Concrete on Asphalt?

[SCEngr1]

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.




("You're only as old as you feel." - Satchel Paige)

 

[concretemasonry]

2" is rediculous and will be guaranteed to fail.

Without knowing the loads and soil conditions, 4" would be a bare minimum, but you could have bigger problems with the site and drainage.

 

[MiketheEngineer]

Roto mill it and put down new asphalt. Done all the time and works well - plus you re-cycle the old asphalt..

 

[BigH]

I wouldn't. The Rotomilling is good idea. You might want to consider cold in-place recycling (you add cement and emulsion when you mill and replace immediately and compact. Then you could use a chip seal on the surface for wearing. (6 to 10 mm stone) would also suggest that all reference the following site:

http://www.highwaysmaintenance.com

---great site for many things

 

[msucog]

cold or hot inplace recycling should work fine even if you have some shallow soil problems. use cold recyclying with cement and it may be the same price or less than putting 2" concrete everywhere and should hold up well.

 

[Drumchaser]

Not enough info. Is the P-lot ACP now? or concrete? Depending on the soils beneath, and what is the root of the problem that caused these pot holes to develope (old ACP or concrete, poor const. and or drainage)has a major bearing on what your possible options for remediation would be.
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.

 

[GeoPaveTraffic]

I agree that 2-inches of new concrete on top of the old asphalt is going to fail and fail quickly. However, depending on the loads involved and the root cause of the existing parking lots failure, it may be possible to place a relatively thin layer of concrete over the existing lot.

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.

 

[LCruiser]

Concrete over the top is definitely not recommended - especially at 2". Asphalt is flexible, concrete is not. Depending on the application you could fill in the potholes with concrete and then overlay with 2" of hot mix asphalt.

 

[GeoPaveTraffic]

LCruiser,

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.

 

[LCruiser]

How "thin"? What is the traffic loading - ESAL's?

 

[Ron]

Lcruiser...soil used as a subbase for concrete is "flexible", so your argument about asphalt being "flexible" under concrete is not valid. It is a thickness issue, not one of "flexibility".

"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.

 

[ACtrafficengr]

If I recall correctly, 4" is called "ultra-thin' white-topping. 6"+ is more typical.

"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928

"I'm searching for the questions, so my answers will make sense." - Stephen Brust

 

[AutoDrill]

I'm not sure where you are located, but keep in mind that salt damages most concrete surfaces so if the existing damage is caused by feezing and thaw sessions *and* the locals like to use salt, it's probably not a very good idea.

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.

Regards,
Joe Agro, Jr.
(800) 871-5022
01.908.542.0244
Automatic / Pneumatic Drills:

http://www.AutoDrill.com

Multiple Spindle Drills:

http://www.Multi-Drill.com

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Regards,
Joe Agro, Jr.
(800) 871-5022
01.908.542.0244
Automatic / Pneumatic Drills:

http://www.Drill-N-Tap.com

Multiple Spindle Drills:

http://www.Multi-Drill.com

 

[GeoPaveTraffic]

LCruiser,

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.

 

[SCEngr1]

Thanks for all of the posts and feedback.

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)

 

[Drumchaser]

SCEngr1

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.