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Concrete Slabs

Old 03-19-2009, 08:35 AM
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Default Concrete Slabs

I have done some rearch, but I am unable to find the answer to this question. Rebar, yes or no. The slab will be 6 inches thick, aprox 30 X 40. Max weight with be 10, 0000 lbs.
Old 03-19-2009, 08:41 AM
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With out a doubt, YES!
Old 03-19-2009, 09:04 AM
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Originally Posted by kingair View Post
I have done some rearch, but I am unable to find the answer to this question. Rebar, yes or no. The slab will be 6 inches thick, aprox 30 X 40. Max weight with be 10, 0000 lbs.
When you say max weight, do you mean the weight of what's going on the slab? Because your concrete will weigh about 85K lbs. although I can't imagine why you'd want to know what the concrete weighs.

Rebar: 6" slabs are a bit tricky because the ASTM standard are 2" and 3" to the ground and the surface. If you use 1/2" rebar in a grid pattern that's 1" diameter of rebar after its tied together. If you place chairs 3" off the ground, the rebar top will be 4" off the ground and 2" off the surface. I will guarantee that you will get what we call "ghosting". After the finish of the concrete, you will more than likely see where the rebar is, no matter how you screed, vibrate, trowel, whatever...

Rebar's main purpose is to prevent the slab from failing to a point where it will seperate. The rebar will hold it together better than mesh or fibermesh.

More important is that you cut the slab. 10'x10' cuts would be what most engineers recommend, but thats a bit of overkill.

I'm getting off subject here.

What are you using the slab for?? That may provide better understanding to answer your question. Is it a KingAir???
Old 03-19-2009, 09:41 AM
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If your doing this on your own make sure its on a day where the chance of rain is 0%. I learned the hard way when the concrete is on the truck its yours and we had to do my garage floor in a pooring rain. We had plastic but this so called isolated thunderstorm dumped rain on us for 6 hours. I guess you could say I have a non slip slab.
Old 03-19-2009, 09:45 AM
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yes on the rebar
Old 03-19-2009, 11:05 AM
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You guy's "crack me up!"

Kingair, you have a pm.

99.9% of the failures regarding slabs on grade are attributed to one or both of the following:
#1: The WWF was simply laid on the vapor barrier and not suspened within the concrete.
#2: Poor sub-base conditions. (settlement due to lack of compaction)

He's not building a runway!

Last edited by Just1more; 03-19-2009 at 11:36 AM.
Old 03-19-2009, 11:11 AM
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Just to continue where Mike left off, and maybe he can expand on this more, concrete will support phenomenal weight, even thin layers of concrete. I think what you need to be aware of is the substrate below the concrete. If it gives the concrete can flex and then it will crack. You will need to properly prep the ground, compress/compact layers of appropriate material/rock -- then you can think about how much rebar to put down.
Old 03-19-2009, 11:32 AM
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Originally Posted by Eyeball View Post
Just to continue where Mike left off, and maybe he can expand on this more, concrete will support phenomenal weight, even thin layers of concrete. I think what you need to be aware of is the substrate below the concrete. If it gives the concrete can flex and then it will crack. You will need to properly prep the ground, compress/compact layers of appropriate material/rock -- then you can think about how much rebar to put down.
Yeah, I guess where I was going with that is that the rebar is not the "end all" in a quality slab. Lots of factors, many of them MORE important than rebar, come into play.

Need more info.
Old 03-19-2009, 12:06 PM
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to most of the above comments.

