FLY ASH AND ITS USAGE IN CONCRETE

Fly ash is defined as that portion of pulverised-fuel ash (pfa) that is fine enough to be taken with the gas from a furnace, before the gas is discharged into the atmosphere. For example, about 15 million tonnes of pfa were taken from UK power stations in 1977. The author states that fly ash as a basic raw material is highly variable, and must be quality controlled if it is to be used in quality concrete. The characteristics of fly ash - colour, chemical composition, pozzolanicity, loss on ignition, physical are discussed and consideration is given to appropriate specifications for its use. The effects of fly ash in concrete is discussed by reference to measurements of such effects on workability, constituent properties, particularly water content and rate of strength development. Test results are presented, and questions of mix design, concrete variability, durability and heat of hydration are discussed. (TRRL)