BITUMINOUS STABILISATION AND TYPES

Bituminous Stabilisation

Bitumens are non-aqueous system of hydrocarbon that are soluble in carbon di-sulphide.Bitumen stabilisation is generally done with asphalt as binder.In any inorganic soil which can be mixed with asphalt is suitable for bituminous stabilisation. In cohesionless soils, asphalt binds the soil particles together and thus serves as a bonding or cementing agent.In cohesive soils, asphalt protects the soil by plugging its voids and water proofing it.It helps the cohesive soil to maintain low moisture content and to increase the bearing capacity.The amount of bitumen required generally varies between 4-7% by weight.The actual amount is determined by trail.

There are four types of soil bituminous stabilisation:

1. Soil Bitumen
2. Sand Bitumen
3. Oiled Earth
4. Water Proofed Clay Concrete

1. Soil Bitumen 

Soil bitumen is a water proof, cohesive soil system.The best results are obtained if the soil satisfies the following criteria:

• Plastic Limit Less than 18%
• Liquid Limit Less than 40%
• The maximum size of the particle should not be greater than one-third the compacted thickness of the soil-bitumen.

The quantity of bitumen varies from 4 - 7% of the dry weight.

2. Sand Bitumen

This bitumen stabilised cohesionless soil system.The sand should be free from vegetal matter or lumps of clay.The sand may require filler for its mechanical stability.However, it should not contain more than 25% minus No.200 sieve material for dune sand and not more than 12% in case in other types of sand.The amount of bitumen varies from 4 - 10%.

3. Oiled Earth

In this system, a soil surface consisting of silt-clay material is made water proof by spraying bitumen in two or three applications.The bitumen penetrates only a short depth into the soil.The amount of bitumen required is about 5 litres per square meter of the soil surface.

4. Water Proofed Clay Concrete

A soil possessing a good gradation is water proofed by a uniform distribution of 1 - 3% of bitumen in this system.Soils of three different gradations have been recommended.  

Factors Affecting Bituminous Stabilisation

1. Types Of Soil

Bituminous stabilisation is very effective in stabilising sandy soils having little or no fines.

2. Amount Of Asphalt

The quality of bitumen-stabilised soil improves with the amount of asphalt upto a certain limit.

3. Mixing

The quality of bitumen-stabilised soil improve if the soil is mixed thorough.

4. Compaction

The dry density of bitumen soil depends upon the amount and type of compaction.It also depend upon volatile content.