Recycling asphalt pavement (RAP) in Ammann plants

Every tonne of reclaimed asphalt pavement (RAP) that goes back into a mix is a tonne of virgin aggregate and bitumen a producer doesn't have to buy, haul in, or extract. That's the economic case for RAP, and it's why Ammann builds asphalt plants engineered to handle it across a wide range, from conventional cold-feed systems processing a modest share, up to the RAH dryer family designed for up to 100%.

This guide walks through how RAP actually moves through the plant, how much a given design can realistically take, what the cost and sustainability payoff looks like, and where mix quality gets fragile if the percentage climbs faster than the process supports.

What is RAP and how is it processed?

RAP, reclaimed asphalt pavement (sometimes called recycled asphalt pavement), is old asphalt removed from a road and reprocessed into aggregate for a new mix. Milling machines strip the top layer of pavement, or full-depth reclamation removes it entirely; either way, the material still carries its original bitumen coating, now aged and oxidized from years of traffic and weather.

That aged binder is the whole point. RAP isn't just recycled stone: the bitumen still clinging to it is usable asphalt cement, and every bit of it that gets reactivated in the new mix is virgin binder the plant doesn't need to add.

Before it reaches the plant, RAP is crushed, screened to a workable gradation, and stockpiled. How consistent that stockpile is, in moisture, particle size and source pavement, has more influence on the finished mix than almost anything that happens afterward, which is why the plant's feed method matters so much.

How does a RAP asphalt plant work?

There are two fundamentally different ways to get RAP into hot mix, and which one a plant uses sets a hard ceiling on how much RAP it can handle. Across both, Ammann's as1 Control System manages the blend in real time: closed-loop control that doses RAP against virgin aggregate according to the active recipe, so the percentage entering the mixer stays where the operator set it, load after load.

Cold RAP fed into the mixer

The simplest route feeds RAP cold, straight into the pugmill alongside superheated virgin aggregate. The hot aggregate transfers enough heat by conduction to dry and warm the RAP on contact.

It works, but there's a physical limit: superheat the virgin aggregate too far to compensate for a larger RAP charge, and it starts scorching the aggregate or overheating the binder film. That ceiling is why cold-feed-to-mixer designs top out at a modest RAP share, covered in the next section.

Dedicated RAP dryers (RAH family)

Ammann's RAH dryers, part of its High Recycling Technology (HRT), remove that ceiling by heating RAP on its own circuit, separate from virgin aggregate. Because the RAP stream has its own dedicated heat source instead of borrowing it from superheated stone, plants built around HRT can process RAP shares up to 100%.

That drying platform isn't RAP-specific technology bolted on as an afterthought. Ammann's counterflow drying, combined with its ADX technology, already runs 15-20% more fuel-efficient than parallel-flow designs, and RAP processing rides on that same efficiency.

A correctly heated RAP stream comes off the dryer within the plant's normal production band, roughly 140-170°C for hot mix or 110-140°C for a warm-mix design, so it merges into the pugmill at a compatible temperature instead of needing a compensating blast of heat from the virgin side.

Indirect, gentle heating

RAH dryers heat indirectly: the RAP never sits in direct flame contact, which is what protects the aged binder from scorching, blue smoke, and the emissions spike that comes with overheating recycled bitumen.

Feed condition still matters even with indirect heating. A 2022 review of recycled hot-mix asphalt production by Sharma et al., published in the Journal of Traffic and Transportation Engineering, found that feeding RAP hot and dry rather than cold can lift how much a plant incorporates by roughly 20 percentage points. Dryer design, not just dryer size, decides the realistic ceiling.

How much RAP can a plant use?

There's no single answer: it depends on the type of asphalt plant and feed method more than on anything else. Before getting into Ammann's own product families, it helps to see where the sector as a whole typically lands.

The Federal Highway Administration reports that mixes with a 30-50% reclaimed binder ratio can perform well when properly engineered, which lines up with the upper end of what conventional drum plants handle. Getting past that range in a batch or drum design generally means adding a dedicated RAP circuit rather than pushing the existing one harder.

RAH35, RAH60 and RAH100 by percentage

Ammann's RAH family is named for the ceiling each model is built to reach: RAH35, RAH60 and RAH100 correspond to plants engineered for RAP shares up to roughly 35%, 60% and 100% of the mix. A producer picks the model that matches the RAP volume it actually expects to run, not the maximum it might theoretically want.

Cold recycling with RAC25 and RAC30

Cold recycling is a different process entirely. Instead of heating RAP for a hot mix, the RAC25 and RAC30 families process it at or near ambient temperature, using an emulsion or foamed-bitumen binder rather than heat to coat the aggregate. It suits base and binder-course work more than surface courses, and the naming follows the same logic as RAH: RAC25 and RAC30 target RAP shares up to roughly 25% and 30%.

