Stabilization using bitumen as an additive is known as bitumen-stabilization. Some of the granular soils like asphaltic bitumen, cut back bitumen and bitumen emulsion are stabilized by adding bitumen in it. Pores of the soil are sealed by the bitumen which reduces its permeability. By providing cohesion between the particles we can also increase the shear strength in it.
For road surfacing this method is useful for the preparation of asphaltic mixture. In middle east usually crude oil is used for this purpose.
The main disadvantage of this method is that the immediate effect in saturated soils is to reduce the shear strength due to the increase in fluid content.
Stabilization using lime as an additive is known as lime-stabilization. When we mix unslaked lime with soil sample usually four chemical reactions take place which are as follow:
- Hydration of lime
- Ion exchange
- Pozzolonic reaction (cementation)
Hydration of lime is the removal of water contents from the soil mass in order to raise its temperature and increase its shear strength. The hydration process gets started immediately. The process is usually completed in a very short interval of time.
Ion exchange method like hydration is completed in a very short interval of time and starts immediately like it. This process results in the formation of water stable aggregates, which possesses low permeability and compressibility as compared to the original soil sample.
The pozzolonic reaction which is also known as cementation is comparatively slow and requires a large time to complete. The cementation result in the increase in shear strength and decrease in compressibility.
The reaction between the lime and air is called carbonation and it is a cause of reduction in shear strength. Its intensity can be minimized if the mixing of lime is made below GWT.