Temporal influence of fly ash on soil bulk density and aggregate size distribution

Abstract

Fly ash is a by-product of coal-fired power generation. In 1992, 2.5 million tonnes of fly ash were produced in Alberta of which most was disposed of in lagoons or disposal sites. There is potential to use fly ash as an amendment to improve certain physical characteristics of problem soils. Fly ash is composed predominantly of silt-sized particles and when added to a soil high in clay, the soil texture and other associated physical characteristics, such as bulk density, can be altered to be more desirable for plant growth. The land surrounding the Sundance power generating plant and Highvale coal mine near Edmonton, Alberta is composed predominantly of Luvisolic and Solonetzic soils that have a high clay content. Fly ash from the Sundance power generating plant was added to a clay loam soil in amounts ranging from O to 100% fly ash. The soil:fly ash mixtures were left outdoors at the Highvale coal mine for 16 months. At select times during this period, the mixtures were periodically analyzed for bulk density and aggregate size distribution. Adding 12.5 to 25% fly ash to this soil produced the highest percentage of soil aggregates within the ideal range (1-5 mm) for seed-soil contact. Soil bulk density increased with fly ash additions of up to 25%, then decreased. Fly ash alone had the lowest bulk density. Hence, fly ash may be a suitable soil amendment, although other environmental issues related to its use must also be addressed.