# How much does a 8" diameter ball of concrete/quikrete weigh?

• posted on November 11, 2006, 5:14 pm
For all you engineers/techs out there..... I want to mold a couple of concrete or quikrete balls about the size of a 8" or 10" cannon ball depending on the finished weight. If I can get a concrete conversion weight formula that would be super too.....
Also, is there any relatively cheap molding material that could be used that would HEAVIER?
-Thanks for any help!
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• posted on November 11, 2006, 5:40 pm
Why don't you get a bocce ball and make a couple of prototypes?
<%= Clinton Gallagher NET csgallagher AT metromilwaukee.com URL http://clintongallagher.metromilwaukee.com / MAP http://wikimapia.org/#yC038073&x=-88043838&z &l=0&m=h

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• posted on November 11, 2006, 5:43 pm

Well, let's see (fires up Excel...)
The formula for the volume of a sphere is 4/3 pi * (radius)^3. That's about 268 cubic inches for the 8" sphere, and 524 cubic inches for the 10" sphere.
I have seen weights for conrete listed from 2000lbs per cy to 4000lbs per cy. I think 2000 is too low; the local ready-mix plant claims 3000.
Assuming that concrete has a nominal weight of 3000 lbs per cubic yard, your 8" and 10" cannonballs would weigh about 17 lbs and 34 lbs respectively.
At 4000, your cannonballs would weigh 23 lbs and 45 lbs respectively.
-Mark
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• posted on November 11, 2006, 6:19 pm
Okay, you have your answer but I want to know what your going to do with them?
wrote:

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• posted on November 11, 2006, 9:01 pm
Mark wrote:

I would agree with the 23 & 45 lb answers ........but your other numbers seem a little low for normal weight concrete
"normal" weight concrete is about 140 to 150 pounds per ft^3 (3800 to 4000 lbs per cy)
Your local mix plant claims 3000 lbs per cy? That's down in the range of lightweight concretes. Maybe they were talking about compressive strengths
Are you sure you're not quoting compressive strengths (2000 to 4000 PSI) & the numbers just turn out close to density as well? The number I always use for weight calcs is 150 (lbs/ft^3), that might be a touch high but it's very close.
In any case the concrete balls will be ~23 & ~45 lbs
to determine weights of other sized balls
as Mark calc'd the volume
4/3 pi * radius ^3. (in^3) * 150 (lbs/ft^3) / 1728 (in^3/ft^3)
units cancel & you're left with lbs
be careful, don't blow yourself up
cheers Bob
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• posted on November 11, 2006, 9:18 pm
I KNEW I CAME TO THE RIGHT PLACE!!
Thanks to all you guys for the answers I was looking for...... And for Ralph...... I am seeing if I can make some inexpensive kettlebells (cast iron cannonball configurations with a handle) They basically are a different shaped dumbbell. They are selling for an outrageously stupid price as far as price to function is concerned. A 35 pounder sells for approx \$50-60 plus another \$30-40 for shipping...... Simply ridiculous! I am thinking that I might be able to mold/cast one out of concrete (inside plastic ball or something with a handle of some sort).... Of course I have been known to spend more than what I can buy it for.... :-) Wish I could find a cheap "more dense material than concrete" so I could make a smaller form but with the same weight..... ideas????? -Thanks again for taking time.
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• posted on November 11, 2006, 11:25 pm
wrote:

Just pick something below concrete on the periodic table...
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• posted on November 12, 2006, 1:30 am

Or if you want heavier, pick an appropriate isotope. Concrete 187 is heavier than the more common concrete 183. It has a few extra graveltons in the nucleus.
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• posted on November 12, 2006, 4:59 am
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The problem being that the equipment needed to separate 187 from 183 is very expensive. And the export of such equipment from the US is on various HLS watch lists...
("Graveltons" -- I like it!)
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• posted on November 13, 2006, 4:04 pm
ROTFLMAO.
Jay
On Sun, 12 Nov 2006 04:59:43 GMT, Karyudo

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• posted on November 13, 2006, 5:00 pm

Laugh if you want, but this is serious stuff. Kim Jong Il has imported thousands of square yards of military-grade hardware cloth for his centrifuges. He will be separating graveltons out of concrete 187 by the end of the year.
Maybe it won't seem so funny to you when Kim is peaing gravel on Seoul and Tokyo.
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• posted on November 12, 2006, 12:18 am
buck wrote:

Matt
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• posted on November 12, 2006, 3:57 pm

Sure, gold!

