# Looking for concrete recipe (ratios by weight not volume)

I'm looking for a concrete recipe that specifies the components (cement, sand, stone) in terms of weight - not volume. It's easier to pre-weigh the components instead of eye-balling them in a graduated bucket. Cement powder is especially hard (and messy) to measure by volume.
I'm mixing this in a 3 cf mixer, my past experience is that the largest batch I can mix is about 170 lbs worth of material.
I'm also wondering how strength is a function of the cement to stone ratio (again, in ratio terms of weight - not volume).
I've been trying to work backwards from the usual formula (1:2:3) by figuring out the density of the components. Based on my own measurements:
Dry "brick" sand: 106 lbs per cubic foot Crushed 1/2 stone (granite?): 97 lbs per cubic foot Crushed 3/4 stone (granite?): 103 lbs per cubic foot
I took my 3/4 stone bucket and filled it with water to see how much void-volume it had. The void volume was 37%. If I correct for voids, my stone has a density of 163 lbs per cubic foot (practically identical to the numbers I found for solid granite).
I haven't measured a sample of cement to get it's density. That's the real important variable I think. No real hard data on that on the net as far as I can find.
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Graduated bucket? Not for me-- I use a 2 gal bucket for my cement, a 4 gallon for the sand & 2-3's for the gravel. [actually 5's with paint marking the 3 gallon mark]
I can't imagine weighing everything for every batch.
Jim
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Dont forget, weigh the water
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ransley wrote:

I don't weigh the water, and here's why:
When I mix, I'll mix anywhere from 4 to 10 batches straight over a 1 to 3 hour period (4 batches for a pier, 10 batches for a verticle wall slab 10' long, 4' high).
I'll have 5 pre-weighed pails ready for each batch, and enough pails ready to do all the batches I need (these are .5 cf rectangular cat-litter pails).
One pail for the cement, 2 for stone and 2 for sand. Remember, these are not equal parts by volume. I have 23 lbs cement, 88 lbs stone and 58 lbs sand. For the piers, I'll go heavier on the cement and lighten up on the sand.
For the first batch, the mixer will be clean, and I could prepare a specially weighed batch of water for that batch. But once I pour and place that batch, I'll take a hose and spray down the lip and inside of the mixer (specifically, the blades) to loosen up what-ever caked cement has formed there).
This places an unknown / variable quantity of water in the mixer prior to adding the components of the next batch. About a gallon or two I would guess.
I then add the following, in this order:
100% of the stone 100% pigment
I let that mix for about 1 minute, let the pigment get distributed equally all over / into the stone. The stone / pigment will absorb most or all of the standing water that was in the mixer already, and I will probably give it a few extra shots of water, then I add
50% cement
Let that mix for a minute, then add
50% sand
Let that mix for a minute. Spray some water into it to keep it from caking up at the back of the mixer. Then add
25% - 40% cement and 25% sand
Let that mix for a few minutes. Spray more water.
At this point, I will throw in 1/2 shot-glass of Airex, and 2 shots of Eukon-37 (super-P). I found that adding the super-P later in the mixing cycle when more of the ingredients were in play was more effective than at the start of the mix cycle. I've also found that the mix needs to be a bit chunky for the super-P to do it's job really well.
The super-P turns the mix into a more runny consistency, perhaps a bit sloppy. At that point I might have a little more cement to add, and about 25% of the sand. This is enough to turn the mix from a bit sloppy into that "rolled-dough" consistency that I aim for.
If I end up with a mix that's too sloppy, I'll add extra cement and stone to thicken it up (I always have a stand-by bucket of stone and cement ready in case I need it).
There are times when I have to take a 3-foot long rebar and dig into the mixer while it's turning to loosen anything that's caking on the blades or at the back of the mixer. I'll do that instead of spraying water at it. My goal is to keep the mixing time down to an absolute minimum, including no downtime to clean the mixer between batches. This is why I spray water into mixer when and as much as I think it needs.
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You are making concrete, not performing brain surgery...
The only situation in which concrete ingredients would be measured by weight would be at a concrete plant when the machines are being used to produce a batch...
Seriously, by proportional volume is close enough for home repairs, you aren't submitting samples afterward for material strength testing...
~~ Evan
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I was kidding about the water, I dont weigh a mix and dont know why you are wasting time doing so, Volume is the way its done.
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Sounds like he is doing pre measured batches so he can just add water when needed. Do this bt volume in some 5 gal buckets would work as well.
Jimmie
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ransley wrote:

I don't understand why you people have a hangup about weighing the components.
It's very easy to fill these pails with sand and stone, and get weight bang-on right off the bat. A household digital weigh scale shows the weight to the closest 1 lb, and most times you just have to add or remove a scoop of sand or stone to get the desired weight.
I have 20 pails of stone, 20 pails of sand, 10 pails of cement, all pre-weighed and lined up and ready to go before I start mixing.
And what's more, I run the sand through a filter screen before putting them in pails - to remove any organic crud, leaves, and other unknown stuff that I don't want in my concrete. I also wash the stone using the mixer (with 10 mm wire screen covering the opening of the mixer). I get about one to two pails (about .5 to 1 cf) of silty-clay mud after washing a ton of 1/2 crushed stone. I don't need that mud in my concrete.
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Unless you totally screw up the proportions of components, most concrete that you custom mix will do the job just fine. A lot of people have a tendency to make it too watery, though, in my observances.
Steve
visit my blog at http://cabgbypasssurgery.com
A fool shows his annoyance at once, but a prudent man overlooks an insult.
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Who are "you people"?! Who has "a hangup"?!
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responding to http://www.homeownershub.com/maintenance/Looking-for-concrete-recipe-ratios-by-weight-not-volume-449048-.htm DA wrote: Joe Guy wrote:

Here is a link to a concrete proportioning chapter in a 95 y.o. document:
http://www.homeownershub.com/library/manual-training-course-in-concrete-1/17.htm
that basically says that proportioning by weight "is scientifically correct, but will seldom be used outside of laboratory practice on account of the equipment required to make the computation accurately"
Few pages down they give different proportions for different applications 1:2:3, 1:2:4, 1:2-1/2:4 etc.
You may just be able to pick the right volume ratios for the application without doing density tests on all your aggregates.
Cheers!
------------------------------------- /\_/\ ((@v@)) NIGHT ():::() OWL VV-VV
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Buy a copy of Pocket Ref by Thomas Glover at Ace, or similar store. A wonderful pocket book for DIYers. Tons of useful information, and it will answer your questions.
Steve
visit my blog at http://cabgbypasssurgery.com watch for the book
A fool shows his annoyance at once, but a prudent man overlooks an insult.
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From "Concrete and Masonry" By Richard Day sixth edition, MCMLXIX
High quality concrete should follow the formula: 26% fine aggregate (sand) 6% entrained air 16% water 42% coarse aggregate
In pounds for one cubic foot that works out to: 21 lbs of cement 10, 9, or 7.5 pounds of water depending on sand being (damp, wet, very wet) 46, 47, or 49 pounds of sand depending on sand being (damp, wet, very wet) 63 pounds of stone 2 tsp of air entrainment agent.
Never bothered with the air entrainment agent myself. The recipe makes a good mix. You can adjust as needed to match the size batch to your recipe.
--
Colbyt
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replying to Joe Guy, Kevin Kirkpatrick wrote: I use a shovel and get close enough for a good mix.
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