New Shop Concrete Thickness

[Superbowl]

I would see if I could rent some big steel plates like they use for road work to drive the fork lift on.

 

[Garwood]

This real simple- Don't let riggers drive a loaded versalift on your slab. I don't know why they would anyway.

H480 Mazak is a really old machine no? That would be early 90's?

Does the main machine weigh 30k? Or is 30k lbs the whole thing.

 

[Orange Vise]

30,000 pound horizontal mill brought in and my biggest nightmare is going too thin and the forklift popping the new slab

t's the rest of the shop that has me concerned as to just getting the machine across the floor.

A properly done 6" slab should easily handle the weight of the forklift + a 30K pound machine, IME.

 

[Overland]

Summary:
Digging out that much dirt, you may/should be down to good dirt. Test it: an engineer, or maybe a fully loaded dump truck and see if it pumps (moves).
If you're bringing in gravel, get the truck to run over your area a few times before it dumps.
Vapor barrier.
Get actual foundation spec from Mazak, no point in making it thicker than necessary.
Rebar top and bottom, surround by 3" of concrete, no point to put in middle.
Don't let riggers bring machine in on forklift; use skates, with plates under them. United Rentals has plates in my area.
Post your location - you'll get better advice and references from locals.
Good luck !
Bob

 

[BT Fabrication]

My bad guys, I left out the detail on the machine pad. I do plan to have a 18" 4500 psi isolated pad with 3 layers of rebar. That part I'm sure of. It's the rest of the shop that has me concerned as to just getting the machine across the floor. I obviously want to do this right and not have any regrets. My knowledge of structural loads of concrete slabs is limited. I know the isolated pad specs because I was at a shop that had a similar machine of similar weight installed and I'm basically copying their formula for that.
My concrete guy suggested 3" of gravel under the the slab with a layer of plastic (don't know the thickness, will have to ask in the morning). Is this substantial or should ask for thicker gravel layers or different substrate material?
This is a personal home shop that will have my business ran out of it until its too small and I need to expand (hopefully) at which point it will be turned into a car garage/general shop/ storage building with a 4 post lift. This is why im trying to avoid over building and trying to go with 6"because it will most likely be unnecessary for the long term life of the building.

As for gravel, you need to go as deep as the top soil is, idiot that built my shop left 6" of topsoil (its 24" thick) for the 6" slab on grade and 12" thickened edge and 6" of gravel.
For any concrete build, id recommend 12" gravel minimum, like 3/4" clear stone and compacted for drainage under the slab. Depending on the terrain you can also get away with 3/4 minus if you are in not a cold climate.
if a good base is put down, 6" concrete with 6x6 wire mesh in it will be plenty,3500ksi concrete, I have had water tank firetrucks drive over my 6" driveway 2 months after i put it in. they weight approx 38K lbs or so on 4 points.
biggest point as said above, let it cure slow, if its warm out, keep water on it to keep it physically wet and don't drive on it for 28 days min. ive broken 6" of concrete after 7 days of rain on new concrete with a single tire of a 9000# skidsteer. on the edge...

 

[Rob F.]

Don't just pour a flat slab, I would form and pour a 6"tall curb all the way around, integral with the slab. (Openings for doors of course)
This is good for many reasons, first is iit is an easy way to do water cure of the concrete. Just block off the door openings and fill it with a few inches of water for the first week. Later the walls are built up above floor level. If you wash the floor with water hose no water to rot or rust the wall. If you ram the wall with pallet jack or forklift forks they wont poke through. Helps keep outside water from coming in as easy in flood. as well as the siding can be higher off the outside ground.

 

[cnctoolcat]

Be cautious with concrete contractors, as they are generally not use to prepping and pouring super-strong slabs!

Inevitably they will try to cut corners on the prep, and possibly shave an inch or two of concrete depth.

I've never been ceased to be amazed by "professional contractors", there only mission seems to be to finish the job as soon as humanly possible, with just good-enough quality to keep the customer happy.

ToolCat

 

[Gearclash]

I replaced some shop floor this past summer with the intent of making it suitable for setting machine tools on it. Asked the dealer I bought a mill from how thick their warehouse floor was, figuring it had to be pretty thick to handle the weight of machines setting there. He kinda shrugged. “6 inches I think.” No problem with that I asked? “Haven’t seen it crack.” Pause. “And we carry machines over it all time with a 45,000 lb forklift.”

I poured my new floor 8” thick with 4” of fill gravel under it, all on reasonably compacted dirt. Some bar in it, not a crazy amount, and kept the surface wet for at least a week. The old floor was cracked and heaved 4” concrete and it has’t caved in under my old crane that weighs 20 tons. One thing about pouring concrete, you will only need to do it once, if it is done right. Amortize that cost out over the expected life, and spending a little more per square foot to make it right is a very small cost long term. It will be cheaper to do it right once than do it twice.

 

[Tyrone Shoelaces]

You are going about it the wrong way. The soil is the most important. Are you building a new slab in a existing building or is this a new building (slab and footing)?

