How do I make concrete float?

Question

We have to make some sort of structure in physics float. We can use whatever mold or anything inside it. It has to be concrete though. How do we do it?

Answer 1

You can mix in bits of styrofoam (like the packaging peanut shape ones) until its average density becomes less than that of water.
Or, you can make your concrete structure shaped in such a way as it displaces more water than its volume, like a boat hull. There are actually boats hull made in this way.

Answer 2

A flat barge constructed of almost anything will float if the sides are deep enough. Find weight per cu ft of concrete, calculate the cu ft of water that is displaced by the amount of concrete you intend to use, then plan and build your barge. It will float. Hint -- the bottom should be wide and long so that the sides do not need to be too high (or deep). Practically I suggest the following:
Materials: One bag of ready mix mortar, two plastic storage bins about 20" x 10" x 4"(one should be smaller than the other), a piece of screen wire about 18" x 30". Place the screen wire in the bottom of the larger bin so that it comes up the sides and ends to the top of the bin. Pour in about an inch of stiff (not a lot of water)prepared ready mix and smear up the sides, put the smaller bin centered into the other one and weight it down, pour more ready mix between the sides. Let this setup for a couple of days. Remove the bins. {If they don't come off easily, cut them off. Putting hot water in a tub and placing the whole thing into this bath should cause the outer one to release.} The screen wire should make this assembly durable enough to handle. My quick calculations indicate this will float well if the bottom and sides are only 1" thick. Good luck. I don't have much time to elaborate. Hope you understand.
PS All boats float according to how much water their hulls displace. That is what this exercise is demonstrating to you.

Answer 3

There are two solutions to this problem.

If you want to make the concrete float in water then you have to lower it's density. The average density of concrete is 2.3g/cm3 and water 1g/cm3. This can be done by constructing the concrete in such a way that it contains enough air to allow it to float. Producing a concrete sphere would give you the most air for the least amount of concrete.

Your question doesn't specifically say it has to float in water. So another solution would be to use a liquid with a higher density than that of concrete. Mercury with an average density of 13g/cm3 more than fits the bill. You wouldn't have to do anything to the concrete to get it to float, though this solution is hazardous.

Answer 4

If the piece has to be "solid"-
Add fine powdered aluminum. It will disassociate the water into hydrogen and oxygen gas thus making bubbles and light concrete (Aerated concrete). Careful to work in a unconfined space and not near any source of combustion. It helps to add soap to the mixture.

How long does it have to float? The pore structure should be closed and the concrete microstructure very fine.

Answer 5

If you make it so there is an air bubble is side the concrete then it will float. You have to make the overall density of the structure less then the desity of water. So in order to see the minimum size of the air bubble you can use the equation below.

{Density of Air*Volume of air + Density of concrete*Volume of concrete}/total volume

Answer 6

By putting it on a ship ( by the way it is made out of steel) SO the buyoncy is the key reason Read about buyoncy

Answer 7

concrete boats float.

Answer 8

lots of balloons