Concept in concrete

I need to pour three anchors (I'll call them that) for a 32' long x 12" wide lean to metal awning. The frame will be made of 14 ga. 8" and 6" C purlin materials. Covered by 26ga. steel sheets. Corners 3" x 3" x .120" posts. Three posts will go on an existing slab, the top purlin will be attatched to the house. At the downhill edge, I will have the three posts that Ill need anchoring.
I have caliche there. I do not want to spend the time and money jackhammering out caliche. So, I want to form and pour concrete. I would like to make it square, and to a dimension that will allow it to be tiled in most any configuration of 6" multiples.
In your expert estimation, how much mass do you think I would need to act as these anchors? I was thinking of 12 cubic feet, a 3' square with a 3' tall square or Snotube column coming up the steel to stave off rust at ground level.
They will also be two staged, that is a small cube sitting on top of a larger one, or a Sonotube going down into a larger diameter base. I really don't want them to come up too high, so will probably go with the two step idea. It will have rebar throughout, and the rebar will be welded to the legs in the concrete.
My Pocket Ref does not give approximate weight of dried concrete per cubic foot.
TIA
Steve
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~150 lbs/ cubic ft
Some comments.......
wind uplift forces on your awning
I'm not a big fan of welding rebar...usually too much carbon.
How about "after pour" drilled & epoxied studs or threaded inserts
cheers Bob
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wrote:

It's all in the planning stage right now, and I did find the 150# figure in my pocket ref when looking under weight of materials. 1800# (12 x 150) x 3 should hold down most anything. I do like your idea about the bolting, though. I could even use threaded J bolts on a plate, and that would give a little adjustment. Then build a cover for the base/bolt assembly.
I was pleasantly surprised today when my steel man came back with a price of HALF what I had figured, and that's cut and delivered on site.
Steve
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About 2/3 cu. ft. per 80 lb. premixed concrete bag. So its about 120 lb. / cu. ft.
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Actually the number commonly used for estimating reinforced concrete weight is typically 150 lbs/ cubic ft. It's slightly on the high side but that's pretty much what people use for "normal weight" concrete.
Your number of 120 is approaching the range of light weight concrete & is low for "normal weight" concrtete for two reasons......
an 80 lb bag only yields .6 cu ft (per mfr's info) & you forgot the water
http://www.quickrete.com/PDFs/SPEC_DATA-ConcreteMix.pdf
the "real" number is probably closer to 140 but 150 is what everyone I know uses.
cheers Bob
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will a gasoline post hole digger get thru caliche? just curious i am from pittsburgh theres none around here. might be easier than jackhammering
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On Thu, 28 Feb 2008 04:58:20 -0800 (PST), " snipped-for-privacy@aol.com"

No! Now way. Caliche (mineral) can add 10-20k for a pool install in our desert. Not easy work and very expensive to those not familiar. Big machines!
The cost is what is below ground ...trying to get through this stuff.
.. cite: http://en.wikipedia.org/wiki/Caliche_%28mineral%29
-- Oren
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