Asphalt emulsions are used in a number of paving applications. Applied by itself, an emulsion can function as a tack coat between layers in a pavement structure or as a fog seal on the pavement surface. In conjunction with spreading aggregate material, an asphalt emulsion may be part of a chip seal or scrub seal. When aggregate and an emulsion are mixed together before application, they can be used for slurry seals or a micro-surfacing treatment.
Bitumen emulsion is a mixture of fine droplets of bitumen and water. But as the bitumen is a petroleum product it doesn’t mix with water and as it is sticky in nature, it doesn’t easily gets disintegrated into fine droplets. To overcome this problem an emulsifier is used.
Emulsifier can be defined as a surface-active agent. Emulsifier keeps the bitumen in its fine droplet state by disallowing it to mix with other droplets. As the droplets are very fine they suspend in water.
Bitumen emulsions can be divided into two classes, in volume terms, is by far the most important:
• Cationic emulsions;
• Anionic emulsions;
The terms cationic bitumen emulsion, anionic bitumen emulsion and nonionic bitumen emulsion refer to the overall particle charge on the bitumen droplet imparted by the emulsifier. If an electric charge is passed through an emulsion containing negatively charged particles of bitumen, the droplets will migrate to the anode; hence the emulsion is termed anionic. Conversely, positively charged particles will migrate to the cathode and these emulsions are known as cationic emulsions.