Modification of Bitumen. The performance of bitumen in road construction can be improved in two ways. First, to improve the production process. Second, to mix bitumen with special additives. At the production stage, tar oxidation is often improved. IT is difficult to do without the process, but it alone is not sufficient. Improving tar oxidation cannot achieve the results required of the modern bitumen materials.
Bitumen application experience shows that the time when bitumen can be used is defined by the time when bitumen remains plastic, i.e. the difference between softening and brittle points. To increase this interval, it is reasonable to reduce settling point and increase softening temperature of the medium.
This can be achieved by one of the following techniques:
- mix bitumen with large amount of asphaltene with products containing low molecular aromatic oils with low viscosity and low settling point. Such oils are extracts from selective oil purification, tower bottoms, deasphalting asphalts, etc;
- oxidize molten bitumen with air. One drawback of the method is that undesired free bonds form in the reaction, which react with ozone and become the centers of binder destruction;
- oxidation by phosphorus oxide or iron chloride. These substances act as catalysts, forming complexes with polar molecules present in asphaltenes and resins. These complexes are poorly soluble in bitumen and form a colloid structure;
- Modification of bitumen by special fillers, stabilizers, plasticizers, synthetic polymers etc.
Using fillers improves the strength of road construction bitumen, but reduces plasticity and elasticity of the bitumen compounds. It also increases material viscosity. Antioxidants may be added to bitumen to reduce aging; antipyrene improve fire resistance.
The addition of plasticizers reduces bitumen viscosity and improves its stability in cold weather, stretching and water resistance. At the same time, this additive reduces heat resistance of bitumen. Some of the plasticizers used are transformer, spinning oil, diesel fuel and other oils.