Anti-stripping agents improve the adhesive bond between aggregate and bitumen. These agents or emulsifiers are made from fatty acids and ethylene amines to yield the amid amine or imidazoline. These emulsifiers are used to prepare bitumen emulsions in water.
Adhesion agents are used in 0.5 – 1.5 % quantities relative to the bitumen depending on the type of bitumen and the kind of operation. The adhesion agent is mixed with the hot bitumen prior to mixing in the aggregate. Advantages of the use of adhesion agents are:
- more effective mixing and easier application of the bitumen mix;
- the stripping of the top-bitumen layer from the bottom is prevented, especially when there is dew, mist, a rain shower or in case the stones are wet;
- road making becomes less dependent on the weather and the conditions on site;
- the effects of frost, and of the freezing and thawing at the binder/aggregate interface are largely eliminated.
The adhesion agents are used in:
- surface dressing: spraying a thin layer of hot bitumen, tar or mixtures on the road surface, followed by the spreading of a layer of road-stone;
- hot-mixing: using a hot mixture of bitumen, adhesion improver and aggregate in constructing the base road;
- road-oiling: existing aggregates are stabilized with inexpensive heavy petroleum fractions (road oils).
The process can be applied to lightly trafficked roads in regions where winters are very cold and road surfaces are often subjected to frost damage.