What psi concrete is the typical warehouse / factory floor?

[bryan_machine]

My 8K boxcar special weighs 13K plus empty. 10K or 12K would be more. As note above several times whether it buckles is more about the subbase than anything else.

 

[Garwood]

I had to drive over 4" concrete on packed dirt with a forklift that weighed 65k and a 17k machine on the forks. That concrete broke apart like driving over thin ice.

You guys ever demolished concrete? 4" and under is pretty easy to break up and deal with. Pick up a 2000 lb steel bar on end with an excavator and just drop it from 8 feet. Or pick up the edge of a section, place something under the edge and drive up on it. 6" and thicker is much, much more difficult/involved. Rebar doesn't make much difference, but thickness sure does.

I don't feel as though thicker sections are a waste of money. I always divide my pours up into 11 cu yard increments (usually 22 or 33 yards a day) and will add an inch or two to slab thickness if it makes sense to do so. If a section takes 9 yards why not spend another $240 to add a couple inches and use an entire 11 yard load?

 

[idacal]

I put 6" of 6 bag mix in my shop but I also dug it out 2'. packed pit run for 18" then topped it with road base and ran a packer until I was shaking in my sleep, had water running on it for a week. I have a few cracks but not much actual movement, it also had metal on 24" centers but I have point loaded it many times with outriggers and no cracking. my biggest issue and most damage has been spalling off when torch cutting in the shop. If your loads are normal you need a normal floor. 100,000 lbs on 4 midget forklift tires probably need more, that's where 1" steel road plates come into use. those are available for rent, the few times the weight is up in those numbers.

 

[thermite]

I also put 1-3 feet of 3" minus under the slab. Packed it with a diesel vibe roller for an entire day and then let it sit for a year before I finally poured.

Spud?

"See above". He got it right.

Subgrade does all the REAL work.

All the slab is for is to prevent disturbing it!

Seriously. Fail that lesson, yer perpetually plucked.

See "water bound Macadam" as the mother of all pavements:

WATER BOUND MACADAM ROADS (W.B.M. Roads) - Engineering TiCh

Egypt, then Rome were doing it before Macadam was born. Or even Roman-Law England.

All he did was formalize the training for the revival.

 

[Antarctica]

Damn - there's a lot of great info in this thread. I need to learn a lot more about concrete prior to any shop build/rebuild.

 

[Antarctica]

Anyone have access to a commercial concrete spec for reference, including finishing? I'd love to know how a Costco floor is spec'd. Every time I go I'm drooling over/on it...

 

[dcsipo]

Wow! That's expensive. It's $120/yard here or if you got enough cash in your piggy bank you can get about 30% off that.

300 aud is 142.90 usd and 1 cubic meter is 1.30795 cubic yard, making 300 aud per cubic meter about 109.25/cubic yard, he wins

 

[john.k]

if you want high spec .you gotta pay extra for fibre reinforced .....In the old days,concrete was like wet dirt and had to be rammed in place .....now its more like soup ,and flows like water......the old rammed concrete is water proof,soup is full of spaces ,and has to be sealed by various coatings.

 

[john.k]

The problem with 4" slab is where it aint 4".....concreters got one thing in mind......finish the job quick as possible.....my slab the concretors pulled every trick in the book.....banned trick ,that is......I was in a big hurry to get the shed up (didnt happen ,due to covid) and had to put up with all kinds of crap from the concretors...like driving over the mesh ,and "hooking" it up......hooking is banned under all the codes and standards here.....It was heavy rain all year (still is) getting six hours fine was touch and go,night before was 4 " of rain which washed sand onto the plastic sheet ....concretors didnt worry about it....I had to hand clear up the pier holes ,as they had already laid the sheet and steel the day before.....pier holes were half full of sand and mud .........I very much doubt there is code 2" of coverage of all steel .....but at my age ,the shed wont be there in 10 years,so why worry?

 

[john.k]

Did I mention ,I had the slab thicker at the door end,but when the shed was installed ,the guy put the doors at the wrong end .....not a giant drama.....but the thickness is wasted,unless I put a door in the other end.....which I may do .

 

[DDoug]

Anyone have access to a commercial concrete spec for reference, including finishing? I'd love to know how a Costco floor is spec'd. Every time I go I'm drooling over/on it...

https://www.concreteconstruction.net/how-to/superflat-floors_o

 

[matt_isserstedt]

So I know a guy who built his own shop for something along these lines.

What I built was:

- jumping jack compacted the disturbed soil
- spread 6" layer of #57 limestone (its 3/4" nominal angular stone, washed of all fines)
- lightly wet and plate-compact the stone in 2 directions
- apply 10 mil vapor barrier
- I used Grip Rite Pro-Lok chairs, 1/2" rebar was placed on 16" centers, 2" up from the bottom of the slab
- wire tied every other junction with the looped wire ties you get at a box store
- I used a 4000psi/6-sack concrete mix, poured 6" thick.
- it was pumped into place so the finishers don't have to screw with the mix by watering it excessively
- eventually power troweled and finally steel troweled by the finishers
- I applied BASF MasterKure CC 300 SB curing sealer as soon as I could walk on the surface without damage
- the finishers saw-cut the slab into 10-12' squares the next day after the pour

Imo a boxcar especial forklift doesn't do anything different than a standard forklift as far as loading, the "2x" weight (at the limit) is found at the front tire no matter how the counterbalance is achieved.

So far its held up to everything I've thrown at it, I only have a 7k forklift I've used up to around 10k, some faint hairline cracks at inside corners just from curing stresses, but someone someday is going to have a hell of a time tearing it out

Heaviest machines thus far are the 7k Monarch below, which did come in on skates due to its length (different loading), it replaced a Barber Colman 16-56 hobbing machine which is equally as heavy and was moved with the forklift.



