100% Recycled Hot-Mix Asphalt production technologies

There are multiple technologies readily available for 100% hot mix asphalt recycling. Many of them are listed here along with links to the websites of the manufacturers and short descriptions.

Detailed description of some of the technologies as well as usage statistics can be found in the article. The paper also describes 100% recycled asphalt mixture design, RAP management practices and the potential economic as well as environmental benefits from 100% recycling.

If you happen to know more resources or have been a part of 100% recycling project, please contact me through jeckabs@gmail.com

RAP Technologies

Website: http://raptech.us/

Location: Queens, New York City

RAP Technologies, LLC (www.RAPTech.us) approached producing 100% RAP hot mix as an air pollution challenge rather than attempting to reinvent established manufacturing processes. The “All RAP Process” technology uses convention hot mix asphalt plant components and a special blue smoke filtration system. Since first producing mix in 2001-2004 demonstration project with NYCDOT, the RAPTech process has been licensed to Green Asphalt, Long Island City, NY and produces 100,000 tons of 100% RAP mixes annually for private paving contractors. Streets paved in 2001 are still in service and provide living record of the durability of 100% RAP mixes on secondary streets. Read more...

100% RAP is produced and placed at temporary city street pavements, parking lots, industrial areas etc. Recently a demonstration project of 100% RAP along with conventional asphalt has been paved by the city DOT in Jewel Avenue & 147th Street in Kew Garden Hills, Queens. Long term performance can be evaluated by visiting 78th street that was paved in 2001.

From producers home page:

The HERA System is the result of years of research into cleaner, better and cheaper asphalt production and recycling. “This is something we can be very proud of,” says Chairman of VolkerWessels’ Management Board, Gerard van de Aast. “The HERA System showcases our innovative strength and helps create a cleaner environment.”

Asphalt is normally produced and recycled by directly heating the raw materials. The HERA System works completely different, by applying indirect heat. The result:

*A higher percentage of reuse of old asphalt

*Much lower emissions of harmful gases

*Virtually no odours

*Asphalt can be recycled an additional 3 to 5 times

*Asphalt lasts longer

*Cost savings; fewer (primary) raw materials and lower fuel costs

SMART Pave

Website: http://www.smartpavesystem.com/index.html

From producers home page:

Step oneThe reclaimed asphalt pavement (RAP) is analyzed for composition qualities including binder and gradations. The binder is analyzed for PG properties. Regional Properties may be used in this analysis. Generally, a very small percentage of rejuvenator agent is introduced to adjust the binder to the desired PG grade. This also provides full replenishment of any oxidized asphaltenes, returning the asphalt cement to its original characteristics. This is usually about .5% (1/2 of 1%) of the HMA produced.

If the existing milled composition comes from a known source and meets specification gradation requirements “as is”, no further RAP pre-processing is necessary.Steps Two and Three would not be required and Step Four would be next - heating the material.

Step Two

If the RAP comes from varied sources, the RAP stockpile is screened and "fractionated" to return the RAP to original gradations. The various gradated RAP products are then fed into their respective cold feed bins.

Step Three

Depending on gradation analysis, the feed bins will introduce the gradated RAP at the correct feed rate. If due to specification gradations, any virgin aggregates adjustment is needed, the virgin aggregates are introduced along with the gradated RAP in the correct proportion via a multi-bin metered cold feed system.

Step Four

An indirectly heated (specifically designed for 100% RAP) drum plant processor is used for full heating of 100% recycled asphalt or any recycled-virgin blend mix.

Step Five

Once material processing has been completed, the fully heated recycled HMA is conveyed into silo storage, awaiting discharge into trucks for transport to the jobsite.

Step Six

At the jobsite, the recycled hot-mix asphalt is transferred to the roadway by the pavement lay down crew. The 100% recycled asphalt pavement actually results in "equal to or better" quality and performance than HMA made from new virgin materials and is handled in the same manner.

