Temporal influence of fly ash on select soil physical properties

Abstract

Fly ash, as a source of calcium, has potential for soil structure amendment. This potential was tested by examining the influence of fly ash on select soil physical properties of an easily clodded clay loam soil. Fly ash:soil mixtures were varied from 0 to 100% (vol/vol). Pots of these mixtures were placed into the soil of a reclaimed surface mine and sampled four times during a 15.5-mo period: upon mixing, after one summer, after one summer and a winter and after the second summer. Bulk density, dry aggregate size distribution, penetration resistance (PR) and modulus of rupture (MOR) were assessed on soils within the pots.Adding fly ash up to 25 to 50% generally increased bulk density; adding more decreased it. Bulk density decreased over time for most of the treatments. Adding 12.5 or 25% fly ash produced the greatest percentage of aggregates within the ideal range (0.5 to 4.0 mm). Blunt-end PR was a more sensitive parameter than cone resistance. Adding 25% fly ash resulted in lower MOR while maintaining a desirable level of aggregation, thus reducing cloddiness. In general most properties varied over time, indicating the need to consider the dynamic nature of them in reclamation. Key words: Fly ash, soil reclamation, bulk density, penetration resistance, particle size distribution