What psi concrete is the typical warehouse / factory floor?
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    Default What psi concrete is the typical warehouse / factory floor?

    If you were building a metal framed shed / warehouse for a shop , and had either a 10K or 12K boxcar special forklift, would 3500 psi concrete be sufficient or would you need to go higher ?

    How thick does the slab/floor need to be ? This would be a slab on grade building.

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    I think an engineer would have to specify that.....if you cut down to hard rock subgrade ,its a lot different to a slab on fill ,no matter how well compacted.....Usual floor is 100mm/4" thick ,some places go to 200/8" thick ,but at around $300/cu m for concrete delivered ,this makes for a big cost increase.

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    The floor under my 60 bullard was 12 inch thick, depends on what machinery you have...phil

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    I started pouring 8" of 5000 PSI mix with 1" aggregate. The 5000 was cracking before I could cut it the next morning. Pretty unhappy. I had a long talk with the plant super (mix plant is 2 blocks away) and decided to go with 3500 mix with the same large rock. I also researched my ass off on what concrete specs mean and how they concoct the stuff. For my needs the slow cure low PSI mix sounded like just the ticket and I don't regret it.

    It was a workout to finish with a lot less cement in the mix, but it turned out good for a shop floor and has almost no cracks after 2 years. In fact one section about 15ft x 60 feet I never even cut it and it hasn't cracked.

    My building is slab on grade with a monolithic 24" footing plus a 4" stem wall tapering in to 7-8" slab with probably not enough metal. I put about $1000 of rebar in it and that was all the money I had to spend.

    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.

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    Quote Originally Posted by Phil in Montana View Post
    The floor under my 60 bullard was 12 inch thick, depends on what machinery you have...phil

    Nothing heavier than 10,000 lbs.

    What does a 12k or 10k boxcar forklift weigh? Being rather compact I presume they exert more psi than a standard forklift.

    So whatever a 10K forklift + 10K machine weighs would be the maximum.

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    Quote Originally Posted by john.k View Post
    I think an engineer would have to specify that.....if you cut down to hard rock subgrade ,its a lot different to a slab on fill ,no matter how well compacted.....Usual floor is 100mm/4" thick ,some places go to 200/8" thick ,but at around $300/cu m for concrete delivered ,this makes for a big cost increase.
    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.

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    Quote Originally Posted by Spud View Post
    Nothing heavier than 10,000 lbs.

    What does a 12k or 10k boxcar forklift weigh? Being rather compact I presume they exert more psi than a standard forklift.

    So whatever a 10K forklift + 10K machine weighs would be the maximum.
    probably 15k-20K forklift plus 10k machine so up to 30k on the front tires. 4" would probably handle it if you have a real good subgrade. If not then go extra thick.

    Concrete is dirt cheap compared to labor. I don't understand why folks cheap out on thickness. I had $25,000 in concrete in my entire shop and I filled some huge sections. My 20 foot wide front door plus the 10 feet on each side is 20"+ thick for the first 6 feet. I wanted my rolling door to stay level.

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    All of ours is plane old 3,000 psi. We've had loaded 80,000 lb forklifts on it without problems.

    With that said, I think local ground conditions and sub-grade have more to do with a good concrete job than the concrete itself. In our locale, if you have good compacted red clay and proper drainage, 4" of 3,000 psi concrete will pretty much hold up anything you put on it. If you don't have a good base though, 12" will fail with the weight of a pickup truck.

    All of our pours are 6" of 3,000 psi with fiber. Has held up anything we've put on it, and I've probably loaded a floor as much or more as anybody here, such as a 60/80 Hoist and a 50 ton Riggers Tri-lifter carrying a 150,000 lb Komatsu press crown across it.

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    If you want a surface that will stand up well to abuse, get 4500 or better concrete. The surface will take more abuse from dropped parts without spalling. The thickness is a matter of point loads and subgrade preparation. If all you do is cut 4" of topsoil and replace it with sand before pouring, you better go 8". If you have to bring in good clay to build up grade and do a good job of compaction you can go thinner. But keep in mind 4" slabs are difficult to keep the bar in the middle, bar on the bottom doesn't do any good.

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    You set the bar on chairs,( little stands to put the rebar in the center) dont count on the cement guys to lift the bars up as they pour they wont. A 12k fork lift will weigh 24k without a load or 36k with a max load.....Phil

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    Quote Originally Posted by Spud View Post
    If you were building a metal framed shed / warehouse for a shop , and had either a 10K or 12K boxcar special forklift, would 3500 psi concrete be sufficient or would you need to go higher ?

    How thick does the slab/floor need to be ? This would be a slab on grade building.
    I think it would be more than enough if what's underneath is solid and there is little to no movement from seasonal humidity. The slab should be over 6" - you can go under but the prep work becomes critical and will cost way more. One factor to keep in mind is the quality of the top surface. I had good results with proper granolithic screed applied a couple of hours after the concrete was poured but then, that is labor intensive. I suggest you ask others what problems they had encountered and use a properly competent professional for the technical bit.

