No description available.

Rational decisions about cost-effective maintenance and structural repair are hampered by the absence of comprehensive data on structural performance of generic repair materials acting compositely with deteriorated concrete elements. In the present climate of durability problems in concrete construction such information is of critical importance. In order to assess long-term structural performance of repaired elements, basic short and long-term properties of generic repair materials are required under various exposure conditions. The principle requirements to ensure satisfactory long-term performance of the repair have always been high dimensional stability and relatively high early bond strength of the repair material with the substrate concrete. As part of a "Brite Euram" project, sponsored by E.E.C., the author has obtained considerable experimental data on properties of three commercially available generic repair materials, which are significant to the subsequent structural behaviour of repaired concrete members. A comparison is also made between the performance of these repair materials with a plain concrete mix of similar strength and stiffness. The following generic repair materials were used: a high performance non-shrinkable concrete, a mineral based cementitious material with no additives and no coarse aggregate size particles, and a cementitious mortar which contains styrene acrylic copolymer with fibre additives. The repair materials are supplied as single component systems by their manufacturers, ready for on-site mixing and use, and require only the addition of clean water. Data on strength, stiffness, post peak-load ductility under compression, swelling, shrinkage and creep deformations under various curing conditions are presented in this thesis. In addition water permeability coefficients and chloride penetration profiles of the materials at various ages of exposure have been determined. A comprehensive compilation of chloride diffusion data is made and an empirical expression is derived for the prediction of long-term chloride penetration profiles based on data obtained at relatively early ages. Application of this prediction model to the field data of some Arabian Gulf structures is made. The influence of repair materials on the performance of reinforced concrete compression members has been studied. A theoretical model is also derived to predict the long-term structural interaction between a repair patch and substrate concrete in short compression members of reinforced concrete. The model is based on the basic properties of materials, such as creep deformation, drying shrinkage and modulus of elasticity. The validity of the model is established on the basis of the experimental data obtained in this study. At the end of the thesis, conclusions and recommendations for future research are made.

M.Ing. / It is generally accepted that successful concrete repair is dependent on seven steps. All seven steps of the concrete repair process were investigated in depth. From the seven steps, three of the steps (removal, application and curing) were selected for experimental investigation. Firstly, the removal of damaged concrete was simulated under laboratory conditions. Concrete blocks were prepared through different removal techniques. Repair material was placed on the blocks, and the adhesion between the concrete repair material and the concrete substrate was determined. Secondly, different repair mortar application methods were used, and the effect of application methods on adhesion strengths was determined. Thirdly, the effect of curing on adhesion was determined by curing samples under different conditions. Some in situ test repairs were done at RAU to get an indication of the appropriate repair systems to be used on the RAU buildings. A questionnaire was given out to the industry and analyzed to get an indication of the common practice used for concrete repair in South Africa.

Structural concrete can be treated using a variety of special methods to produce aesthetically pleasing effects. This type of concrete is called architectural concrete. It is possible to produce structures with colourful, smooth or textured surface finishes that will satisfy any of the demands of modern architecture. It is clear that matching the colour and texture of repair work in architectural concrete is problematic. Concrete surfaces with different types of finishes require different rehabilitation processes, just as different ages of concrete require different repair methods. The concrete life cycle is set up for aesthetic repair in this research. Before a repair project is undertaken it is important to ascertain the type of failure. The causes of the failure should be identified and removed if possible. The factors influencing the appearance of the concrete surface should be discussed, in order that the right skills and technical methods are employed during the rehabilitation process. The repair method should be divided into two categories, one is for the young concrete, and another is for the old concrete. A good starting point for the patching mortar of both young and old architectural concrete are suggested as a result of the experiments. Two new factors have been established as a result of this research, namely the colour coefficient and the colour influence coefficient, both of which will be beneficial to future research projects. KEYWORDS: architectural concrete, colourimetric method, discolouration, young and old concrete, colour coefficient, colour influence coefficient. / Mr. Deon Kruger

M.Ing. / The importance of maintenance in industry and specifically in the electrical distribution industry has never really been challenged. Maintenance has none of the glamour of other functions such as Marketing or Research, nor has it enjoyed close attention received by other aspects of business such as production and sales. Yet management remains painfully aware of the consequences and cost to the business when the maintenance job is not properly executed. What has, in recent years, exacerbated matters somewhat (in the electrical distribution business) is the reluctance of utility undertakings to invest heavily in a business that is to undergo a vast transformation arising from the creation of the National Electricity Regulator (NER). This will entail the amalgamation of some 400 plus different electricity distributors, by far the most in the guise of municipal undertakings, into a few Regional Distributors and Metro's. During this phase of uncertainty, the electricity departments of many municipalities have been allowed to deteriorate as maintenance and refurbishment funds were moved into other areas that would remain within the control of the municipalities. Eskom also has allowed, to a certain extent, its own distribution infrastructure to deteriorate over the last decade or so due to a focus being placed on the distribution and delivery of electric power to remote and informal settlement areas. Now on the eve of the re-organisation of the electricity supply industry into Regional Distributors and Metro's, the existing network infrastructures are far from being in an ideal situation to cope with the added business constraints to be placed on the supply industry under the scope of Regulation. This dissertation looks at an integrated maintenance strategy for one component of the electricity infrastructure namely, the distribution substation. The Electricity Supply Industry (ESI) is on the brink of vast changes that will reform the industry. Already there are cracks developing in the existing supply infrastructure resulting in power blackouts in several major centres. With the coming of the Regional Electricity Distributors, additional constraints will be placed on the supply industry. It is vital that maintenance management in the ESI start to work proactively in optimising maintenance to achieve a best return on hard gained funding in the coming years.

M.Ing. (Engineering Management) / Please refer to full text to view abstract

M.Ing. / Until very recently reactive maintenance was still used in the mining industry. Equipment failures occurred without warning and resulted in catastrophic breakdowns and large production losses and maintenance cost. As a result, the mining industry turned to preventative maintenance that focused on changing parts before they fail. Although preventative maintenance was an improvement over reactive maintenance practices, equipment reliability did not necessarily improve. Next came predictive diagnostics, which monitored the health of components within assemblies, and thereby predicting the life expectancy of assemblies through vibration analysis, infrared thermography, lubrication and oil analysis and ultrasonic detection. However, the level of success could not be achieved. Many hours and a lot of money are spent in developing and implementing a maintenance management system, but without the correct approach, efficient maintenance might not be achieved. The overall objective of this dissertation is to introduce a logical approach to managing the maintenance of mining equipment over the economical life of the equipment. This concept can be defined as Life Cycle Management. The research included in this dissertation is partially aimed at developing the Life Cycle Management program for P&H MinePro Services A division of Joy Global (South Africa) (Pty) Ltd. The dissertation also includes case studies on the P&H Mining Equipment (Blast Hole Drills) and their alliance partners (LeTourneau Front-end Loaders). The dissertation focuses on the cradle to grave approach of maintenance for mining machinery, referred to as the Life Cycle Management of Mining Machinery.

No description available.

published_or_final_version / Applied Statistics / Master / Master of Social Sciences

No description available.