Browsing by Subject "Civil Engineering"
Now showing 1 - 20 of 398
Results Per Page
Sort Options
- ItemOpen AccessA numerical investigation of the dynamic behaviour of continuous, multi-span railway bridges(2018) Ludwig, Chad; Moyo, Pilate; Busatta, FulvioThe dynamic behaviour of railway bridges has been investigated for over a century [Ichikawa et al., 2000]. With the introduction of high speed trains in recent history, a host of complex problems regarding resonance have been observed and studied. These studies, which include Bjorklund [2004]; Gabald´on et al. [2009]; Goicolea et al. [2002]; Rigueiro et al. [2010]; Kumaran et al. [2003]; Kwark et al. [2004] and Xia and Zhang [2005], have focused on resonance in relatively short-spanned simply supported railway bridges. New design methods were incorporated in design codes such as Eurocode (EN 1991-2) [2003] to address these problems in practice. In the past, railway bridges were designed for static effects, while dynamic effects were accounted for by the application of an amplification factor. It has become increasingly necessary to perform a full dynamic analysis, especially with regard to high speed trains. In the case of continuous, multi-span railway bridges carrying heavy haul trains, such an analysis is not explicitly specified. Design codes, even as recent as the modern Eurocode (EN 1991-2) [2003], do not address scenarios where axle loads are higher than 30 tonnes/axle, or trains become very long. Previous work on the dynamic behaviour of continuous bridges is limited. The dynamic properties of continuous beams was studied as early as Lin [1962], and more recently by Saeedi and Bhat [2011]. The response of continuous beams or bridges subjected to moving forces or masses was studied by Cheung et al. [1999], Johansson et al. [2013] and Ichikawa et al. [2000]. These investigations were limited to analytical methods to determine the dynamic properties (natural frequencies and mode shapes) and response of beams or bridges. In this research, the response of multi-span, continuous bridges trafficked by heavy haul trains travelling at low to moderate speeds was investigated. The study comprises an investigation of bridges with spans ranging from one to ten, and span lengths of 40 m, 45 m and 50 m modelled using the Finite Element Method in SOFiSTiK. Loading is based on heavy haul trains, which were modelled using the moving forces load model. Natural frequencies and mode shapes were obtained, and displacements and accelerations were calculated for train speeds varying from 20 km/h to 100 km/h. A case-study of the Olifants River Viaduct (ORV), the longest continuous railway bridge in South Africa, is also carried out. From the study it is evident that as the number of bridge spans increase, the envelope of natural frequencies in the concentrated zone increase but the frequencies become very closely spaced, indicating that the modes might be difficult to determine experimentally. Displacement and accelerations were generally higher in the first and last span of the multi-span models. A difference in maximum displacements was only noticeable when comparing models with the number of spans ranging from 1 – 4, thereafter maximum displacements were not affected by the number of spans in the model. Accelerations increased as the speed increased. At low speeds, the number of spans did not significantly influence the peak deck acceleration, however, at higher speeds models with the greater number of spans generally had lower maximum accelerations.
- ItemOpen AccessA Practical Carbonation Model for Service Life Design of Reinforced Concrete Structures(2021) Harold, Romuald Fotso Lele; Beushausen, Hans-Dieter; Alexander, MarkThe increase in atmospheric carbon dioxide concentration due to global warming has a direct impact on the amount of carbonating concrete structures. For the past years, numerous studies have been done in South Africa on the subject and models developed to predict carbonation in concrete structures. Despite the large amount of resources and research effort put into developing these models, the translation from theory to practice represents a great challenge for design engineers in the field of durability design. This study presents a design tool based on existing models for use in practical applications. The proposed design tool assists in computing the service life of carbonating concrete structures and provides reliability values associated with the service life. It accounts for different binder compositions and binder types, as well as different locations and environmental land uses in South Africa. The validation of the design tool was done by comparing the service life prediction results to existing models, which generally showed good agreement. The developed design tool can be applied for predicting the long-term performance of new RC structures as well as improving the basis for quality assessment of existing, newly built RC structures. For the design of new structures, the designer is required to make certain assumptions concerning the information to be used for the simulation. These include values for the binder type, binder content, OPI, cover depth, land use and exposure parameters. For the quality control of new structures, the way in which the model parameters are obtained differs from that of new structures. As the structure already exists, both the concrete quality, cover depth and environmental loading can be measured directly on the structure with appropriate testing procedures. The outcome of applying the design tool for the analysis of concrete produced for the Gauteng Freeway Improvement project (GFIP) is also presented, with a case study of precast and in-situ structures chosen for the analysis.
