Overview of Asphalt Emulsions

The use of asphalt emulsions began in the early part of the 20th century. Today 5% to 10% of paving-grade asphalt is used in emulsified form, but the extent of emulsion usage varies widely between countries. The United States is the world's largest producer of asphalt emulsion. The advantages of asphalt emulsion compared to hot asphalt and cut back binders are related to the low application temperature, compatibility with other water-based binders like rubber latex and cement, and low-solvent content. The paper gives an introduction to the chemistry of asphalt emulsion. The role of the emulsion components--asphalt, emulsifiers, acids or alkalis, and additives--in determining the physical properties and reactivity of the emulsion is described. Recent advances in the understanding of the setting process are outlined. The classification of emulsions into grades according to their reactivity, particle charge, and physical properties is explained and typical recipes of various emulsion grades are given. The selection of the correct emulsion grade for the various applications based on emulsion reactivity and physical properties of the emulsion is covered in general terms. The past 20 years have seen considerable progress in the understanding of how emulsion chemistry influences performance. Consequently formulations can be developed to optimize the performance of the construction material or construction process rather than simply to meet standard specifications. The result has been faster-setting surface treatments, quick-drying tack coats, penetrating emulsion primes that are superior to cut backs, and cold-mixed materials with improved properties.