The influence of controlled environmental conditions on the potential durability of concrete

Griesel, Eben Johannes (1999-10)

Thesis (M.Sc.Ing.) -- University of Stellenbosch, 1999.

Thesis

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.

AFRIKAANSE OPSOMMING: Die doel van hierdie projek was om die invloed van temperatuur, lugvogtigheid en windspoed op die potensiele duursaamheid van OPC beton te ondersoek. Drie verskillende betonsterktes is ondersoek, en die monsters is nabehandel vir 1, 3 of. 7 dae, voor blootstelling aan die omgewing. Die blootstellingstemperature wat ondersoek is, was 20, 28 en 35°C (by 50% relatiewe lugvogtigheid), en die relatiewe lugvogtighede was 54, 66 en 82% (by 20°C). Die ondersoek van windspoed was beperk tot 5,6 m/s. Die massaverliese van die betonmonsters is gemonitor tydens die blootstellingstydperk, en die duursaamheidsindekstoetse is gebruik om die kwaliteit van die beton aan te dui. Die kwaliteit van beton wat nie behoorlik nabehandel is voor blootstelling nie, is benadeel deur hoe temperature. In die geval van goeie nabehandeling, het die betonmonsters hulle interne vog behou en gebaat by die hoer tempo van sementhidrasie. Die resultate van monsters wat blootgestel is aan 'n lugvogtigheid van 82%, was naastenby dieselfde as monsters wat ten volle nabehandel is. Benede hierdie waarde was die resultate nie sensitief ten opsigte van lugvogtigheid nie. Die invloed van windspoed was gering. Nabehandeling vir ten minste 3 dae was noodsaaklik, ten einde te verseker dat die beton genoegsame duursaamheidskwalitiete ontwikkel (uitsluitende die geval van hoe lugvogtighede tydens blootstelling). 'n Teorie is ontwikkel om die uitdrogingsproses van verharde beton te beskryf, wat gebruik kan word om die porositeitseienskappe van die beton te bereken. Die model neem blootstellingstoestande van verskillende lugvogtighede en 'n konstante temperatuur (van 20°C) in ago Daar was 'n goeie verband tussen die teorie en die resultate van die ondersoek na die invloed van lugvogtiheid.

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