This study focused on the design and implementation of a low-resource graphics engine, MicroGE, which can be implemented on an FPGA. MicroGE uses a minimal amount of FPGA resources when compared to other graphics engines. After researching existing graphics engines, it was discovered that most make use of a memory space to store frame buffer data. Because of the restrictions that were imposed on the design of MicroGE, it could not incorporate a large enough memory space to store a frame buffer. It was specified that MicroGE should be able to fit on low-resource FPGAs, without any external memory components. Also, MicroGE should be able to fit on modern, high-resource, FPGAs without using a significant amount of those FPGAs’ resources. These goals were achieved by designing MicroGE according to an architecture which differs from the ones of existing graphics engines. MicroGE only renders parts of the video frame, which can be stored in a small memory space, before those parts are transmitted to an HDMI or DVI monitor. After the design was completed, MicroGE, along with other components, was implemented in a VHDL design. Hardware was developed, which contained a Spartan-6 LX25 FPGA, to verify this VHDL. Other verification methods, including the use of VHDL test benches, were also used to verify the VHDL design. A software library, MGAPI, was developed on an Arduino Due microcontroller board. This software library allowed the Arduino Due to display graphics on an HDMI monitor via MicroGE. The Arduino Due was able to update the display of 1000 graphics primitives within 111 ms. The internal FPGA RAM resource usage of MicroGE, 792 kb, was found to be significantly lower than the amount of memory required for a frame buffer. Even though these results were satisfactory, there are still many improvements that can be made to MicroGE. These improvements include increasing the number of rendering capabilities, optimisation of power usage, and increasing the control and video output interfaces.

The world’s exponential growth in urbanisation has placed significant pressure on the construction industry to support development by expanding its provision of infrastructure. There is expected to be a rapid increase in the consumption of structural concrete to meet the associated requirements. This increase in concrete consumption has adverse effects on the environment. Firstly, the production of cement, one of the main components of concrete, is regarded as a system of energy-intensive processes. Secondly, the production of Portland cement (PC) releases a substantial amount of greenhouse gases (such as carbon dioxide), which in turn contributes to the global warming phenomenon. In addition to the change in demand for concrete over time, its composition and mix proportions have indeed also undergone a significant evolution. Concrete is becoming more sophisticated and complex. The construction industry has introduced mineral admixtures as partial replacement of PC in the attempt to mitigate the negative environmental impact of cement production. The use of mineral admixtures has positive economic and environmental benefits. In the context of concrete durability, the use of mineral admixtures has the potential to improve the performance of concrete by mitigating the deterioration processes occurring in concrete structures, such as reinforcement corrosion. Reinforcement corrosion is one of the most pervasive concerns within the construction industry. Carbonation is considered as of the main causes contributing to the corrosion phenomenon. The carbonation mechanism entails the reaction between atmospheric carbon dioxide and the cement paste and leads to an altered chemistry within concrete, which eventually causes the depassivation of steel reinforcement. The deterioration of the concrete caused by carbonation can be predicted using the oxygen permeability index (OPI) test results as an input parameter in the appropriate carbonation prediction model. While South Africa has developed carbonation durability prediction models that can predict the performance of conventional concrete mixes (concrete containing 30% fly ash, 50% slag, 10% silica fume) relatively well, this formulation of the carbonation model was instituted approximately twenty years ago and is considered outdated. Therefore, this research seeks to investigate whether the previously established correlation between carbonation and oxygen permeability is still relevant for modern South African concretes. In this study, concrete constituting of different mineral admixtures at varying PC replacement levels or the use of chemical admixtures is defined as modern concrete. The experimental work included investigating the permeability and carbonation performance of modern concretes made with modern binder types at varying binder replacement levels and binder combinations, including binary and ternary cement blends at two water:binder ratios of 