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.