- ItemOpen AccessA System Modelling Approach to Assessment of Hybrid Water Supply Solutions in eThekwini Municipality(2021) McKune, Danica; Carden, KirstyWater security in South Africa is a major concern, particularly in the context of urbanisation, the concomitant increases in water demand, and the potential for climate change to aggravate water shortages. Provision of basic services remains a significant challenge. Improving economic and social equity, vitally supported by adequate water supply and water quality, while ensuring environmental sustainability (maintaining water resources requires healthy ecosystems) is the dual challenge facing South Africa. There is growing recognition of the need for alternative approaches to water management, such as Sustainable Urban Water Management (SUWM). Decentralisation and integration to allow consideration of the total water cycle are fundamental themes of the SUWM paradigm. There is theoretical and experiential evidence that the current infrastructure archetype (of conveying a particular water stream from origin to destination by the most efficient means) could benefit from inclusion of such principles. SUWM is purported to have three core benefits: (1) A more natural water cycle, (2) Improved water security through diversification of sources, and (3) Resource efficiency. A complete transition to alternative water provision models is neither economical nor practically feasible in already developed areas, necessitating innovations in new areas and as retrofits to existing systems; systems where the water services configuration is evolving in this way are termed hybrid systems. Alternative water provision models bring dynamic changes to existing systems which may not be intuitive: the complexity of urban water systems and the resulting uncertainty means an intervention may achieve one SUWM objective yet undermine another. Thorough evaluations of alternative water provision models are therefore essential, while recognising that less learned experience on the performance of innovative solutions means uncertainty remains part of the evaluation. This research therefore aims to contribute to the theoretical body of knowledge on the net system effects of integrated management of the water cycle where alternative and decentralised solutions are introduced to existing systems. The overarching research objective was therefore application of an assessment framework, which was underpinned by the development of a systems dynamics model in GoldSim software. The systems dynamics model has been tailored for application to the selected case study area – eThekwini Municipality in South Africa. Akin to most South African cities, this region is home to a diverse range of consumers (fully serviced urban suburbs, informal settlements, peri-urban settlements, and rural areas), is experiencing urbanisation and growth in demand, and is supplied by catchments whose water resources are fully developed and are at risk of becoming significantly stressed. This is set against a backdrop of challenges in service delivery, environmental concerns as a result of water practices, potential impacts of climate change in the future, and ultimately sustainability of service provision. The developed systems dynamics model is a macro-scale integrated flow model, capable of assessing implementation of water servicing scenarios (specifically any combination of Water Conservation and Water Demand Management, rainwater harvesting, stormwater harvesting, groundwater use, greywater reuse, wastewater recycling, and desalination) at a regional level. Monte Carlo analyses were carried out to test system sensitivity to uncertainty in particular parameters. Of the possible interventions, five scenario paths were assessed: (1) Baseline, or “business as usual”, (2) WCWDM, (3) rainwater harvesting and real loss reduction, (4) greywater reuse and WCWDM, and (5) wastewater recycling and real loss reduction. Considered against the three core benefits of SUWM, each of the intervention scenarios yielded positive results. The developed model proved valuable in the scoping of SUWM interventions, and understanding the system-wide effects SUWM interventions may have on the water cycle. Such systems modelling approaches may therefore be considered to provide the framework and parameters within which further detailed and project-specific hydraulic and contaminant transport analysis could take place.
- ItemOpen AccessA System-Wide Model for Solid Waste Separation and Food Waste Discharge to Sewer Systems(2022) Angula, Shalongo; Ikumi, David S; Gaszynski, ChrisThe emergence of the circular economy, together with the changing paradigms in resource and environmental management, has resulted in a call to (1) convert wastewater treatment plants (WWTPs) to water resource recovery facilities (WRRF) and (2) diversion of organic waste (i.e., food waste) from landfills. Due to excess anaerobic digester (AD) capacities at most WWTPs, it has been proposed to co-digest sewage sludge and food waste in the AD at WWTPs to enhance resources (mainly energy and nutrient) recovery. However, suitable options for sustainable food waste handling (i.e., separation and transport) and the characteristics of food waste have not been established, particularly in South Africa. Without characterising food waste, it is impossible to include it in WWTP simulation models. In this study, food waste and sewage sludges were limited to the household food waste and primary sludge categories, respectively. A detailed review on alternative sustainable solid waste separation and food waste transport systems was carried out and a review paper was submitted to Environmental Challenges journal for publication. The experimental investigation of the study focused on identifying the biodegradable organic composition of selected substrates, i.e., primary sludge (PS), food waste, and PS and food waste blend. PS was obtained from Belville Wastewater Treatment Works (BWWTW) in Cape Town, while food waste was manually simulated. The augmented biomethane potential (ABMP) experiment was used to obtain the required research data. The ABMP data was used to determine the substrates' biodegradable composition. The biodegradable composition was carried out using two approaches. The first approach is the mass balanced bioprocess stoichiometric calculations, which used the measured start and end concentrations of the ABMP experiment. The second approach is the parameter estimation procedure, which used the mass balanced steady-state AD model of Ikumi et al. (2015) together with its built-in parameter estimation function. With the exception of methane COD produced, there were slight to moderate differences between the measured and modelled experiment results. However, the modelled experiments produced significantly higher methane COD than the measured experiment, suggesting a high-level error associated with the gas measurement. As a result, the modelled experiment and the substrates' composition obtained using parameter estimation were chosen to be more accurate and reliable. The results revealed that anaerobic digestion of food waste and co-digestion of primary sludge and food waste produces 41% and 21% more methane than the anaerobic digestion of primary sludge, respectively. The methane produced is equivalent to the potential energy recoverable. These findings suggest that diverting food waste from landfills to WWTP's AD systems can potentially enhance energy recovery. This highlights the potential need to revise urban wastewater systems to include solid waste separation and food waste diversion to AD systems to enhance resource recovery.
