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Old 03-08-2013, 10:45 PM   #1
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To pour concrete ove asphalt or not to pour concrete over asphalt.


Hi Guys, I am looking for some professional opinions here. I have a 28' x 98' shop that currently has an asphalt floor. The asphalt floor has been in place for 40+ years and is very compacted. It is 2 1/2" thick and is Not cracking anywhere. I HAVE to put in a concrete floor, I am just getting thoughts on pouring concrete over the asphalt. I am looking to pour 6" 4000psi self compacting concrete (reinforced of course). Height/Depth of the concrete is a non issue. The asphalt is on dirt, it has no other sub-base, but as I said before has not cracked under pressure and the soil beneath is extremely hard (I have to take a pic-axe to break the soil). Yes, I could rip it out and do new sub-base and concrete..but if all the work is unnecessary, then I wont bother and I would pour concrete over the asphalt. So, all thoughts are appreciated.

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Old 03-08-2013, 10:55 PM   #2
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To pour concrete ove asphalt or not to pour concrete over asphalt.


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Hi Guys, I am looking for some professional opinions here. I have a 28' x 98' shop that currently has an asphalt floor. The asphalt floor has been in place for 40+ years and is very compacted. It is 2 1/2" thick and is Not cracking anywhere. I HAVE to put in a concrete floor, I am just getting thoughts on pouring concrete over the asphalt. I am looking to pour 6" 4000psi self compacting concrete (reinforced of course). Height/Depth of the concrete is a non issue. The asphalt is on dirt, it has no other sub-base, but as I said before has not cracked under pressure and the soil beneath is extremely hard (I have to take a pic-axe to break the soil). Yes, I could rip it out and do new sub-base and concrete..but if all the work is unnecessary, then I wont bother and I would pour concrete over the asphalt. So, all thoughts are appreciated.
Google the term "whitetopping"

I can't say for sure if it's a good idea in a shop or not, but it is done often on roadways and that is what they call it.

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Old 03-08-2013, 10:57 PM   #3
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To pour concrete ove asphalt or not to pour concrete over asphalt.


Thank you, yes, I have looked up whitetopping.. and according to that it is fine.
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Old 03-08-2013, 11:00 PM   #4
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To pour concrete ove asphalt or not to pour concrete over asphalt.


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Thank you, yes, I have looked up whitetopping.. and according to that it is fine.
When you say you "have to" have concrete, is it a requirement by someone, or just something you want to do?
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Old 03-08-2013, 11:01 PM   #5
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To pour concrete ove asphalt or not to pour concrete over asphalt.


Its a requirement by me. I need it for equipment/tools
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Old 03-08-2013, 11:01 PM   #6
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To pour concrete ove asphalt or not to pour concrete over asphalt.


Just got you know, why do "have" to do this? And why so thick?
My main concern would be how to keep the unpressure treated wood from coming in contact with the new concrete, how to deal with no longer having a bottom plate to attach rock to if you want to finish it out..
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Old 03-08-2013, 11:06 PM   #7
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To pour concrete ove asphalt or not to pour concrete over asphalt.


Wood (of any kind) will not be in contact with the floor at all. The walls are concrete block. Lift requirements are a minimum of 4" thick 3500psi. I would prefer to overbuild a little. Thanks.
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Old 03-08-2013, 11:14 PM   #8
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To pour concrete ove asphalt or not to pour concrete over asphalt.


I wonder if the asphalt is in good shape if you could just cut out the areas where the lifts are going, excavate just that area and pour new thick pads for the lifts to attach.

I would just be leery of pouring concrete over asphalt and then installing a lift on it.

That concept might just be where whitetopping is not a good idea.
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Old 03-08-2013, 11:18 PM   #9
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To pour concrete ove asphalt or not to pour concrete over asphalt.


Yeah thats what I am trying to figure out.. I will do the shop 100% reinforced concrete no matter what, I have lots of other equipment that I need a smooth & strong surface for. From what I have been finding I meet all the requirements and then some, so.. had to ask around and see what others think. Thanks.
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Old 03-09-2013, 03:31 AM   #10
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To pour concrete ove asphalt or not to pour concrete over asphalt.


The dept of transportation here just finished a 3 year job on the interstate (I-15) which is now 12" thick concrete, intended to last 40 years. Guess what they used for the base? 4" layer of asphalt. There are likely other layers of compacted stuff beneath that, but from your description, I'm guessing you're in good shape considering your uses as a shop.
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Old 03-09-2013, 06:16 AM   #11
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To pour concrete ove asphalt or not to pour concrete over asphalt.


Moved to 'concrete and masonry'
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Old 03-09-2013, 07:53 AM   #12
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To pour concrete ove asphalt or not to pour concrete over asphalt.


easily done... IF it were our job, we'd place expansion jnt mtl about the perimeter then place the conc,,, IF you place 5" floor, wire mesh is fine - 4" won't need anything,,, aci recommends 2" ' cover ' about any reinforcement,,, the biggest issue you'll have is a proper jnt pattern to which will prevent random cracking,,, i'd suggest sawcuts OR const jnts every 7' - that's 3 slabs/cuts wide X 12 long either formed or sawed 1/3rd deep X slab thickness.

5" is overkill - 6" is totally unnecessary
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Old 03-09-2013, 08:57 AM   #13
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To pour concrete ove asphalt or not to pour concrete over asphalt.


Yes I am doing expansion joints on the perimeter and will do the cuts. Thank you, so it sounds like I will be in good shape. I appreciate all the input.
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Old 03-09-2013, 06:56 PM   #14
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To pour concrete ove asphalt or not to pour concrete over asphalt.


" The asphalt is on dirt, it has no other sub-base."

That's the part that would raise a red flag for me, there's usually at least a 4" stone base put down,then compacted and a base course of 2 1/2" of asphalt placed on that before a finish course of 2" on the base course, and you want to overlay 2 1/2" of blacktop with no base,might want to rethink this.
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Old 03-10-2013, 12:26 AM   #15
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To pour concrete ove asphalt or not to pour concrete over asphalt.


Asphalt in itself has very little strength, like 150psf. All the strength is in the subgrade. If you're going to put a lift on there, some subgrade work might be in order.

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