How many feet does the machine have, it's a quick way how I go about designing pads for shops, then add a safety margin. Take the machine weight and divide it by how many feet it has. Then take that number and divide by the area of the feet to get your acting force on the concrete.
Thickness/ PSI only goes so far. How it reinfroces is the important way. I can build a 4" slab that is 3k psi that is wrong than 6" slab that's 3,500 psi.
Concrete is going to need reinforcement. At least 2 rebar mats (mat on the bottom and mat on the top. Rebar needs to be surrounded 3" all the way around. I would go up to #6 (3/4) 18" on center. On the corners of the mat's have L bars 3' x 3' long this reinforces the corners. Make *damn* sure you see teh guys out there with a viberator getting the air pocks out as they pour. Then cutting control joints at the right depth. Typically 1/4" thick and ever 12 to 15 feet.

Rebar is cheap. I do this for the living, machining is my secondary job.

I don't know where you live at but I would also put 6mil vapor barrier under the slab.

Another vote for the vibratory poker to settle the concrete. You’d be amazed how much the level goes down once the poker goes in. Keep the foundation wet, we used wet sacks laid down on the concrete and we kept them wet.

Rdgards Tyrone.

 

[ncjeeper]

I did 6 inch thick 4000 psi for my shop floor and dug out a 10x12 area 10 inches deep for a future HBM to sit.

 

[david n]

I swear what's under the slab has got to be 70-80% of the equation. I've been to places where the old buildings had 4"-5" of crete.........places buzzin with forklifts, VMCs, lathes, press brakes, shears, heavy assembly, etc...................floors are holdin up just fine...............

Here at my place I'm lucky enough to have great soil for foundations(crummy for growin' anything).............the excavator came out and scraped off the corn stubble and leveled out a pad. Basically poured the slab right on the ground. The "top soil" is only bout 12" of a light clay and gravel composition. It's all straight coarse gravel below that............. Basically class 5 gravel............pack it and it just doesn't move and doesn't get muddy....................

 

[SND]

For heavier machines better to have them on their own pad. If you know where they'll go pour it now, if not, make sure you can do it later.
Thickness depends a lot on base too.

When I called last year about concrete it was $138/yard(CAD$) and 10% fuel surcharge, not sure if it's gone up since. Sounds like you guys are getting some crazy high prices. I know rebar had gone up about 3X, not sure if that started coming down with all the construction happening still.

 

[Wenglish120]

For heavier machines better to have them on their own pad. If you know where they'll go pour it now, if not, make sure you can do it later.
Thickness depends a lot on base too.

When I called last year about concrete it was $138/yard(CAD$) and 10% fuel surcharge, not sure if it's gone up since. Sounds like you guys are getting some crazy high prices. I know rebar had gone up about 3X, not sure if that started coming down with all the construction happening still.

We have one main concrete company that controls the bulk of the market in whole northeast Ga area. They pretty much have the market as a take it or leave it type thing cause the nearest concrete facility besides them is about 30 minutes away. There are smaller guys, but they probably wouldnt be able to supply large amounts of concrete at one time like the big company can thats 10 minutes up the road.

 

[john.k]

My puny 4" slab got a test straight off.....the truck delivering the Landis and drill drove on the new slab,put crane outriggers on the slab with just rubber sheet ......gross 28 tons ....plus whatever the outrigger load was ..probably 12 tons on 2sq ft .......no cracks ,no marks ,no problems.

 

[john.k]

If you pay for extra thickness concrete ,be there when the forms ,mesh,rod,tie and pour is happening.......see the formwork and steel layout tied in place on the day of the pour......and let the concretors know you will be there ,wearing rubber boots,and with a depth measure spike.

 

[Garwood]

If you pay for extra thickness concrete ,be there when the forms ,mesh,rod,tie and pour is happening.......see the formwork and steel layout tied in place on the day of the pour......and let the concretors know you will be there ,wearing rubber boots,and with a depth measure spike.

You know John, if you'd like to learn more about concrete, I suggest taking a look at how us millennials do concrete- Ya see, we can't afford to hire contractors because the boomers control all the wealth. So we do the digout, the rock, the compaction, the forms, the rebar, the pouring, the finishing and the cutting. That's how we know it's done right.

 

[FJsapper]

It’s all about what is under the concrete. You can see 60” of various sub grade layers on surfaces like runways that see big live loads. Remove all organic soil, get to good competent earth, build up with an appropriate gravel mix not just one size rock, sands and fines help lock everything together when compacted. If you have clay type soil underneath you need to isolate that from your sub grade using some manner of geotextile.

 

[Bondo]

My 30,000# Cincinnati 230 ton press brake requires a 6" 4,000 psi concrete slab minimum.

So that would be a reference for your machine

 

[Djstorm100]

Not a good comparison, how many feet, whats the diameter? If no feet under it whats the L and W?

 

[Illinoyance]

There is a lot more to design of a floor slab than most people realize. Some of the factors to be considered are:
maximum wheel load
number of load repetitions
nature of the underlying soil
thickness an quality of base course

For machinery foundations it is also necessary to consider the allowable deflection under load.

There are design guides available for industrial cloors. Look on line.