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Pincushion
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278 Posts
I don't have an answer for you, but if this project is supporting a critical structure, I'd be careful. 100 lbs of concrete costs only $6-7. If you find a way, I might test it on a sidewalk or stepping stones or some other simple project.
 

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ke4sky
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190 Posts
Concrete is Science, Not Art

For concrete to have any strength it requires lots of sand and aggregate and just enough Portland Cement to hold it together. SakCrete and Quikcrete have the aggregate in it already. You can buy them at Lowes or Home Depot. If when you pour the pre-mix out, you cannot see lots of rock, add more 1/2 inch to 3/4 inch crushed stone to the mix. With some brands it is necessary to add more sand and rock to the mix because it is mostly cement.

If mixing concrete from scratch use 1/3 Portland cement, 1/3 sand and 1/3 gravel or crushed stone. You can use less cement and it's still OK. For outdoor cold weather applications reduce the cement ratio substantially in masonry applications where you are mortaring rock structures to get the mortar to expand and contract most closely with the rocks when temperature changes or it'll all break apart after a few winters.

Use the least amount of water required to get the mix to a "cake dough" consistancy. You do this by adding water to dry mix a bit at a time and mixing together with a rake or a hoe. Pouring dry mix and water into fence post holes and trying to mix in the hole is no good. There is a tendancy for premixes to separate in the bag, so you need to re-mix the entire bag before adding water. You will achieve a best results using a mortar pan, but if you don't have one use a 4x8 sheet of plywood as a clean surface to do the mixing.

For bigger jobs this link has some helpful information:

Concrete Mix Design - The Right Concrete Mix - The Concrete Network
 

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ke4sky
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190 Posts
Make little ones out of big ones.

How do you get aggregate ?
Go to Jackson, MS, go into any 7-11, buy bag of potato chips, pack of Lucky Strikes, Moon Pie and A Doctor Pepper.

Enter Interstate 10, merge into traffic and head eastbound, eating Moon Pie, wash down with Doctor Pepper, light up a Lucky, much on the chips and puff on the cigarette as you lob the Moon Pie wrapper out the car window.

Mississippi DPS trooper sees you throw the Moon Pie wrapper out the car window and pulls you over. Sees your New York license plate and runs it for points and warrants.

You get impatient waiting for the PW check and say something stupid.
Trooper charges you with littering and being a stupid Yankee white boy.

You go to jail awaiting trial for littering because they won't accept your AAA bail bond.

Magistrate Judge sentences you the next day to ten days on a road gang cleaning up leftover hurricane debris down in Gulfport. Good news is that you get all the grits and cornbread for breakfast and all the red beans and rice you can eat for lunch. Black eyed peas and ham hocks for supper Oh Boy!

You are issued the biggest hammer you ever saw and are pointed to this large piece of concrete debris the size of a small japanese car. Trooper says when you have that one broken up and put in the dump truck you can eat lunch.

So you MAKE AGGREGATE!
 

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Seeker of Knowledge
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30 Posts
Well Key4sky you have told them and given them the links can they learn if not what we have here is like the other day a failure to communicate
 

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Registered
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15 Posts
Go to Jackson, MS, go into any 7-11, buy bag of potato chips, pack of Lucky Strikes, Moon Pie and A Doctor Pepper.

Enter Interstate 10, merge into traffic and head eastbound, eating Moon Pie, wash down with Doctor Pepper, light up a Lucky, much on the chips and puff on the cigarette as you lob the Moon Pie wrapper out the car window.

Mississippi DPS trooper sees you throw the Moon Pie wrapper out the car window and pulls you over. Sees your New York license plate and runs it for points and warrants.

You get impatient waiting for the PW check and say something stupid.
Trooper charges you with littering and being a stupid Yankee white boy.

You go to jail awaiting trial for littering because they won't accept your AAA bail bond.

Magistrate Judge sentences you the next day to ten days on a road gang cleaning up leftover hurricane debris down in Gulfport. Good news is that you get all the grits and cornbread for breakfast and all the red beans and rice you can eat for lunch. Black eyed peas and ham hocks for supper Oh Boy!

You are issued the biggest hammer you ever saw and are pointed to this large piece of concrete debris the size of a small japanese car. Trooper says when you have that one broken up and put in the dump truck you can eat lunch.

So you MAKE AGGREGATE!
Best response ever; that made my day! :D
 

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Registered
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1,512 Posts
I buy ready mix and mix it up with a shovel in the wheelbarrow and add some stone and pour. Then I vibrate the pour so all the air bubble and air pockets come to the surface. Then again I only use very small amounts.

For big amounts you can get the truck to come. They even have a truck with a hose on a boom so you can pour directly into the spots you want from the truck.

If you use ready mix wear a mask when you open the bag. The dust will go everywhere and you don't want to breathe it in. That stuff is way bad for your lungs.
 

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performing monkey
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4,230 Posts
How Portland Cement is Made | Portland Cement Association (PCA)

There are eight types of Portland cements, each with special use and chemical requirement. Their manufacturing process, however, is essentially the same. Portland cement is a product of a kiln operation. The kiln is where ground raw materials undergo chemical transformation. Raw materials used in Portland cement manufacturing must contain the appropriate proportion of calcium oxide, silica, alumina, and iron oxide. Most of these necessary ingredients are usually contained in shale, dolomite, and limestone. When deficiencies in these ingredients are encountered in the rock normally used in cement production, additional silica and alumina are added. Since sand is a good source of silica, alumina, and iron oxides, it is often used in the production of Portland cement. Specifications for suitable sands include a minimum silica content of 80% (Leidel et al. 1994). Foundry by-products can also be used as a source of minerals. For example, slag is a source of aluminum oxide and magnesia and foundry sand is a source of silica. Also, the clay fraction of foundry sand is a source of iron and aluminum oxides.

According to the Portland cement industry, foundry sand can be beneficially reused in the manufacturing of Portland cement when it possesses the following properties: (1) silica content 80%, (2) Low alkali level, and (3) uniform particle size. In addition, large quantities of foundry sands must be available for it to be used by Portland cement manufacturers.

Foundry sand used in Portland cement manufacturing should be separated from other foundry by-products. Most Portland cement plants also require that core butts be ground to a uniform grain size.
 

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Premium Member
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1,733 Posts
I make my own concrete mix with a proportion as follows: one shovel full portland cement, 2 shovels of sand, and 3 shovels of crushed rock or aggregate( this can be from pea size 3/8" to 3/4" rock). Remember concrete is the combination of the three above and 'cement' is processed limestone, commonly called portland cement. You can add additional amount of portland cement to increase the strength, but not too much. I use the sieved decomposed granite from my shelter excavation to replace the sand component in the mix. There is a engineering link to support this: Properties of Concrete with Decomposed Granite as Fine Aggregate Science Links Japan | Properties of Concrete with Decomposed Granite as Fine Aggregate
 
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