Influence of high content fly ash on concrete durability

Abstract

Abstract - The use of fly ash products by the South African cement and construction industries has saved the country over 6 million tons of harmful greenhouse gas emissions. Fly ash is an industrial by-product that is normally consigned to landfills and the re-use of it as cement extenders provides an immediate benefit for the environment while still improving the quality of concrete. Fly ash blended cements in concrete perform better than pure cement in providing better concrete properties. Current specifications limit the use of fly ash in concrete to 30%, although an increase of this amount can be very beneficial in concrete structures, economically and environmentally. In South Africa the durability index of concrete is commonly determined by performing the Oxygen Permeability test, Water Sorptivity test and Chloride Conductivity test, developed by the Universities of Cape Town and the Witwatersrand. Performing these tests in this study, the results obtained showed that concrete mixes with fly ash content that is higher than the specification limit can result in concrete with acceptable good durability qualities, and with age, the durability qualities are improved due to pozzolanic reactions. Substituting high volumes of cement with fly ash in concrete can provide high quality concrete and a relief in the environment without compromising the quality of concrete.