I am going to be pouring 13’x13′ concrete pads for my driveway. There will be 8″ between each of the 5 pads to accomodate a row of brick pavers. The concrete will be 6″ thick on 4″ of 2B stone.
What is the most appropriate rebar configuration/spacing?
Any other suggestions?
Thanks for your input.
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Replies
#5 rebar at 6" oc both directions will give you good results. Keep the bars at least an 1-1/2" off the subbase and make sure the subbase is well compacted.
6" O.C. ???
Never heard of putting rebar that close together. Why so close?I am the bad thing that happens to good people.
To minimize cracking for freeze/thaw cycles and the live loads from vehicular traffic and possible delivery trucks, you'll need a good amount of rebar.
Up here in New York, our engineer has designed a slab for a school with similar rebar and that's only for a live load of people..
Never seen a driveway poured with rebar closer than 3' O.C.
If you're gonna put it that close, why not just use the rolls of wire that are 5 or 6" square? (Don't know the correct name)It looks to me like the ugly fairy kissed you on both cheeks.
6" welded wire mesh really should be used for interior slabs. Slabs that are going to be exposed to the weather should have rebar in them.
The frost heave that the concrete will be subjected to will require rebar.
We have #5's at that exact spacing................but as a 6' x 6' footer under a column supporting a W16x100, an 8" slab, and an entire floor above that. :)
Before "engineering" the slabs to match one climate, it'd help to know what the climate is where the original questioner lives, and what traffic and loads he's expecting on his pads.
http://www.concretenetwork.com
Lots of good information here.
I certainly have no concrete experience for cold climates & frost heave, but in the Texas area, #5 @ 6" o.c. would be overkill for residential. I have had driveways 5" thick with #4 (1/2") rebar 16" to 18" o.c. remain crack-free and in excellent condition for many years.
Edited 11/19/2002 11:25:34 PM ET by ORACLEDESIGN
#5 bars at 6" is unnecessary. This is a driveway, not a containment vessel for a nuclear reactor! #5 bars at 12" is still overkill for a residential driveway. A 6" slab with 6x6x10ga. wire mesh is more than adequate for this application.
A firm, well drained base is the first critical element. A well designed concrete mix with air entrainment and chert-free aggregate is next. The last critical element for longevity is the quality of the finishing operation.
Overengineering is not a virtue.
Eric
rebar is not needed for driveways. Rebar has little effect on freezing and thawing. It has some but little. Rebar is design for load, welded wire and fiber is designed for shrikage cracking(freezing and thawing) The weight of the vehicle is not much per sq ft , concrete itself without reinforcement can hold it easily. Concrete strength is in compression and not tension, for every compression load the bottom half of concrete is in tension. It create a bending of the slab. rebar strength is in tension, so by adding rebar to BOTTOM of foundation, it counter acts the load of compression.
a car weight about 5000lb. It has a foot print of four tires about 10 inches by 10 inches time 4. that is 2.74 sq feet 5000/2.74 equals 1824 lbs per sq feet. a weak concrete has a compression strength of 3000 lbs most do not failure till 4000-5000 lbs. If the subsoil is compacted to spec, the concrete will not bend under this load. Remember 5000 lbs is a heavt vehicle. Mined weight 2200.
By added area of steel, concrete can be made to hold heaver loads than the strength of concrete.
so cracking is controlled by welded wire and fiber but loads are not controlled by ww and fiber. They are not replacement for each other. I like fiber because of labor saving.
in conclusion " If you want" to add rebar to your driveway it is not hurting anything but by calculation loads it is not needed. I got some laying around that I plan on throwing in my driveway when I pour. Also these are for an everyday driveway, if you drive a dumptruck for a living put rebar in it.
Statement: I know somebody going to rebluff my statements about rebar but this is what I do for a living everyday, pull the textbooks out first.
let me have it.
Johnny, that was nicely written and well explained.
you're preaching to the choir here my friend.
Eric
PS. 3" clear if the concrete is in contact with dirt or the exterior.
I allways use 6" x 6" welded wire for any slab. Rebar or wire will not keep the slab from cracking. It will hold the pieces together when they do crack. My concrete garentee which is given to all slab customers is. " it will get hard, it will crack and nobody will steal it"
Nobody will steal it. ROFL.
I'm no expert on concrete or foundations but I did work on a building that suffered a 3 month delay because the final sample cores showed lots of clay deep. The entire foundation system had to be redesigned. The amount of concrete easily tripled and the amount of steel went up, according to an engineer, about ten times. The reason being that it, as installed, is now capable of being supported at both ends when the clay shrinks in the middle.
What's this have to do with a slab on grade? Wouldn't the bearing capacity and the consistency of this capacity have a great influence on the amount of reinforcement needed? On solid rock a slab could be thinner and have little reinforcement. A large slab on an uncertain base might be required to act as a unit with large portions of it less well supported than others. Wouldn't this require more reinforcement?
A common technique I have seen in some areas is to double the thickness at the edges and to install a double run of #4 or 5s. I hear this makes the unit less likely to shift and more likely to function as a unit. I will confirm that the edges are less prone to being undercut after a heavy rain.
There are many differences between a structural slab and a driveway. If you want to talk structural slabs we can, but this is a driveway thread.
Eric
Actually what I described, doubled edge thickness and rebar around perimeter, is a common design for a parking slab. It is a fairly heavy duty one for extended longevity in more difficult conditions but it is not, by commercial standards, unusual. Even in residential construction I have seen similar ones used around some high end homes for parking or repair pads. Whatever the customer is willing to pay for. The extra features limit undermining and failure of the edges as they are driven over.
No. 4 at 18"oc is used in northeast bridge decks to take advantage of plate action while minimizing the actual steel in the deck. A slab on grade gets more benefit from a well compacted, free draining subbase, proper concrete placement and curing, and fiber mesh reinforcing. Edge rebars are good for odd angles, but are usually left out when 80 to 100 degree angles are used....that's not a mistake, it's rustic