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Old 10-01-2010, 08:05 PM   #1
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Mixing Portland


Well I'm building a 16x22 shed built on piers. I'm mixing the concrete using 3, 2, 1, method...I can't get a straight answer from anyone on what kind of "gravel" to use. The package says use gravel not stone. Everyone looks at me crazy when I tell the this. to me gravel is like the 3/4" road gravel with the sand mixed in, where I look at stone is clear washed stone. Any advise???? Thx Fred

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Old 10-01-2010, 08:34 PM   #2
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Mixing Portland


I understand your confusion. Typically around here, "gravel" draws the assumption of a mix of stone and fines together. That's at least what I think of for gravel. But, that's definately not what you want here. Road gravel makes a great base, but contains too much "dirty" contaminents like clay, soil, etc... to be used in concrete.

What you need is #1 washed stone (pea stone if pouring thin) and torpedo sand, which is washed as well.

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Old 10-01-2010, 08:57 PM   #3
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Mixing Portland


Jomama is quite correct. All concrete is mixed using four fundamental ingredients, namely cement (typically Portland cement Type 2), sand, aggregate (what you are referring to as gravel), and water. The typical ratio is one part cement, two parts sand, and three parts aggregate, by volume, with the proper amount of water added to make the mix placeable, but the least amount necessary. The actual ratio can be varied depending on the required strength, and whether you are using a plasticizing agent.

Gravel is a badly defined term that means many different things to different people, and should not be used to describe aggregate in concrete. To a geotechnical engineer, gravel refers to a minimum particle size, typically about 1/4 inch in diameter or larger. However, as noted by others, gravel can mean a mix of materials to some people, bank run material to others, or it may not mean anything at all.

Why the package would tell you to use gravel not stone is beyond me. Typically around MA the aggregate is anywhere from 1/2 inch to 1 inch diameter crushed stone, washed to remove fines. You don't want any silt, clay or organic material in concrete. You can use almost any type of crushed stone, example limestone, sandstone, granite, even hard shale pieces in concrete, as long as it is clean and appropriately sized. And the more angular the better, round stone makes for a weaker concrete.
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Old 10-02-2010, 08:18 AM   #4
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Mixing Portland


Thanks guys..that's what I thought. I usually buy "all in one bags" but with a big project I thought i'd mix it myself

Jomama45, where you at in WI?

Last edited by Bucky Badger; 10-02-2010 at 08:20 AM.
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