Re: concrete weight

[DaveIrons@aol.com]

Steve McColman, Vancouver Island wrote:

>Does anyone know how much concrete weighs per cubic foot???
                                 
I cannot give you a simple answer.  The weights I have read range
considerably 140, 145, 155 pounds per square foot.  One researcher
authoritatively pronounced that high strength concrete weights
5,020 pounds per square yard, that is 5,020 / 27 = 186.67 lb./sq. ft. 
The weight depends on the type of aggregate the amount of water,
the size of the air spaces, and the total weight of the sand and
cement.  To be safe, I would use the highest figure in doing
buoyancy calculations.  Before construction it would be wise to
measure and weigh a sample.  It is important that all components in
the concrete be measured, or better yet weighed.  If any of the
ingredients are wet it will change the water content.  The 
cement/water ratio is the factor that usually determines the ultimate
strength of the concrete.  It would be better for an undersea structure
to be more buoyant.  You can always add ballast.  Adding
buoyancy would be complex and expensive.

To make the matter more complicated, concrete absorbs more
water as pressure increases.  The amount of water absorbed can be
up to about 3%.  If the exterior was waterproofed with polymer and
the interior was kept dry by heating or air conditioning the concrete
would probably retain a consistent amount water.  

David Irons