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How Thin Of A Concrete Pour Can Be?

10/30/2013 1:58 AM

I want to make the following permanent formwork

Can I make the concrete layer 48mm thick. Without vibrating table, which concrete mix should I use?

Thanks

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#1

Re: How thin of a concrete pour can be?

10/30/2013 2:56 AM

Does this sandwich stay together or you want to separate it? How big - in Length and Width is this formwork? Is it supposed to be load bearing? Horizontal? As drawn or can you also use it upside down?

If these stay together and it is load bearing with support at the ends, you better turn it upside down and use steel plate with high carbon content - otherwise the expansion will be to different. You might use a bonding plasticizer to have a better bond between steel and concrete.

You can make concrete as thick as you want. In principle as thin as the biggest size rock you will be using. You can make regular strength with 2 parts of sand and 1 cement.Rocks, when pebbles from a river bed can be added as long as you have a good fill left between the pebbles. More cement adds to the strength. Use as little water as possible. When products are used the concrete will fall in place easily without vibrating.

You'd better make water tight concrete when you want to use a mesh or mesh with a good coating to not let it rust and crack up the concrete after time.

Rusting steel can expand about up to a factor 7.

As usual, you give not a lot of info. I tried the best and with more info we can do the rest.

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#6
In reply to #1

Re: How thin of a concrete pour can be?

10/31/2013 1:47 AM

Not to be a wet blanket but you can not even in theory make functional concrete structures as thin as the thickest aggregate. See your ACI standards for aggregate sizing. Field rules of thumb are generally 3 times the thickness of your largest particles and that's pushing the envelope. For higher strength concretes you generally will have 3/5ths to 2/5ths or greater ration of rock to sand. ( more rock ) The greater your ability to reduce the void ratio and maintain the largest particle size, the less cement you need and the stronger your mix. Remember that more cement you use along with more sand, you increase your water demand and thus your shrinkage/ cracking probability. More cement isn't always stronger. New addmixtures can reduce water demand and maintain workability as well as provide water proofing and corrosion resistance. See BASF and WR Grace websites for more information. As you say though, without loading, sizing etc info, we can only offer so much advice.

Oh well.

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#9
In reply to #6

Re: How thin of a concrete pour can be?

10/31/2013 4:03 PM

Have you seen the drawing? Of course you need more thickness than the thickest aggregate or you end up with not being able to finish it neathly. But in this example it is possible and I am waiting for the OP to give more info. Concrete is supposed to be used on compression strength and the aggregates have to be that strong too. We have been producing deco panels in concrete (assorted pebbles) where afterwards the pebbles were accentuated by washing away the sand+ plus cement mixture. So with what the OP states, we, and unless you have more info, also you have to go with what we have.

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#2

Re: How thin of a concrete pour can be?

10/30/2013 6:00 AM

Try non-expanding grout as they use under base plates for erecting steel columns on foundations. Use a rust inhibiting primer on bottom side of steel plate.

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#3

Re: How thin of a concrete pour can be?

10/30/2013 8:30 AM

sure you can.......but, what is your application, what load are you expected to carry?

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#5
In reply to #3

Re: How thin of a concrete pour can be?

10/30/2013 11:13 PM

concrete canoe?

Just a thought....

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#4

Re: How Thin Of A Concrete Pour Can Be?

10/30/2013 10:34 PM

You will find all answers in this link:

http://www.buildingresearch.com.np/newfeatures.php

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#7

Re: How Thin Of A Concrete Pour Can Be?

10/31/2013 10:39 AM

At approx. 2" thick you are thinner than most all standard slabs. What are you trying to accomplish? Is it load bearing? How big? In my opinion I would say no! I wouldn't use a thickness less than 4" thick.

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#8
In reply to #7

Re: How Thin Of A Concrete Pour Can Be?

10/31/2013 10:50 AM

In the seventies research into ferro-cement demonstrated that thin sections, rel. heavily reinforced with wire netting without gravel at 5:1 sand to cement did act more or less exactly as reinf conc. did. with scaled down performance of course, also. Questions of rust dealt by 'high-strength mix' and 1 -2mm cover. Paul and Pama operating in Thailand published on the subject. I have ,still, copies of some-enough to get the gist,. Rajiva

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#10

Re: How Thin Of A Concrete Pour Can Be?

10/31/2013 4:59 PM

Read up on ferro-concrete. (for thin cement structures)

I'm a bit tied up now to find the links, but worth doing.

jt.

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#11

Re: How Thin Of A Concrete Pour Can Be?

11/12/2013 10:24 PM

Friend,

I have played Ping-Pong (table tennis) on a ferro-cement table approximately 4-5cm thick. It was at least 10 years old--that was about 25-30 years ago (it had been outdoors its entire life, in weather including ice, snow, heat...). In terms of mixes, what comes to my mind is the patented group of mixes from Lafarge, called Agilia. They are self-leveling and can fill very small voids, and are not supposed to separate as they spread. I have used them a couple times and they are really amazing, in terms of how they spread but still have a very low water content. Strengths can be specified to be quite high, so that should not be a problem.

always interesting, to be looking at questions with little response from the original poster. Hope you are still there. --John M.

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