REQUIREMENTS OF BITUMEN

The describable properties of bitumen depend on the mix type and the construction. The general problems while using bitumen in paving mixes are:

1. Mixing.
2. Attainment of desired stability of the mix.
3. To maintain the stability under adverse weather conditions.
4. To maintain sufficient flexibility and thus avoid cracking of bituminous surface. 
5. To have sufficient adhesion with the aggregates in the mix in. presence of water.

Keeping above problems in view the bitumen should possess the following desirable properties,

1. The viscosity of the bitumen at the time of mixing and compaction should be adequate. This is achieved by heating the bitumen and aggregate prior to mixing or by use of cut backs or emulsions of suitable grade.
2. The bituminous material should not be susceptible too much to temperature. Bituminous material should not become too soft during the hottest weathers of the region. Similarly it must not become too hard and brittle during cold weather which may cause cracking of the bituminous surface. The material must be durable.
3. Bitumen should not strip off from the aggregate in presence of water.
4. Affinity and adhesion between the bitumen and the aggregate used, in the mix should be adequate.