Chemistry of Asphalt Emulsions

What chemicals are present in the emulsion?

The main components of the emulsion are asphalt (bitumen) and water. Emulsions come in different grades but typically contain between 55 and 75% asphalt. In addition to the asphalt and water, asphalt emulsions contain 0.1-2% of an emulsifier or ‘soap’ which functions to stabilize the emulsion. These soaps are similar in nature to the soaps and detergents used in household cleaning and personal care. The asphalt emulsions may also contain minor amounts (< 1%) of other ingredients such as pH (acidity) regulators, and viscosity regulators.

Tell me more about the emulsifying agents.

The most common products are fatty acids and lignins derived from wood, these form soap by reaction with sodium hydroxide. The soaps become negatively charged in water and give “Anionic” asphalt emulsions. Another class of emulsifiers, amines are derived from wood acids (tall oils) or animal fats (tallow). These emulsifiers form soaps, which become positively charged in water and give “cationic” asphalt emulsions.

How are asphalt emulsions made?

Hot asphalt is mixed with a water and soap (emulsifier) in a high-speed mixer called a colloid mill. The combination of the soap and high shear breaks the asphalt up into small droplets, which remain dispersed in the water.

How do they work?

When asphalt emulsion is mixed with the aggregates used in road construction, the emulsion is destabilized and the droplets of asphalt fuse together providing a strong adhesive bond to ‘glue’ the aggregates together. Water evaporates but the emulsifiers remain behind in the asphalt where they provide a valuable function in helping the asphalt stick to the aggregate

Where can I learn more about the chemistry of asphalt emulsions?

You can order AEMA’s Basic Asphalt Emulsion CD-Rom right here on this web site – just click here.

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Asphalt Emulsion Manufacturers Association
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Glen Ellyn, IL 60137

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