Problem Asphalt

[bank]

A parking lot we designed was recently completed. Visual inspection revealed areas with what appears to be fine, loose asphalt on the surface. Core density reports done on the pavement showed compaction below what was specified in 14 of 16 samples. Twelve of the samples show a core depth more than 10% thinner than the 2.5 inches specified.

The specification says if the sample is more that 10% thinner than what's specified the section is to be removed and re-paved. The contractor is offering as an alternative to do an overlay over the entire parking lot. If the overlay will satisfy the thickness and compaction requirements, would this be an acceptable option?

 

[TGLG]

I am going to answer your question with several other questions.

Ten percent of 2.5" is 1/4". How much of an overlay is the contractor offering?
Will the overlay be thick enough to hold together?
How will the contractor deal with transitions at the edge of the overlay?
What will the overlay do to the curb reveals?
How will the contractor handle the drainage inlets and manhole covers? Will they be raised to the new overlay grade?

Unless there are a great many small areas of unacceptable pavement, or the majority of the lot is unacceptable, I find it hard to imagine that overlaying the entire lot would be a more cost-effective option the fixing the bad spots. Or is the GC worried about patches hurting the appearance of the finished pavement?

 

[Ron]

bank...what you are seeing is called "raveling". That occurs when asphalt is undercompacted or the gradation is wrong for the application (typically too coarse for hand-spreading operations sometimes necessary in parking lots). Undercompaction is often associated with hand-spreading( the asphalt cools too quickly before it is appropriately compacted).

I have the same questions as TGLG.

I would suggest that to salvage any of the existing asphalt, that you consider milling to a depth equal to 3 times the nominal coarse aggregate size and then provide an overlay back to the original thickness using properly compacted asphalt. Inspection should also be provided during laydown to make sure that temperatures are maintained and appropriate compaction is done. If the current mix is too coarse, change the overlay mix to a smaller nominal coarse aggregate size such as a 10-12mm max. size.

 

[dicksewerrat]

Tell the contractor to:
1. remove the asphalt.
2. regrade the lot
3. Recompact the lot
4. Place the asphalt with new material. No recycled material.
5.Do nuke testing as he compacts the asphalt.
6. core the lot.
7. If it does not pass, don't pay.


Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[dantalbot]

Take it the 2.5inch is split into different layers i.e. 20mm of small stone (6-10mm) then 50mm of larger stone. you can ask for the top layer to be planned off and relayed. but no contractor is going to openly do this and they might want more cost. Make sure you have your contract agreed and signed at the start. but as others said, this work needs to be done as they have broke your agreement and not completed the side of their contract. Don't pay a penny till they have agreed on how to fix their problem.

 

[Hoaokapohaku]

In addition to what others have said, investigate the properties of the mix placed in the parking lot verses the design properties in the job mix formula (JMF). Often these problems have their root in a poorly designed JMF, or a JMF designed for a different purpose than the intended use (like a highway design placed in a parking lot) or the properties of the production mix are different than the design mix. Given the problems with compaction and raveling that you describe, high air voids, low asphalt content, high VMA, or variances in stone gradation or texture could be the cause.

Also, even if a contractor is equipped with an ideal mix and excellent practices, a quality pavement cannot be constructed unless constructed over a quality base. Was the base constructed by the same contractor or others?