- ItemOpen AccessAbrasion resistance of IV-RCC used to construct spillway concrete steps of South African dams(2018) Poyo, Myezo; Beushausen, HansThis dissertation outlines the investigation on abrasion resistance of roller compacted concrete designed for the spillway steps of dams owned by the Department of Water and Sanitation. Literature on abrasion resistance of concrete has been reviewed and factors affecting abrasion resistance are discussed. Among these include hardness of concrete, aggregate/paste bond, type of aggregates, concrete compressive strength, curing, surface treatment and the quality of the concrete surface which is influenced by the finishing method. Available test methods as outlined by ASTM International Standards are also discussed in the literature review but only two methods (sandblasting method and wire brush method) were used in this research. These have been chosen because of their availability (at the UCT Civil Engineering Laboratory) and relevancy to this research. The sandblasting method is the most relevant in this research because it stimulates similar abrasion action as waterborne action on the concrete surface. The other method has been chosen for its availability in the UCT lab, to compare its results with the sandblasting results, and to evaluate whether if it can be used to assess abrasion resistance of hydraulic structures. A two-way experimental approach was adopted to achieve results for this research. The first approach was a laboratory investigation, where concrete cubes were produced under controlled conditions and tested for abrasion resistance, compressive strength, oxygen permeability index (OPI) and Sorptivity test. The durability index tests were conducted to get a general evaluation of the concrete’s microstructure. If the OPI values are acceptable (more than 9) then the concrete’s general microstructure would be accepted to be durable. Materials (aggregates) from De Hoop Dam and those readily available at the UCT laboratory were used to cast different types of concrete to be investigated and compared. The types of concrete included conventional concrete, fly ash concrete and slag (GGBS) concrete. DWS uses fly ash in the majority of their mass concrete projects due to its pozzolanic properties which help slowing down the heat of hydration. The slag was included in these mixes in order to have available results when it is used in future projects as it is highly likely to be used for areas in the KwaZulu-Natal province which have a less reactive type of slag in terms of heat of hydration. The raising of the Hazelmere Dam, close to Durban, is currently using GGBS as an extender. The second approach of this research was based on abrasion testing of cores drilled from the stepped wall of De Hoop Dam. These cores were drilled and taken to UCT laboratory for investigations with the same test methods used for laboratory cubes. A comparison was drawn between the test results of the laboratory made cubes and those drilled from the dam spillway, and a correlation was investigated between these two. Furthermore, the sandblast test method was compared with the wire brush method to assess which one produces more reliable results. The abrasion results showed small differences in abrasion resistance performance between the conventional concrete and the roller compacted concrete mixes. In fact when the percentage of the extender was adjusted from 70% to 65% these two concrete mixes performed equally. It was confirmed that beyond 45% replacement of Portland cement with fly ash, there is no improvement in abrasion resistance of concrete. However, there were no significant differences between abrasion resistant values of concrete with 45% or 65% fly ash replacements. It was observed that abrasion resistance of concrete was compromised beyond 65% fly ash replacement. Aggregates with sub-angular shape and rough texture have proven to yield high abrasion resistant concrete. The concrete made with blends of GGBS and Portland cement showed slightly improvement in abrasion resistance of concrete when compared to fly ash concrete. The cores drilled from the structure had abrasion resistance values 3 times more than the laboratory produced cubes and this was consistent with both the sandblasting and wire brush method, indicating that the actual structure has adequate abrasion resistance. The sandblasting method has proven to be reliable and more sensitive and it is recommended for assessment of abrasion resistance of hydraulic structures, while the wire brush method can be used for general quality control. Recommendations based on the results and literature study will be made available to the Department of Water and Sanitation to update their specifications, which was one of the key goals of this research.
- ItemOpen AccessAcid fermentation of primary sludge at 20v C(1990) Lilley, Ian David; Marais, Gerrit van RooyenFull scale studies on biological excess phosphrous removal plants have demonstrated the biological excess phosphorous removal can be increased by acid fermenting the settled sludge in the primary settling tank, and adding either the fermented sludge, or the acids elutriated from the sludge, to the influent of the biological phosphorous removal plant. Considerable uncertainty still exists, however, as to the mass of short chain fatty acids that can be generated and the degree of improvement in phosphorous removal that can be expected. This study was undertaken to (1) evaluate short chain fatty acid production in laboratory scale batch, single and in-series completely mixed reactor systems, (2) development of a model for acid fermentation, and (3) theoretically estimate the effect of acid addition on biological excess phosphorous removal.
- ItemOpen AccessAcid resistance of sewer pipe concrete(2007) Fourie, Clyde William; Alexander, Mark GavinA hydrochloric acid solution laboratory test was developed to assess the resistance of concrete used in the manufacture of pipes to sulphuric acid environments encountered in sewers. A hydrochloric acid solution (pH of 1,00) simulates the attack on concrete sewer pipes at the average daily sewage level region and in severely corrosive sulphuric acid environments (pH of less than 1,00) commonly encountered in South African sewers. Calcium sulphate, which precipitates in a sulphuric acid solution and masks further attack, is eliminated simulating the constant dissolution of the precipitate at the average daily sewage level region and loosely attached precipitate in the severely corrosive sewer environments. A straightforward procedure is used to determine the acid resistance of dolomite aggregate concrete used in the manufacture of sewer pipes for exposure to sulphuric acid sewer environments. Acid resistance and neutralisation capacity of the concrete are measured as functions of mass loss and hydrogen ion consumption with time (over a period of approximately 96 hours or less). A procedure to determine the acid resistance of siliceous aggregate concrete requires a longer test period (approximately 200 hours or more). A concrete containing calcium aluminate cement and a synthetic alag™ aggregate made from the calcium aluminate cement clinker gave the best resistance to the hydrochloric acid solution (pH of 1,00) and a severely corrosive biologically-induced sulphuric acid environment (pH of less than 1,00). A similar concrete containing dolomite aggregate gave poorer resistance to the respective solutions. A dolomite aggregate concrete containing calcium aluminate cement gave better resistance in the biologically-induced sulphuric acid environment than a similar concrete containing ordinary portland cement but both concretes were of similar resistance in the hydrochloric acid solution. A poor quality dolomite stone (low strength and high porosity), which fractures during pipe manufacture gave poorer resistance in the hydrochloric solution than a concrete containing a sound dolomite stone but better resistance in the biologically-induced sulphuric acid environment. Concrete containing siliceous aggregate gave the poorest resistance to both the acidic environments. Assessing acid resistance using the hydrochloric acid solution test method illustrates the manner in which the physical and chemical properties influences the attack and dissolution of concrete in an acidic environment, which is crucial in the development of a sewer pipe concrete to resist and neutralise a biologically-induced sulphuric acid sewer environment.