A key part of the Smart Pave

System is RAP stockpile discipline. Control of your RAP source and inventory will pay for itself many times over. A properly worked RAP stockpile along with screening/fractionating will create a very uniform composite mix, usually more consistent than virgin material from a quarry. Screening of RAP may be necessary to eliminate unwanted tramp material, but crushing should be avoided if possible as a) it may add substantial unnecessary cost, and b) it creates added fines to the mix – an undesirable attribute that may actually place your valuable RAP out of specification bands. Generally speaking, RAP milled from highways and roadways with upward cut milling heads will generally stay within 10% of original specifications.

AMMAN RAH 100

Website: http://www.ammann-group.com/fileadmin/ammann/syncfiles/International/images/ammann_asphalt_mixing-plant_brochure_en.pdf Location: Birmensdorf, Switzerland, BAB Belag AGBAB Belag AG in Switzerland, Birmenstorf operates Amman “Uniglobe 200” plant with “RAH100” reclaimed asphalt dryer drum. The plant utilizes a unique dryer designed by Amman to allow RAP heating without direct contact to flame.

The drum is installed on top of the tower to ensure gravity-driven handling of the hot RAP. A counter flow dryer with two phase drum is used. The material heating and drying phase of the drum rotates, while the combustion chamber is static. The RAP is heated with hot air and is discharged before getting in contact with the flame. Thus it does not get in direct contact with flame, reducing emissions and limiting RAP binder aging.

Usual RAP discharge temperature is 165-180°C. The air recirculation system improves drying efficiency in comparison to conventional systems by 10%, ensures low oxygen content to further reduce aging and reduces emissions (6). After discharge gravity drives the material into hot storage silo which has a capacity of 28t. The RAP is further released to the weight hopper and asphalt pugmill of 3t capacity. The recycling agent and virgin binder, if any, is added in the pugmill and mixed together with RAP for 30 to 40 seconds.

Marini Master Tower 100% RAP plant

Website: https://marini.fayat.com/en/products/batch-plants/master-tower

ports are placed inside the drum to introduce hot air at drum center. Fins are welded on the exterior of the drum at 45° angle to aid at churning of air and work as secondary thermal mass conductors. The burner output is controlled by three infrared readers that are set to maintain the inner drum surface temperature between 480 to 540°C. The burners operate between 650 and 900°C and, based on temperature readings, are typically set to three different output levels, ranging from 100% at the entrance of materials to 50% (or less) of maximum output at the exit of the drum. Fuel use of 3.8 to 5.7 liters per ton of mixture produced has been recorded at ambient temperatures ranging from 10 to 30°C. The final mixture temperature can be adjusted as required and the maximum stack temperature is 80°C.Any virgin binder or recycling agent can be added at the mixing zone at the end of the drum though a pipe that penetrates the rear wall.

RAP is fed into triangular recycling drier using vertical elevator where it is indirectly heated by hot air of 200-400°C and directly exposed to 120-200°C as illustrated. This reduced temperature compared to conventional plants helps limiting the aging of RAP binder and lowers the emissions. A controllable speed spiral conveyor is spreading the RAP slowly between the drier’s plates where it is heated through the hot surfaces of the channel and the driving plate surfaces to desired temperature. The driving plates are designed to limit sticking of RAP and reduce segregation. After heating the RAP is released to RATech mixer via weighing unit. Any recycling additives or virgin bitumen are added in at this stage and 45 second mixing time is suggested. The hot RAP is kept in a heated silo until ready for discharge. The production capacity of the plant significantly varies based on the RAP moisture content. It will drop from 180t/h for 1% moisture to around 80t/h for 5% moisture content

Astec RAP King

producer website: http://www.astecinc.com

From producers website:

• Dryer is a hot-oil tube type rotary drum

• RAP flows across internal hot-oil filled tubes as the drum rotates

• Heating of RAP is done without direct flame or hot gas exposure

• Air is displaced from the drum by steam produced in the drying process. Drying is accomplished in a near oxygen-free atmosphere thereby minimizing oxidation of the liquid asphalt held in the RAP

• Steam and any hydrocarbons produced in the drying are ducted to the combustion chamber of the hot-oil heater where hydrocarbons are destroyed