Recyling of Pavement in Compacted Fill

[kcall2]

I often get requests to allow old AC pavements to be grinded and mixed with soil to be placed as a fill. Besided environmental issues, are there any legitimate reasons why this is a bad idea?

 

[fattdad]

Not sure what you mean by environmental issues (after all the pavement has been in the environment for its prior life, eh?

I'd say the biggest problem (to me) is that the concrete pieces are reduced to less than 3 inches (i.e., one-third the lift thickness) and whether the technician understands oversize correction and the use of field proctors in variable soil materials (i.e., one-point confirmations). You'd need a good fix on the specific gravity of the asphalt pavement also (to properly perform oversize corrections).

If the compaction control get's out of control, failures related to the use of asphalt pavement will result in fingerpointing. While the contractor owns the requirement to place as specified, if you are doing testing, you'll be dragged through the mud (and maybe even deserve it?).

Just a few thoughts.

f-d

¡papá gordo ain’t no madre flaca!

 

[TDAA]

I have used it plenty of times. One thing to watch for is the need for oven moisture. A nuclear gauge is a bad idea, from the moisture side of things. The hydrogen in the oil would require an offset, but the variability of the mix could lead to issues getting a good one. Best to avoid that part.

One reason it can be a bad idea, is that the material is likely to be more cost effectively reused as RAP in an asphalt mix. The virgin aggregate and binder is way more costly than the soil you are using it as.

 

[msucog]

it's more difficult to provide the numbers with test results. if it's a minor amount of fill, i prefer to take a more practical approach and document it with observing the placement/compaction efforts and proofrolls to avoid density testing if possible (but test above and below it). i'd try to find a RAP application because it typically makes some jam-up soil cement or foamed asphalt.

 

[cvg]

seems like it would be a lot easier to monitor compaction if it was not mixed with the soil. Also would not require the effort to mix. However, if mixing is desired, I would require that to be done to provide a well graded mixture before placing and compacting. This might require constructing a stockpile and getting it approved? Use the recycled asphalt as base or subbase layer or possibly for drainage layers instead of general fill.

 

[iandig]

Best way to deal with re-cycled road planings is to keep them seperate from other materials. There have been quite a number of papers and reports done on the use of these materials (in the UK refer to TRL 216), and one of the main things to take from this is that the material needs water to compact it. Previously people had assumed that because the material was coated in bitumen, and that it was vry granular, moisture was not that important. However after a number of failures due to settlment of the material, the culprit was the lack of moisture during compaciton.

 

[VAD]

kcall2:

I think that there is some environmental ruling that this material (Asphalt concrete) is unacceptable for fill under residential dwellings. Henc use of material becomes important. Seems that ther is no issue wiwith concrete in fill from an environmental perspective.

Regarding compaction issues for other fills such as parking lots etc. If fill is to be placed below the zone of significant stresses from say below 1 to 1.5 m then I would not be carried away with Proctors. Rather use a numer of passes and watch the process. Isn't this concept still in use. For example use of rockfills etc.

 

[dicksewerrat]

Crushed AC pavement has too much value to be thrown away. Contact the nearest Asphalt plant. Yo may be able to sell it. And look at getting some kind of carbon credit for the recyling effort.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com