Masters Degrees (Civil Engineering)

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Browsing Masters Degrees (Civil Engineering) by browse.metadata.advisor "Alexander, Mark"

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    The influence of controlled environmental conditions on the potential durability of concrete
    (Stellenbosch : Stellenbosch University, 1999-10) Griesel, Eben Johannes; Alexander, Mark; Maritz, Gerhard; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: The primary objective of this investigation was to determine the influence of temperature, relative humidity and wind speed on the potential durability of OPC concretes. Three concrete grades were investigated, and the samples were wet cured for periods of 1, 3 or 7 days before the start of exposure. The exposure temperatures investigated were 20, 28 and 35°C (at 50% RH), and the relative humidities were 54%, 66% and 82% (at 20°C). The investigation of wind speed was limited to 5,6 m/s. Moisture losses from the concrete samples were monitored during the drying period, and the durability index tests were used to indicate the quality of the covercrete. The quality of poorly cured concretes were impaired at elevated temperatures, while well cured concretes were able to retain their moisture and benefit from the increased rate of hydration. Results obtained from concretes exposed to 82% relative humidity were similar to fully cured results. Below this value, the results obtained were insensitive to relative humidity. The influence of wind speed was insignificant. Wet curing for at least 3 days was necessary to obtain durable covercrete, except in the case of high relative humidity exposure conditions. A theory was formulated for the drying processes of hardened concrete, which can be used to calculate the porosity characteristics of the covercrete, when exposed to varying relative humidities and a constant temperature of 20°C. This theory could be related to the durability indexes obtained from the drying regimes of varying relative humidity and constant temperature.
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    Practical implementation of index tests for assessment and control of potential concrete durability
    (Stellenbosch : Stellenbosch University, 1998) Bouwer, Susanna Margaretha; Alexander, Mark; Maritz, Gerhard; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: An investigation into the validity and practicability of performing the water sorptivity, oxygen permeability and chloride conductivity index tests on actual concrete structures is presented. Each test measures a different transport property of fluids or ions through cover concrete. The resistance of concrete to these transport mechanisms governs the rate of deterioration of the concrete and the embedded reinforcement. Current though is that the tests may assist estimation of potential concrete durability and could form the basis of specifications for the assessment and control of cover concrete quality.