing stability equations of toroidal shells of any cross section are presented. These are specialised for the problem of a multi-shell toroid under uniform external pressure, and approximately solved to obtain the critical buckling solution for this geometry. The proposed solution approach provides accurate failure loads of pressurised multi-shell toroids when compared with those from a finite-element analysis. Finite element modelling is then used to study the nonlinear effects on the buckling response, post-bifurcation behaviour and geometric imperfection sensitivity of this type of vessel, as well as two other cross-sectional geometries (parabolic-ogival and circular-elliptic). Extensive parametric studies on each of these toroids reveal significant aspects of shell behaviour. This thesis represents a significant extension of the work of the group of Prof. Zingoni at the University of Cape Town, and provides much-needed information on the design of new forms of toroidal vessels. The simplified theory developed for the determination of stresses and buckling behaviour has facilitated the investigation of the effects of the various geometric parameters, which in turn has led to new insights on the behaviour of the toroidal shell. It has been found that perfect toroidal vessels under external pressure loading can generally have stable post-buckling behaviour and may, therefore, be able to resist further load beyond the elastic bifurcation loads. The imperfection sensitivity of each of the toroids investigated is seen to vary from shell to shell.

Electrical Impedance Tomography (EIT) is a noninvasive imaging technique that reproduces images of cross-sections, based on the internal impedance distribution of an object. This Dissertation investigates and confirms the use of a dual current stimulation EIT (DCS EIT) system. The results of this investigation presented a size error of 2.82 % and a position error of 5.93 % in the reconstructed images, when compared to the actual size and position of the anomaly inside a test object. These results confirmed that the DCS EIT system produced images of superior quality (fewer image reconstruction errors) to those produced from reviewed single plane stimulating EIT systems, which confirmed the research hypothesis. This system incorporates two independent current stimulating patterns, which establishes a more even distribution of current in the test object, compared to single plane systems, and is more efficient than 2.5D EIT systems because the DCS EIT system only measures boundary voltages in the center plane, compared to 2.5D EIT systems that measure the boundary voltages in all electrode planes. The system uses 48 compound electrodes, divided into three electrode planes. Current is sourced and sunk perpendicularly in the center plane, to produce a high current density near the center of the test object. Sequentially, current is sourced through an electrode in the top electrode plane and sunk through an electrode in the bottom plane, directly below the source electrode, to produce a high current density near the boundary of the test object, in the center plane. During both injection cycles, boundary potentials are measured in the center plane. Following the measurement of a complete frame, a weighted average is computed from the single and cross plane measured data. The weighted measured voltages, injected currents and Finite Element Model of the object is used to reconstruct an image of the internal impedance distribution along a cross-section of the object. This method is applicable to the biomedical imaging and process monitoring fields.

High Frequency Surface Wave Radar (HFSWR) is used around the globe for the mapping of sea currents and coastal monitoring of the Exclusive Economic Zone. Decision to build an HF radar at the University of Cape Town (UCT) was made by Daniel O’Hagan and Andrew Wilkinson in February 2015 immediately after seeing a demonstration of the CODAR system at IMT. Their intention was subsequently discussed at several meetings, including a South African Radar Interest Group (SARIG) meeting and one at IMT in order to gauge interest and raise funding. There was both interest (mainly for ocean current monitoring) and scepticism (expressed by CSIR and SARIG members) of the value of HF radar for ship monitoring. This reports the design, construction, test, and evaluation of the UCT HFSWR demonstrator. A modular approach was taken in its design and construction making it easy to replicate and upscale. A pillar of this work is to prove the feasibility of a software defined radar (SDR) based HF radar demonstrator. Every part of the demonstrator was designed and constructed from scratch as UCT had no prior HF activities, and therefore no legacy antennas or components to utilise. A low-cost RF frontend follows the HF antennas, which were also designed for this project. Combined with an SDR platforn known as the Red Pitaya (RP), a complete HF radar demonstrator was assembled and trials were conducted at the UCT rugby field and at the IMT facilities in Simon’s Town. A preliminary assessment of the results reveal the effects of Bragg resonance scatter and detection of two stationary targets (mountains) distinguishable by both range and azimuth. This assessment of the results indicates that the demonstrator is operational.

The fields of digital image processing (DIP) and computational photography are ever growing with new focuses on coded aperture imaging and its real-world applications. Research has shown that coded apertures are far superior to traditional circular apertures for various tasks. A variety of coded aperture patterns have been proposed and developed over the years for use in various applications such as defocus deblurring, depth estimation and light field acquisition. Traditional coded aperture masks are constructed from static materials such as cardboard and cannot be altered once their shapes have been defined. These masks are then physically inserted into the aperture plane of a camera-lens system which makes swapping between different patterned masks difficult. This is undesirable as optimal aperture patterns differ depending on application, scene content or imaging conditions and thus would need to be changed quickly and frequently. This dissertation proposes the design and development of a programmable aperture photography camera. The camera makes use of a liquid crystal display (LCD) as a programmable aperture. This allows one to change the aperture shape at a relatively high frame rate. All the benefits and drawbacks of the camera are evaluated. Firstly the task of performing deblurring and depth estimation is tested using existing and optimised aperture patterns on the LCD. A light field is then captured and used to synthesise virtual photographs and perform stereo vision. Thereafter, exposure correction is performed on a scene based on various degrees of illumination. The aperture pattern optimised online based on scene content outperformed generic coded apertures for defocus deblurring. The programmable aperture also performed well for depth estimation using an optimised pattern and existing coded apertures. Using the captured light field, refocused photographs were constructed and stereo vision performed to accurately calculate depth. Finally, the aperture could adjust to the different levels of illumination in the room to provide the correct exposure for image capture. Thus the camera provided all the advantages of traditional coded aperture imaging systems but without the disadvantage of having a static aperture in the aperture plane.

The MeerKAT radio telescope in South Africa is required to tag the arrival time of a signal to within 10 ns of Coordinated Universal Time (UTC). The telescope has a local atomic clock ensemble and uses satellite based remote clock comparison techniques to compare the telescope time to UTC. The master clock timing edge is distributed to each telescope antenna via an optical fibre precise time transfer. Although the timing accuracy of the telescope time was measured internally by the telescope, there is a need for an independent method to verify how well each antenna and its associated processing stages are aligned to UTC. A portable GNSS time-pulse radiator (GTR) device for testing the time-stamp accuracy was developed. The GTR was calibrated at the National Metrology Institute of South Africa and laboratory characterisation tests measured its RF timing pulse to be 1.32 ± 0.100 µs ahead of the UTC second. The telescope’s time and frequency reference clock ensemble consists of two hydrogen masers, an ultrastable crystal and GPS disciplined Rubidium clocks. During operation, the GTR radiates a broadband GPS time synchronised RF timing signal at a known distance from the telescope antennas and the corresponding timestamps were compared to the expected value. Recent GTR timing tests performed on one of the MeerKAT antennas showed that the telescope’s generated timestamps associated with the GTR’s RF timing signal coincided with the expected delay of approximately 16 ± 0.1 µs measured from an antenna 4.8 km away from the telescope’s master clock transmitter. Ultimately we used the GTR to verify that the telescope time and UTC were aligned to within 100 ns. Future work is planned to improve the profile of the transmitted signal and timing critical hardware in order to reduce the GTR’s error budget.