Plasticity and Density-Moisture-Resistance Relations of Soils Amended with Fly Ash

Abstract

Fly ash is a by-product of coal combustion that requires disposal worldwide. Few studies have been conducted on the potential utilization of fly ash to improve soil physical properties and workability. The objective of this study was to investigate the impact of fly ash amendments on the plasticity, water retention and penetration resistance-density-moisture relationships of three soils of sandy loam, loam and clay loam textures in order to determine the potential compaction of these soil/fly ash mixtures if they were worked at different moisture ranges. For all 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 soils 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 densification occurs at these moisture contents. In all three soils the addition of fly ash increased water retention, especially in the sandy loam. Correlation analysis indicated significant (p≤0.05) positive correlation between critical moisture content and field capacity, critical moisture content and plastic limit, and plastic limit and field capacity. Fly ash amendments increased penetration resistance of the clay loam, but decreased penetration resistance of the sandy loam. For the loam there was an inconsistent response of penetration resistance to fly ash additions. Regression analysis indicated that penetration resistance of sandy loam/fly ash mixtures and loam/fly ash mixtures was significantly (p≤0.05) dependent on bulk density. For the clay loam/fly ash mixtures penetration resistance was significantly (p≤0.05) dependent on both bulk density and volumetric moisture content.