Chemical Soil Stabilisation

In chemical soil stabilisation, soils are stabilised by adding different chemicals.These chemicals react with the soil which in return cause its structure to be changed.The chemical seal the space between particles, leaving no room for water to penetrate through.Among the most common chemicals that are used for soil stabilization include sodium chloride, calcium chloride and sodium silicate.The main advantages of chemical stabilisation is that setting time and curing time can be controlled. Chemical stabilisation is however generally more expansive than other types of stabilisation. The following chemicals have been successfully used:

1. Calcium Chloride
2. Sodium Chloride
3. Sodium Silicate
4. Chrome Lignin
5. Polymers
6. Other Chemicals

1. Calcium Chloride

Calcium chloride is an inorganic compound, a salt with the chemical formula CaCl2.When calcium chloride is added to soil it causes colloidal reaction and amend the characteristics of soil water.When calcium chloride is dissolved it reduces the loss of moisture from the soil.It also reduces the chances of frost heave, as the freezing point of water is lowered.This method is very effective for stabilisation of silty and clayey soil which lose strength with an increase in water content.

2. Sodium Chloride

Sodium chloride is commonly known as salt with the chemical name NaCl.Sodium chloride is mixed with the soil either by the mix-in place method or by the plant-mix method.It should not be applied directly to the surface.When sodium chloride is added to the soil, crystallisation occurs in the pores of the soil and it forms a dense hard mat with the stabilised surface.

3. Sodium Silicate

Sodium silicate are colorless glassy or crystalline solids or white powders.Sodium silicates, as well as other alkali silicates have been successfully used for soil stabilisation.Sodium silicate gives strength to soil when it react with it and make the soil impervious.This method of stabilisation is relatively inexpensive but its long term stability is doubtful.

4. Chrome Lignin

Lignin is an organic substance binding the cells,fibers and vessels which constitute wood and the lignified elements of plants.Chrome lignin is formed from black liquor obtained during sulphite paper manufacture.Sodium bicarbonate or potassium bicarbonate is added to sulphite liquor to form chrome lignin.It slowly polymerises into brown gel.

5. Polymers

Polymers are long-chained molecules formed by polymerising of certain organic chemicals called monomers.Polymers may be natural or synthetic.When a polymer is added to a soil reaction takes place.Polymers mainly affect the aggregation and strength of soils through their interactions with fine clay particle.Coating of adsorbed polymers on clays can increase their steric stabilisation by preventing clay particles from approaching each other as closely.

6. Other Chemicals

Apart from the above mentioned chemicals some other chemical are also used for soil stabilisation which are as fallows:

 

A. Some water proofer such as alkyl chloro silanes, siliconates amines and quaternary ammonium salts have been used for water proofing of soils.

B. Dispersant such as sodium hexa-metaphosphate, are used to increase electrical repulsion and to cause dispersed structure.

C. Coagulating chemicals such as calcium chloride and ferric chloride have been used to increase the electrical attraction and to form flocculated structure in order to improve the permeability of the soil.

Advantages Of Chemical Soil Stabilisation

• It gives more strength to the soils.
• It improves the permeability of soil.
• It this method the setting time and curing time can be controlled.

Disadvantages Of Chemical Soil Stabilisation

• Require extra experienced labor.
• Chemicals should not be used directly to the surface.
• This method of stabilisation is more expensive relatively to other methods.