- ItemOpen AccessAerobic digestion of waste activated sludge from biological nutrient removal activated sludge systems(2007) Mebrahtu, Michael Kidane; Ekama, George A; Wentzel, Mark CWaste activated sludge (WAS) is a biological sludge that contains biodegradable and non-biodegradable volatile suspended solids (VSS) and non-volatile inorgainic suspended solids (ISS). Stabilization for safe disposal of the WAS is a process of paramount importance at wastewater treatment plants (WWTPs). Hence, aerobic digestion of the WAS from biological nutrient removal (BNR) activated sludge (AS) systems was carried out under batch conditions to (1) measure changes in nitrogen and phosphorus concentrations in solid and liquid phases during aerobic batch digestion tests (2) simulate the parent system with Activated Sludge Model No. 2 (ASM-2) in AQUASIM computer program to obtain the initial conditions for batch test simulation (3) simulate the batch aerobic digestion process with ASM-2 and compare with experimental data (4) develop VSS-based and total suspended solids (TSS) (with the addition of ISS to the VSS-based) batch reactor and steady state models for aerobic digestion of nitrification denitrification biological excess phosphorus removel (NDBEPR) WAS based on the individual biomass die-off rates of phosphorus accumulating organisms (PAOs) and ordinary heterotrophic organisms (OHOs), and (5) evaluate the ASM-2 simulation results with steady state aerobic batch digestion model.
- ItemOpen AccessAggressive water attack on carbonated cement materials(1991) Mackintosh, Grant Stewart; Loewenthal, Richard EricAggressive attack on samples was monitored by measuring changes in chemical characteristics of the water exposed to cement concrete samples, inter alia pH, calcium and alkalinity. Over the period of the investigation (100 days) the following observations were found to apply to both brown and white water: (i) Generally uncarbonated OPC experiences significantly higher calcium mineral dissolution rates than both carbonated OPC and 30% fly ash OPC cement concretes. (ii) Once steady dissolution rates were attained, measurements indicated that 30% fly ash OPC and carbonated OPC concrete undergo closely the same calcium mineral dissolution rates. Before these findings are implemented, the following practical considerations need to be addressed: (i) An economic assessment of the benefits of using carbonated OPC, fly ash OPC and carbonated fly ash OPC as a means of resisting aggressive attack. (ii) The investigation should be upgraded from laboratory scale to pilot scale. (iii) The influence of accelerated carbonation on corrosion of steel reinforcing.
- ItemOpen AccessAlkali-Aggregate reaction in Western Cape concrete(2018) Mahomed, Zubair Lall; Alexander, MarkAlkali-aggregate reaction, AAR, was first discovered in 1938 by Stanton in the USA. Subsequently, researchers across the globe have reported incidences of the reaction with different aggregates in their respective countries. The reaction entails the interaction between reactive silica found in aggregates and alkali in the pore solution of concrete. Through research, the reaction has been categorised into three main classes depending on the type of aggregate used. Alkali-silica reaction, ASR, being one of those classes, is the most common one and is the primary concern in the local concrete industry in the Western Cape, where reactive greywacke aggregates are used. In South Africa, the problem has often been dealt with using low alkali cement. However, those low alkali resources have been depleted and more alkali-rich resources are now being used in the production of cement. This completes the three requirements needed for ASR reaction to occur, namely a high alkali source, presence of reactive silica and moisture conditions. Furthermore, the introduction of greywacke crusher sand as a partial substitute to natural sands in local concrete mixes, implies that more reactive silica is available in the mixes. The research aims at finding whether the current concrete mixes are prone to alkali silica reaction and how to mitigate this expansion using cement extenders, which is the most common ASR mitigation measure. The long-term performance test, which allows testing of concrete, generally takes a minimum of 6-12 months to complete. As such, attention was turned towards the use of an accelerated mortar bar test (AMBT), which is generally used as an indicator test in the preliminary stages of the testing. However, the AMBT test imposes material limitations such as cement type and aggregate grading. Consequently, modifications were made to the AMBT test to allow for the concurrent use of reactive fine aggregates and coarse aggregate as well as a commercial cement. The first stage of this project involved the use of a modified AAR-2 AMBT test and was subdivided into three phases. Phase A was centred around investigating the use of reactive fine aggregates and reactive coarse aggregates in conjunction. For this purpose, 40% of the total aggregate blend by mass was constituted of a sand blend having both reactive (greywacke) and non-reactive (Philippi dune sand) components, while the remaining aggregate portion was a 9.5 mm greywacke coarse aggregate. The reactive fine aggregate level was varied in the sand blend and the ASR expansion recorded. A limited pessimum effect was observed at around 40-60% reactive greywacke by mass in the sand blend, whereby the expansion recorded peaked. Phase B of Stage 1 then involved the use of a 50/50 greywacke crusher sand/Philippi dune sand in the sand blend as a base mix. Cement extenders were then substituted in different levels for the cement. For this work, common replacement levels of 20, 30 and 40 percent fly ash and 40, 50 and 60 percent corex slag were used. It was found that all the mixes mitigated the ASR expansion to acceptable levels, that is below the 0.10% expansion, while increasing cement extender levels reduced the expansion further. It was also found that fly ash was more effective at reducing ASR than corex slag. Phase C of Stage 1 involved identifying the mechanisms behind which cement extenders mitigate ASR. Subsequently, the mixes used in Phase B were replicated with the exception that an inert limestone filler, “Kulubrite 10”, was used instead of the reactive cement extenders. It was observed that the