Forensic investigation for loose aggregate

[hobbie]

We have a newly constructed asphalt pavement that has a small isolated area (1ft by 3 ft) under left wheel path showed surface loss, mainly big aggregate loss. The initial thought after looking at the pictures are due to the gasoline spillage. Is there any lab tests we can use to verify this speculation? Thanks!

 

[SirAl]

We recently cored a segment of ACP along a taxiway subject to fuel spill leaking from a fuel truck (malfunctioning valve) returning to its docking station from the apron after fuelling an airplane. Upon examination of the cores it was amazing to see the depth of impregnation of fuel as the affected ACP was notably 'rotten' relative to the sound lower portion of the core. From this we were able to specify a depth for a mill and inlay reparation. You could also take the 'environmental approach' and test a core or other type sample for hydrocarbons, keying on the components commonly found in fuels.I have to say that I'm not that knowledgeable in this area.

 

[Ron]

hobbie...post the pictures for us to see. Could be fuel spill, could be just surface ravelling from underconsolidation of a coarse mix, or could be mix segregation. How does it match with the surface texture at other locations?

 

[Drumchaser]

hobbie

If the remainder of your mats (ACP pavt. area) test results, cores, % air voids, and overall appearance contains no other surface irregularities; this would most likely be a fuel, hyd. oil, or release agent spill.

We have found the culprit to routinely be a ruptured hydraulic line failure (leaks onto the mat) in most cases.

Your spec.s should include language to perform corrective actions on these areas irregardless of the source.

 

[hobbie]

Thanks for all the replies. I just attached a picture for you guys to see. I am wondering if there is any low-cost test can easily identify the cause so we can use it to recover some costs from the owner. We just cut the whole slab out and replace it.

 

[Ron]

It appears to be a spill of some material. As drumchaser noted, it could be one of several materials. Based on the flushing appearance at the edge of the spill and the asphalt within the depression, the culprit is an aliphatic hydrocarbon (oil, gasoline, diesel, etc.).

There seems to be a lot of raveled aggregate nearby...is that from the same depression or is it occurring overall? If occurring in a lot of areas, you might want to make sure your mix has adequate binder and that is was placed at the right temperature. Raveling can be caused by undercompaction, cold placement, low asphalt content, high voids, poor gradation, etc.

There are not any really inexpensive ways to conclusively test for the damaging material. Most aliphatic hydrocarbons are closely akin to asphalt cement, since it is one as well.

Fortunately, this is a relatively small area. The source could have been anything from a parked piece of equipment to the paving machine, though if the paving machine, you would likely see repetitive spots of the same condition.

Unless the owner has a lot of equipment or processes that might have contributed to this, it is unlikely you'll be able to tag him for it. The construction process usually has more opportunity to cause this type of damage than the owner; however, only field investigation and evaluation can tell that...not a forum response.

 

[Drumchaser]

Looking at the picture provided.....it looks as if it could be a contaminated load of mix, Sometimes the supplier uses the same trucks to ferry materials other than ACP to and from the plant site and is not always diligent about cleaning the truck out before hauling hot mix.
Just a guess.
Also, the fuel leaks/spills I have seen usually are very fat looking on top of the mat. This looks a little different.
Again, your contract language should include methods to remediate theses areas at no cost to the owner, irregardless of the cause. If not, this is a prime example of why spec.s should be incorporated into bid documents.

 

[SirAl]

Thanks for the photo. It would not appear to be a large area justifying a costly testing program. Its hard to get a handle on the depth affected from the photo provided. To rectify the deficiency I would probably have the pavement within and surrounding the affected area ground uniformly to 1.5" min. depth, tacked, and inlayed with an ACP patch. Alternatively, a shallow blemish could be slurry sealed.

 

[hobbie]

Thank you all very much again for your replies. The pavement was already open to general public when the problem was identified. It was not there when the construction was just completed. Again, this area is the only area had the problem.

The problem area was in the middle of area paved that same shift. The chance for cantaminated load from truck is small since the truck should already be loaded a couple times before it returned to this area.