Concrete Submarines??!

[coquina]

Uhmmm.... I don't think concrete is the ideal material to subject to millions of tons of water pressure... even if the information I got came from a site for concrete sealer, the sealer only coats the outside - it can't penetrate all the way through the material.

 

http://www.concretesealer.com/porosity.htm

 

Porosity

 

Webster's New World Dictionary defines porosity as, "Being full of pores, or tiny holes, through which fluids, air, or light may pass."

 

Normally, concrete is a mixture of four basic ingredients: sand, gravel, cement, and water. In the mixing process, as certain amount of air is mixed into the concrete. The water and air take up space inside the concrete even after the concrete is poured in place and during the early stage of setting.

 

When the concrete is "worked" in place and begins to polymerize, the heavier ingredients have a tendency to settle to the bottom and the lighter ingredients have a tendency to float to the top. Water being the lightest of the four basic ingredients, floats to the top and is evaporated away, or is squeezed out the sides or bottom. As the water is squeezed out, it moves in all directions. Water, being a solid in that it takes up space, leaves millions of small rivulets and pores crisscrossed in all directions. As the air escapes, it has the same effect.

 

These small rivulets or hollow spaces tie together creating what we call pores. Quite often the pores create hairline cracks inside the concrete, weakening the concrete. As the capillary action of the concrete draws water up into the concrete, or rain hits the side of a concrete wall, or water hydrology bears against a concrete basement wall, the water travels via these pores through the concrete.

 

The pores are interwoven and interconnected, thus allowing a slow seepage of water through the concrete. The denser the concrete, the tighter the pores, and less water is allowed to pass through.

 

A pad of concrete may resist 80-90% of the water trying to soak through the concrete. For this reason, a concrete sealant need not resist 100% absorption of water through the concrete. If the sealant can resist only the percentage which the concrete itself can't resist, then the sealant has effectively sealed the concrete pad.

[jsatan]

From what I know the sub you are talking about wouldn’t be too good at detecting anything, as there’s a band of different water density which reflects the sonar signal back, just like light refraction on hot air(e.g. tarmac)

[atinymonkey]

Okay' date=' I'd like to know: Why does it have to be able to expand and contract?

[/quote']

 

Go inflate a balloon, and push it to the bottom of a bath of water. Watch what happens.

 

Or, read a paper on the effect of pressure on concrete:-

 

http://www.brebookshop.com/details.jsp?id=30315

 

All in all, it's not a smart idea.