Pavement Preservation Journal
Winter 2016, Vol. 9, No. 4
By Erik Updyke and Dennis Ruh
Despite recent increases in allowable reclaimed asphalt pavement (RAP) content in hot-mix asphalt concrete, both in the Caltrans Standard Specifications and in the Standard Specifications for Public Works Construction (“Greenbook”), a surplus of RAP continues to exist in most urban areas of Southern California.
New and innovative uses for RAP in slurry seals, micro surfacing, and chip seals will help consume some of this surplus, as well as reduce the demand for virgin aggregate. These uses are becoming increasingly common among Southern California agencies.
RAP aggregate is produced by crushing and screening RAP to the gradation required for the specific seal coat application. After processing, RAP aggregate will typically have a residual asphalt content of between 5 and 8 percent, a specific gravity of approximately 2.4, and an absorption rate of approximately 1.5 percent, based on testing performed by Los Angeles County.
MAKING RAP CHIPS
The use of RAP aggregate (RAP chips) in chip seals has the longest history. Los Angeles County first used RAP chips in a scrub seal on a half-mile section of Avenue J in the unincorporated area of Lake Los Angeles area in February 2008.
Since then, RAP chips have been used in numerous chip seals. For chip seals placed under a contract, RAP chips are a contractor option. The Avenue J scrub seal, and subsequent chip and scrub seals – placed using polymer-modified rejuvenating emulsions and RAP chips – continue to perform well.
In April 2013, a state of California Department of Resources Recycling and Recovery (CalRecycle)-funded chip seal composed of hot-applied PG 76-22 tire rubber modified paving asphalt and RAP chips was placed in the Lake Los Angeles area.
The intent of this project was to determine if non-preheated (ambient temperature) RAP chips would adhere to a hot-applied binder. Three-eighths-in. RAP chips were placed on a two-mile segment of Avenue K, and 5/16-in. RAP chips were placed on a two-mile segment of Avenue M.
A problem was encountered during the first day of placement on Avenue M that was traced to moisture content and cleanliness. RAP chips used with hot-applied binders must be dry and clean, as hot-applied binders do not have the forgiveness of emulsions. Despite adverse weather conditions, there were no subsequent placement problems. To date, this project continues to perform well.