0,50 and 0,65. This included addition of fly ash (FA) (20%-50% in 10% increments), blast furnace slag (BS) (20%- 60% in 10% increments), Corex slag (CS) (20%-60% in 20% increments), and limestone (10% and 20%). For ternary blends, the concrete was limited to three mixes, that is, 5% SF with either 25% FA, 25% BS or 25% CS. Furthermore, two commercial blended cement products were tested namely CEM II A-L, and CEM Il B-M (L-S) 42,5N, referred to as A-L and B-M. A-L and B-M cement nominally contain 8% L, and 8% L coupled with 25% CS respectively. The OPI test was conducted after 28-days of wet curing. The accelerated carbonation tests were conducted using a phenolphathein indicator solution at 6, 9 and 12 weeks of exposure. Prior the testing, the samples were wet cured for seven days and underwent a preconditioning regime in attempt to minimise the influence of the internal moisture of the concrete affecting the carbonation depth results. A statistical analysis was done on both OPI and the accelerated carbonation results to determine the significance in results with the increase in binder replacement percentage, different binders of the same binder replacement percentage and significance of using ternary mixes in comparison to binary mixes. In conclusion it was found that, generally, mineral admixtures had a statistical insignificant influence on the permeability. This can be attributed to the fact that the control mixes already possessed a high permeability performance i.e. concretes exhibiting relatively low permeabilities. Therefore, the inclusion of a mineral admixture would result in a minor influence on the performance. Regarding carbonation depths, the inclusion of mineral admixtures resulted in a decrease in carbonation performance, as expected. This is attributed to the dilution effect and the pozzolanic effect to some degree, which decreased the amount of carbonatable material that is calcium hydroxide, subsequently decreasing the concrete’s resistance to carbonation. Finally, reasonable correlations were identified between carbonation depth and permeability when all concrete mixes were considered. The direction of the trend showed a positive and negative association when the carbonation coefficient was plotted against k-permeability and OPI respectively. Further investigation of the correlation between carbonation depth and a singular binder type regardless of the replacement level showed an increased in correlation strength between permeability and carbonation. It was concluded that using this approach may provide reasonable correlations for carbonation prediction modelling. However, more testing would be required to confirm the previous statement.

Tumbling mills are considered to be among the most energy intensive devices in comminution circuits and are designed to achieve size reduction and transport. These functions are influenced by the mill speed, filling and the configuration of the lifter bars attached to the mill shell (height, width, face angle, etc.). The lifter height has been shown to influence the charge motion and power draw of the mill. Most of the predictive power models used in industry do not consider lifter heights as a variable. In comminution, Positron Emission Particle Tracking (PEPT) is used to track the charge motion of particles in tumbling mill systems. The data has been used to derive a velocity profile for particle motion between the mill shell and centre of circulation (COC), a region that highlights the distinct particle motion in tumbling mills. In prior work, a laboratory scale mill and PEPT was used to develop a velocity profile model incorporating the lifter height influence on charge motion. The agreement between PEPT and the model predictions was limited to regions closest to the mill shell and the analysis was restricted for conditions where the lifter height was significantly smaller than the particle diameter. The current study aimed to supplement the PEPT results by using the Discrete Element Method (DEM) to simulate the collective effect of individual particle interactions on the charge motion. The DEM results were used to analyse the influence of the lifter height on the charge motion, velocity profile and power draw for an identical tumbling mill system. The PEPT and DEM results agreed on charge motion and power draw changes. The assumption of a constant axial pressure drop (dP/dx) along the cross-section of the mill resulted in deviations between DEM and model predictions of the velocity profile. The calculated axial pressure drop varied non-linearly along the mill radius and followed a similar trend at all operating conditions. The relationship between the velocity profile and axial pressure drop was found to vary non-linearly and followed a similar trend to the stress-strain relation of granular media. It is recommended that further research be conducted on the axial pressure drop and its influence on the velocity profile.

