PLASTICITY AND DENSITY-MOISTURE-RESISTANCE RELATIONS OF SOILS AMENDEDWITH FLY-ASH

Fly ash is a by-product of coal combustion that requires disposal worl dwide. Few studies have been conducted on the potential utilization of fly ash to improve soil physical properties and workability. The obje ctive of this study was to investigate the impact of fly ash amendment s on the plasticity, water retention and penetration resistance-densit y-moisture relationships of three soils of sandy loam, loam and clay l oam textures in order to determine the potential compaction of these s oil/fly ash mixtures if they were worked at different moisture ranges. For ail three soils the addition of fly ash decreased the plasticity index, but slightly increased the Proctor maximum density-This implies that fly ash amendments reduce the range of moisture within which soi ls are most susceptible to compaction. However, for the sandy loam and loam textured soils amended with fly ash, cultivation must be avoided at moisture contents close to field capacity since maximum densificat ion occurs at these moisture contents.ln all three soils the addition of fly ash increased water retention, especially in the sandy loam. Co rrelation analysis indicated significant (p less than or equal to 0.05 ) positive correlation between critical moisture content and field cap acity, critical moisture content and plastic limit,and plastic limit a nd field capacity. Fly ash amendments increased penetration resistance of the clay loam, but decreased penetration resistance of the sandy l oam. For the loam there was an inconsistent response of penetration re sistance to fly ash additions. Regression analysis indicated that pene tration resistance of sandy loam/fly ash mixtures and loam/fly ash mix tures was significantly (p less than or equal to 0.05) dependent on bu lk density. For the clay loam/fly ash mixtures penetration resistance was significantly (p less than or equal to 0.05) dependent on both bul k density and volumetric moisture content.