4 DIFFERENT FORMS OF BITUMEN USED IN ROAD CONSTRUCTION
1. CUTBACK BITUMEN
The normal practice is to heat the bitumen to reduce its viscosity. In some situations, preference is given to using liquid binders such as cut bitumen. In cut bitumen a suitable solvent is used to reduce the viscosity of the bitumen. From the environmental point of view, reduction bitumen is also preferred. The solvent from the bituminous material will evaporate and the bitumen will bond to the aggregate. The reduction bitumen is used for the construction and maintenance of cold bituminous roads. The distillates used for the preparation of cut bitumen are naphtha, kerosene, diesel oil and furnace oil. There are different types of cutting bitumen such as fast curing (RC), medium curing (MC) and slow curing (SC). RC is recommended for surface dressing and patchwork. MC is recommended for the premix with less quantity of fine aggregates. SC is used for the premix with an appreciable amount of fine aggregates.
2. BITUMENE EMULSION
The bitumen emulsion is a liquid product in which the bitumen is suspended in a finely divided condition in an aqueous medium and is stabilized by a suitable material. Usually cationic type emulsions are used in India. The bitumen content in the emulsion is around 60% and the balance is water. When the emulsion is applied on the road it decomposes, resulting in the release of water and the mixture begins to set. The placement time depends on the degree of bitumen. The viscosity of the bituminous emulsions can be measured according to IS: 8887-1995. Three types of bituminous emulsions are available, which are Rapid setting (RS), Medium setting (MS) and Slow setting (SC). Bitumen emulsions are ideal binders for the construction of hill roads. When heating bitumens or aggregates is difficult. Fast setting emulsions are used for surface coating work. Medium-sized emulsions are preferred for premixing and patch repairs. In the rainy season, slow-running emulsions are preferred.
3. BITUMINOUS PRIMERS
In the bituminous primer the distillate is absorbed by the surface of the road on which it extends. Therefore, the absorption depends on the porosity of the surface. Bitumen primers are useful on stabilized surfaces and on water-bound macadam base courses. Bituminous primers are generally prepared on the roads by mixing penetration bitumen with petroleum distillate.
4. MODIFIED BITUMEN
Certain additives or mixtures of additives called bitumen modifiers can improve the properties of bitumen and bituminous mixtures. The bitumen treated with these modifiers is known as modified bitumen. Modified polymer bitumen (PMB) / crumb rubber modified bitumen (CRMB) should only be used in the course of wear depending on the requirements of extreme climatic variations. The detailed specifications for the modified bitumen have been issued by IRC: SP: 53-1999. It should be noted that the performance of PMB and CRMB depends on strict temperature control during construction. The advantages of using modified bitumen are as follows:
Less susceptibility to daily and seasonal temperature variations
Higher resistance to deformation at high pavement temperatures
Better properties of resistance to age
Longer fatigue life for mixtures
Better adhesion between aggregates and binder
Prevention of cracking and cracking by reflection