Bitumen Emulsions

CATIONIC EMULSIONS

When asphalt is milled into microscopic particles and dispersed in water with a chemical emulsifier, it becomes an asphalt emulsion. The tiny droplets of asphalt remain uniformly suspended until the emulsion is used for its intended purpose. In the emulsion state, the emulsifier molecules orient themselves in and around droplets of asphalt. The chemistry of the emulsifier/asphalt/water system determines the dispersion and the stability of the suspension. When emulsions are used in the field, the water evaporates into the atmosphere, and the chemical emulsifier is retained with the asphalt.

Emulsions were first developed in the early 1900s. It was in the 1920s when emulsions came into general use in pavement applications. Their early use was in spray applications and as dust palliatives. The growth in the use of asphalt emulsions was relatively slow, limited by the type of emulsions available and a lack of knowledge as to how they should be used. Continuing development of new types and grades, coupled with improved construction equipment and practices, now gives a broad range of choices. Virtually any roadway requirement can be met with emulsions. Judicious selection and use can yield significant economic and environmental benefits.Emulsions are less hazardous to use and can be applied in a wider range of conditions.

An asphalt emulsion consists of three basic ingredients: asphalt, water, and an emulsifying agent. On some occasions, the emulsion may contain other additives, such as stabilizers, coating improvers, anti-strips, or break control agents. It is well known that water and asphalt will not mix, except under carefully controlled conditions using highly specialized equipment and chemical additives. The blending of asphalt and water is the same as an auto mechanic trying to wash grease from his hands with only water. Only with a detergent or soapy agent can grease be successfully removed. The soap particles surround the globules of grease, break the surface tension that holds them, and allow them to be washed away.

Anionic, non-ionic and cationic emulsifiers are all available, which will successfully emulsify bitumen and provide storage stable emulsions. Cationic emulsifiers offer additional advantages, which arise from the fact that most naturally occurring aggregates are negatively-charged in aqueous media, and have a capacity to absorb cationic emulsifiers. Choice of emulsifier type, and emulsion formulation enables the rate of breaking of the emulsion to be controlled. The emulsifiers remain in the cured seal and are concentrated at the interface between bitumen and aggregate and act as antis tripping agents.

This is a test Post from multiply.com