Rare earth elements (REEs), La to Lu including Y, are vital elements in manufacture of catalysts and metallurgical industries, and play a critical role in meeting future energy demands, such as through their use in permanent magnets in wind turbines. China has dominated more than 90 % of the REE market, with heavy REE (HREE) clay deposits in South China accounting for 35 % of their total REE output. This has prompted the evaluation of ion-adsorption clay (IAC) deposits in tropical regions outside China, namely Madagascar. Clay minerals such as kaolinite are part of the phyllosilicate class, containing structures of shared octahedral aluminium and tetrahedral silicon sheets. Isomorphous substitutions within the lattice leads to a charge imbalance, which accounts for negative charge on kaolinite, thus giving the ability to attract REE cations from aqueous solution to the surface of the clay particle. IAC deposits are formed from the tropical weathering of granite with REE enrichment from accessory minerals. IAC clay samples of two regolith profiles, the pedolith (A1) and saprock (A2, B and F) from northern Madagascar were collected and subjected to a suite of characterisation techniques to investigate the properties of the clay mineral. This included particle size distribution (PSD), X-ray fluorescence (XRF), X-ray diffraction (XRD), quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN), inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The geochemical leaching characteristics of the clay mineral were investigated using a sequential leaching program, targeting ion-exchangeable REE on kaolinite, halloysite, REEorganic matter and mineral phase. Ammonium sulphate leach experiments were conducted, varying the ionic strength to determine optimum leaching concentrations. Seawater is easily available at the coastal mine, therefore simulated seawater (NaCl) experiments were conducted with the addition of ammonium sulphate to improve the REE recovery. Compound leaching agents were investigated including varying magnesium / ammonium ratios in a sulphate system as well as ammonium in a varying nitrate / sulphate ratio system. The magnesium ion was investigated to correct the Mg deficiency in soils after leaching and the nitrate ion was investigated due to its high ionic permeability in kaolinite. Ion-adsorption clay leaching includes the leaching of impurities such as Al, Fe, Mg, K, Na, Ca and Mn. Ammoniumsulphate experiments with increasing amounts of ammonium acetate were conducted. Ammonium acetate acts a buffering agent to inhibit the leaching of the main impurity Al. The texture of sample A1 (5 to 6.5 m) was homogenous, with the QEMSCAN results showing Fe minerals distributed through the kaolinite, giving it a red appearance. The saprock samples A2, B and F have a heterogeneous texture due to the preservation of the primary texture. The QEMSCAN results show that this texture is composed of pure white kaolin, kaolin with red staining due to Fe minerals, tawny staining due to Al minerals and black phases containing Mn minerals. These Mn minerals show Ce deposited as the mineral cerianite, unavailable for ion-exchange. The pedolith sample was light REE (LREE) enriched but depleted in total REE (TREE = 1 503 ppm) compared with the saprock samples (TREE = 7 006 ppm on average). The saprock samples show LREE and HREE enrichment with samples A2 and F having La / Gd ratio of 17.4 and Gd / Lu ratios of 1.2. The more crystalline samples A2 and F (Hinckley index 0.40 and 0.44 respectively) are more REE enriched than the more weathered sample B (Hinckley index 0.32). The geochemical characterisation of sample A1 showed decreasing REE recovery from LREE to HREE from kaolinite whereas sample A2 showed consistent recovery across the REEs from kaolinite with both showing little Ce recovery. The best TREE recovery for samples A1 and A2 in the chloride system achieved with was NH4 + (44.3 % and 83.1 % respectively) followed by Na+ (39.5 % and 72.2 %) and Mg2+ (28.9 % and 72.1 % respectively). For sample A1 the recovery from the kaolinite fraction was 37.7 %, halloysite 5.1 %, organic 1.6 % and mineral 55.7 %. The proportion of ion-exchangeable REE is increased in sample A2 showing a recovery from the kaolinite fraction of 66.9 %, halloysite 12.7 %, organic 3.5 % and mineral 16.9 %. The results from increasing the ionic strength of ammonium sulphate shows that TREE leachant concentration increases as the concentration increases but decreases above 0.25 M. This indicates that the ammonium sulphate concentration saturates at 0.25 M and any further lixiviant increase eliminates access to the kaolinite surface. The simulated seawater experiments indicate that some addition of ammonium sulphate is beneficial as the addition of 0.05 M ammonium sulphate almost doubled the TREE leachant concentration. However excess addition of ammonium sulphate above 0.05 M had adverse effects on the leachant concentration of the LREEs. It was concluded from the compound leaching experiments that the Mg2+ ion can be used to supplement ammonium leaching with the greatest leachant concentration using a Mg2+:NH4 + ratio of 1:2 (equal charge). This ratio would produce a high REE leachant concentration while keeping Mg available for plants (flora). Compound leaching with the nitrate ion shows that the greatest REE leachant concentration was with a NO3 - :SO4 2- ratio of 2:1 (equal charge) due to increased nitrate ion permeability. The results from the addition of ammonium acetate as a buffer showed that the buffer inhibited the leaching of Al in both samples A1 and F, with the greatest inhibition at 0.05 M. The characterisation experiments illustrate the complexity of the in-situ clay deposit and further work should use this information to construct leaching models that take into account the heterogeneity of saprock samples. The leaching experiments show that compound leaching can improve REE recovery and further work should incorporate multiple lixiviants in in-situ leaching models.

