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Please read the abstract in the section 00front of this document / Dissertation (M Eng (Mechanical Engineering))--University of Pretoria, 2004. / Mechanical and Aeronautical Engineering / unrestricted

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering / The sudden failure of oil paper-insulated current transformers has become a problem of considerable concern due to the cost of the resulting destruction, and danger to personnel. The aim of the dissertation is to determine the most suitable method of detecting incipient faults in current transformers, test this method on an experimental current transformer, and finally implement this technique in a low cost on-line monitor. A literature survey indicated that hydrogen gas-in-oil on-line monitoring would be the most suitable technique.(Abbreviation abstract) / Andrew Chakane 2019

The purpose of this study was to investigate the hypothesis that a dispensing program utilizing rehabilitative follow-up in the form of a post-fitting check appointment would show: (1) less return for repairs for hearing aids; (2) higher patient satisfaction with the aid; and (3) higher patient satisfaction with the service received during the hearing aid dispense than would a clinic with no follow-up. Data for comparison between the two clinics were drawn from medical chart review, frequency of hearing aid repairs, and from a questionnaire which assessed satisfaction levels. Patients were also asked to estimate the amount of use with the aid and success with manipulation of the aid for purposes of comparison with other groups previously studied.

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A new method to evaluate the performance of sealants, used in rigid pavement joints, was developed. A special fixture was designed to transfer cyclic in-line deflection, applied by a testing machine, to cyclic normal and shear deflections on a sealant sandwiched between two-2 x 2 x 2 in. portland cement mortar cubes. The normal and shear deflections were applied simultaneously at a specific ratio controlled by the developed fixture. The new testing method simulates field conditions, where shear deflection is caused by vehicle loads while normal deflection is caused by slabs contraction or expansion due to temperature variation. The developed fixture was used to evaluate the performance of three commercially available one-component sealant types: (A, B, and C), A is a low modulus sealant, B is a self leveling type, while C is a sealant which is used with primer. The effect of joint width on sealant performance was investigated using two joint widths (0.25 in. and 0.75 in.), while the weathering effect was evaluated by exposing specimens to 50 cycles of rapid freezing and thawing prior to testing. / Master of Science

Hydrodemolition is the use of a high pressure water-jet to remove concrete. It is a new method of concrete removal which is becoming increasing specified by state Departments of Transportation for bridge rehabilitation work. The technical, financial and contractual aspects of using hydrodemolition are examined and a brief explanation of salt induced concrete deterioration in bridges is presented. Interviews were conducted with state DOT engineers, general contractors, specialty hydrodemolition subcontractors and hydrodemolition equipment manufacturers. These interviews identified problems encountered with using hydrodemolition. Possible solutions to these problems are presented. These possible solutions are based on both suggestions made by the persons interviewed and the author. / Master of Science

Due to the increasing rate of deterioration of concrete bridges caused by exposure to chlorides, it has become apparent that effective protection methods need to be employed which will prevent chlorides from reaching critical contamination within the life of the structure. One method of protection is the application of concrete surface sealers which form water-resistant barriers and reduce chloride intrusion. It is imperative to know how effective sealers are and how long sealers retain their effectiveness in order to plan reapplication and estimate life cycle costs for comparison to other maintenance activities. This research was conducted to predict the service life of concrete sealers for both horizontal and vertical bridge components. As a secondary goal, the use of a rapid, non-destructive Surface Absorption Test (SAT) was investigated as a possible substitute for analyzing the condition of sealers. This was done by comparing SAT results with the standard concrete sampling and chloride analysis technique typically employed. Four sealers were applied to horizontal laboratory specimens (slabs), vertical laboratory specimens (wall sections), and bridges (high-volume and moderate-volume). Control sections were also included in all specimen types. The laboratory specimens were exposed to a 3% NaCl solution for 30 1-week cycles, each cycle being three days of exposure and four days of air drying. Background chlorides and the chloride ion profiles were determined after 10, 20 and 30 cycles of saltwater exposure. The surface absorption test was conducted at various intervals throughout the cycles. The surface absorption test was also used to attempt to measure the traffic wear effect on the field specimens. The results indicate that the two epoxies exhibited very little effectiveness in preventing chlorides from entering the concrete. The silane and siloxane sealers performed much better in the laboratory settings, retaining over 90% reduction of chlorides throughout the test period. A service life model which includes laboratory performance and considers application exposure conditions is suggested. It has been discovered that, at present, surface absorption testing may be used on a limited basis to obtain results which indicate sealer effectiveness, but only if the testing occurs under extremely limited or controlled environments. / Master of Science

The purpose of this study is to determine the financial adequacy for highway maintenance in Virginia during the period from the year 1981 to 1990. Future highway maintenance expenses were projected using regression analysis and hypothesized to be a function of travel. The forecasts of maintenance expenditures were performed for each district in the state and for the three major highway systems-- interstate, primary and secondary-- which are responsible by the Virginia Department of Highways and Transportation. Maintenance expenditure projections were also made for three economic scenarios--high, moderate and low inflation rates. The results showed that with high inflation, there will be a shortfall of maintenance funds under the present taxation policies. To avoid the future shortfall, an increase in an additional fuels tax of three percent of the price of gasoline was assumed and also a deferment of maintenance activities was considered. The results of both cases show a need for a further increase in highway taxes in order to cope with the increasing highway costs in the next decade. / Master of Science

M.S.