For prime coating to work, it must penetrate into the top layer of the base course to a depth between 5 and 10 mm. Tests showed that just spraying an emulsified asphalt prime coat onto a base material did not provide adequate penetration. However, mixing the emulsified asphalt into the top two inches of the base material before compacting it ensures the asphalt is distributed into the base course to an adequate depth. The stabilized layer that results from mixing the aggregate and prime coat contributes significantly to the strength of the pavement. Using emulsified rather than cutback asphalt prevents the release of VOCs into the air.
Emulsified oils containing little or no asphalt content are generally no danger to the environment.
They do not, however, protect the base from damage by traffic or rainfall as well as asphalt primes. Researchers have determined that priming with these oils could be effective when traffic is light and the primed base is not exposed to traffic for more than one or two weeks. While mechanically mixing the emulsified asphalt prime coat into the aggregate base course does require more labor than simply spraying on a cutback asphalt prime coat, TxDOT engineers indicated the cost difference is insignificant when viewed as a part of the total construction cost. Using emulsified asphalt completely eliminates the release of VOCs into the atmosphere. Emulsified oils containing little or no asphalt, when traffic conditions permit, can also dramatically cut down on air pollution.