The bitumen is the binding material which is present in asphalt. It is also sometimes called as the mineral tar. It is obtained by partial distillation of crude petroleum. It is chemically a hydro-carbon. Bitumen is insoluble in water, but it completely dissolves in carbon bisulphide, chloroform, benzol, coal tar, naptha, alkalies, alkaline carbonates, petroleum spirit ad oil of turpentine. It is found on analysis to compose of 87 percent carbon, 11 percent hydrogen and 2 percent oxygen by weight.
The bitumen is black or brown in colour and it is obtained in solid or semi-solid state. Its application is same as that of residual asphalt.
Forms of bitumen
Following are the usual forms of bitumen:
- 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 it is suspended in the aqueous medium with the help of some suitable stabilizing agents.
- 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 & damp-proofing felts, in the manufacturing of pipe asphalts & joint fillers, as heat insulating material, etc.
- Cut-back bitumen: It is obtained by fluxing asphaltic bitumen in presence of some suitable liquid distillates of coal tar or petroleum. It can be applied cold as bitumen paint.
- Plastic bitumen: It consists of bitumen, thinner and suitable inert filler. The amount of inert filler is about 40% to 45%. It is used for filling cracks in masonry structures, for stopping leakages, etc.
- Straight run bitumen: When the bitumen is being distilled to a definite viscosity or penetration without further treatment, it is known as the straight run bitumen.