Concrete paving over asphalt

[ben3929]

I am working on a project to install industrial shop in an existing storage area. Existing floor in the storage area is 18 inch thick asphalt pavement and the shop needs a concrete pavement. golf carts and forklifts will be operated over the new concrete pavement. I was told to remove 6" of the existing asphalt and fill with concrete pavement. I am concerned if the remaining asphalt is crumble and create problems for the concrete. Any thoughts please.

 

[oldestguy]

I'd treat it like a base course under the concrete. Before placing concrete I'd use a vibrating roller to compact any loose material. The design thickness of the concrete probably would consider the support as good (what ever that means) knowing the subgrade below the "base", the wheel loads as traffic, etc. Chances are you don't have much of that data, but a 6" slab and 4,000 psf concrete normally can carry reasonably heavy highway traffic. You may have access to some PCA pavement or floor loadings charts. That "base" would be considered quite good. Remember the joints at no more than 15 feet spacing.

 

[cvg]

if you "mill" the 6 inches of asphalt out and leave a rough but relatively level surface, than that would probably be adequate subbase. however, if you saw cut, jack hammer or otherwise "dig out" the asphalt, than you will not have a good base to pour your concrete on. In that case, you might as well go deeper so that you can bring in a leveling course of sand or gravel.

 

[darthsoilsguy2]

agree with OG and cvg and i could see a contractor using milling to get rid of the bulk demo and then using jackhammers and saws for fine work. don't know how much area you are talking about, geometry of work, or travel path constraints. Know that milling machines work best at doing lines. there is an area of work threshold that the project size will need to be before the contractor would prefer to full demo and replace over selective demo.

do you know why it is so thick? This is about 3 times the maximum thickness i would ever had expected without knowing anything about your situation. there just is a point where you're better off switching to a thinner concrete pavement section if this was all by design... and it is less than 18-inches for sure. is there a possibility that multiple overlays have happened because the subgrade was poor and caused paving failures....?

 

[Ron]

Milling is very expensive. Most asphalt/sitework contractors of any size have in their stable of equipment a "reclaimer". This is equipment that is similar to a huge roto-tiller. It can reach about 8 inches of depth. If you do the first lift (6") with the reclaimer and then spoil that material, you can then do a second pass of the equipment to create a very good subbase material that can be compacted and the concrete surface pavement placed on top of it.

Generally 6 inches of concrete pavement, 4000 psi as OG noted, will handle most light industrial traffic loading. You will need to pay particular attention to the joint and I would make the joint spacing even tighter than OG recommended.....max. 12 feet. You might also consider plate dowels for load transfer at the joints, although you'll have a very good subbase and this would amount to "belt and suspenders". For the concrete mix design, use the largest coarse aggregate you can place. This will cut down shrinkage and reduce the joint widths for the long term.

 

[ben3929]

Should I place rebar or welded wire mesh for the concrete pavement.

 

[Ron]

Neither is really necessary; however, WWF is acceptable, as long as place properly.