Make sure that when you do use the rebar that you wire it together. Wire the cross pieces and wire the cross pieces to the uprights which hold the rebar off of the stone. Plus I would still use the fibermess for added bonus.
Old 03-19-2009, 01:11 PM
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I believe it would be better to use 6x6 10/10 welded wire mesh with visgueen(Will help keep moisture in concrete and help curing keep wet) and termite treat the soil.Just in case you decide to build on slab. Also, make sure you compact the soil and have a density of no less than 95 %Check Yellow page for testing companies inyour area. .4" slab with a thickened edge (perimeter)measuring 12"x 24" Mono footer with at least 1 foot in ground . Rebar 2 #5 should be enough for the thickened edge .6" slab is not needed. 3000psi concrete and don't add alot of water 6" slump max. But this is Florida.Up north they always do it different .
Old 03-19-2009, 01:36 PM
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Originally Posted by reel pleasure View Post
I believe it would be better to use 6x6 10/10 welded wire mesh with visgueen(Will help keep moisture in concrete and help curing keep wet) and termite treat the soil.Just in case you decide to build on slab. Also, make sure you compact the soil and have a density of no less than 95 %Check Yellow page for testing companies inyour area. .4" slab with a thickened edge (perimeter)measuring 12"x 24" Mono footer with at least 1 foot in ground . Rebar 2 #5 should be enough for the thickened edge .6" slab is not needed. 3000psi concrete and don't add alot of water 6" slump max. But this is Florida.Up north they always do it different .
I've built a lot of these over the years with a 100% success rate. Some building depts. balk at this simply because they do not know sh!t. You can always build your monolithic slab like the above design with an extended section of thicker concrete at the load points.

Lots of right ways of going here, some wrong ways of going..

The principles of concrete go deeper than you probably want, but for practicle purposes, we can certainly steer you correctly if you want. Wet cure is invaluable (we should do this 100% of the time, but don't);?

Of course, all you really asked about was rebar and here we are going on and on and on.....Want more???
Old 03-19-2009, 01:48 PM
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Yeah, if you just want to throw away $1200 for the steel!!
Old 03-19-2009, 01:50 PM
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Originally Posted by Just1more View Post
Yeah, if you just want to throw away $1200 for the steel!!
Old 03-19-2009, 02:10 PM
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I knew very little about concrete. I do know steel and concrete expand and contract at the same rate with changes in temp -- they were made for each other, a phenomenal combination as a building material. There is something about embedding steel cables stretched under tension that makes a concrete slab incredibly strong. No idea how it is done.
Old 03-19-2009, 02:46 PM
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Originally Posted by Just1more View Post
You guy's "crack me up!"

Kingair, you have a pm.

99.9% of the failures regarding slabs on grade are attributed to one or both of the following:
#1: The WWF was simply laid on the vapor barrier and not suspened within the concrete.
#2: Poor sub-base conditions. (settlement due to lack of compaction)

He's not building a runway!

Ding Ding Ding.

Old 03-19-2009, 03:04 PM
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This stinks, I just compiled a reply and when I went to post it my laptop went on strike! ugh.

Anyway, Kingair is this for your friends building?
Old 03-19-2009, 04:17 PM
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Originally Posted by Eyeball View Post
I knew very little about concrete. I do know steel and concrete expand and contract at the same rate with changes in temp -- they were made for each other, a phenomenal combination as a building material. There is something about embedding steel cables stretched under tension that makes a concrete slab incredibly strong. No idea how it is done.
For god sake, don't even bring up post tensioning!!
Old 03-19-2009, 04:29 PM
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Originally Posted by bsmit24 View Post
This stinks, I just compiled a reply and when I went to post it my laptop went on strike! ugh.

Anyway, Kingair is this for your friends building?
Yes, he is leaning towards a steel building for the cost and ability to "take" it with him. The call for a "gutter edge". It looks like 6X6X6 is the way to go.

Runway, now that was funny
Old 03-19-2009, 04:35 PM
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Originally Posted by kingair View Post
Yes, he is leaning towards a steel building for the cost and ability to "take" it with him. The call for a "gutter edge". It looks like 6X6X6 is the way to go.

Runway, now that was funny
A term I'm not familiar with. gutter edge.. Monolithic?? possibly?

steel buildings are another animal. Piers first, slab second. The steel building company has the detail on the slab. Now we can fight about how to get anchor bolts right
Old 03-19-2009, 04:42 PM
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Originally Posted by kingair View Post
Yes, he is leaning towards a steel building for the cost and ability to "take" it with him. The call for a "gutter edge". It looks like 6X6X6 is the way to go.

Runway, now that was funny
I just did a concrete parking lot and where the main drive plan for trash truck and delivery truck would drive we did it 6' + with 3000 psi concrete . On that job the Engineer said we could use fiber mesh instead of 6x6 10/10 welded wire mesh.If you are going to put in a steel building check with the manufacturer for the foundation sizes.Metal buildings flex with wind load etc. Depending on height etc.The building guys will know what to do.Good Luck and I will shut up now.Clarence

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