Soil Stabilization and Modification Treatments

Soil Modification

A wide range of chemical and propriatary agents are currently available to modify a subgrade soil. Soil Modification can be used to:

• Improve the workability 
• Reduce the plasticity index (PI)
• Decrease the shrink swell potential
• Achieve a slight gain in srtength

of a subgrade soil.

Soil Modification is achieved with the addition of lime (hydrated or quicklime), lime kiln dust (LKD), self-cementing class C fly ash, class F fly ash (when used in combination with other additives), cement,  cement kiln dust (CKD),  calcium chloride, magnesium chloride to the pulverized materials. There are many other agents that are used to modify soils and these include enzymes, polymers and other proprietary products. Lime is generally used with high PI soils (fat clays).

Soil Stabilization

With chemical soil stabilization a chemical based stabilizing agent is added to the subgrade soil to achieve the same improvements as with soil modification but with an additional improvement in strength. Bituminous stabilizing agents work best with low PI materials and therefore provide mainly an improvement in strength. Many agencies require a minimum unconfined compressive strength before a soil can be treated as a stabilized layer in a pavement structure. The selection of a stabilizing agent is a function of:

• Planned thickness of the pavement structure 
• Subgrade material properties (gradation, plasticity, etc.)
• Amount of strengthening required 
• Availability of stabilizing agents
• Economics

A wide range of chemical and bituminous stabilizing agents are currently available. Table 15-1 from the BARM provides recommended bituminous and chemical stabilizing agent selection criteria based on properties of the proposed reclaimed materials for FDR. The same table is generally applicable for soil stabilization.

Chemical Stabilizing Agents: Chemical stabilization is achieved with the addition of lime (hydrated or quicklime), lime kiln dust (LKD), self-cementing class C fly ash, class F fly ash (when used in combination with other additives), cement (portland or hydraulic), cement kiln dust (CKD), calcium chloride, magnesium chloride, enzymes or proprietary products. Lime stabilized materials are generally used with fine grained, highly plastic materials. They generally yield moderate strength gains and have some limitations with respect to release of traffic. Cementitious stabilizing agents work with a wide range of materials and can accommodate higher plasticity materials than bituminous stabilized materials. There can be limitations on release of heavy traffic and special requirements to minimize shrinkage cracking. 

Bituminous Stabilizing Agents: Bituminous stabilization is accomplished with the addition of emulsified asphalt or foamed (expanded) asphalt. Bituminous stabilizing agents maintain a flexible structure and have little restrictions to the release of traffic. However, they have tighter gradation requirements and require subgrade soils to be of lower plasticity. More information on bituminous stabilizing agents can be found in the same Materials section under Base Stabilization and FDR.