What are Asphalt, Bitumen and Tar?
The asphalt, bitumen and tar are construction materials which are hydrocarbons. The three materials are termed as bituminous materials. The asphalt and bitumen are that possess petroleum product origin. And the destructive distillation of coal,wood and the bitumen shale give us the tar.
These materials are used as a binder in building as well as road construction. The detailed explanation on each is explained below:
What is Asphalt??
A mixture of bitumen and a inert mineral matter in substantial proportion will give Asphalt. The binder used in the asphalt manufacture is bitumen. There can be bitumen without asphalt. But No asphalt exist without the bitumen content.There are two types of asphalt:
- Natural Asphalt
- Petroleum Asphalt or Residual Asphalt
What is Bitumen??
The "bitumen" is a word which has its origin in Sanskrit. The material is derived from petroleum product either through natural or refinery process. The fractional distillation of crude petroleum mainly give bitumen. After this process the evaporation of certain components of crude oil, like the spirit, kerosene, fuel oil and the lubricating oil is carried out, so that at the end bitumen is left behind. This extend of evaporation will determine the purity of bitumen. There are different types of bitumen:
- Blown Bitumen
- Cutback Bitumen
- Modified Bitumen
- Plastic Bitumen
- Straight run Bitumen
What is Tar??
The destructive distillation of coal, wood or any other bituminous minerals will produce tar. The tar have low bitumen content. Based on the source from which tar is produced, it is classified as:
- Coal Tar
- Wood Tar
- Mineral Tar
Comparison of Bitumen and Tar
The bitumen have less affinity to water compared to tar. Tar have a chemical composition with more carbon content than bitumen.This result tar to have higher viscosity, making it less workable compared to bitumen. The tar also possess a higher susceptibility to temperature compared with bitumen.
As bitumen have less temperature susceptibility compared to tar, it acts more harder and stiffer compared to an equivalent grade of tar. This property made bitumen structures to be more resistant to temperature effects and cracking. With the increase of traffic, the performance required from the bituminous materials also increased.This fact increased the demand of bitumen than tar.
Comparison Between Bitumen, Asphalt and Tar
|Fig.2. Asphalt Pavement|