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• posted on November 12, 2006, 1:56 am
Concrete weighs +/- 150 lbs/cubic foot. This web site http://www.tesarta.com/www/resources/library/weights.html has the weight per cubic foot of other materials, so anything that weighs more than 150 lbs/cf would be good candidates for your use. I would point out that gold is over 1200 lbs/ cf but the price might be out of reach.
Is there a need for your shape to be round? I would think that you could make up some open wood cubes with broomstick or other handles. Fill with lead shot from a reloading store, steel ingots, whatever. You could adjust the quantity in the box or change the material to increase the weight as needed.
___________________________ Keep the whole world singing. . . . DanG

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• posted on November 12, 2006, 2:26 am
Buck, Concrete in this area weighs avbout 148 lbs per cubic foot. This is using aggegates, or stone that has a specific gravity of 2.65. This means that it weighs over 2.5 times the weight of water for a given volume. To increase the weight of a gi en volume of concrete, you need to use a heavier aggregate. Try lead shot to replace some of the sand, and a trap rock type of aggregate to raplace the larger rocks.
Avoid cement thay is air enytrained, as using this type of cement will cause the creation of small air bubbles that will equal approx. 6% of the volume and so reduce the weight of the sample. The use of silica fume and other pozzolans will increase the weight of the cement sample as well.
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• posted on November 12, 2006, 3:53 am
Thanks..... All good stuff. I guess I want them round rather than square cause then I will feel like I have conquered the complete clone. I guess I can add lead shot or gold but the cost goes up fast pretty fast..... especially the gold (yuk). I think lead shot is running about \$1/lb around here. I suppose if I could come up with something pretty heavy for the middle of the mold I could incase it in concrete and end up with a smaller sphere - maybe something out of steel or lead. Can you buy chunks of lead or steel, which would be cheaper than lead shot? Anybody got a "round" anvil? -My head hurts!

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• posted on November 12, 2006, 5:09 pm
buck wrote:

Round up an assortment of basketballs and the like, sized to suit your intended weight, that will serve as the form for your set of weights. Cut a 1.5" hole in the top. Mix up a bag of fiber-reinforced concrete mix. One bag will get you two weights or more.
For increased weight in the same volume add old nuts, bolts, washers, etc., the bigger the better, that litter everybody's shop and stir them into the concrete mix or place them in the ball form as you fill it with the concrete. Steel is about 3 times denser than concrete so the weight will add up quickly. I have a few buckets I know I'll never get around to sorting, much less using, and they're yours if you'll come get them. Soon. Seriously. I need the space. ;)
What were you planning on using for the handles? A bent piece of rebar would be nice, you'd need a pretty large bar - beyond your bending capabilities probably - to keep it comfortable with the larger weights. Use some Plastidip on the handles for color coding and to keep rust off of your hands. Or you could use old suitcase handles with bolts embedded in the concrete.
I don't think I'd be very concerned with small surface voids that wouldn't affect the strength. They'd probably look better if the surface was a little rough. So, don't make the mix too wet, and don't worry about trying to vibrate small bubbles out of the surface.
Cut off the rubber balls after a few days curing and let the weights set up for a month - the generally accepted period of time for the concrete to come to its full design strength.
You could paint them, but unless you liked the chipped paint look that's probably not the way to go. Staining them and waxing or sealing the surface would be interesting.
Sounds like a fun project, so start working up the sweat now. Enjoy!
R
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• posted on November 12, 2006, 5:52 pm

Or leave the basketball molds on them, and set one in the neighborhood basketball court and watch the fun as someone tries to steal it :-)
-- Dennis
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• posted on November 12, 2006, 6:24 pm
R .................. What great ideas. Thanks man!
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• posted on November 13, 2006, 9:59 am
On Sat, 11 Nov 2006 20:53:01 -0700, buck wrote:

Go to a tire store that sells a lot of tires... If you ask nice, they might give you the lead weights that they take off the old tires prior to balancing the new tires... Melt them down and make the balls out of lead... You'll still need some round stock steel for the handles though... Lead melts easily enough... Just get an old pot that you never want to use for food again and do it outside... The fumes can be hazardous, so rigging up a fresh air supply mask will make it safer...