Considering the depletion of high-grade ore deposits, the mining industry is faced with the challenge of processing low grade and more complex ores in order to meet the growing demand for metals and metal products. Therefore, it is of paramount importance to have a fundamental understanding of minerals processing operations in order to improve the recoveries of valuable metals on an industrial scale. It has been acknowledged that the chemical conditions during grinding as well as pulp chemistry have a significant influence on the recovery and selectivity of most sulphide minerals in the flotation process. Floatability of ores is mostly determined by surface properties and the surface properties are essentially controlled by the grinding conditions. The flotation response of sulphide minerals is influenced by factors such as: collector-mineral interactions, mineral surface oxidation, deposition of iron hydroxides/oxides from grinding media and the attachment of inorganic ions on the surfaces of minerals. These factors are on the other hand affected by dissolved oxygen (DO), pH, ionic strength of process water and other pulp chemistry factors. With the highly instrumented Magotteaux Mill® , the effects of these variables may be investigated during grinding. Several studies have shown that the grinding environment plays a vital role in the selectivity and recovery of sulphide minerals. During wet grinding, water allows the flow of electrons within the pulp (galvanic interactions between minerals themselves and minerals and grinding media). Pyrite is reactive and can easily oxidise when exposed to air or oxygen. Pyrite and most sulphide minerals are more inert than the electrochemically reactive grinding media. Therefore, during grinding, grinding media come into frequent contact with sulphide minerals and a galvanic couple is created between the grinding media and sulphides. Due to galvanic interactions, oxygen reduction occurs on the sulphide mineral surface and iron oxidation takes place on the steel media. The redox reaction results in the formation of iron oxy-hydroxides on the surface of sulphide minerals. The oxy-hydroxide species prevent the adsorption of collector onto the mineral surface, making the mineral less floatable. Dry grinding limits the galvanic interactions present during wet grinding, due to the absence of water. Studies have been conducted and it has been shown that dry grinding yielded significantly less media wear relative to wet grinding owing to the absence of corrosive abrasion in the form of electrochemical oxidation of media during grinding. Reduced grinding media wear may imply that lesser iron hydroxide precipitates build up on the surface of the mineral hence improving collector adsorption and subsequently mineral recovery. Therefore, this suggests that dry grinding could result in improved sulphide mineral recovery as compared to wet grinding. It is necessary to consider the fundamental aspects of both grinding and flotation in order to improve concentrator performance as well as sulphide mineral recovery in the presence of nonsulphide minerals. Previous studies have investigated the influence of the grinding pulp chemistry factors on the flotation response of pyrite and other pure sulphide minerals. The possible influence that the presence of a non-sulphide gangue mineral may have during grinding and flotation has been ignored. The non-sulphide gangue cleans the surface of the sulphide minerals. Studies have shown that presence of quartz influences the formation of layers of hydrophilic species on the surface of sulphide minerals. The metal hydroxides will preferably deposit on the surface of non-sulphide mineral such as quartz rather than sulphide minerals. These studies also did not investigate the combined effects of pulp chemistry factors under dry and wet grinding. It should be noted that it is not possible to control pulp chemistry during dry grinding, thus these variables are controlled in the flotation cell in order to understand their effect on mineral surface after dry milling on pyrite flotation recovery relative to how they change the minerals surface properties during grinding. Change in chemical, surface properties of sulphide minerals can take place during milling and froth flotation. Therefore, this study aims to investigate the effects of DO, pH and grinding media type (forged steel and ceramic media) during milling and flotation process on the flotation response of pyrite (sulphide mineral) in the presence of quartz (non-sulphide gangue material). Wet milling was conducted in a Magotteaux Mill® while a Sala Batch grinding mill was used to carry out dry grinding. DO concentration and pH were controlled and measured in situ during wet grinding and were manipulated inside the flotation cell after dry grinding. The effects of the DO and pH, with changing