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    Ditto on the underneath prep

    Unless you have a specific need for more expensive concrete or thicker than normal, you are wasting money

    Eventually you can find a way to crack any slab if you are moving heavy enough things

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    well the concrete is only as solid as the sub grade.

    if the sub grade is soft as baby poo, then it won't support ****.

    need to get a test on how hard the sub soil is and if you need to excavate and rock fill and pack before concrete is installed.

    I have a solid sub grade, 6" is more then plenty for most compressive loads. had a full fire truck on mine. doesn't budge or crack.

    rebar or mesh wire is a must to prevent cracks. with super heavy equipment like that, id go #3 rebar min 12-18" on center and 6"

    but i'm only guessing what you have there. like i said, it all depends on the PSI of the ground and what it will hold.

    and 3000psi will work fine. just ask for the larger aggregate, like driveway stone.

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    Commonest cause of structural damage to concrete floors I see is ceramic tile warehouses......these guys put so much weight down ,they can crack anything.......Second most common is vegetable oil spillage ...this is a silent killer of concrete.

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    The PSI is its compressive strength and has about bugger all to do with it cracking. Really, what the slab does is distribute the load over the base. A typical base might be 10-18" compacted aggregate, but the whole floor is engineered including what you're going to do with it, bearing quality of the sub soil, cuts, rebar/mesh etc. The floor is the most important part of an industrial building. i've done a lot of large industrial design builds in my previous life. I used to be able to rhyme off all the specs....but its fading. Point being, I know you say its just a shed, but it wouldn't hurt to talk to an engineer and a reminder to put as much effort into figuring out the aggregate base as you do the slab

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    Surface wear is another consideration, particularly where there is heavy traffic and grit on the floor. The worst surface wear i ever observed was at the Farmall (RIP) plant where there was heavy forklift traffic in front of Wheelabrator. The shot spilled on the floor cut away the concrete under the forklift wheels.

    There are products to harden the surface. If I remember correctly one was Master Plate that consisted of iron aggregate that was troweled into the surface of the concrete.

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    Quote Originally Posted by gbent View Post
    If you want a surface that will stand up well to abuse, get 4500 or better concrete. The surface will take more abuse from dropped parts without spalling. The thickness is a matter of point loads and subgrade preparation. If all you do is cut 4" of topsoil and replace it with sand before pouring, you better go 8". If you have to bring in good clay to build up grade and do a good job of compaction you can go thinner. But keep in mind 4" slabs are difficult to keep the bar in the middle, bar on the bottom doesn't do any good.


    Well you need to have a look at that sentence again as its not correct on bending moments in for suspended slabs or slabs on ground ( this case )
    That if you need two layers of steel, one layer is most inefficient when you look at the moments.
    The OP is not getting good information and needs to check with a actual USA Civil Engineer do do a design.
    There is more such as shrinkage control steel
    chairs are for bar placement due to cover requirements....more to do with lifespan of steel.
    Pay the man the money and get a good job.

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    I'll stick with the accuracy of the statement given the depth of this article. Every moment that wants the bar at the bottom of the slab has opposing moments that want the bar at the top. And 4" is just to thin. Someone is always walking through the concrete during the pour. Sometimes they step on the bars, sometimes the chairs sink into the sand, etc. Concrete is a difficult job and do-overs are incredibly expensive. Spend a little more to insure the worst case is still acceptable.

    As for engineers and stamped drawings on small personal projects? Spend that money on more, stronger concrete and better concrete finishers.

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    Yes you've answered if its 4 inch if thats what he's doing is too thin to fit it with cover allowance.

    Not sure how deep he's going on the slab and just how big a area he is doing, just says a shop. Maybe my idea of a shop is bigger than the actual he is doing and or information needs to be stated to see what's what.

    Even a moderate area if he gets it wrong is a big expense to dig it up if its no good.

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    Quote Originally Posted by BT Fabrication View Post
    well the concrete is only as solid as the sub grade.

    if the sub grade is soft as baby poo, then it won't support ****.

    need to get a test on how hard the sub soil is and if you need to excavate and rock fill and pack before concrete is installed.

    I have a solid sub grade, 6" is more then plenty for most compressive loads. had a full fire truck on mine. doesn't budge or crack.

    rebar or mesh wire is a must to prevent cracks. with super heavy equipment like that, id go #3 rebar min 12-18" on center and 6"

    but i'm only guessing what you have there. like i said, it all depends on the PSI of the ground and what it will hold.

    and 3000psi will work fine. just ask for the larger aggregate, like driveway stone.
    Reinforcing wire or rebar won't prevent cracks, it will keep the concrete from separating and elevation changes at the cracks though.

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