I work in a truck freight warehouse converted to a factory which has thousands of square feet of concrete in ~16'6" saw cuts, the slab has terrible "curl" near the edges which I attribute to it being placed as fast as the crews can go, its 8" thick nominal, less under-prep and the thickness is hugely variable. Easily withstands 30k forklifts used by riggers installing machinery.

 

[idacal]

I popped someones driveway last week with the drill rig, double 4' railroad ties under the out riggers about 100,000 of combined weight with pull, a deep low pop a 6x7 section cracked out, I had warned them in writing though, do to positioning, it was likely to happen. it can't be repeated enough the substrate is the most important 3" poured across solid basalt will take a whole lot more abuse than 12" on wet sand and reactive clay, no getting around it. spend the money on the substrate. now one of those hard tired super heavy lift forklifts probably need plate under them. but to actually put 3500 psi onto concrete takes a bit of doing, and it will crumble from the surface if you do. 99% of failures are subsurface failure, concrete is almost useless in tension, I think its 10 to 1 compression to tension and when the substrate gives tension is the force on the concrete

 

[MaxPrairie]

Concrete footings are typically designed based on the soil underneath. If there is no geo report, 2000 psf is used. The concrete will be designed thick enough to transfer the load over the required square footage. Rebar at bottom 1/3 of the footing to take tensile stress. When designing concrete beams for example (on typical loading) the majority of the rebar will be at the bottom of the beam where tension occurs and the bars needed on the top of the beam are there to meet minimum reinforcement.

I just poured some concrete the other day and asked for standard flatwork mix, design strength was 4500 psi. Sat in a conference years ago where one of the engineers who designed the Burj Dubia was talking. He said they used 20k psi concrete there.

 

[JoeE.]

A plant I worked in had portions that were probably built in the 1920's. The building was a hodge-podge of additions.
The previous occupant (the Bush Hog corporation) had moved out and my employer bought the huge building at moved part of our production into it.
So, when Bush Hog left, they took what machinery they wanted, auctioned off most of the rest, and we ended up with a couple of big stamping presses that didn't sell. The big one was a Minster straight sided, double crank press... think it was a 150 ton machine. We never used it in the 10 years I was there.
It was in the oldest part of the building, and was taller than the overhead crane ways that straddled it.
A rigging company was called to move some other machinery in our plant one year, and while they were there the plant manager offered them the machine if they'd just move it out. They wheel and deal in that stuff, so the deal was made.
I don't know the exact name of the forklifts they brought in to move that thing... but they had dual, solid tires on the lift end... and the counterweight end was extendable to allow heavier capacity.
So, the first lift came in under the craneway and got out of the way behind the machine. The second came in and pulled up in front of the machine, whereupon they placed a couple of railroad ties on it's forks, drove on in and got the forks in the die area and began lifting on the ram. They were going to lift it up off the ground a few inches, carry it away from the wall and lay it on it's back out in the open. Then, one lift on each end and they'd carry it out from under the craneway and across the shop and to the waiting drop deck trailer they were going to haul it home with.
Well, the lift got the press up off the ground a few inches and started backing up. He made it about 5 feet and all of a sudden the floor caved in under the duals and the press sat right back down on the floor with a huge thud. The old concrete floor was basically hollow underneath... the tires could get no traction and he couldn't get out of the hole he'd made. No weight on the forks, but he was basically high centered on the edge of the hole.
Finally got the other lift around behind him and they hooked some straps between the two, and with both lifts' engines roaring and a little wheel spinning... they got him drug out of the hole.
Can't remember how they evaded that big hole to get the press moved after that, but they did. Had it out of there in no time flat and off the property. Wish I'd have had a cellphone or camera back then to take a picture of the scene!

 

[neilho]

You should probably take this question to the concrete contractors. Come on dude, it's not easy to choose concrete. If you choose it wrong then your floor's gonna be all cakey and unsmooth. Overall, just terrible. You certainly don't what that to be the first thing that is looked upon when people come over right? So just go to the professionals, they know the best. And Idk how many times I've said this but when it comes to building, please don't do it by yourself!

Is that link to your website? I thought so.

This site is full of people who have been doing it themselves for years, had you read the thread - we ain't gonna stop just cuz you tell us to. You've irritated us and lost credibility. (Yeah, the french roast just kicked in.) Ask knowledgable questions about the work or tell us what to do to achieve what we want and you'll fit in just fine.

 

[gbent]

For a working shop I recommend a minimium of 4500psi, 5,000 is even better. Even if you don't need it for the strength of the slab, you do need it for the resistance to surface damage from dropped parts, traffic, and general abuse from every day wear and tear.

 

[m16ty]

I’ve seen 4” slabs hold up some massive loads, and I’ve seen 12” slabs come all to pieces with light loads. What is below the concrete has more to do with how much it will hold than the thickness. Of course you can span compete voids if it’s engineered right.

With a decent sub grade, 6” 3,500lb mix with reinforcing wire will be fine for most shops.

 

[scsmith42]

There are two things that are really more important than the psi rating of the concrete. First, how well compacted the base material is (and the type of base material - you don't want any organic matter or topsoil). Second, the slump of the wet concrete mix.

Low slump mixes (4.5" slump range) have less water in them and thus the concrete shrinks less as it dries than high slump mixes. The less shrinkage, the stronger the concrete.

 

[ncjeeper]

I went with 6 inch and 4000psi mix for my shop slab. We dug down an additional 4 inches (for a total of 10) in the area where my future HBM will sit.