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Concrete 102 "Mixtures"

Posted by Jim -ATS on April 20th, 2000 11:32 AM
In reply to Help on mixing Concrete by Sam on April 19th, 2000 09:04 PM [Go to top of thread]

Moderator Post (s) for this thread:
> Hey David.....your slab by doug seibert on 05/29/2006

Do you already own the materials? I would recommend just using premix in a bag, and renting a mixer. Your water content should be ONLY enough to get the mix to pour, and thatís it. Soupy concrete is weak.

You need to consider adding rebar to the bottom of your wall, and probably going with two pours, one for the footing of your wall, and one for the wall itself. I am wondering why you have to pour so much concrete for a deck, instead of just pouring post footers (a 1í hole, 3-4í deep.), but itís your design, not mine.

At any rate, for basic structural concrete with the materials you describe, you could go for the following mix:

Percentages are given by absolute VOLUME, so measure by cups or pints or quarts or whatever.

Cement 15%

Water 20%

Sand 35%

Gravel 30%

Do not overload your mixer, and keep in mind that sand carries a lot of water, and the amount will vary depending on what part of the pile you take it from. You must pour your entire wall in one session, or risk creating cold joints. (these are bad). You should have rebar in the wall, both vertical and horizontal. Make sure the rebar does not impede your gravel, and that the gravel is not too big to fill the spaces. Use a spare piece of rebar to work the mix into the forms by using a plunging motion after every pour.

Over build your forms, and make sure they are watertight, or you will lose cement out the gaps leaving weak concrete at the leak points.

Good luck!

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