grinding media type, on water and solids recovery, pyrite recovery and grade as well as flotation kinetic constants were studied. The EDTA extraction technique was employed to quantify the percentage of extractable oxidized iron leached from the mill product. The findings of this study have shown that under both wet grinding and dry grinding, an increase in pH from 9 to 11 resulted in increased water and solids recovery due to an increase the total concentration of OH ions in the system which led to increased froth stability owing to the reduction in pulp bubble size, as well as reduced bubble coalescence. This shows that the control of pulp chemistry during milling and flotation affected flotation process in the same way. The study has further shown that the highest recovery of pyrite, 100%, was achieved with inert grinding media (ceramic) under dry grinding. This might be due to cleaner pyrite surfaces created during dry grinding, since the prevention of media corrosion may lead to improved recoveries. During wet grinding, iron hydroxide is generated and reduces the flotation response of pyrite. Dry grinding generally produces much faster pyrite flotation kinetics than wet grinding because of the generation of particles with high surface energy and that leads to highly activated particles. It was therefore concluded that the grinding environment indeed has an effect on the flotation response of pyrite in the presence of gangue. This study has shown that careful manipulation of pulp chemistry, selection of grinding media and grinding environment may be used to manage pyrite recoveries within flotation.

Continuing urbanisation in Sub-Saharan Africa provides many development challenges including; energy provision, waste management and sanitation. On-site biogas has the potential to provide renewable energy to meet primary energy needs, whilst also addressing waste management and possibly sanitation. In urban settings, up to 50% of the municipal waste in urban can comprise organic waste which typically remains an untapped energy source, while the total waste volume continually increases with population growth. Whilst some countries (including Ethiopia and Uganda) have support via national government and/or foreign investment for biogas deployment, their focus is on rural biogas for agricultural waste, not urban biogas for municipal waste. This thesis investigates the case for small-scale biogas as a technology to assist sustainable urban development through understanding factors which will ensure operational success to safeguard investment. The factors investigated were productivity, stability and the need for remote monitoring. The research was divided into three distinct phases which occurred chronologically. The first phase was observational and developmental, in which one biogas unit in a semi-controlled environment was monitored. Some initial insight into the factors which caused instability (in this case, the addition of simple carbohydrates) as well as two methods of mitigation of instability (namely addition of lime and a cessation of feed) were noted for future investigation. Also, in this phase, a mobile phone application, called the “Biogas Monitoring Tool” was developed and refined, accompanied by a monitoring methodology to collect information on measured variables which were considered to inform productivity and stability of small-scale biogas units. Of the variables mentioned, the laboratory method of evaluation of two in particular (pH and temperature) was replaced with more practical and rudimental measuring techniques. The appropriateness of the replacements was statistically analysed, evaluated and found to be acceptable for the intended purposes. The second phase of research involved the widespread rollout of the Biogas Monitoring Tool developed in the first phase. The platform was used to gather data from ten small-scale biogas units across southern Africa to further investigate and analyse the factors which affected the productivity and stability of smallscale biogas units. Readings of pH, burn time, pressure, mass and type of feed were captured through the Biogas Monitoring Tool over twelve months. The analysis showed episodes of instability of biogas units linked to changing feeding regimes of simple carbohydrates, organic loading rates as well as changes in feed ratios/frequency. In terms of productivity of the biogas units, seasonal fluctuations in the five units which were monitored over the winter months was evident, as well as potential underutilization of biogas produced. Furthermore, it was noted that there was better utilisation of gas for institutional installations compared to domestic installations. It was also shown that in five of the biogas units, the stability of the unit had an influence on the quality of gas produced, and it was indicative that it had an influence