Bituminous stabilization is generally done with asphalt as binder. Asphalt acts as a binder for coarse-grained soil. In cohesive soil asphalt protects the soil by plugging its void and water proofing it. It helps the cohesive soil to maintain low moisture content and to increase bearing capacity. There are four types of Bituminous Stabilization. They include:
- Soil Bitumen
- Sand Bitumen
- Water Proof Clay Concrete
- Oiled Bitumen
Soil Bitumen – The soil bitumen is used to stabilize clay soil. The stabilized soil becomes water- proof. The quantity of bitumen required varies from 4 to 7 % of dry weight.
Sand Bitumen – This is bitumen stabilized cohesionless soil system. The sand should be free from vegetable matter or lumps of clay. The sand should not contain more than 25 % minus 200-sieve material for dune sands and not more than 12 % in case of other types of sand. The amount of bitumen required varies from 4 to 10 %.
Water – proofed Clay Concrete – It is water proofed soil made by adding 1 to 3 % of bitumen. In general, three gradations are in use to successfully stabilize the soil. The percentages passing 75 micron sieve are specified as:
- 8 to 12 %
- 10 to 16 %
- 13 to 30 %
Oiled Bitumen – It is a bitumen treated silty clay material. The material is made waterproof by spraying bitumen in two or three applications. Slow or medium curing bitumen or emulsions are used. The bitumen penetrates only a short depth into the soil. The amount of bitumen required is about 5 liters per square meter of the soil surface.
Stabilization by Geo – Textiles
Geo-textiles are fabrics made of synthetic materials, such as polyethylene, polyester, nylon, polyvinyl chloride and so on. They are manufactured in varieties of ways in the woven, non-woven or grid-form. A geo-textile has high tensile strength. When properly embedded in the soil, it contributes to its stability. It is used in the construction of unpaved roads over soft soils. The geo-textile is laid over the soil. Aggregates are laid directly over the geo-textile. When traffic passes over the road, the geo-textile deforms and its strength is mobilized. The more a geo-textile deforms, the greater the load it can carry.