limestone filler does reduce the expansion but to a much lesser extent than the reactive cement extenders. This implied that the cement extenders not only dilute the alkali content but also undergo further reaction which removes more alkali from the pore solution. The second stage of the project dealt with the influence of ASR gel formation on compressive strength. Compressive strength tests were performed on 2 sets of cubes for each mix, which were exposed to different curing conditions, namely a water bath at 22-25 ̊C and an alkaline solution of 1M NaOH at 80 ̊C. It was observed that there is reduction in strength as the expansion increases. Scanning electron microscopy, SEM, performed in Stage 3, of the samples confirmed that this phenomenon is due to the increased number of cracks as the expansion increases. Other subsidiary tests conducted in Stage 3, such as light microscopy and EDS, resulted in inconclusive results and need to be further investigated. Lastly, Stage 3 involved conducting long-term testing using a modified version of the AAR-4 test and field performance test. Five ‘real-life’ concrete mixes, based on the mixes in Stage 1, were cast and are still under observation. The initial measurements on the AAR-4 samples showed no sign of expansion as of 15 weeks of testing. This was thought to be due to the un-boosted alkali content of the cement, 0.7 % Na2O eq, which may have not been enough to start the reaction. The preliminary results of the field testing at 15 weeks of age showed that apparent shrinkage was occurring, likely due to the environmental influences over this period (summer months). This could be attributed to the fact that the ASR gel formation mechanism is still in its early stages in those specimens or has not started yet. The final results of these tests, at 6 months and 2 years respectively, are however needed to confirm whether the modifications made in Stage 1 of this research resulted in a good approximation of what is to be expected from the use of reactive greywacke fine and coarse aggregates in conjunction. In general, it can be concluded that the concurrent use of reactive greywacke crusher sand and reactive greywacke coarse aggregate in concrete mixes, would not be deleterious to structures. Nevertheless, it is advised that a minimum of 20% fly ash or 40% ground granulated corex slag by mass of the total binder content is used, as per the current conventional precautions.
- ItemOpen AccessAlternative patch repair materials for rebar corrosion damage(2017) Jassa, Primesh; Beushausen, Hans-Dieter; Ngassam, Ines TchetgniaReinforced concrete (RC) is extensively used in the construction industry. It is particularly used to guarantee that infrastructure assets around the world last for multiple years whilst ensuring that the structural integrity and serviceability of the structure is maintained. However, in practice countless RC constructions are failing prematurely due to a large number of factors of which the corrosion of steel embedded within concrete is the most significant (Matthews et al., 2003). Steel corrosion is particularly pernicious to concrete due to the expansive nature of the corrosion by-products formed, which commonly leads to cracking and spalling. One of the most common methods adopted in the rehabilitation of corrosion damaged concrete is the patch repair procedure. However, in practice this method has shown to often be unreliable as a consequence of the widespread occurrence of shrinkage cracking and poor substrate-patch adhesion leading to debonding of the patch repair. From a practical point of view, such failed repair systems essentially restore the repaired concrete back to a deteriorated state. The underlying cause of poor durability in patch repairs is attributed to a range of reasons including, the lack of understanding of the substrate-patch composite system and the limited availability of appropriate design standards. Furthermore, there is a lack of understanding in the repair industry on the critical material properties actually required for durable patch repairs. There is a common belief that repairing concrete with specialised proprietary repair materials would guarantee durability. However the widespread premature failure of patch repairs conducted using such materials has proven the contrary. A proper patch repair process includes treatment of the corroded steel, adequate substrate surface preparation, installing sacrificial anodes (at least for chloride contaminated concrete) and surface coating. In principle, if this process is correctly followed then the material requirements for a durable, non-structural repair would be to fill in the cavity created by removing contaminated concrete, resist shrinkage induced cracking and/or debonding and provide protection against chloride ingress (in chloride environments). The material used for patch repairs could be any appropriate repair material and it does not specifically need to be a specialised cementitious repair mortar. This dissertation presents an understanding of the materials and issues concerning the durability and serviceability of patch repairs, with the aim of identifying alternative non-structural patch repair materials for the durable repair of corrosion-damaged concrete structures. The potential patch repair materials studied in this dissertation were rubberised waterproofing bitumen, polymer (copolymer of vinyl acetate and ethylene) with 5% cement replacement and 60%, 80% and 100% fly ash (FA) mortar. Patch repairs were conducted on substrate moulds to test application and observe cracking/debonding occurrence. Furthermore, compressive strength, durability index, accelerated drying shrinkage, restrained shrinkage, workability and SEM tests were conducted. It was concluded that the 60% FA repair material had the best overall performance with the polymer-cement concrete exhibiting good bonding and crack resistance properties. This research established that innovative alternative repair materials such as a 60% FA or polymer-cement concrete material, can be developed for non-structural patch repairs with improved long-term performance relative to conventional materials. The research has further provided a foundation for the development and design of durable repair mortars by identifying the principal material performance properties required of such materials.
