slab thickness

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My contractor has specified a 4" thick slab on grade for a new garage floor. Is this the accepted thickness? I've read that driveways should be 5" thick and house foundations 8-10" thick. The plans *do* call out reinforcement.
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snipped-for-privacy@bigfoot.com wrote:

4" is standard for a residential driveway, gge slab as well as the house floor.
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snipped-for-privacy@bigfoot.com wrote:

What about beams to support the walls? Stirrups/vapor barrier? Rebar/mesh? These are equally important IMHO.
Gary
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On 14 Jun 2005 13:28:13 -0700, snipped-for-privacy@bigfoot.com scribbled this interesting note:

Four inches is sufficient for the floor of the garage. Of course you will still need beams around the perimeter of the garage (perhaps more in the center, depending upon the complexity of the design), a sand pad to control expansion and contraction under the foundation, a moisture barrier, and reinforcement steel, properly supported so it is in the center of the concrete instead of sitting on the bottom against the moisture barrier where it does no good whatsoever.
If I were building my own garage, say a 20X24, single story, where we live, I'd most likely dig perimeter beams about ten to twelve inches wide, at least a foot below grade and sixteen to eighteen inches would be better, and possibly dig piers on either side of each corner as well. Otherwise, standard pad design, moisture barrier, and steel.
If I got fancy and wanted a two story garage then the beams would be wider and deeper and there'd be more piers. Otherwise the rest would suffice, even the 4 inch floor. But that's where we live where the soil has an unbelievable amount of expansion and contraction. A slab in this area, built to minimum standards, even just for a garage, will fail unless you take extra precautions to keep the soil around the building stabilized by maintaining even moisture content year 'round. -- John Willis (Remove the Primes before e-mailing me)
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Just what are you planning on driving on a 5 inch slab? A Fire Truck?
4 inches is standard, usually 3500 psi concrete. Some use rebar some use steel mats. Saw cut every 10 feet for expansion.
Foundations are broken up into parts called footings and stem walls. The thickness is directly proportional to the height of the building. Where I live the footings are minimum of 12 deep x 18 wide about 18 inches below grade. That makes the stem walls 10-12 inches wide and 20-24 inches high. If you live in frost country, other considerations are necessary.
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SQLit wrote:

The OP said he read the info. Must have been a handout from the National Concrete Mfger's Association
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Some use fiberglass fiber reinforcement instead. I did ;-)

Yeah, you generally need to get below the frost line. Here, it's at least 4'.
--
Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
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My motorhome is 21,000 #. Now, I don't put it in the garage because it is too tall, but I do drive on the driveway. And when I go visit, I drive it on other people's driveways, too. Hope they have a good one, and didn't get the cheapo economy cut cost save a little money now and pay for it later kind of deal from their contractor.
The way I think of it, I want to know if I ever wanted to drive a fire truck on it, I could.
Steve
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Anybody answer how thick and what PSI concrete one should have for a driveway to support a 25K# truck or trailer?
Also how pricey is it to have a testing person to do a slump test on site.
In my neck of the woods (S WI) the big bear of a problem here is chert - for some reason in the winter the stuff explodes leaving divots in the concrete. Seems the cheap jobs and the city sidewalks all have these divots.
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I think this needs 6", plus a well compacted gravel base, and rebar/mesh. 4000PSI or better methinks.

It shouldn't be necessary - just stress to the supplier that it needs to be on-spec.

Sounds like "spalling", rather than issues with chert. Usually caused by inadequate air entrainment. This is something you specify when you order. You're best off hiring a "real" concrete contractor to do the job or at least spec it out for you. A civil engineer could be used to spec the thing if you're going to contract it out yourself.
--
Chris Lewis, Una confibula non set est
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In a previous post butch burton says...

I would go with a minimum of 6-inch thick on a minimum 6-inch compacted crushed rock (3/4" minus) base. You can help spread loads if you use a geotextile between the gravel and native material.
Specify a minimum 3500 psi low-slump concrete with 6% air entrainment.
Provide 1-1/4" deep crack control joints - either tooled or saw cut every 150 sq.ft. (maximum). For example, if the driveway is 12 feet wide then put a joint every 12 feet. Joints should be cut as soon the surface is hard enough to walk on.
--
Bob Morrison, PE, SE
R L Morrison Engineering Co
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snipped-for-privacy@bigfoot.com wrote:

Your driveway may be expected to support a truck, your garage will not likely ever need to.
--
Joseph Meehan

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In a previous post says...

For residential structures, I always recommend a 5-inch UNREINFORCED slab on a 6-inch compacted gravel base. Sawcut or tooled crack control joints every 150 square feet max.
Unreinforced = no welded wire fabric, no rebar, no fibermesh
No amount of reinforcing will prevent cracking. The only thing that will do that is pre-stressed or post-tensioned concrete.
--
Bob Morrison, PE, SE
R L Morrison Engineering Co
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Slab strength and thickness depends on extenuating circs, type of subsoils, frost, use of salt on roads, etc. Reinforcing, if properly applied, greatly improves perform of crete, as does limiting the amount of H2O
-- Troweller^nospam^@canada.com
Remove the obvious to reply. Experienced and reliable Concrete Finishing and Synthetic Stucco application in the GTA.

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In a previous post ConcreteFinishing&StuccoGuy says...

CF&SG is correct in that rebar and lower water content will improve structural performance. However, only the latter will have any effect on crack control.
Most cracks come from shrinkage. Shrinkage comes from having more water in the concrete that is necessary to make the chemical reaction happen.
If left unspecified most batch plants will give you about 6 gallons of water per 94 lb. sack of cement. Only about 3 gallons is required for the chemical reaction. The rest is there so you handle and place the concrete.
There are several ways to reduce the amount of water, including adding more air to the mix which isn't a bad idea for exterior slabs. The added air ("air entrainment") will also improve freeze-thaw resistance.
--
Bob Morrison, PE, SE
R L Morrison Engineering Co
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Bob Morrison wrote:

Don't they measure or test that by measuring the "slump?"

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Joseph Meehan

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Don't they measure or test that by measuring the "slump?" ************************************************************* Yes they do but if the concrete measures a 6 slump, there is no way to take water out of the concrete. (the only way to stiffen up the concrete is to add more sand, aggregate and cement)
--
JerryD(upstateNY)
> If left unspecified most batch plants will give you about 6 gallons of
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Joe wrote:

And if it measures a 6" slump and you wanted a 4", then you send the truck back to the plant and ask for one that is to your specifications. You don't just take what they give you.
--
Robert Allison
Rimshot, Inc.
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.... and watch that the driver doesn't add water to move the mix down the chute. The Navy had to rework a three story building because the inspector didn't pay attention. Engineer and lawyers spent a couple of months strugglng over that until a fired employee spilled the beans. TB
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It is a little more difficult to send back when the test cylinders don't meet compression days later :-)

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