Moving Fly Ash Utilisation in Concrete Forward: A UK Perspective

This paper addresses some of the issues that have long been problematic to the fly ash industry, ie why is utilisation far less than production, the impact of the changes to production methods (flue gas desulphurization etc) on ash characteristics and, given the volumes involved, how large volume use in concrete be maintained without the significant on-costs of processing and beneficiation. The paper does not purport to have all the answers, indeed after half a century of large scale use there are not likely to be any quick fixes, but instead reviews the benefits, unprocessed, conditioned, run-of station, low lime fly ash can bring to both normal weight concrete and to foamed concrete. The crux of the argument is that this type of fly ash can be used to partially or fully replace the fine aggregate, if use in a carefully balanced way. Perhaps more importantly, concrete producers can stockpile and use existing equipment to handle this type of ash similarly to sand. This overcomes issues of investment in specialised handling and storage bins, which often deters smaller companies from using fly ash. It is shown that used in this way the heat evolved, strength and durability properties can be enhanced and the use of primary aggregate reduced. However, the results show that the direct substitution of even coarse fly ash for sand does reduce the workability of normal weight concrete and greatly increases drying shrinkage strain in foamed concrete.