What is an asphalt emulsion?


  • A homogenous mixture of two substances
  • Individual molecules of one substance (solute) are
    surrounded by molecules of the other substance (solvent)
  • Examples: Table salt in water; Metal alloys; Water (humidity) in air

Colloid or emulsion

  • A homogenous mixture of two insoluble substances
  • Particles of one substance (dispersed phase) are surrounded by molecules of the other substance (continuous phase)
  • Examples: Milk, butter, mayonnaise; Smoke or fog Asphalt


  • Composed of crystalline particles generally classified as “asphaltenes”
  • Asphaltenes are suspended in an oily liquid continuous phase generally classified as “maltenes”
  • The balance of composition determines asphalt physical properties such as rheology

Why emulsify asphalt?

  • Viscosity reduction and safer use at lower temperatures
  • Change from “oil” based to “water” based system
  • Reduced energy use, worker exposure, and job site odor
  • Properly formulated emulsion systems provide long term performance benefits





  • The asphalt particles will stick together (the emulsion will break) if only water and asphalt are used
  • The emulsifier is added to coat the asphalt particle surfaces and keep them from sticking together


  • Average 3-7 microns diameter
  • Asphalt is usually 57-70% of the emulsion
  • 1 gram of asphalt will form more than 10 billion particles
  • The total surface area of 1 gram of asphalt is 1-2 m2
  • One drop of emulsifier would stabilize as much as 100 billion particles 10-20 m2 of asphalt particle surface area