I have a 10 ft. high 3 inch diameter pole which I filled with concrete (sand/topping mix). It took one and a half bags to fill the pipe.
I am doing this for a satellite dish antenna so the pole will be more stable and not "wiggle".
Basketball mounting poles also have this done I am told....
Question: All that concrete is basically enclosed in the pipe and there is just the opening at the top. How would the concrete cure? How long would it take to cure? (Just curious...)
First of all I doubt that filling the pipe with concrete will have much affect on the overall stiffness of the pole. The mount to the ground is the most critical element.
The concrete will harden just fine. It's a chemical reaction taking place, not drying in the typical sense. Remember concrete will set up underwater if need be.
Having done a lot of these (for satellite dishes, no less) yes, it does make a difference. Not to understate the need for a really good base.
IMHO it will setup better in the pipe as it won't dry. Drying cement won't cure properly anyway.
When they built Hoover Dam they put cooling pipes through it because of the heat buildup. When that section was set, they pumped the pipe full of concrete and sealed it so sure it will set up. And yes it will be stiffer. For a pipe to bend, a wall has to collapse a fraction to full collapse. Full of concrete, that action is curtailed.
Er... Bob, OP is referring to the construction material, concrete. You must have misunderstood, and somehow you went off talking about about your experience with Viagra.
-- (||) Nehmo (||)
A properly sized pole will be as stiff as it needs to be to get the job done.
I think the concrete stiffens the pole to better dampen out the vibrations that can occur when the ball hits the rim. Also, alot of the basketball pipes are multiple sections, so the concrete helps it act like one structure instead of 3 pieces of pipe. I think the concrete is a good idea for a satellite mount, as the wind can cause similar vibrations and bending. I think you did good.
To answer your question, It will take 28 days to reach full strength but just a few to hit 75%
I suspect it is more an issue of adding mass to the pole to change its resonant frequency than it is of adding stiffness.
Matt
IMHO, the response that alluded to the pole's mode of failure (collapse) being blocked by the cement is more the factor, but I'm sure resonence is a factor too.
Pouring concrete into a small diameter post seems a waste of effort to me. It's a heck of a lot easier to just get a bigger pole.
You've been reading that spam again, Bob.
Several years ago I filled a basketball pole with concrete. I put a 5/8" rebar down the center and then poured in the concrete. It was an improvement but it didn't make it as strong as I had imagined that it would. Concrete cures by chemical reaction so it doesn't matter if the mix is inside a pipe or under water - it will still cure.
Why don't you just admit you weren't thinking when you wrote your post, and move on. Lots of times I write stupid stuff too. Well, I'm afraid I don't write things *that* stupid, but you get the idea. If you try to defend a untenable position, it just gets worse.
It's really hard for me to understand how you could have said, "I doubt that filling the pipe with concrete will have much affect on the overall stiffness of the pole."
_Are you still standing by that statement?_
A pipe filled with concrete, a 3" pipe for this example, is much stronger (and stiffer, if that's the term we want to use). Think about it. For a pipe to fail, it has to deform. It can't deform easily if it's filled with concrete. It's hard even to dent such a pipe with a sledge hammer.
I could excuse you for not having experience with pipes filled with concrete. But, considering you write "PE, SE" whenever you write your name, and you advocate getting an engineer for almost everything, I can't excuse you for missing the mechanics of how concrete would make a pole stronger (or stiffer). In short, you're asking for it.
-- (||) Nehmo (||)
Yes I stand by the statement. You have assumed that the concrete remains uncracked. If that is the case then one could rightly argue (as you have) that the concrete helps make the pole stiffer. Once the concrete cracks then the pole is at least theoretically no stiffer than an unfilled pole. In reality this will depend on where the cracks in the concrete are located.
However, I should like to remind you that the first rule of concrete is, "Concrete always cracks."
As someone else pointed out: the concrete adds mass and this will change the natural period of vibration of the pole and may even give the apparent feeling that the pole is stiffer.
Now you tell me which is easier to install: a 3-inch pipe with a 3/16" wall that has to be filled with concrete into the 3" opening, or a 3-inch pile with a 5/16" wall that doesn't have to be filled with concrete. I know which I would choose.
The argument as you present it is kind of silly. Of course if the walls are thicker it will be stiffer, go all the way and say it is solid 3" rod. The question was, would a pipe filled full of concrete be stiffer and the answer is, yes of course. For a pipe to bend it has to deform slightly. If it is full of concrete, even cracked all over the place, it will resist deforming more. All the Wal-Mart stores have pipes in front of the doors to stop a car. They are filled with concrete to make them stiffer.
Ah, but there's the rub: the antenna is designed for a certain sized pole (usually 4") so you are not going ot get something bigger in there without a lot of work.
Stiffness and strength are two completely different concepts. Come back when you understand the difference.
Matt (not an SE yet, but really close now)
You also are confusing stiffness with strength. Buckling of the pipe is more of an issue with strength than with stiffness. Stiffness is relevant at all deflections from small to large, whereas, strength isn't much of an issue until the load and thus deflection is rather large. Bob is correct in saying that filling the pipe with concrete will have very little affect on its stiffness. I will increase the strength if the pipe is slender enough that buckling is the main failure mode.
Matt
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