Reclaimed asphalt pavement, commonly called RAP, is old asphalt road material that has been removed, processed, and reused in new pavement. When a road is resurfaced or rebuilt, the material that gets torn up still contains valuable stone aggregate and asphalt binder. Rather than sending it to a landfill, contractors crush and screen it into a reusable product that can replace a portion of the virgin materials in a fresh asphalt mix. In the United States, about 97% of removed asphalt pavement goes back into new road construction, making it one of the most recycled materials in the country.
How RAP Is Produced
Asphalt pavement is removed from roads in two main ways: milling and full-depth removal. Milling uses a large rotating drum with carbide teeth that grinds the road surface, typically removing up to 2 inches of material in a single pass. This is the method you see when a highway crew resurfaces a road, leaving behind a rough, grooved surface before the new layer goes down.
Full-depth removal is more aggressive. Crews rip and break the entire pavement structure using heavy equipment like bulldozers with specialized attachments or pneumatic breakers. The broken chunks are loaded into haul trucks and taken to a processing facility. There, the material goes through a sequence of crushing, screening, and sorting operations that break it down into consistent, usable sizes before it’s stacked in stockpiles and ready for reuse.
What’s Inside the Material
RAP is essentially the same thing as new asphalt pavement, just aged. It contains crushed stone aggregate bound together by asphalt binder, the petroleum-based glue that holds a road together. The critical difference is that the binder in RAP has changed chemically over years of exposure to air, sunlight, and traffic. Through a process called oxidation, the binder becomes stiffer and more brittle. It loses its ability to flex and absorb stress, which is why old roads crack before they’re replaced.
This aged binder is both the opportunity and the challenge of using RAP. It still has binding value, which means producers need less new binder in their mix. But its stiffness affects how the final pavement performs, especially in cold weather. The longer a road has been in service, the more oxidized and brittle its binder becomes.
How Much RAP Goes Into New Pavement
The national average percentage of RAP used in asphalt mixes rose from 15.6% in 2009 to 21.1% in 2018, where it has roughly plateaued due to limitations in mix design technology. Most state highway agencies allow RAP in both surface courses and base layers, but the allowable percentage varies.
Current guidelines from the American Association of State Highway and Transportation Officials treat RAP content in tiers. At lower percentages, producers can use standard binder grades without adjustment. Once RAP exceeds 25% of the mix, producers must follow more detailed blending procedures. They recover and test the old binder from the RAP, then select a softer virgin binder grade that, when blended with the aged material, hits the target performance grade for the climate and traffic conditions.
Performance Tradeoffs at High RAP Content
Using more RAP saves money and resources, but pushing the percentage too high introduces real performance risks. The primary concern is low-temperature cracking. Because aged binder is stiff and brittle, pavement with high RAP content is more prone to cracking in cold conditions, sometimes early in the road’s life. These cracks then expand under repeated traffic loading, eventually undermining the cost savings that motivated the higher RAP content in the first place.
Research has shown that at 50% RAP content, mixes can fail to meet standard flexibility requirements, particularly when the old and new binders don’t fully blend together during production. Fatigue life, the number of load cycles a pavement can handle before cracking, also drops noticeably as RAP content climbs. This is why most producers stay in the 15% to 30% range for surface courses, where cracking resistance matters most.
Rejuvenating Aged Binder
To make higher RAP percentages workable, producers can add recycling agents, sometimes called rejuvenators, that soften the aged binder and partially restore its flexibility. These products come in several forms: vegetable oils, bio-oils derived from plant waste, aromatic extracts, paraffinic oils, and tall oil (a byproduct of paper manufacturing).
Research at Texas A&M University found that vegetable oils and bio-oils were the most effective at reducing the stiffness of aged binder blends and producing a more uniform final product. Paraffinic oil was the least effective. Tall oil performed well initially but lost effectiveness as the binder continued to age in service. The choice of rejuvenator matters not just for immediate mix properties but for how the pavement holds up years down the road.
Cost Savings
The economic case for RAP is straightforward: every ton of old pavement reused is aggregate and binder you don’t have to buy new. Federal Highway Administration data shows that savings scale predictably with RAP content. At 20% RAP, producers save about $1.64 per ton (14% less than all-virgin material). At 30%, savings hit $2.46 per ton (21%). At 50%, the savings reach $4.10 per ton, a 34% reduction in material cost.
Nationally, these per-ton savings add up fast. A survey across U.S. regions found an average savings of 18% compared to using entirely new materials, with total annual savings exceeding $104 million. The south-central and southeastern states, which produce large volumes of asphalt, saw the greatest absolute savings.
Environmental Benefits
Using RAP reduces both energy consumption and greenhouse gas emissions during asphalt production. Research from the University of California Pavement Research Center quantified the relationship: a mix with 25% recycled content produces roughly 6.5% fewer greenhouse gas emissions and uses 6.3% less energy than an all-virgin mix. At 60% recycled content, those numbers jump to reductions of about 21.8% in greenhouse gases and 20.9% in energy.
When researchers also accounted for the embedded energy in the petroleum used to make virgin binder (not just the energy to process it, but the energy value of the raw material itself), the savings were even more dramatic. A 60% recycled mix showed a 46.1% reduction in total energy demand. Every ton of RAP reused also means less aggregate quarried from the earth and less old pavement occupying landfill space.
Cold Central Plant Recycling
One of the most promising developments in RAP use is Cold Central Plant Recycling, or CCPR. Traditional hot-mix asphalt production heats materials to high temperatures, which requires significant energy. CCPR works at ambient temperature, mixing RAP with either foamed asphalt or asphalt emulsion at a central facility. Small amounts of water (1% to 3%) and a filler like cement or lime (often around 1%) are added to improve the mix.
CCPR can use both freshly milled material and stockpiled RAP, making it versatile for new construction and rehabilitation alike. Projects using this method have saved an average of 54% in cost compared to conventional hot-mix applications, while reducing environmental impact by approximately 16%. The technique also allows for thicker pavement layers than other cold recycling methods, which improves structural capacity and moisture resistance. Recent studies have demonstrated that CCPR can perform well even on high-traffic roads, expanding its potential use across entire road networks rather than just low-volume rural routes.