Concrete on Asphalt?
Concrete on Asphalt?
(OP)
If an existing parking lot for a private ambulance service has a lot of chuck holes and broken pavement areas, is it feasible to clean the loose debris and then cover the entire lot with concrete?
The parking lot has approximately 50% of the total area with broken pavement that needs either patching or replacing. The owner is wanting to know if filling the holes with concrete and then covering the entire parking lot with about a 2" concrete surface would be feasible.
That may limit him when it comes to modifications in the future.
The parking lot has approximately 50% of the total area with broken pavement that needs either patching or replacing. The owner is wanting to know if filling the holes with concrete and then covering the entire parking lot with about a 2" concrete surface would be feasible.
That may limit him when it comes to modifications in the future.
("You're only as old as you feel." - Satchel Paige)





RE: Concrete on Asphalt?
Without knowing the loads and soil conditions, 4" would be a bare minimum, but you could have bigger problems with the site and drainage.
RE: Concrete on Asphalt?
RE: Concrete on Asphalt?
www.highwaysmaintenance.com ---great site for many things
RE: Concrete on Asphalt?
RE: Concrete on Asphalt?
If half of the P-lot has open failures in it then more than likely your subgrade is saturated. That would be a big concern.
Sometimes the cheap way out ends up costing more than if you had done it right to begin with.
2" of concrete would not work, at all.
RE: Concrete on Asphalt?
First thing that must be done is hire someone who understands pavements and pavement failures to examine the lot and determine the cause of the existing failures. THe failed areas then need to be remediated, then the entire lot repaved.
Milling may be the best course of action, however, it is possible that the cause of the failure was that not enough pavement was placed the first time. In that case, milling will not be an option.
RE: Concrete on Asphalt?
RE: Concrete on Asphalt?
I have to disagree that concrete is never recommended over asphalt. There has been quite a bit of white topping done, where relatively thin concrete is placed over asphalt. It works very well in intersections or other locations where you have channelized traffic that tends to rut the asphalt.
RE: Concrete on Asphalt?
RE: Concrete on Asphalt?
"Whitetopping" is the term applied to putting a relatively thin concrete overlay over asphalt pavement. It can be done but requires care and experience with the process. I would go for the in-place recycling process....works well.
RE: Concrete on Asphalt?
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RE: Concrete on Asphalt?
I'd also avoid it unless you can drop 8" of reinforced concrete (rebar, etc) on top of the surface to begin with... Anything less than that will crack, let water underneath, freeze (???) etc.
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RE: Concrete on Asphalt?
Sorry I missed your post and question.
I have seen ultra-thin, i.e. 4-inch white topping on resedential streets on top of very poor asphalt. Five years in and it is performing very well.
I have also seen a standard white topping of about 6-inches placed on a major 4 lane road with a lot of quarry trucks. I don't have the ESALs. About 6 years in and holding up very well.
AutoDrill,
As for salt, if there is no steel in the pavement (typically the case these days) then salt has no real impact. I'm in the midwest where we use a lot of salt and have a lot of concrete streets. As for water between the asphalt and concrete, the concrete bonds too well to the asphalt for that to be a problem.
RE: Concrete on Asphalt?
Drumchaser, this is an existing ASPHALT parking lot.
The larger pothole areas indicate a very thin (1.5" - 2") asphalt directly on clay (no gravel or crusher run sub-base). So, I guess milling would not be an option, is that correct?
Would recycling still be a good option with this condition? What about the roto milling?
The basic steps should be: patch/repair, overlay with new asphalt, add top seal.
The 6" whitetop of concrete would not be an option, due to the elevation difference that would create a problem for the site.
("You're only as old as you feel." - Satchel Paige)
RE: Concrete on Asphalt?
Thanks for the clarification.
1.5"-2" of ACP on "clay" is not a good construction practice for starters. Depending on the P.I. (plasticity index) of the clay (how suseptable to expansion and contraction) would have a bearing on the best way to remedy the situation. We would not want to overlay with neither conc. or new ACP if the subgrade is ca-ca.
We have tried the "roto mill" option in a parking lot with not so good results, we used some "rejuvinator" as well. Our loads were probably more than yours, but it sounds like we had better subgrade.
I am guessing the "TOP SEAL" is a chip seal or Seal Coat?
A seal coat (hot liquid asphalt sprayed at 300+ degrees with aggregate sprinkled and rolled behind the distributor) is good in that it "seals out moisture and provides (in some cases) good skid qualities. However, in a parking lot with lots of turning movements.....I would not recommend it. (just my opinion) Lots of variability in this type of operation. Very weather, materials, equipment and skill dependant. It could get gooey for people afoot if it is not done correctly.
So you are tied elavation-wise.
OPTION 1----cheap--------
You could saw out the chuckholes to neat lines, patch with 3-4 inches of ACP (dense-graded hotmix), and overlay the entire mat with 2-3 inches with the same ACP...at the grade tie-ins (C&G?) could you can taper down to tie in?
OPTION 2----not so cheap
1. Rotomill or "mix" the existing ACP with the subgrade to a depth of 8-10 inches.
2. Depending on your clay P.I., calculate 3-5% @ 8-10 inches deep of LIME (I like quicklime, but you could use slurry or powder)re-mix the subgrade ( ACP, clay, and lime) adding the required moisture content (enough to activate the lime) mix until you have an acceptable gradation, then compact (with a compactor) and finish to drain.
3. Place 2" of dense graded ACP.
I know this sounds like lots of $$$$, but if it is done correctly it is cheaper than adding a good aggregate sub-base.
If water stands on the parking lot now (minus the chuck holes) you need to re-construct/grade it to drain. Water standing on ACP is not good, especially in high traffic areas.
Hope this helps.