Asphalt Concrete - Recycling

Recycling

Asphalt concrete is often touted as being 100% recyclable. Very little asphalt concrete — less than 1 percent, according to a 2010 survey by the Federal Highway Administration and the National Asphalt Pavement Association — is actually disposed of in landfills.

There is asphalt recycling on a large scale (known as in-place asphalt recycling or asphalt recycling performed at a hot mix plant) and asphalt recycling on a smaller scale. For small scale asphalt recycling, the user separates asphalt material into three different categories:

1. Blacktop cookies - Chunks of virgin (new), un-compacted hot mix asphalt. Virgin asphalt is the easiest material to recycle because it is low in density and reheats well. To make “Blacktop Cookies”, tailgate off new asphalt material to a thickness of 4” to 8”. Allow the virgin asphalt to cool to ambient temperature then break the asphalt into pieces with a backhoe or loader bucket.
2. Reclaimed asphalt pavement (RAP) – Chunks of existing asphalt pavement that have been removed from the street when making a sub-surface repair, replacing manholes, catch basins, sewer mains or generally making pavement repairs is commonly referred to as asphalt chunks or RAP. Because the asphalt has been compacted, RAP is a denser asphalt material and typically takes longer to recycle than blacktop cookies.
3. Asphalt millings – Smaller size pieces of asphalt produced by grinding asphalt surfaces are referred to as asphalt millings. Large millings that have a rich, black tint indicating a high asphalt cement content are best. Surface millings are recommended over full depth millings. Full depth millings usually contain sub-base contaminants such as gravel, mud and sand. Asphalt milled from asphalt is better than asphalt milled from concrete because the dust created from concrete millings is not compatible with asphalt products. Avoid very small millings and asphalt dust from concrete millings.

Small scale asphalt recycling will usually involve high speed on-site asphalt recycling equipment or overnight soft heat asphalt recycling. More information on this equipment can be found here.

Small scale asphalt recycling is used when wanting to make smaller road repairs vs. large scale asphalt recycling which is done for making new asphalt or for tearing up old asphalt and simultaneously recycling / replacing existing asphalt. Recycled asphalt is very effective for pothole and utility cut repairs. The recycled asphalt will generally last as long or longer than the road around it as new asphalt cement has been added back to the material.

For larger scale asphalt recycling, several in-place recycling techniques have been developed to rejuvenate oxidized binders and remove cracking, although the recycled material is generally not very water-tight or smooth and should be overlaid with a new layer of asphalt concrete. Cold in-place recycling mills off the top layers of asphalt concrete and mixes the resulting loose millings with asphalt emulsion. The mixture is then placed back down on the roadway and compacted. The water in the emulsion is allowed to evaporate for a week or so, and new hot-mix asphalt is laid on top.

Asphalt concrete that is removed from a pavement is usually stockpiled for later use as aggregate for new hot mix asphalt at an asphalt plant. This reclaimed material, commonly known by the acronym 'RAP' for recycled or reclaimed asphalt pavement, is crushed to a consistent gradation and added to the HMA mixing process. Sometimes waste materials, such as asphalt roofing shingles, crushed glass, or rubber from old tires, are added to asphalt concrete as is the case with rubberized asphalt, but there is a concern that the hybrid material may not be recyclable.