4.6.4 Bitumen Emulsion
Bitumen emulsions are usually two-phase systems consisting of two immiscible liquids, bitumen and water. 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. That is, like charges on each dispersed bitumen particle repel and prevent the particles from coalescing and settling from the suspension.
Emulsions can be used for almost any purpose for which conventional bitumens, polymer modified binders and cutback bitumens are used, and are suited to a number of other applications where the use of cutbacks is not appropriate.
The types and grades of bitumen emulsions are given in AS 1160. Proprietary emulsion binders with improved properties are also available. Several factors will influence the selection of the type and grade of emulsion as described in Austroads (2017).