- ItemOpen AccessAlternative water sources for urban consumers – A novel technology for the City of Cape Town urban resident(2019) Yiannou, Angelos; Ikumi, David; Ekama, GeorgeSouth Africa is classified as being the 30th driest country in the world and is regarded as a water scarce country. However, for the urban residents of the City of Cape Town, the ability to reduce their municipal water consumption through initiatives, other than simply using less water, is limited. Hence, there is a need for affordable, simple and compact technical solutions which allow urban populations residing in high density developments to make use of alternative sources of water, specifically greywater, to reduce their municipal water demand. Existing commercial technologies were considered, together with the socio-economic and technical constraints of an illustrative middle-income urban household in the City of Cape Town (CoCT). It was found that each commercial technology considered satisfied some, but not all, constraints characteristic of the household. For instance, the treatment device may produce treated water of a high quality. However, it may not be financially feasible for the consumer. Of the commercial technologies considered, there is no single commercial technology which can offer a complete solution within the socio-economic and technical constraints of the household. For this reason, the opportunity exists to produce an innovative technical solution. The proposed greywater treatment device consists of four cylindrical chambers in a vertical arrangement. Raw greywater enters the top chamber and treated greywater is extracted from the bottom chamber forming the base. The treatment processes undergone as the greywater flows through the treatment device include, in the following order, pre-filtration, biological treatment (Activated Sludge), clarification, filtration and disinfection. The process is driven by a combination of gravity and electrical energy. The proposed design is constructed using readily available materials and components. It is modular in its construction, allowing for easy maintenance, assembly and an increase in design flexibility. Evaluating the design against the same evaluation criteria stipulated for the existing commercial technologies showed that the proposed design may be an appropriate solution for the illustrative middle-income household within the City of Cape Town and is a novel technical solution.
- ItemOpen AccessAmbient vibration testing of concrete dams(2011) Bukenya, Patrick; Moyo, Pilate; Beushausen, Hans-DieterIn this thesis, seven techniques namely; rational fractional polynomial, complex exponential, frequency domain decomposition (FDD) based techniques which include; frequency domain decomposition (FDD), enhanced frequency domain decomposition (EFDD), curve fitting frequency domain decomposition (CFDD) and stochastic subspace identification (SSI) methods namely; unweighted principal component (UPC), principal component (PC) and canonical variant analysis (CVA)) have been applied to data from ambient vibration testing of two concrete dams namely; Roode Elsberg and Kouga dams.
- ItemOpen AccessAn economic evaluation on FRP for bridge construction in South African coastal areas(2022) Ndeutapo, Samuel; Moyo, PilateFibre Reinforced Polymers (FRP) have been used for approximately 30 years as concrete strengthening materials in structural applications. This is primarily due to Steel Reinforced Concrete (SRC) being susceptible to the corrosion of reinforcing steel, especially in coastal environments. However, the use of FRP composites for bridge construction is faced with challenges. These challenges arise from uncertainties regarding the high material and initial construction costs. Additionally, there is limited research available on the costs involved when incorporating the fibres in bridge constriction. It then becomes critical to understand the life cycle costs of FRP in bridge construction. Furthermore, suitable economic and deterioration models can be used to predict these life cycle costs by employing a LCCA. The research aim was to investigate the economic viability of using FRP as reinforcing elements in bridge construction. This was done by conducting a life cycle cost analysis (LCCA) on two highway beam bridge superstructure designs: a SRC superstructure and a GFRP-RC superstructure to determine the preferred design, which was used to conclude on the economic viability of FRP in bridge construction. The deterministic approach to the LCCA was selected and the outcome was expressed in terms of Present Worth of Costs (PWOC). The initial construction costs were found to be the bulk, while the disposal costs were the least of the total LCC for both superstructure alternatives. Furthermore, initial construction costs of the SRC superstructure were found to be less than that of the GFRP-RC superstructure, by a margin of R 873 094. This was primarily due to the cost of E-glass reinforcement, approximately 2.1 to 2.9 times more expensive than the cost of steel reinforcement. Moreover, the cost of GFRP was seen to have decreased over the years. LCC savings were seen from the GFRP-RC superstructure over the SRC superstructure, by a margin of R4 627 830 in terms of maintenance costs. This was mainly due to the application of a corrosion inhibitor (concrete surface treatment) and the use of a cathodic protection system on the SRC bridge superstructure. Furthermore, the GFRP-RC superstructure was found to be the least cost-effective investment from approximately 34 years of a 75 year LCCA period. At the end of the analysis period, the SRC bridge superstructure was found to have cost savings of approximately R 753 921 in PWOC over the GFRP-RC superstructure. Furthermore, a sensitivity analysis of the various input costs and discount rates of the LCCA was also conducted. Initial construction costs were found to have the highest positive correlation on the outcome of the LCCA. The other costs and as well as the discount rate were all found to have an insignificant effect on the outcome of the LCCA. It was concluded that it was not economically viable to include FRP as reinforcing elements in bridge construction at the time. However, since the cost of FRP was seen to decrease over time, the inclusion of FRP rebars in bridge construction might be economically viable in the future.
