Pouring new concrete floor on top of old

[PHACMGR]

I'm trying to find the best (and cost effective) way to replace 2 inch wood floor blocks. The blocks sit on a concrete reinforced floor. I currently pay about $25/sq foot to cut out the old floor, repack, and lay rebar and pour a new floor. I have about 25,000 square feet to do. I would like to lay 2 inches of concrete on top of the existing floor but I worry that if I do not select the correct materials and process the floor will fail.

Does anyone on this forum have a suggestion for methods/material selection?

Is there an asphalt grade that is suitable for factories. I bought some asphalt blocks from a company in Pennsylvania..these blocks are rated close to 1500psi. That might be OK for light forklift traffic...but these blocks have brittle edges and need a perfectly flat surface for installation.

 

[GeoPaveTraffic]

I'm not sure I understand the existing floor system. If I'm following you, there is a reinforced concrete floor, with wood blocks on top of the concrete and acting as the current wearing surface. A few questions:

How thick are the wood blocks?
What size are the wood blocks?
What is the condition of the wood blocks?
Do you know the condition and thickness of the concrete beneath the wood blocks?
What is the loading of the reconstructed floor?
Is the area temerature controlled?

 

[PHACMGR]

How thick are the wood blocks? 2 inch thick

What size are the wood blocks? 4in x 6in

What is the condition of the wood blocks? wood blocks are beat up. In a metalworking environment the wood blocks expand and contract with moisture resulting breakage and loose blocks. Its a poor worksurface for employees as well as for the fluids oils and water that it is exposed to.

Do you know the condition and thickness of the concrete beneath the wood blocks? at least six inches everywhere...condition is for the most part excellent....it is 70 years old...has some wear from multiple machine installations over the years...and some buried conduit.

What is the loading of the reconstructed floor? I don't have specifics...but some machinery is over 10k lbs...load distributed

Is the area temerature controlled? factory temps...some higher heat around furnaces...for the most part 60-80 degrees

 

[jike]

I think that the concrete overlay directly on the concrete slab would be OK but not directly over the wood. As you stated, the wood has a tendency to "expand and contract". This would likely crack any concrete overlay. The flexibility of the wood may not be compatible with the stiffness of the concrete overlay trying to support concentrated loads form fork trucks or machinery.

Make sure that whatever weight you add can be supported by your base slab, if it is other than a soil supported slab.

 

[dik]

You might consider a latex or acryllic bonding agent on top of the exist conc... check with suppliers regarding preparation of existing surface...

Dik

 

[GeoPaveTraffic]

I agree with the others, don't put the concrete on top of the wood. However, if you place the new concrete directly on top of the old concrete, you should expect the new to crack everywhere that the old concrete is cracked. Therefore, the new concrete may not be much better than the old.

As an alternative, you could install a bond break between the new concrete and the old. This is done in some concrete paving operations, know as whitetopping. For pavements, 1 or 2 inches of asphalt is most commonly used as the bond break. ACPA's website,

http://www.pavement.com,

has information on the process. There may be other bond breaks that could be used in your case, I'm just know sure what they would be.

 

[Ron]

To expand on GPT's comments, an unbonded topping would work; however, if stresses are high, you might want to consider reinforcing the topping. The bond can be prevented by using plastic sheeting (Visquene). I would install a leveling course on the old floor before installing a topping, in any case.

You can also consider cutting joints in the old floor to cause future movement to occur there, but you'll have to cut them deep and you'll have to repair any cracks in the existing slab by epoxy injection or gravity feed if they're large enough. Then you can use a bonded topping on the floor and cut the joints directly over the underlying joints and you should get pretty good service.

 

[GeoPaveTraffic]

Good points Ron.

One question though; wouldn't the existing concrete floor have to be very smooth for visquene to act as a bond break?

 

[PHACMGR]

I've rcvd some local advise to remove the wood blocks, scarify, repair cracks and lay down latex mix concrete which should eliminate shrinkage cracking and cure in 7 days. Has anyone worked with latex concrete?

 

[Ron]

It won't eliminate shrinkage cracking. Put joints in anyway.

 

[facca]

Have you looked at ripping the floor out.You would end up with a nice new look and new flloor instead of a patch job.
You may not even pay much more for it.

 

[PHACMGR]

Thanks to all who wrote

I've got quotes of $20-25/sqare foot to pull remove the old concrete and pour an entirely new floor. Our other options seem to be removing the wood blocks and filling (2 inches)with a Latex mix concrete and topcoat at $8.50/sq foot or 2inches of epoxy mortar mix with topcoat at around $12/sq foot.

 

[davesatt]

If you intend to bond the new concrete to the old concrete surface I would sugest get a petrographic analysis to determine the depth to be removed to achieve a good bond.

 

[civilperson]

The epoxy concrete overlay has proven cost effective for bridge deck overlays at depths ranging from 3/8" to 1 1/2". Perhaps a leveling couse with an epoxy surface might supply needed cost and strength requirements.

 

[concretemasonry]

If you have more than 2", you could install 60 mm pavers on a sand setting bed (1"). The pavers are 8000+ psi with chamfered edges.

I have seen this in heavy duty repair shops for steel tracked equipment. No need to wait for curing of concrete is one of the reasons it is used.

Dick