What? A scrub seal is an application that is very close to a chip seal treatment where asphalt emulsion and crushed rock are placed on an asphalt pavement surface. The only difference is that the asphalt emulsion is applied to the road surface through a series of brooms placed at different angles. These brooms guide the asphalt emulsion into the pavement distresses to ensure sealing the road. These series of brooms, known as a “scrub broom”, give the treatment its title, “scrub seal.”

Why? Chip seal treatments are very cost effective methods of treating roads. Sometimes it may be cost effective to treat heavily distressed roadways with an effective interim solution. A scrub seal provides an excellent treatment opportunity to treat a heavily distressed road cost effectively.

The scrub broom helps push the asphalt emulsion down into the cracks and ensure they are better filled and creating a better seal. When the chips are applied to the emulsion it creates a further seal to the roadway.

When? The basis of frequency of application is similar to that for a chip seal except scrub seal treatments typically last 5 to 7 years.

How? The application of a scrub seal is very similar to how a chip seal is placed, except the distributor truck tows a scrub broom. The rate of asphalt emulsion application and travel speed of the distributor truck are adjusted to result in a small “wave” of asphalt emulsion being generated in front of the forward brooms. The brooms force the wave of asphalt emulsion down into the cracks resulting in the cracks being better filled. The rear brooms ensure the asphalt emulsion is uniformly applied and that any excess is swept forward.

For more details, refer to SECTION 906 - SCRUB SEAL COAT of LA County Special Provisions - Section R - Roadway

Sources for more information:
LA County Special Provisions - Section R - Roadway (2015 Edition)