Asphalt Emulsion Properties. Asphalt emulsion, like any other material, has a certain range of properties, which define the requirements to its production, storage and use.
Viscosity. Viscosity is a very important performance parameter. If viscosity is low, the emulsion is not thick enough, while excessively high viscosity means the emulsion will stay on the surface without permeation of the underlying materials.
Viscosity is influenced by the amount of asphalt in the emulsion, temperature and the type of emulsifier used. Besides, not all asphalt types give the same viscosity to emulsions. However, this can be adjusted by mixing calcium chloride into the emulsion.
Flocculation. Flocculation is the phenomenon when particles of a certain material attach to each other. In asphalt emulsions, a large droplet often assembles several smaller ones. To prevent this, simple stirring is usually enough.
Coalescence. This is a continuation of flocculation; it means that emulsion droplets stick to one another, creating larger particles. If this process is not stopped, the asphalt emulsion simply separates.
Coalescence may occur due a number of reasons:
- incompatible type of asphalt;
- incorrect selection of emulsifier;
- insufficient amount of emulsifier;
- incorrect temperature in the production process;
- incorrect storage temperature;
- mechanical influence, such as operation of a circulation pump for a long time or transportation.
Sedimentation. Viscosity of asphalt may exceed that of water, causing the droplets to lower to the bottom of the tank. If a solvent is added, the viscosity of asphalt is reduced and it may float to the top of the container.
To prevent this, the following methods are possible:
- better storage conditions (higher temperature and stirring at regular intervals);
- reduction of asphalt density by adding a thinner;
- increased asphalt content;
- increases emulsion viscosity;
- change stabilizer and emulsifier type and concentration;
- change emulsion рН.
Separation. One of the main requirements to asphalt emulsions is the stability in storage, transportation and use. Ensuring stability for cationic emulsions is easier, since their separation depends on the contact with mineral materials. The emulsifier is positively charged causing mutual attraction. Separation can be controlled by using a certain type of emulsifier in correct concentrations.
In case of anionic asphalt emulsions, the situation is somewhat more complicated. They do not chemically separate, and the desired effect is only achievable by evaporation of water, which often occurs slower than desired.