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04072006, 07:48 PM  #1 
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Concrete Columns?
I am building a deck using 8" sonatube 4 ft deep. I need to figure out how many 80lb bags of ready mix concrete to buy to fill each tube.Can you tell me how I determine this number. There are 12 tubes to be filled all together. Thank you.

04072006, 08:46 PM  #2 
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Concrete Columns?
Well the formula for the area of a circle is:
Pi X radius squared which in your case would be, radius 4" or .34 squared = .1156 pi = (3.142) 3.142 X .1156 =.3632 .3636 X 4' of depth of tube = 1.45 cubic feet per tube 1.45 cubic feet per tube X 12 tubes = 17.43 cubic feet. How many cubic feet are in an 80 lb. bag of sacrete I have no clue, but it should be listed on the bag. If I were you I would get a few extra bags, it is surpising how much you can loose on the ground when filling those things. Tom Somebody check my math please. I have been known to order way too much, and way too little concrete. Just ask the dispacthers. 
04072006, 08:59 PM  #3 
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Concrete Columns?
That sounds pretty good to me, but rounding your #'s off makes it a little off. I came up with 16.75404 cu. ft. I Would just say that it takes 2.4 bags per pier x12=28.8 bags. Plus whatever waste you want to account for.....
Bob 
04072006, 09:21 PM  #4 
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Concrete Columns?
Too many decimal points for me Bob. :o
Thanks for the verification. Tom 
04082006, 07:08 AM  #5 
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Concrete Columns?
thanks for you help, I will buy extra for waste like you said. What a great forum.

04082006, 07:33 AM  #6 
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Concrete Columns?
after reading your reply, I was wondering why you used a radius of 4" wouldnt I use 8"? since the tubes are 8". I am not questioning your knowledge, just want to be able to figure this out on my own if needed. Thank you again for your help...

04082006, 10:56 AM  #7 
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Concrete Columns?
8" is the diameter of the tube, 1/2 of the diameter would be the radius, 4"
Tom 
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