Bitumen is the binding material which is present in asphalt. It is also sometimes called mineral tar. It is obtained by partial distillation of crude petroleum. It is chemically a hydrocarbon. It is insoluble in water, but completely dissolves in Carbon bisulphide. Bitumen is black or brown in colour and it is obtained in solid or semi solid state. Its applications are same as residual asphalt.
Forms of bitumen:
Following are the usual forms of bitumen:
1. Bitumen Emulsion: It is a liquid product containing bitumen to a great extent in an aqueous medium. The bitumen is in a very finely divided state and is suspended in the aqueous medium with the help of some suitable stabilizing agents.
2. Blown Bitumen: It is a special type of bitumen which is obtained by passing air under pressure at a higher temperature. Such bitumen can be used as roofing and damp proofing felts, in the manufacture of pipe asphalts and joint fillers, as heat insulating material, etc.
3. Cut-back bitumen: It is obtained by fluxing asphaltic bitumen in presence of some suitable liquid distillates of coal tar or petroleum.
4. Plastic Bitumen: It is consists of bitumen, thinner and a suitable inert filler. The amount of inert filler is about 40-45 percent. It is used for filling cracks in masonry structures, for stopping leakages, etc.
5. Straight run bitumen: When the bitumen is being distilled to a definite viscosity or penetration without treatment, it is known as straight run bitumen.