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Thread: weight 4 inch concrete can hold
04-24-2011, 08:32 PM #1
weight 4 inch concrete can hold
What is the most heavy machine you think I can put on 4" of concrete? I tried looking up what lbs per foot concrete can hold but only got back how much concrete weighs.
Please let me know thinking about putting a 7500 lbs machine on 4" of concrete
04-24-2011, 08:37 PM #2
The answer depends on a few things which you will need to provide:
- The strength of the concrete mix
- The concentration of the weight at support points (i.e. 2500 lbs each on three feet or 1250 lbs each on 6 feet)
- The distance between each support point
- Any reinforcement in the slab?
04-24-2011, 08:38 PM #3
Hard to say exactly without knowing the specs of your particular floor, but, I think the average slab pour is done to ~ 3,000-3,500 psi. So I should venture a guess that a 7,500# machine should not have any issues. I'm sure others more knowledgeable than I will chime in...
04-24-2011, 08:38 PM #4
I don't know what the psi per sq ft is but I park my forklift on my shop floor and it is 4" deep. The lift weighs 9000lbs, Plus I don't know what it weighs but I have a 16" hd cincinnati shaper sitting on the same floor.
04-24-2011, 08:42 PM #5
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04-24-2011, 08:45 PM #6What is the most heavy machine you think I can put on 4" of concrete?
jigbore pictures by johnoder - Photobucket
04-24-2011, 08:57 PM #7
Seems like a lot of people are holding a lot more weight than I plan on putting on it with no problem.
04-24-2011, 09:21 PM #8
What is under the concrete? If its granite then you can put the Great Pyramid of Giza on it. If you basement is floating on water then it will depend on the breadth of the machine in the longest dimension, and the distance from the wall. Usually if a foundation cracks its because there is bad subsurface. For example, let's say it is like this
Where "X" is rock and "." is sand. If you put a heavy object over the sand the concrete will crack depending on how heavy the object is and how far away it is from the nearest X. Engineers call it a "cantilever".
04-24-2011, 09:26 PM #9
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04-24-2011, 10:19 PM #10
No one has yet mentioned it, but in several older threads there is discussion of how much the concrete floor will flex under heavy weights. In other words, if you are putting a lathe on the floor, someone walking by could actually move it, which could affect accuracy. Also, placing the ends of a lathe across two slabs separated by a joint is not a good idea, as they can move in relation to each other.
04-25-2011, 12:10 AM #11
...but again, that all depends on what's under it... I see flex all the time with concrete building floors (data centers have some very heayy loads), but not on good grade slabs.
On a correctly compacted base of suitable material, it's not going to "flex". If it's garden soil, or uncompacted backfill, well....
04-25-2011, 01:07 AM #12
Come on guys:: Don't forget the types of concrete, the amount of rebar, and/or the amount of fibre, the amount of tamping, use of a vibrator, etc. There is not a simple answer. Also, hand pour or truck, amount of cement to sand, to gravel. It varies. Ask a professional cement outfit. Wayne.
04-25-2011, 04:31 AM #13What is under the concrete
04-25-2011, 05:03 AM #14
+ another for WHAT'S UNDERNEATH?
If you don't know,......... I'd borrow / hire / scrounge a 4" core drill and cut a few holes for a looksee.
04-25-2011, 05:21 AM #15
That new pad may still sink, but since it is not attached to the slab, the slab shouldn't crack.
Years ago, someone proposed a series of small spindly piers, along the line of "stab in a digging bar and wiggle it around" as a way to allow a somewhat thin slab to avoid cracking (aid work in developing regions, perhaps).
Frank Lloyd Wright's 'lily pads' worked, but that was on another scale.
Soil Bearing Capacity Table
Type of Soil Load Bearing
(Pounds Per Square Foot)
Rock w/ Gravel 6,000 psf +
Gravel 5000 psf
Sandy Gravel 5000 psf
Sand 3000 psf
Silt Sand 3000 psf
Silt Gravel 3000 psf
Gravel w/ Clay 3000 psf
Clay 2000 psf
Sandy Clay 2000 psf
Silt Clay 2000 psf
04-25-2011, 08:01 AM #16
04-25-2011, 10:10 AM #17
As for "use a proper slab min 6 inches reinforced...8 is better." with that "logic", why not 18" with 24" being better? Useful advise is being sought here.
MBG, unless the slab is already showing signs of failure, I wouldn't hesitate to bring that machine in. Let's suppose that you are unlucky and the 4" slab doesn't easily hold it, what better test?
Won't go to China.... push the machine out of the way and cut a hole in the floor, excavate, compact a 12" layer 3/4" CRB (crusher-run-base), pour a 6"* reinforced slab and let it cure for a month. But fer crimminy sakes, don't go to all that silliness unless the need is proven, which is highly unlikely!
*6" because that will still be below the minimum ready mix delivery charge and you'll be adding useful anti-vibration mass. With that kind of prep, 4", 4,000 PSI, reinforced mud would be overkill for strength on that moderate load.
Don't dink around with "expansion joint"* between the old and new, too many people don't understand that. The new slab WILL SHRINK! Guarenteed. It can never apply pressure to the hole in the long-ago-cured slab around it. You'll just make a hard to keep clean recess around your lathe. Do dowel them together, help the old slab to remain stable, that's "flush" to the new.
*Do use expansion joint around an existing slab, before you pour around it.
Oh yeah MBG, how do you get around all those "sink holes" on the way to.. wherever?
04-25-2011, 04:53 PM #18
+3 for what's under the slab.
What I find is if you run an empty pallet jack across a poured floor you can probably find where it's solid and where it's hollow so to speak. There's a different sound that you can pickup with your ear.
04-25-2011, 05:17 PM #19
If you don't know the mix etc, if you do core drill the slab the slug will tell you a lot.
04-25-2011, 05:39 PM #20
Here's one of your Floriduh SINK Holes....