Reclaimed asphalt pavement (RAP) is the term used for recycled asphalting materials used to pave roads and highways. RAP is the number one recycled material in the United States and is classified as industrial waste.
As of 2013, nearly 68 million tonnes of material used for highway repair and maintenance was processed from recycled materials. Using RAP has saved American taxpayers over $2 billion in repair and roadway construction costs. RAP is usually incorporated into the top layer of the road (paving) but materials can also be used to line the base or subbase of the road. In the event that the RAP isn’t used in current construction, it is stockpiled and used for other projects or in the following year.
RAP materials are usually obtained from older structures or roads. During repairs or other maintenance processes, contractors mine the road for usable material that can be incorporated into RAP. Milling is a removal process that focuses on the removal of pavement surfaces, which can be concrete or asphalt. Usually these are 2-inch layers.
The other process is known as full-depth removal, which involves breaking the road up into large pieces. This necessitates the use of a road breaker or a machine that breaks down through the upper layers of pavement into the road structure below.
Chunks of road are then transported into a facility for processing. Processing involves a series of operations that include crushing the old material and screening impurities. Usually RAP made in this manner results in high-quality yield material with a mixture with pure aggregates and strong binding.
A more cost-effective strategy that asphalt builders employ is to crush and create RAP on-site. Old pavement is milled or removed in place and incorporated into the road using pulverizing machines. Usually, if this process is used, the asphalt company will use either hot-mix or cold-mix recycling processes. This depends on the grade needed for the road. Highways normally need hot recycling, which results in stronger RAP.
During the process, asphalt builders mix additives into the hot/cold mixture such as softening agents or binders. During the pass, they pulverize, build and compact the road during the sweep. This faster process benefits drivers too. Roads built or repaired in this manner come back into use quicker, which is good news for motorist. If warm-mix recycling is used, the material exudes less emissions and is more environmentally-friendly.
RAP technology continues to evolve. Currently, think tanks are looking at using RAP for Thinlays™, which is a thin layer of asphalt used for road repair and maintenance.