Durability of concrete containing high-calcium fly ash

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The proposed research program is aimed at addressing concerns regarding the poor performance of some concrete containing certain types of Class C fly ash. Fly ash is an industrial by-product of burning coal in electricity generating stations. The material has been used as a cementing material in concrete, partially replacing traditional portland cement, for a number of decades in Canada. Its use results in many technical, economic and environmental benefits. However, there are different types of fly ash produced in Canada, which vary widely in composition. Recently there has been concern expressed over the use of fly ashes with relatively high quantities of alkali or sulfate, or both, as these compounds can be injurious to the performance of concrete. There are also concerns over the recent trend to replace larger proportions of traditional cement with fly ash as this may result in poor performance at early age, especially in low strength concretes used in typical residential applications. The impact of fly ash chemistry on the composition and performance of cement, mortar and concrete products will be tested in this research program. The aim is to establish whether more stringent chemical limits are necessary for fly ash and whether the use of certain fly ashes needs to be restricted on the basis of concrete quality or application. Developing a better understanding of the role of fly ash composition in concrete performance should lead to an increased use of fly ash in cement-based products. More than 4 Mt per annum of fly ash are sent to landfills each year and increased use of this material will reduce environmental dereliction. A further environmental benefit is that the increased use of fly ash will result in a reduced consumption of portland cement, the manufacture of which is the chief producer of greenhouse gases in the construction industry.