Sources of asphalt
It is a natural part of bitumen. Whenever crude petroleum is evaporated in the atmosphere due to rising of temperature or due to action of wind. Remaining residue is called native asphalt.
It is available in the form of semi rock depositing in California and Brazil. Its presence is 5-10 % in the world.
It is the major portion of asphalt which is used in world and is obtained by the distillation of crude petroleum.
Types of bitumen/Asphalt
It is a semi solid hydrocarbon which is obtained when fuel oils and lubricating oil have been removed from petroleum. All the asphalt cannot be used as a binding material but Asphalt cement is preferably used for the road construction.
There are two types of grades for Asphalt cement.
- Hard grade 60-70 for high temperatures areas.
- Soft grade 200-300 for low temperatures areas.
It is divided into two types.
- Cut back.
Cut back is an asphalt whose viscosity has been removed by the addition of volatile diluent. It is very efficient in case of utilization at low temperature. Mostly the patch work in low temperature zone or road construction process is done with the help of cut back.
It is available in the following grades:
R.C 70, R.C 80, R.C 100, R.C 300.
Negative aspects of cut back:
- It is health hazard.
- It is costly.
- It causes pollution.
Coal tar is a by product which is obtained by the destructive distillation of coal. It is available in the market with the brand name RT 1 to RT 12. RT 1 is less viscous, as the RT number increases viscosity increases. RT 12 is more viscous than RT 1.