New concrete over asphalt driveway

Old 09-28-11, 03:36 PM
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New concrete over asphalt driveway

Maybe this isn't a DIY job...:>). Was wondering if the asphalt can be scored, and concrete poured on top...? Or must the asphalt be taken up. Don't know how deep or good the base is under asphalt. Also what's the minimum thickness concrete should be for a good job. Wisconsin climate.
Old 09-28-11, 03:53 PM
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I have never seen concrete installed over asphalt but I'm not an expert (I just watch actors pretending to be experts on TV). If the asphalt good and solid I don't see why it could not be considered foundation but I think you would need to do a full thickness slab as if you were pouring it over a gravel foundation.
Old 09-28-11, 03:59 PM
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I'm not an expert either but I would wonder if the weight of the concrete would compress the asphalt any..... that might not be good
Old 09-28-11, 04:17 PM
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Everything I've ever seen is the other way around....asphalt on top of concrete. That said...I swear I've seen highways built the way you suggest.

My 40 year ADOT neighbor is gone hunting...or I'd ask him.
Old 09-28-11, 07:49 PM
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Until Vic gets an official opinion, it's like anything else, soft over hard. You pour over asphalt and the concrete, IMO, would compress the asphalt and cause serious cracks in the concrete's finish. Likewise, I don't do pours. I just watch them and wait for them to dry so I can build.
Old 09-29-11, 07:45 AM
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I'm also seeing the potential for some height problems here - how thick a slab do you intend to pour?
Old 09-29-11, 02:03 PM
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Got to go with Pilot Dane on this one. I've never seen concrete on asphalt either, usually the other way around. How ever asphalt is usually not too difficult to remove, unlike concrete. Most concrete driveways are 4" thick minimum, 5" is better. And reinforce it with rebar, #3 or #4. Have it run both ways like a giant checkerboard. Good Luck.
Old 09-29-11, 02:32 PM
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concrete over

in my 40 plus years of masonary work and flat work never heard of putting concrete over asphalt always the other way i would take out the concrete that is just my opinion
Old 09-29-11, 03:40 PM
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Actually, it's done quite often on highway or parking lot applications. It's called whitetopping. You'd need to pour full depth, just like you are pouring on top of stone.
The asphalt (and stone beneath it) are just like a very compacted subgrade. The weight wouldn't crush the asphalt. When it's still wet the concrete weighs more than it will when it's set, and when it's set, it is very rigid. It's like a giant snowshoe, distributing the weight evenly. If the wet concrete doesn't crush the asphalt (which it won't), then the dry won't crush it either.
As long as you've got proper slope and the added height doesn't cause problems at thresholds, you should be good to go.
Old 10-05-11, 02:07 AM
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One slight (possible) problem in Wisconsin will be a layer of water collecting and being trapped between the new concrete and asphalt. When it freezes and expands, the concrete could crack and heave differentially--not a pretty scenario. Can easily be avoided by what's called "cracking and seating" the asphalt before placing concrete. That is, creating enough cracks in it (if not already present) to allow any water infiltration to drain through the asphalt into the base underneath. Usually done in the industry by gravity drop-hammers, but a residential driveway could possibly be broken up with a case of Schlitz or Leinenkugels and a few buddies wielding 10-pound mauls.

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