on the quantity of gas produced. For the third and final phase of research, theories developed from insight gleaned in second phase were tested on one biogas unit in a controlled environment. There were three sets of experiments conducted on this unit which had a pre-determined feeding regime. Also, the biogas stove was burned daily until the biogas ran out, to quantify the productivity of the biogas unit. Firstly, a stepwise addition of the organic fraction of municipal solid waste was introduced into the feeding regime. In this case, it was demonstrated that the organic fraction of municipal solid waste can in fact be the sole feed-stock for biogas unit, with the proviso that there was appropriate knowledge support which includes quick mitigation strategies for periods of instability. Secondly, the effect of pre-treatment of the organic fraction of municipal solid waste was investigated. It was found here that the pre-treatment did appear to improve the stability of the biogas unit, a consideration which may be significant for potential widespread adoption of the technology. Finally, the effect of temperature on gas production was confirmed and quantified, with higher average temperatures showing higher gas production. In conclusion, it was found that all the small-scale units which formed part of this research showed episodes of instability. When considering this technology for energy provision for urban development, there are important considerations around feedstock variability by way of feed type, volume, and frequency affect the stability of these unit. With reference to productivity, it was shown, not only that temperature naturally does affect gas production, but also that the productivity is linked to the stability. Furthermore, it was deemed that the type of setting (institutional versus domestic) was in fact more significant than the ambient temperature or the feeding regime when considering gas use and gas utilisation as indicators of productivity. Finally, with regard to knowledge support via remote monitoring, it was shown that simple and practical measurements were able to provide insight into factors which affected productivity and stability of small-scale biogas units. The final phase further utilised the remote monitoring tool to actively manage the operation of the biogas unit and quickly mitigate instability. Thus, small-scale biogas has the potential to be adopted as technology for energy provision in urban development. The limitations of the application are that waste-based biogas would meet only an portion of the total energy requirement in any particular urban area and that based on the findings of this research, all units are subject to periods of instability. There are various mitigation strategies for instability, some of which involve active management, which may be supplied remotely.

This research is part of an on-going project aimed at describing the mechanotransduction of Rheumatic Heart Disease, in order to study and predict long-term effects of new therapeutic concepts to treat inflammatory heart diseases and ultimately, estimate their effectiveness to prevent heart failure. Attention is given to Rheumatic Heart Disease (RHD) - a valvular heart disease. RHD is a condition which is mostly common amongst poorer regions and mainly affects young people, of which claims approximately 250 000 lives per annum. The Theory of Porous Media (TPM) can represent the proliferative growth and remodelling processes related to RHD within a thermodynamically consistent framework and is additionally advantageous with application to biological tissue due to the ability to couple multiple constituents, such as tissue and blood. The research presented will extend an existing biphasic TPM model for the solid cardiac tissue (solid phase) saturated in a blood and interstitial fluid (liquid phase) [21], to a triphasic model with inclusion of a third nutrient phase. This inclusion is motivated by the reason to constrain the volume of the liquid phase within the system in response to the description of growth, which is modelled through a mass exchange between the solid phase and liquid phase within the biphasic model. Although the nutrient phase acts as a source for growth, the proposed mass supply function used to correlate the deposition of sarcomeres in relation to growth is predominantly mechanically driven and bears no connection to any biochemical constituent, which therefore renders the nutrient phase as a physiologically arbitrary quantity. However, the provision of the nutrient phase is a platform for the inclusion of known constituents which actively contribute towards growth, of which may be explored in future research. The triphasic model is applied to a full cardiac cycle of a left ventricle model, extracted from magnetic resonance imaging (MRI) scans of patients diagnosed with RHD.

