Bitumen emulsions are created when bitumen and water are mixed together with the aid of one or more additives. The bitumen phase can be dispersed in the aqueous phase by mechanically shearing it in a colloid mill. The dispersion of bitumen particles is held in suspension in water by a chemical emulsifier which usually imparts an electrical charge so that the resulting electrostatic forces prevent the globules from readily coalescing.
Emulsions can be used for almost any purpose for which conventional bitumen’s, polymer modified binders and cutback bitumen’s are used, and are suited to a number of other applications where the use of cutbacks is not appropriate.
Bitumen emulsions can be divided into four groups. The first two are, by far, the most widely used:
- Cationic emulsions
- Anionic emulsions
- Non-ionic emulsions
- Clay-stabilized emulsions
The terms anionic and cationic stem from the electrical charges on the bitumen globules. Emulsions which are made with negatively charged emulsifiers called anionic emulsions while emulsions made with positively charged emulsifiers are called cationic emulsions.