concrete parts by volume vs weight


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Old 06-24-07, 03:28 PM
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Thumbs down concrete parts by volume vs weight

A push in the right direction is all I ask. I understand the basics of mixing concrete, but I'm floundering as I view the UNITS OF MEASUREMENT. Cement, sand, gravel by volume = 1:2:3. I got this part. Cement & water by weight = 2:1. Now, here's where my mind refuses to wrap itself around the concept: 1 cubic foot of water weighs 62.4 lbs, whereas 1 cubic foot of cement weighs 94 lbs, yet I'm using a 1 gallon plastic pail to measure the Cement, sand, gravel by volume in a 1:2:3 ratio. SO, I have 6 volumetric gallons of dry ingredients - can anyone tell me the volumetric equivalent of the water (in the same 1 gallon container)?
 
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Old 06-24-07, 05:29 PM
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The amount of water required is not volumetric.
 
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Old 06-24-07, 05:57 PM
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concrete parts by volume vs weight

You use as little water as necessary to make the concrete placeable and workable. It is not a part of the "recipe".
 
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Old 06-24-07, 07:47 PM
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To convert the appropriate amount of water (measured by weight) to a determined volume. OP is trying to calculate the volume of water needed by first determining the weight, then converting it to volume. Easy to do.

1 gal of water is 8.345404 lbs and a cubic foot of water is 62.42796 lbs.

other needed conversion factors

1 gallon [US, liquid] = 0.133680556 cubic foot or conversely:

1 cubic foot = 7.480519481 gallon [US, liquid]

1 gallon [US, dry] = 0.155557003 cubic foot or conversely:

1 cubic foot = 6.428511597 gallon [US, dry]

so by OP's number of 94 lbs per cubic foot of cement and a 2:1 ratio of cement to water by weight and accepting OPs number of 6 gallons of dry (not sure but do you mean to use the cement only or the cement/sand/gravel mixture here. You seem to use both in a somewhat confusing manner) would be 87.75 lbs. So if you need half that weight in water, you would be 43.86 lbs of water which should be 5.25 gallons of water.

Now after all that calculating, I would still listen to the other guys since they work with this stuff for a living (or at least I believe so)
 
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Old 06-24-07, 08:17 PM
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concrete parts by volume vs weight

Proportioning concrete by the volume volume is just an easy approximation for average quality concrete and is not used for any serious conrete use because the the vagueness (bulking of materials, gradtion and moisture content). It is fine for DIY use where controls are not necessary.

I really do not know where the 2:1 ratio for cement and water comes from except that may have been another "rule of thumb" from the past and always was on a weight ratio and not a volume ratio. Admixtures have made that sort of thing passe'.

It sounds like someone is trying to make something very simple too complicated without having any real controls or knowledge of the effect of other factors that have more effect.

The old volume ratios are adequate. Use only as much water as you have to use. Extra water does more harm than good.

I will not bring up the question of admixtures since that only fuels the confusion for the DIYer. If you want good concrete, call the ready mix supplier and tell them what you are building.
 
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Old 06-24-07, 09:55 PM
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Along with the other posters, I'll concure, just add water while mixing to get the consistency you need to make the mix workable. Chances are really good that if you just measure it out, you are going to end up with to much water, and the only cure for that is to add more concrete.

When mixing bagged concrete, I pour a bag or two into a wheelbarrow, get out my mixing hoe and start adding water while mixing. Add water, mix, add water, mix until I've got the mix I need for that application. I can only describe the result as a very thick cake batter that looks like it needs more liquid (plaster of paris is another good example). "Plastic like consistency" is what you usually hear, but who's seen liquid plastic?
 
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Old 06-25-07, 09:47 AM
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Cement block wall repair

Hi,
I have a cement block wall, which is corroded by the time. It has whole in them. How can I repair it.
Thx
 
 

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