Bitumen emulsions are sophisticated two-phase systems consisting of bitumen, water, and various additives that enhance formation, stabilization, and property modification. In these emulsions, bitumen is dispersed in the aqueous phase as discrete globules, with diameters typically ranging from 0.1 to 50 microns. These globules are maintained in suspension by electrostatic charges, which are stabilized by emulsifiers.

Bitumen emulsions can be categorized into four primary classes: Cationic Emulsions, Anionic Emulsions,          Non-Ionic Emulsions, and Clay-Stabilized Emulsions. The classification as “anionic” or “cationic” refers to the electrical charges of the bitumen globules. According to electrostatic principles, like charges repel one another, while unlike charges attract. In an emulsion containing negatively charged bitumen particles, these particles will migrate toward the anode, thus categorizing the emulsion as “anionic.” Conversely, in a system with positively charged particles, the particles will move toward the cathode, marking the emulsion as “cationic.” Non-ionic emulsions feature neutral bitumen particles that do not migrate to either electrode.

Regarding setting characteristics, bitumen emulsions are classified as Rapid Setting (RS), Medium Setting (MS), and Slow Setting (SS).

The cationic rapid-setting emulsion is particularly prevalent in the Middle East. The setting of emulsions is an irreversible process that transpires when the water phase evaporates or is absorbed by aggregate materials. This phenomenon leads to the disappearance of the water phase and a reduction in the space available for the bitumen particles, allowing the bitumen to migrate gradually toward the surface and effectively coat the aggregate.