Water Bitumen Emulsion. Emulsion, in general, is a dispersed system which consists of small droplets of a fluid evenly dispersed in another fluid. In the case of bitumen emulsion, the droplets of bitumen are dispersed in water, which also contains a surfactant emulsifier.
Depending on which fraction is dispersed, emulsion can be direct (oil in water) or reverse (water in oil).
Emulsifier also plays an essential role in the emulsion. In not only forms protective film around the droplets of the dispersed phase, but also reduces interfacial tension, making the emulsification process simpler.
Depending on the charge, there are cationic, anionic and neutral emulsifiers. Neutral emulsifiers have limited use.
In general, both anionic and cationic bitumen emulsions are electrically neutral, since each charged particle of bitumen is enveloped in a layer of ions of the opposing charge.
One of the main factors defining the technical properties of bitumen emulsion is the sign and magnitude of bitumen particle charge. This, as well as surfactant activity, defines the behaviour of bitumen bitumen in contact with various construction materials. For limestone and dolomite, anionic emulsion should be used, while for granite or quartz cationic emulsions are applied. If the selection of the emulsion was correct, its separation occurs relatively quickly, due to the chemical interaction of the mineral and the bitumen particles.
Breaking of the emulsion depends on water evaporation and absorption of moisture by the filler. At low temperature and at high humidity, the breaking process is slower, degrading the quality of road construction. Even if the breaking process of anionic emulsion looks normal, the road top will still be sensitive to moisture.
Cationic emulsion break due to a somewhat different mechanism, not related to water evaporation. This is why they are used with equal success with most currently used road construction materials.
Cationic emulsion are used in the case of high humidity and low temperature (above 5ºС).