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Difference between Asphalt, bitumen and tar, their types and comparisons of their properties is discussed. Asphalt, bitumen and tar have similar properties generally used for pavements Construction.
What is Asphalt?
The asphalt is a mixture which consists alumina, lime, silica and asphaltic bitumen. At low temperatures, it is in solid state and at high temperatures it is in liquid state.
Asphalt is produced in two different ways as follows.
- Natural asphalt
- Residual asphalt
Natural asphalt is obtained directly from the nature especially from the two resources lakes and rocks.
The lake asphalt contains 40 to 70 % of pure bitumen which is boiled in tank and water content evaporates and impurities are separated. The final product is called as asphalt which a=can be used for laying roads etc.
Rock asphalt contains 10 to 15% of pure bitumen and calcareous matter. These rocks are crushed and heated and consolidates by sudden cooling. This asphalt is used for paving tiles etc.
Residual asphalt is obtained artificially by the distillation of crude petroleum oil with asphaltic base.
Forms of Asphalt
The available forms of asphalt are:
- Cutback asphalt
- Asphalt emulsion
- Asphalt cement
- Mastic asphalt
Cutback asphalt is in liquid state. Asphalt is dissolved in a volatile solvent to get this cutback asphalt. It is used for manufacturing bituminous paint, repairing roofs etc.
Asphaltic emulsion is obtained by adding 50 to 60% water to the asphalt in presence of 1% emulsifying agent. The emulsifying agent forms water proof film when water evaporates. So, it can be used in cold conditions.
Natural asphalt is subjected to high pressure air under high temperature to get asphalt cement. Asphalt cement is plastic in nature and it is used for flooring, roofing, water proofing material etc.
Mastic asphalt is obtained by heating natural asphalt with sand and mineral fillers. It is impermeable matter does not contain any voids.
Hardness and melting point of mastic asphalt can be managed during the process of heating. It is in solid state and by heating it can be brought to liquid state. It is used for damp proofing course.
What is Bitumen?
Bitumen is obtained by the partial distillation of crude petroleum. It is also called as mineral tar and is present in asphalt also. It contains 87% carbon, 11% hydrogen and 2% oxygen.
Forms of Bitumen
The forms of bitumen are generally 5 types as follows.
- Cutback bitumen
- Bitumen emulsion
- Plastic bitumen
- Blown bitumen
- Straight run bitumen
Cutback bitumen is obtained from the distillation of asphaltic bitumen with the addition of coal tar or petroleum. Cut back bitumen can be used as paint in cold weather conditions.
Bitumen emulsion is obtained by dissolving very finely divided bitumen in aqueous medium. Suitable stabilizing agents are added to this solution.
Plastic bitumen majorly contains inert filler about 40 to 45% and bitumen and thinner is the other material. It is used as sealing material for leakages, cracks in masonry structures etc.
Blown bitumen is special type of bitumen. It is manufactured by subjecting bitumen to air under heavy pressure at high temperature. It can be used as damp proofing material, heat insulating material etc.
Straight Run Bitumen
Straight run bitumen is obtained by the distillation of bitumen into definite viscosity. It is also available as rocks.
What is Tar?
Tar is a high viscous liquid which contains high amount of carbon content. It is used for laying surface layer for pavements, preserving wood etc..
Forms of Tar
General forms of tar are as follows.
- Coal tar
- Wood tar
- Mineral tar
Coal tar is the by-product obtained during the production of coal gas. It is used for preserving timber, laying macadam roads etc.
The process consists of coal heated in closed iron vessels and the evaporated gases are collected in tubes. These tubes are circulated with cooling water. So, some matter is deposited in these tubes and it is nothing but coal tar. It is dense and strong-smelling liquid. It is in black color.
Wood tar is obtained by the distillation of resinous woods like pines etc. The distillation of resinous wood provides the creosote oil which has very good preservative property. So, wood tar is well suitable for preserving wood.
Mineral tar is produced by the exploitation of kerogens. Kerogens are generally obtained from bituminous shale’s which are nothing but rocks. Volatile content of mineral tar is very less.
Comparison Between Asphalt, Bitumen and Tar Properties
|Color||Blackish brown||Dark color with slight reddish tinge||Deep black|
|State||Solid or semi-solid||Solid||Viscous Liquid|