The purpose of this study was to investigate how particular business practices, focusing on those occurring in multi-site non-governmental organization (NGOs), could be enhanced by use of a knowledge management system (KMS). The main objective of this KMS is to enhance business processes and save costs for a multi-site NGO through streamlining the organizational practices of knowledge creation, storage, sharing and application. The methodology uses a multiple perspective approach, which covers exploration of the problem space and solution space. Under exploration of problem space, interviews with employees of the NGO are done to identify core problem that the organization faced. Still under exploration of problem space, organization’s knowledge management maturity was assessed through an online questionnaire. The methodology then moved on to exploration of problem space. During the exploration of problem space, the requirements gathering and definition process was done through a combination of interviews with company employees and by completing a systematic literature review of best practices. The requirements were used to design system architecture and use-case models. The prototype for a Community of Practice (COP) support website was developed and investigated in test cases. The tests showed that the prototype system was able to facilitate asynchronous communication through the creation and management of events, creation and management of collaboration groups, creation of discussion topics and creation of basic pages. Furthermore, security capabilities were tested in terms of login functionality. Lastly page load times were tested for eight different scenarios. The system performance was found to be satisfactory because the scenarios covering crucial system requirements aspects had a response time of below 11 seconds. An exception was the landing page, which after login took 26 seconds to load. It is believed that creation of a platform that enables, and records, user interaction, easy of online discussions, managing groups, topics and events, are all major contributors to a successful knowledge management approach.

The aim of this research was to investigate the effects of using hydrogen as a temporary alloying element in the manufacturing of titanium (Ti) and Ti-6Al-4V by the powder metallurgy (PM) route using commercially pure titanium (CP Ti), titanium hydride (TiH2) and Ti-6Al-4V powders as starting materials. Several powder blends were selected and respective samples were pressed at compaction pressures ranging from 300-500MPa for green density and strength measurements. It was found that the higher the level of TiH2 in the powder blend, the lower the green density and strength. However, powder blends containing more than 40wt% of TiH2 did not result in considerable decrease in green strength and density. The selected powder blends underwent thermal decomposition analysis. The results show that hydrogen introduction is more beneficial in the form of a hydrogen atmosphere rather than using TiH2. Samples of selected powder blend were pressed and sintered at 1050°C under argon and partial hydrogen atmospheres. While the general trend was that sintered densities improved with TiH2 content as well as in the presence of hydrogen in the sintering atmosphere, there was an unexpected decrease from green to sintered density for the TiH2-6Al-4V samples sintered in partial hydrogen at 1050°C. These results were supported by the microstructural analysis. Additional sintering trials for CP Ti-6Al-4V and TiH2-6Al-4V for different sintering conditions were also conducted and their relative sintered densities were concurrent with the density results obtained in the current literature (>97%). Elemental mapping conducted proved that the diffusion of the MA particles were the same for both TiH2-6Al-4V and CP Ti-6Al-4V. The decrease from green to sintered density in the TiH2-6Al-4V samples was due to the formation and trapping of H2O (g). At 1050°C the rate of H2 and subsequent H2O gas release is lower as compared to 1200°C. Hence, H2O gas molecules are trapped for longer causing the formation of larger pores that are harder to shrink especially at 1050°C. In a negative pressure atmosphere like vacuum, the higher pressure gradient between sample and atmosphere will favour faster diffusion rate of H2O gas which prevents big pore formation thus favouring faster densification. Sintering TiH2 based compacts in a partial hydrogen atmosphere has not proven to be very beneficial in aiming to decrease the sintering temperature.

