Asphalt emulsions are typically comprised of a highly engineered mixture of asphalt, water, and an emulsifying agent (also called a surfactant). Often, additives such as polymers are incorporated in the formula to achieve specific performance characteristics.

The ingredients are pumped through a colloid mill, which shears the asphalt into microscopic molecules.

The asphalt microscopic droplets become coated by the surfactant (or soap molecules) with hydrocarbon “tails” that are soluble in asphalt and electrically charged or ionic “heads,” which are soluble in water. The asphalt droplets are surrounded by the ionic charge, causing the droplets to repel each other and stay suspended in the water.

This stable emulsion can then be transported, stored, pumped, or mixed with aggregate and applied in roadway construction or maintenance.

Once applied, emulsions are engineered to “break” or revert back to a state of separate water and asphalt. Some formulas break chemically as the surfactant destabilizes, others break through evaporation and some by a combination of the two. Engineers design emulsions to break at certain speeds to accommodate the needs of various application methods.

As water is expelled, the asphalt “cures.” The particles dry and form a film over the aggregate or surface. This creates a durable, water resistant end product.