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#11630 - 09/02/07 08:18 PM Accurate cured concrete weight estimates?
sixleggedinsect Offline
Junior Member

Registered: 09/02/07
Posts: 1
Howdy. I need to make an object i can hang that weighs somewhere between 145 and 160 pounds. i was planning on pouring concrete in a 5 gallon bucket with rebar attachment points embedded.

various sites ive seen make it sound like this would be between 1.5 - 1.9 bags of 80# ready mix, or just over a cubic foot of concrete. the various sites dont match up all that well, though.

any ideas about how to get within that range? when sites refer to using a certain volume of concrete, are they referring to pre-mix, or after the water has been added? when concrete is cured, does it lose all its added-water weight?

for example: if i wanted a 160# weight, could i just mix up two full bags, and when the concrete has cured it will be back to 160#s? or will it weight a lot more?

when you add water to ready-mix concrete, how much does the volume change? ie: if i fill a bucket 75% full with concrete, and add water until it is at the correct ratio, any guesses as to how full will the bucket be?

finally- (and i do hope someone has the patience to get this far..) what is the best way to do this bucket-form project? does it need more curing time? less water? anything special i should think about?

many many thanks,
anthony

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#11634 - 09/03/07 10:01 AM Re: Accurate cured concrete weight estimates? [Re: sixleggedinsect]
Rojellio Offline
Member

Registered: 06/09/05
Posts: 708
Loc: Grand Junction Colorado
Quote:
when sites refer to using a certain volume of concrete, are they referring to pre-mix, or after the water has been added?


The weight of concrete is an approximate theoretical weight. The only way to prove that theory on any given batch is to weigh it after curing.

To the best of my knowledge it includes water weight. The theoretical cured weight of an 80# bag of concrete sack mix including water would be about 85 lbs. OTOH if there is way too much water in the mix, you will loose some to bleed water.

I would go with an 80# and 60# bag of quickcrete. With just enough water to make the mix plastic these two bags will put you right in the target area of 148 lbs per cubic foot. You will loose some concrete to the mixing process, either in the wheelbarrow or mixer.

Another way to do the mix would be with 2qty 80# bags of quickcrete, then weigh the 5 gallon bucket while filling it with concrete.

The best way to add water to mixer or wheelbarrow is with a Dramm "fogg-it" fogg nozzle. The 1 gpm or 1/2 gpm nozzle would be ideal. Not only will the water be introduced at a controlled rate, but the fogg/mist will hit all exposed cement particles at once rather than sloshing some water into one spot.

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#11649 - 09/06/07 12:04 PM Re: Accurate cured concrete weight estimates? [Re: Rojellio]
RWCconcrete Offline
Member

Registered: 09/06/07
Posts: 21
Regular weight concrete weighs 140-150 lbs. per cubic foot; therefore, if you made a box of dimensions 1'x1'x1' and poured your concrete into it, you'd get about that weight after it cured.

For your bucket do the same thing, assuming a cylinder for the bucket, take pi x radius x height = volume. You want the volume to be approximately 1 cubic foot. When you find the right height, make a mark and fill it with concrete to that mark. Then you don't have to weigh anything.

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#11658 - 09/06/07 12:55 PM Re: Accurate cured concrete weight estimates? [Re: RWCconcrete]
RWCconcrete Offline
Member

Registered: 09/06/07
Posts: 21
Addenda: that's "radius squared".

Oops.

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