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Soil amendment is the chemical and/or mechanical modification of soil properties to improve its engineering performance. Properties most often modified are strength, plasticity, density and water content. Typically, construction companies use fly ash along with lime, cement or lime kiln dust to achieve the desired effect. Using amendments can save a construction project significant time and money.

Using fly ash as a soil amendment:

  • Enhances soil strength properties
  • Improves the control of shrink/swell properties of expansive soils
  • Eliminates the need for expensive borrow materials
  • Expedites construction by improving excessively wet or unstable sub-grade
  • Improves sub-grade conditions allowing for reduced pavement thickness
  • Reduces the need for expensive aggregates in pavement cross sections

Soil Amendment and Soil Strength

Use fly ash to improve soil's compressive and shearing strength. Fly ash can effectively improve sub-grades, base courses and backfill, reducing lateral earth pressures and improving slope stability on embankments.

Soil Amendment and Shrink Swell

Some soils undergo extensive volumetric changes when subjected to fluctuating moisture content. If not controlled, these volumetric changes can impose loads that cause movement to structures and lead to premature failure. Fly ash reduces the potential of a plastic soil to undergo volumetric expansion by bonding the soil grains, restricting or reducing soil particle movement.

Soil Amendment and Water Content

Soil must be compacted to the maximum practical density to achieve a firm base for overlying structures. Fly ash serves as a drying agent for soils that are too wet to achieve the required density. The drying effect of fly ash in wet soil occurs rapidly, allowing you to quickly proceed with construction activities. Fly ash also makes soil more resistant to water infiltration.

Before using fly ash a soil amendment, consider:

  • The rate of hydration reaction upon exposure to water
  • Soil moisture content at the time of compaction
  • Fly ash's sulfur content (>10-% may cause soil expansion)

The use of fly ash in soil amendment may be subject to local environmental requirements pertaining to leaching and interaction with ground water which should be considered.


For more information on how you can use fly ash as a soil amendment, contact us today.


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