What are the benefits of higher RAP: cost, sustainability and performance?

The cost case is well documented at industry level. NAPA-compiled figures put the average savings at close to $9.98 per tonne compared with a mix made entirely from virgin material, once lower binder and aggregate purchases are weighed against processing cost. At plant volumes, that adds up fast.

New York City's own Department of Transportation is a useful real-world reference point. Its two in-house asphalt plants run an average of 40% RAP, and the agency credits the higher recycling rate with avoiding roughly two million miles of truck hauling to landfill every year.

Sustainability and cost move together here: less virgin aggregate quarried, less old pavement trucked away, and less bitumen to produce and transport, since RAP already comes pre-coated in binder. That's the operating-cost side of the equation; for the fuller economics of an asphalt plant investment, see Ammann's asphalt plant economics guide.

None of that counts for much if emissions and particulates from processing more recycled material go up to compensate. They don't. Ammann's baghouse filter captures more than 99.8% of particulates from the drying and mixing process regardless of RAP share, so a higher percentage doesn't mean trading air quality for material savings. For the wider picture on emissions and lifecycle impact, see Ammann's environmental impact page.

Performance is the part producers tend to worry about most, and it's also where the honest caveats live, covered next.

How do you keep mix quality consistent at high RAP rates?

Consistency at a high RAP percentage isn't really about the percentage. It's about controlling the two things that vary in every RAP stockpile: moisture and binder condition.

Here is the trade-off that needs to be stated clearly. Push past roughly 25% RAP without adjusting the virgin binder grade, and the mix tends to get stiffer and more prone to low-temperature cracking, because the aged, oxidized binder already in the RAP raises the overall stiffness of the blended binder. FHWA's own guidance on high-RAP mixes flags this exact failure mode.

The fix isn't complicated, but it has to happen deliberately: use a softer virgin binder grade to offset the RAP's stiffer aged binder, or add a rejuvenator formulated to restore some of the lost flexibility. Skipping that step is the most common reason a high-RAP mix underperforms in the field.

Stockpile discipline matters just as much. RAP pulled from different source pavements, or stored without separating by gradation, introduces batch-to-batch variability no control system can fully compensate for downstream.

Plant Guard adds a second layer here. Its Condition Monitoring and Maintenance Manager modules track things like burner performance and dryer condition over time, so drift gets flagged as a maintenance issue before it shows up as an inconsistent mix.

Frequently asked questions

What does RAP stand for in asphalt paving?

RAP stands for reclaimed asphalt pavement, sometimes written as recycled asphalt pavement. It's old asphalt milled or fully removed from a road and reprocessed into aggregate that keeps its original bitumen coating, for reuse in a new mix.

Why is it called "reclaimed" rather than just recycled?

"Reclaimed" is the standard technical term used by transportation agencies and industry bodies, including the Federal Highway Administration, and it's more precise than a general "recycled" label. RAP keeps its aggregate structure and binder coating intact; it isn't broken down into separate raw materials before reuse.

What are the disadvantages of RAP?

The main one is stiffness: without adjusting the virgin binder grade, mixes above roughly 25% RAP get more prone to low-temperature cracking, because the binder in RAP is already oxidized and stiff from years in service. Stockpile variability is the second issue, since inconsistent moisture or gradation from load to load makes the mix harder to control. And not every plant can process a high percentage without upgrading equipment: a cold-feed-to-mixer design has a lower practical ceiling than a plant built around a dedicated RAP dryer.

How much does using RAP actually save?

Industry figures put the average savings at close to $9.98 per tonne versus an all-virgin mix, once reduced binder and aggregate purchases are netted against RAP processing costs. The exact number for any one plant depends on local material prices and how much of the RAP processing already happens in-house.

What hardens asphalt millings?

Years of heat, oxygen and UV exposure while the pavement is in service oxidize the original bitumen binder, driving off the lighter oils and stiffening what's left. That aging process is why RAP's binder behaves differently from virgin binder, and it's the root cause of the stiffness trade-off at higher RAP percentages.

How much RAP is realistic for your plant

The honest answer depends less on ambition than on equipment. A cold-feed design has a real ceiling somewhere in the 25-35% range; a plant built around a dedicated RAP dryer can be engineered for anywhere up to 100%, provided binder grade and stockpile quality get the same attention as the percentage itself.

That's why Ammann builds the RAH and RAC families as a range rather than a single product: matching the plant to the RAP volume a producer actually expects to run, with the control systems and service support to keep that percentage consistent, batch after batch, for the life of the plant.