Ashalt, bitumen and tar are referred as bituminous materials, which are essentially hydrocarbon materials. The asphalt is a mixture of inert mineral matter lime alumina, lime, silica etc. and a hydrocarbon known as asphaltic bitumen. In some places like Trinidad and Bermudez, asphalt is available in nature at a depth of 3 to 60 metres. It is known as natural asphalt. Common variety used all over the world is residual asphalt, which is obtained by fractional distillation of crude petroleum oil. Bitumen is the binding material which is present in asphalt. It is a hydrocarbon. It is obtained by partial distillation of crude oil. It contains 87 per cent carbon, 11 per cent hydrogen and 2 per cent oxygen.
Tar is obtained in the distructive distillation of coal, wood or other organic materials. When coal or wood is heated to redness in an closed chamber, it yields volatile product and residue coke. After separating and cooling volatile product gives tar. Comparison between asphalt, bitumen and tar is presented in Table 5.1.
