Asphalt emulsions are mixtures of asphalt and water with a chemical emulsifying system such as soap to make the system stable since asphalt and water are immiscible. The emulsions normally contain 25 to 30 percent water, which evaporates when the emulsions set. Emulsions differ from cutbacks by the fact that cutbacks are mixtures of asphalt and petroleum distillates. They are preferred instead of cutbacks for the following reasons; the petroleum distillates (kerosene and naphtha) required for cutbacks are increasing in cost; emulsions are pollution free since only water evaporates into the atmosphere; emulsions can be applied to damp pavements; there is little danger of fire with emulsions; and emulsions are applied at relatively low temperatues in comparison to cutbacks, meaning less repair, maintenance, and fuel costs for equipment. There are two types of emulsions - anionic and cationic. The charge on the emulsified asphalt droplet is determined by the emulsifying system, which may be alkaline or acidic. The aggregates to which the emulsions are applied also bear a charge when in contact with water. The charge is negative for most siliceous aggregates and positive for limestone aggregates. A given asphalt emulsion-aggregate combination will result in a mix that is well coated and has good adhesion when the charges on the emulsion and aggregate are different. This anionic emulsions are suitable for limestone aggregates and cationic emulsions for siliceous aggregates. Depending upon the rate at which they start breaking (or setting) on application, the emulsions have been divided into three grades and are manufactured as such. These are rapid setting emulsions, medium setting emulsions and slow setting emulsions. This report, after reviewing the basic facts about asphalt emuslions as discussed above, presents guidelines on the use of emulsions for seal coats and surface treatments and guidelines on the use of emulsions for base and surface course mixes.

  • Corporate Authors:

    Pennsylvania Department of Transportation

    Bureau of Materials, Testing and Research, 1118 State State
    Harrisburg, PA  United States  17112
  • Authors:
    • Kandhal, P S
  • Publication Date: 1974-4

Media Info

  • Features: Figures; References;
  • Pagination: 26 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00126839
  • Record Type: Publication
  • Report/Paper Numbers: Info. Rpt.
  • Created Date: Nov 5 1975 12:00AM