Cement Pad Thickness for Water Tanks?

I'm installing two water tanks. One is an 8' Diameter 2500 Gallon tank and the other is a 12' Diameter 5000 Gallon tank. I'd like to set them both on a cement pad Maybe 2' wider then the tank itself.
How thick should I make the Pads?
Thanks, Scott<-
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It maybe matters a bit more on what the soil is that the pads rest on. The loads are not extreme. The small one will weigh over 20,000 # when full resting on a base of over 48 square feet. Load per SF = 400# plus. Most soil tables will allow 1000#/SF unless you're in a swamp.
I would pour 6" with #4 bar each way on 1 foot centers using 3,000 # concrete or better, air entrained if in a cold climate. Cure and do not load for at least 7 days, 28 preferred. ______________________________ Keep the whole world singing . . . . DanG (remove the sevens) snipped-for-privacy@7cox.net
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Thanks Dan!
I wanted a Pad as Its a much cleaner look and will give a place for the pump and pressure tank. I was hoping to not have to go to 8" and 4" seemed too small.
I think we are at least 28 days from filling tanks with water, so I should be pretty good there.
What do you mean by 3000# concrete? I've heard of 3 sack, 5 Sack, etc, though not in 3000# terms. We will be having someone come in and frame up a Driveway ramp to the Garage, its 13' wide by maybe 20' We were going to see if we could get the Pads all framed up by then so they can just pour the pads with the Driveway. Would the concrete they use for the Driveway be sufficient?
Thanks again!
Scott<-

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Scott Townsend wrote:

Scott-
By 3000# concrete, Dan means a 28 day compressive strength of 3000 pounds/ square inch (ie..... psi)
that's pretty decent stuff, most residential work is spec'd closer to 2000 psi so they don't need any inpsection....it's really difficult to make a mix that comes in less than 2500 psi
from http://www.charleston.net/stories/?newsID 460&section=garden

There are many different kinds of concrete, and the many combinations of rock (or gravel), sand and cement can result in various concrete strengths.
Concrete should not be bought based on the "number of sacks of cement" it contains. Five-sack concrete mix (five sacks of cement per cubic yard) is not always stronger than four-sack mix.
Buy concrete based on its "compressive strength," that is, how much pressure it will take to crush it. The higher the compressive strength, the stronger the concrete. Concrete rated 2,500 PSI is about standard, but 3,000 PSI is worth the extra cost. <<<<<
from http://www.trmca.org/solutions/faq19.htm

Concrete is not usually by the sack designation today - most concrete is sold by a strength designation such as 3000 psi (pounds per square inch). A four sack mix would be equivalent to about a 2500 psi mix, again substandard in my opinion. <<<<
Scott, take a look at the info at the links I posted.
Talk to your concrete supplier, let them know what you're building (flat work, a tank pad), have them spec a mix design & guarantee a compressive strength.
The cement content (per yard) & water cement ratio are probably the most important characteristics that drive the concrete strength. If you're going to tailgate the stuff (not pump) you can go with bigger large aggregate & less small agg. Bigger agg & less small agg means higher strength with less cement. The cement is just there to "glue" everything together; bigger large agg & less small agg means less surface to coat with glue.
Beyond mix design, curing conditions matter most.
cheers Bob
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Hey Bob!
Thank you for all the info and Links! I'll check them out!
regards, Scott<-

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One more thought on this. How is the tank supported? If it is evenly distributed with a flat bottom over a large area, that is the consideration. If, however, the tank is supported by four feet, you may save money and get a better job with a different approach. I'd pour a deep footing with sonotubes where the feet are, then pour a standard 4" slab around them for the rest of the hardware.
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It is a flat bottom tank, so the entire bottom of the tank would be on the pad.
Thanks!
Scott<-

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That being the case, 1" would do it as would a couple inches of gravel but I wouldn't pour less than the standard 3.5" (2 x 4 form) and I do like steel in everything but with even weight distribution, I doubt it is going anyplace.
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Hi Scott,
I did a pad last year for my 2500 gallon water tank; 6" thick with rebar on 12" spacing both ways. Also put in 12" deep footer around the perimeter (mine is enclosed with walls and roof). Absolutely no problems with cracking (yet)
Chris
Scott Townsend wrote:

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snipped-for-privacy@gmail.com wrote:

Well, just wait. The rule is that at exactly 23 months, that slab will disintegrate into tiny marble sized pieces, the rebar will twist in the wind and the tank will slide over to a 45 degree angle leaking contents out of the top. That's just how it is.
Kidding of course :)
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