Reclaimed Asphalt Pavement
Hot mix asphalt (HMA) is one of the most recycled products in North America.
Industry and Government estimates range as high as 100 million tons of HMA are recycled annually. According to a recent report issued by the Federal Highway Administration and the EPA, 80 percent of the asphalt pavement that is removed each year during roadway repair and replacement projects is reused as part of new roads, roadbeds, shoulders and embankments.
“Asphalt pavement admittedly isn’t prominent on the public’s radar screen for recycling. But every year, approximately 73 million tons of reclaimed asphalt pavement (RAP) are reused, or nearly twice as much as the combined total of 40 million tons of recycled paper, glass, aluminum and plastics,” said Mike Acott, president of the National Asphalt Pavement Association.
EPA figures show that Americans recycle less than half of their discarded paper and less than one-third of their discarded aluminum and glass. Overall, only 28 percent of items in the municipal solid waste stream were recycled in 1997, the latest year for which the EPA has figures. The EPA established a target recycling goal of 35 percent of municipal solid waste by the year 2005.
“For the asphalt pavement industry already to have an 80 percent recycling rate is quite impressive. The recycling of asphalt pavement is an everyday business practice,” said Acott.
The Recycle Division of Graniterock was created and has been actively involved in this recycling effort for many years by offering several locations that accept HMA millings and Portland Cement Concrete (PCC) rubble reclaimed from the demolition of parking lots and roadways. As part of our commitment to the community, environment, and customer service, the Recycle Division has two crushing/screening plants, one of which is permanently located in the San Jose market area. Graniterock’s other plant, located on the Peninsula in Redwood City, is portable and can be relocated to project sites or other Graniterock branch locations when stockpiles are ready for processing. With controlled blending of the reclaimed PCC and HMA materials, both crushing/screening plants regularly produce Class 2 Aggregate Base that meets State and local specifications. Another valuable asset of Graniterock’s Recycle Division is a portable screening plant that can be set up to produce reclaimed asphalt pavement (RAP) and other aggregate products.
RAP is old pavement that is reclaimed and processed for use again.
The recycling process begins when Graniterock receives HMA millings, typically from city street or State highway overlay, repair and rehabilitation projects. The asphalt grindings are stockpiled separately from the concrete rubble to avoid contamination if they are to be used in RAP. The asphalt grindings are processed through the portable screening plant to a 5⁄8″ minus size, and stockpiled for future use.
The Research Technical Services Division of Graniterock has completed RAP mix designs for Caltrans ½″ and ¾″ mixes that utilize 10–15% RAP. At the present time, Graniterock only offers these RAP mixes at the Peninsula Road Materials Drum Plant in Redwood City.
The most common RAP use is as a constituent in HMA. HMA is produced at a hot plant with a predetermined percentage of RAP added. Studies have shown that HMA that incorporates RAP performs as well as HMA produced using virgin aggregates only. The two primary benefits of RAP are:
- The RAP aggregate can be used in place of a portion of the virgin aggregate, which lowers costs and reduces waste.
- The RAP asphalt binder is reheated and used in place of a portion of the virgin asphalt, which lowers cost and conserves petroleum resources.
The value of RAP even in today’s Superpave mixes has long been acknowledged. “The materials present in old asphalt pavements may have value even when the pavements themselves have reached the ends of their service lives,” said Rebecca McDaniel and her colleagues in National Cooperative Highway Research Program Project 9-12, Incorporation of Reclaimed Asphalt Pavement in the Superpave System. “Use of RAP has proven to be economical and environmentally sound,” McDaniel wrote.
The Federal Highway Administration, Caltrans, Standard Specifications for Public Works Construction (Greenbook) endorse use of RAP in HMA production. County and City acceptance is varied. The allowable percentage of RAP that can be used to replace virgin aggregate and asphalt cement varies by agency. Currently Caltrans allows the use of up to 15% RAP. Many State specifications allow much higher than 15% RAP use in their mixes, so long as the HMA mix design meets a strict set of testing standards and HMA production facilities comply with environmental emissions regulations.
In addition to the obvious benefits of reducing production costs and providing HMA that is equal to, or better than a virgin mix, recycling asphalt pavements have added environmental benefits of:
- Reusing valuable aggregates
- Reducing the amount of virgin asphalt binder needed
- Conserving valuable landfill space from unnecessary disposal of old asphalt.
Using RAP provides cost savings, conservation of resources and long lasting, quality pavements in an environmentally responsible manner.