Corrosion of steel in reinforced concrete structures is a large problem facing engineers today. The marine environment is considered to be the most severe owing to the high levels of chlorides available, and so structures located here are particularly vulnerable to chloride attack and chloride induced corrosion of steel. In order to intervene and address the concern of premature deterioration in the marine environment, design guidelines and frameworks have been developed and implemented. For example, the Eurocode (EN 206, 2013) provides three class designations in order to predict the severity of potential steel corrosion. The three exposure zones, namely i) structures exposed to airborne salts but not in direct contact with sea water, ii) submerged structures, and iii) structures in the tidal, splash and spray zones are given here in order of increasing assumed probability of corrosion. However, it has been found through condition assessments of structures along the Atlantic Ocean and Indian Ocean coasts of Southern Africa that structures in the tidal zone generally show no signs of corrosion damage despite having high levels of chlorides at the depth of reinforcement. Often, on a structure where both zones have the same cover to reinforcing, the splash and spray zone will show significant damage while the tidal zone shows no signs of reinforcement corrosion. These findings challenge the existing idea that the tidal zone can be characterised as the most severe exposure zone. In order to further understand the mechanisms of reinforcement corrosion within different marine environmental conditions, a total of 36 corrosion cells were manufactured with dimensions of 120 × 122 × 380 mm and placed in simulated marine environmental conditions. These three environmental conditions included submerged, cyclic wetting and drying, and periodic splashing. In order to simulate the submerged environment, the cover surface of the specimens were permanently saturated with a 5% NaCl solution while for the splash zone concrete specimens were sprayed with 5% NaCl solution every second day. The tidal zone attempted to simulate natural tidal conditions by exposing the corrosion cells to 12 hour cycles consisting of 6 hours wetting and 6 hours drying All 36 corrosion cells were connected to a data logger where the voltage was measured weekly across a resistor of 100Ω. Ohm’s law was then used to determine the current flowing through the circuit. The concrete cover depth was varied in the corrosion cells (10, 20 and 30 mm) as well as the w/b ratio (0,5 and 0,8). The corrosion current resulting from these corrosion cells were used to infer relationships between all 3 parameters (cover depth, w/b ratio, and exposure conditions) and their influence on the corrosion current. Three companion moisture specimens were cast per mix in order to establish moisture profiles in the different exposure zones. From these specimens, the relative humidity of the concrete at different cover depths and w/b ratio’s could be determined for corrosion cells located in differentexposure conditions. Companion cubes were also cast with the corrosion cells in order to determine the durability index values. The results of the experiments indicate that the exposure condition has a very large impact on the availability of oxygen, and hence the corrosion rate. High relative humidity (or moisture content) in concrete stifles the supply of oxygen to the steel, and hence prevents active corrosion. For concrete submerged and partially or completely saturated with water, oxygen accessibility can become limited at the steel surface. The results obtained conform to the widely accepted principle that submerged concrete is less vulnerable to corrosion as a result of insufficient oxygen supply at the reinforcing steel. For concrete exposed to a 6 hour cycle of wetting and drying, the corrosion rate was significantly lower at higher cover depths due to the short cycle durations, the pores surrounding the steel were still partially or fully saturated with water. As a result, oxygen diffused slower through the cover layer. Consequently, where the concrete in the tidal zone has drying times of about 6 hours and a cover depth exceeding 30 mm, the steel will be deprived of oxygen, and corrosion will be stifled. This means that the concrete in the tidal zone would theoretically perform as if it were permanently submerged (provided sufficient cover depth exists). Specimens exposed to a splash environment performed as expected. A low moisture content showed that oxygen is able to diffuse through the pore system and facilitate corrosion in the specimens. This is owing to the pores around the steel not being saturated with moisture, and oxygen being readily available to participate in the cathodic reaction. In the case of these specimens, the electrical resistivity of the specimens was found to be the main limiting factor in controlling the corrosion rate (and not cathodic control as with tidal and submerged specimens). As a result, it is recommended that the current SANS exposure classification be broadened to include concrete exposed to cyclic wetting and drying (i.e. tidal zone exposure) a separate category, and not be classified as having the same severity as the splash zone. The application of these research findings is in infrastructure that is primarily exposed to only tidal and submerged marine conditions.