- ItemOpen AccessAn evaluation of the pressure-leakage response of selected water distribution networks in South Africa(2019) Levin, Seamus Jay; Van Zyl, Jakobus EPressure is one of the major factors influencing leakage in water distribution systems. For this reason, pressure management has become standard practice in reducing leakage in water distribution networks around the world. A range of N1 values have been published following studies of the impact of pressure management. Further studies have contributed towards the development of leakage parameters which represent physical properties of the pressure management system. This study aims to add to, and improve, the information on leakage parameters and their relationships.This study will seek to add to previously published data on the impact of pressure on leakage in field studies and determine the respective leakage parameters and identify relationships with respect to the latest findings on pressure and leakage behaviour. Significant research and investigations have been done at laboratory scale however theoretical developments have not been applied on field studies, and hence there is a lack of reports published in peer reviewed journals.The principal aims of this dissertation were to consolidate information from pressure management zones collected around South Africa and the analysis of results using a conventional methodology as well as alternative methodologies that used different pressure and flow inputs that represented the extreme range of pressure and flow.The relationships between the calculated leakage parameters were then studied and where leakage parameters were determined to be not physically possible, these were studied for errors.The dissertation is the result of research collected and conducted since February 2015 on 141 pressure management zones (PMZs) across South Africa.The data, collected from the field, consists of the zone characteristics, measurement data such as flow and pressure logging, and consumption data, including night time usage. From the 141 PMZs, only 107 were considered for this study due to exclusion of 34 PMZs for various reasons.From the analysed data, the significant results were that when using the conventional method (AZP as pressure input and QRL as flow input), 12% of head-area slope (m̄) values and 39% of initial leak area (Ā₀) values were negative. The calculated FAVAD N1 values ranged between -0.34 and2,20 (outliers were determined as N1=-31,88 and N1=6,77 but these are not impossible and can be explained through physical issues with the pressure management zone). The relationship between the calculated Leakage Exponent (N1) and the Leakage Number (LN) were determined to be consistent with theoretical studies. The Infrastructure Leakage Index (ILI) was determined for each PMZ for before and after pressure management and it was found that although leakage reduces with pressure management, the ILI is notalways reduced In fact, the ILI increased after pressure management for 39% of the PMZs. The relationships for the various leakage parameters were studied and illustrated. The only notable relationships revealed was that when N1 < 0,5 then m̄< 0 and when N1 > 1,5 then Ā₀< 0. Whilst this can be explained mathematically, a negative m̄ and Ā₀ are not physically possible. Therefore possible errors such as assumption errors and data errors were explored. For m̄, it was determined that four PMZs could not be explained from the correction of possible assumption or data errors. For Ā₀, it was determined that 11 PMZs could not be explained from the correction of possible assumption or data errors however the errors may be the result the presence of leaking/open boundary valves. The research undertaken is the first systematic study that is published where the parameters are explored to this extent in this detail, and using such a range of the latest conventional and the latest leakage theory. The result is that various pressure management zones can be analysed using standardised methodologies and calculations and these water distribution systems of different locations, sizes and characteristics can be compared and scrutinised. Furthermore, there are significant benefits of using the modified orifice equation which include determination of errors in assumptions or data collection or identifying the possibility of an open/leaking boundary valve. Finally, N1 values that fall outside of the typical range can often be explained by assessing the physical properties of the leakage parameters calculated from the modified orifice equation.
- ItemOpen AccessAnaerobic digestion of Fischer-Tropsch reaction water : submerged membrane anaerobic reactor design, performance evaluation & modeling(2008) Van Zyl, Pierrie Jakobus; Ekama, George A; Wentzel, Mark CIncludes abstract. Includes bibliographical references (p. 209-217).
- ItemOpen AccessAnaerobic Digestion Steady State model parameter estimation for determination of waste activated sludge characteristics(2021) Du Toit, Johan; Ikumi, David SPhosphorus (P) is an essential nutrient which supports growth and life. A need has developed to recycle P due it being a finite mined resource. At present, most P is lost due to runoff or wastewater (WW) effluent and ending up in rivers and oceans. In order to recycle P and other nutrients, Wastewater Treatment Plants (WWTPs) will need to be converted to Water and Resource Recovery Facilities (WRRFs). However, for WRRFs to be feasible, a better understanding of the current models predicting the fate of P and other material components in place are required. The objective of this study is to utilise augmented batch tests to determine the characteristics of the Waste Activated Sludge (WAS) containing Polyphosphate Accumulating Organisms (PAOs) from a full-scale WWTP as input variables in the Steady State (SS) Anaerobic Digestion (AD) model to ensure accurate prediction of AD performance. The experimental setup used in this research consisted of two completely mixed laboratory scale (20 litres volume, mesophilic 36 ̊C) Anaerobic Digesters (ADrs). The ADrs were operated at SS for 15 day and 32-day Solid Retention Times (SRT) and were fed WAS from a full-scale treatment plant which consisted of a Membrane Bioreactor (MBR) Nitrification-Denitrification (ND) Biological Excess Phosphorus Removal (BEPR) Activated Sludge (AS) system. Two different methods ((i) a novel approach by Maake & Ikumi, (2021) and (ii) the method used by Harding, (2009)) were compared in determining the saturation kinetic rates and the WAS characteristics as input variables for the SS AD models. It was determined that the novel approach by Maake & Ikumi, (2021) was very reliable in determining Chemical Oxygen Demand (COD) removal, Free and Saline Ammonia (FSA), system effluent pH and total alkalinity. With respect to the Ortho-Phosphates (OP), the parent system from where the WAS is sourced, had a long SRT. This resulted in a low predicted PAO count and Poly-Phosphate (PP) content, which resulted in low amounts of Organically bound Phosphate (OrgP) being released into the Anaerobic Digester Liquor (ADL), which equated to an underprediction of OP. Due to the low PP content found in the WAS fed to the ADrs, the ADL was not fully saturated, resulting in no struvite precipitation taking place. This was accurately modelled for both Maake & Ikumi, (2021) and Ikumi, Harding & Ekama, (2013) modelling scenarios.
