Bitumen is a viscous liquid or a solid consisting essentially of hydrocarbons and their derivatives which is soluble in trichloro-ethyelene and is substantially
Bitumen is an effective binder for most road surfacing applications and mainly used in spray seals and asphalt. It is of petroleum origin and behaves as a thermoplastic material. It is produced from the refining of crude petroleum oil and its properties of chemical inertness, water resistance and natural adhesion make it an ideal material for a variety of applications. Bitumen is obtained by vacuum distillation or vacuum flashing of an atmospheric residue.
Road construction requires a variety of bitumen grades with strict quality specifications, such as narrow ranges for penetration
The desirable properties of bitumen depend on the mix type and construction. In general, Bitumen should possess following desirable properties.
The bitumen should not be highly temperature susceptible: during the hottest weather the mix should not become too soft or unstable, and during cold weather the mix should not become too brittle causing cracks.
The viscosity of the bitumen at the time of mixing and compaction should be adequate. This can be achieved by use of cutbacks or emulsions of suitable grades or by heating the bitumen and aggregates prior to mixing.
There should be adequate affinity and adhesion between the bitumen and aggregates used in the mix.
Viscosity Range at 60°C
170 140–200 Pa.s
Different forms of bitumen used in roadmaking
Bitumen in its original form:
There are different types of cutback bitumen like rapid curing (RC), medium curing (MC), and slow curing (SC). RC is recommended for surface dressing and patchwork. MC is recommended for premix with less quantity of fine aggregates. SC is used for premix with appreciable quantity of fine aggregates.
The advantages of using modified bitumen are as follows:
Lower susceptibility to daily and seasonal temperature variations
Higher resistance to deformation at high pavement temperature
Better age resistance properties
Higher fatigue life for mixes
Better adhesion between aggregates and binder
Prevention of cracking and reflective cracking
Tests on bitumen
There are a number of tests to assess the properties of bituminous materials. The following tests are usually conducted to evaluate different properties of bituminous materials.
Softening point test
Specific gravity test
Flash and Fire point test
Water content test
Loss on heating test