What is an asphalt emulsion?

Asphalt emulsion is a combination of three basic ingredients: asphalt, water, and a small amount of an emulsifying agent. These components are introduced into a colloid mill that shears the asphalt into very small droplets. The emulsifier, a surface-active agent, keeps the asphalt droplets in a stable suspension. The result is an asphalt-based product with a consistency ranging from that of milk to that of heavy cream, which can be used in cold processes for road construction and maintenance.

Why use asphalt emulsions?

Asphalt emulsion does not require a petroleum solvent to make it liquid, and in most cases, asphalt emulsions can be used without additional heat. Both of these factors contribute to energy savings. Additionally, asphalt emulsions offer great flexibility in their application since they offer the end-user a great variety of characteristics not found in other paving and maintenance materials. Asphalt emulsions are environmentally friendly. There are little or no hydrocarbon emissions created with their use.

Are asphalt emulsions new?

Asphalt emulsions were first prepared in the early part of the 20th century, and today, they are used internationally. The use of asphalt emulsions is growing, and 10-20% of all asphalt is used in the form of asphalt emulsions.

How are asphalt emulsions classified?

Asphalt emulsions are classified into three categories: anionic, cationic, or nonionic. The anionic and cationic classes refer to the electrical charges surrounding the asphalt particles. The absence of the letter “C” denotes anionic emulsions. Asphalt emulsions are further classified on the basis of how quickly they coalesce; i.e., revert to asphalt cement. The terms RS (Rapid Set), MS (Medium Set), SS (Slow Set), and QS (Quick Set) have been adopted to simplify and standardize this classification. Additionally, trailing numbers are used to delineate the relative viscosity of the emulsion, and the letters “H” and “S” indicate whether hard or soft base asphalt is used to make the asphalt emulsions. Thus, a CSS-1H is a cationic slow set emulsion with a relatively low asphalt emulsion viscosity made with hard base asphalt.

Do asphalt emulsions have any uses around the home?

Driveway sealers, roofing repair materials, caulks and mastics may contain specially formulated asphalt emulsions.

What chemicals are present in the emulsion?

The main components of the emulsion are asphalt (bitumen) and water. Emulsions typically contain between 55-75% 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 trace amounts 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 do they work?

When asphalt emulsion is mixed with or exposed to the aggregates used in roadway applications, the emulsion is destabilized, and the droplets of asphalt fuse together providing a strong adhesive bond to “glue” the aggregates together. The water evaporates, but the emulsifiers remain in the asphalt where they provide a valuable function in helping the asphalt adhere to the aggregate.