- ItemOpen AccessAnalysing the application of “Reblocking” of informal settlements in the City of Ekurhuleni(2019) Basson, Annelien; Smit, WarrenDealing with the challenge of informal settlements is one of the biggest issues facing South Africa and other countries of the global South. There is an urgent need to document and reflect on attempts to intervene in informal settlements. This dissertation investigates and analyses the application of ‘reblocking’, a particular approach to informal settlement upgrading, in the City of Ekurhuleni in Gauteng Province, South Africa, and assess the extent to which it complies with the accepted principles of good informal settlement upgrading. Reblocking essentially involves the realignment of structures in an informal settlement to enable basic services to be delivered, and can also result in reduced fire risk and more usable communal spaces. The process of reblocking is also valuable as collaborative planning tool to build grassroots capacity. First of all, based on a review of the literature and interviews with practitioners and scholars, the principles of what can be regarded as ‘good’ informal settlement upgrading were collated. The policy context of upgrading in South Africa (particularly the Upgrading of Informal Settlements Programme) is reviewed, and the history of the reblocking approach in South Africa (first implemented by Slum Dwellers International with the City of Cape Town, and subsequently adopted by the City of Ekurhuleni) is examined. The case study of reblocking in Ekurhuleni Municipality is then discussed in detail. Finally, the dissertation compares the experiences of reblocking in Ekurhuleni with the principles of ‘good’ informal settlement upgrading and with the other South African approaches to reblocking, and makes recommendations for how informal settlements could be better addressed in Ekurhuleni (and elsewhere). The key findings of the dissertation are that, while reblocking can be very beneficial in terms of providing services and empowering communities, the approach used in Ekurhuleni is less participatory and thus has fewer social benefits than its counterpart in the City of Cape Town. In addition, all South African reblocking initiatives avoid providing de jure security of tenure, and can even decrease de facto security of tenure (as many reblocked settlements are still at risk of relocation), which negates one of the major advantages of initial public investment. The dissertation highlights that there is a need for transformed mindsets, policies and bureaucratic systemsthat are better aligned with the complex and dynamic nature of informal settlements, in view of the growing housing backlog in the CoE, South Africa and the global south.
- ItemOpen AccessAn analysis of leakage parameters of individual leaks on a pressure pipeline through the development and application of a standard procedure(2015) Malde, Rahil; Van Zyl, J EWater is a vital and scarce resource. Providing a sustainable and efficient means of transporting water is essential to the wellbeing of humankind. Most water distribution systems worldwide are ageing and deteriorating, as a result, leakage is a common problem. Modern water distribution systems use a variety of methods to minimise leakage, one of them is pressure management. However, the relationship between leakage and pressure is a complex one. The goals of this study were to develop a standard experimental procedure to determine the leakage parameters of a pipe with an individual leak, and to test a series of pipes using the newly developed procedure to determine their leakage parameters. There have been numerous experimental investigations into the leakage parameters; however, these investigations have variation in their methodologies. Therefore, developing a standard procedure will provide a consistent method for the accurate determination of the leakage parameters. Leakage parameters are important as they help to improve the understanding of the relationship between leakage and pressure. They are also important for use in the two main equations used to relate leakage and pressure, i.e. the N1 equation and the FAVAD equation. The determination of a variety of leakage parameters will help to determine whether both equations explain the behaviour of a variety of pipe samples, and which equation is better suited for use in leakage prediction.
- ItemOpen AccessAn analysis of residential trip generation in Cape Town(1974) Pas, Eric Ivan; King, W HSome of the factors contributing to the growth of a 'transportation problem' in Cape Town are outlined, and the main trends are illustrated. A brief introduction to the Urban Transportation Planning Process is presented, and the importance of the trip generation sub-model within the conventional traffic forecasting model is highlighted. A review of past and current practice in the analysis of residential trip generation is presented. The least-squares and category analysis techniques are compared, and the dummy variable method is briefly described. The unit of analysis to be used in the development of residential trip generation models is discussed. The independent variables frequently incorporated in models of residential trip-making are examined, and their effects on home-based trip generation are analysed. Some of the problems associated with the development of regression models are examined. The planning and execution of a home questionnaire survey of households in the Cape Town area is described.