The aim of the research was to find an effective, reliable and cost-effective method for long-term monitoring of moisture in concrete structures. The slow diffusion rate of moisture through concrete requires that monitoring should be done over time scales of several years without periodic re-calibration. The solution arrived at was to use a quasi-coaxial transmission line, termed a cagecoaxial transmission line, as the sensing element. The transmission line, terminated in a short circuit, is encapsulated in a porous dielectric medium. It was found that the microstructure of the encapsulating medium had to be similar to the concrete in terms of capillary characteristics in order to track the moisture content of the material under test. The moisture in the encapsulating medium would change the electrical length of the transmission line by increasing the relative permittivity of the medium. The method used makes it possible to measure moisture levels to full saturation. Moisture content can be measured in terms of a percentage of saturation, which will be of considerable help as an early warning system of possible frost damage. A mathematical model was derived to calculate the relative permittivity in terms of moisture content in concrete. It was shown that to calculate the total permittivity of a solid porous medium with a dielectric mix formula, the formula must be expanded to include air, water and solid, before realistic values for the permittivity of the ingredients could be assigned. A dielectric mix formula was derived to account for the liquid to solid boundary effect on the permittivity of water in a solid porous material. The foundations were laid for the development of a reliable and cost-effective probe based on an oscillator, operating around 1 GHz, using the transmission line as a tuning element. The frequency of oscillation is a function of the apparent length, determined by the permittivity and therefore the moisture content, in the transmission line dielectric material. A method to convert this frequency to a format that can be monitored on a data logger system is described. The high oscillation frequency eliminates the effect of ionic conduction from dissolved substances.

No description available.

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

Degree Not Listed / Department of Civil Engineering / Asadollah Esmaeily / This report is contingent upon research and literature reviews, targeting steel fiber reinforced concrete (SFRC). It will explore all aspects involved, detailing both properties and functionality. Historical development of the modern application mix and design procedures will be discussed. A critical investigation based on laboratory testing is examined and a comparative discussion is provided. This report will also highlight the structural uses, benefits, applications and deficiencies acquired by SFRC.

This investigation involved creep and moisture movement measurements for about six months on 13-course clay (Engineering class B) and calcium silicate brickwork, and 5-course concrete blockwork, consecutively. Four different geometries of masonry were built, namely: single-leaf wall, cavity wall, hollow pier and solid pier, respectively having volume/surface area (V/S) ratios of 44,51,78 and 112 mm. Deformations were also measured on one-brick wide 5 or 6-stack high model brickwalls which were partly sealed to simulate the V/S ratios of the corresponding 13-course brickwork. At the same time, deformations were also measured on individual mortar prisms and brick or block units in order to verify composite model expressions for predicting masonry movements. Simulation of moisture diffusion of the corresponding mortarjoints and embedded bricks or block were made in terms of V/S ratio by partial sealing of the individual mortar prisms and brick or block units. The tests reveal that the modulus of elasticity to be independent of masonry geometry. However, there is a clear influence of geometry on the vertical ultimate creep and moisture movement of all the masonry types i,.e. creep and shrinkage increase with a decrease of V/S ratio. A similar trend occurs for horizontal shrinkage except for the clay brickwork which undergoes moisture expansion. Deformations of the model walls show reasonable agreement with the 13-course brickwork. When results of individual mortar and brick/block specimens are inserted in composite models,the predicted strains show good agreement with the measured strains, particularly in the vertical direction. There is no consistent pattern in the distribution of load and moisture strains for the different masonry geometries, and the measurements reveal that actual strains can be up to 100% higher than the average strains.

No description available.

M.Ing. (Electrical and Electronic Engineering) / An extensive literature survey revealed that the existing process design methods for specifying the power requirements of industrial mixers depended either upon an assumption of laminar flow conditions, or on a comparison with a Newtonian liquid, or both. In fact, real industrial mixers often experience flow regimes ranging from laminar near the walls of the vessel to fully turbulent in the impeller zone. Moreover, industrial liquids are rarely Newtonian in character. A method of torque monitoring is proposed for fully describing the power requirements of an industrial mixer to suspend a mineral slurry. This method, by incorporating a critical dimension, the impeller diameter, is suitable for scale-up. It was tested in a uranium leaching application with good results. The "comparative viscosity" of the slurry can also be derived. This parameter is suitable for process control purposes.

M.Ing. (Mechanical Engineering) / An investigation was made to determine the feasibility of using existing international developed compositions of furfuryl alcohol polymer concrete in South African applications. Problems were encountered with these formulations and modifications were required in order to enhance the application possibilities of the material. After these modifications were made, tests were conducted to determine the effects of temperature, humidity, specimen size and variations in constituent quantities on the polymerisation reaction and properties of the material. Engineering characteristics, such as, compressive strength and durability were investigated and large scale field tests were performed to demonstrate the feasibility and simplicity of using polymer concrete. The final mix design selected for use in South Africa, polymerised within 20 minutes obtaining a compressive strength of 20 MPa in that period. This material proved stable under adverse chemical conditions and was able to withstand elevated temperatures of up to 200°C. Tests on road pothole rehabilitation slabs showed that polymer concrete can resist high stresses successfully under repeated loads and can be installed in less than 30 minutes in order to minimize traffic hold-ups. Furfuryl alcohol polymer concrete can be made at a cost of approximately 50c/kg and proves to be cost-effective when compared with epoxies.

M. Phil. / The purpose of this research is to see if on-site portable pull-out tests in South Africa on post-installed chemical and mechanical fixings can produce similar results to internationally laboratory tested fixings. The method used in the field study was to use typical South African 25 MPa, 75 mm slump ready mix concrete as supplied by a reputable supplier and to test several types of fixings in common situations, some covered in the European Technical Approval Guidelines (ETAG) and some not. The results were analyzed against published international values and theoretical calculations for the fixings. The findings showed that the results produced using the portable equipment can show values similar to the published and theoretical values. It was also shown that this methodology can be used as a diagnostic tool to reveal installation errors. The pull-out test operator needs to be skilled to ensure a satisfactory outcome of the tests. The implications of the findings have direct bearing on: The on-site pullout testing of post installed anchors in South Africa; The diagnosing of bad anchor installation. And secondarily bearing on: The education of post-installed fixing installers and designers; The lack of standards for post-installed anchors in South Africa; The transportability of data from international research to South African conditions.