The asphalt material used in highway engineering is usually a semi-solid viscous substance at room temperature. To be used in highway engineering, it must be made into liquid before it can be used for spraying or mixing with mineral aggregate.
In order to make asphalt liquid, there are generally three methods: 1. Heating method; 2. Diluting petroleum asphalt into liquid asphalt with gasoline, kerosene, diesel and other solvents; 3. Emulsify the asphalt.

Emulsified asphalt is heated to the flow of viscous asphalt, and then through high-speed centrifugation, stirring and shearing and other mechanical action, and the formation of fine particles (particle size of about 2~5 microns), asphalt dispersed in a small droplet state in the aqueous solution containing emulsifier, forming oil in water asphalt emulsion, due to the role of emulsifier stabilizer to form a uniform and stable dispersion system. This emulsion is liquid at room temperature.
The emulsion consists of two kinds of water in oil and oil in water. When the continuous phase is water and discontinuous phase is oil, it is oil in water and vice versa.

In water in oil emulsion, according to the size of its particles, it can be divided into ordinary emulsion and fine emulsion. The particle size of ordinary emulsion particles is generally 1~20um, and the particle size of fine emulsion particles is generally 0.01~0.05um.

At present, hot asphalt is widely used, but hot asphalt needs to consume a lot of heat energy, especially a large amount of sand and gravel needs to be baked, the construction environment of operators is poor, and the labor intensity is high. When emulsified asphalt is used for construction, it does not need to be heated. It can be sprayed or mixed and paved at room temperature, and the pavement of various structures can be paved. Moreover, emulsified asphalt can flow by itself at room temperature, and can be made into emulsified asphalt of different concentrations according to needs. It is easy to achieve the required asphalt film thickness by pouring or prime coat, which can not be achieved by hot asphalt.

With the gradual improvement of the road network and the upgrading requirements of low-grade roads, the use of emulsified asphalt will be greater and greater; With the enhancement of environmental protection awareness and the gradual shortage of energy, the proportion of emulsified asphalt in asphalt will be higher and higher, the scope of use will be wider and wider, and the quality will be better and better.

Emulsified asphalt has the characteristics of non-toxic, odorless, non combustible, fast drying and strong adhesion. It can not only improve road quality, expand the scope of asphalt use, prolong the construction season, reduce environmental pollution and improve construction conditions, but also save energy and materials.