Re: Concrete reinforcement

[DaveIrons@aol.com]

> I would recommend that test samples should be made and tested to
>destruction.

>Concrete is certainly cheap enough to test out a few hulls.

Studies show that testing a scale model can accurately predict the performance
of a full sized hull within a 9% margin of error.  The scale model tests can
be
considered conservative.  The scale models had flaws in them that would not
occur in a full sized hull.  A full sized hull could be cast to more precise
hull
thickness and out of roundness.  

The test samples I was referring to, would be samples taken from each batch
of concrete.  The samples would later be tested at a lab.  The device they use
at the lab does not look real scientific.  A hydraulic ram compresses the
sample until it fails.  I would not be difficult to build a test rig.  An
independent lab test would give the test results more validity.  Taking
samples
would cost little.  The test could be done only if the need arises. 

> Adding polymer (PIC) in place of water produces a 20,000 psi pressure
> hull.  The depth rating increases to 4,000 feet.

>Sorry, what hull thickness?  I think you mentioned that in a previous post. 
>Must have missed it.

That would depend on the diameter of the hull
A slightly buoyant submersible would could have a hull thickness of . 08 the
outside diameter of the hull.  Example.  A five foot diameter hull = 4.8 inch
hull thickness.  A two meter diameter hull = 16 cm.  Most of the pressure
hulls
studied were slightly buoyant.  Most were thinner than . 08 so the numbers are
a little conservative.

> Polymer-Impregnated Concrete (PIC) has a tensile strength of 1,600 psi.
> The durability of PIC is better than concrete.  It is more resistant to
> chemical attack and it is impermeable to water.

>How much more expensive is it?

About twice the cost of concrete.  
The studies refer to polymers in generic terms brand names are not mentioned. 
I have worked with Acryl 60.  It cost $80 for five gallons.  A half gallon
treats
one 80 pound bag of cement.  A six bag per yard mix would cost about $50
per yard.  The cost would be more if smaller aggregate is used and less if
large
aggregate is used.  I'll need to do more research before recommending any
brand of polymer.


> Although concrete is waterproof prolonged immersion in water saturates
> the concrete and reduces the strength by about 10%.

>I wonder if there would be any seawater weeping through the inner wall . . .

In the Seacon project no water penetrated into the interior of the hull.  The
test
was conducted for 314 days at 600 feet.  A tiny leak was found to be the
result
of a hull penetration.  Concrete spheres have been left in the ocean for up to
eleven years and the interior remained water free.

> Adding polymer (PIC) in place of water produces a 20,000 psi pressure
> hull.  The depth rating increases to 4,000 feet.

>Sorry, what hull thickness?  I think you mentioned that in a previous post. 
>Must have missed it.

That would depend on the diameter of the hull.  A slightly buoyant
submersible would could have a hull thickness of . 08  the outside diameter of
the hull.  Example:  A five foot diameter hull: 60" X .08= 4.8 inch hull
thickness.  A two meter diameter hull=200cm X. 08 = 16 cm.  Most of the
pressure hulls studied were slightly buoyant.  Most were thinner than . 08 so
the numbers are conservative.  

>I wondered how you would apply pre-tensioning.

Do you mean how would I pretension the cables or why use pretensioned
cables?

I'll answer the first question: That would depend on the size of the steel
cables.  Smaller cables spaced closer together would more effectively prevent
cracking.  Smaller cables would also produce a smoother hull with less drag. 
Small cables could be pulled tight using a ratchet cable puller.  Pairs of
cable
on opposite sides would be pulled and welded into place.  The hydraulic jack
method is similar to how it is done in mass produced pretensioned concrete. 
The moral is that there are many ways of accomplishing a task.  At viewport
openings or other hull penetrations a steel ring can be imbedded in the
concrete.  The cable would be welded on each side of the opening and the
cable inside the opening cut away.

David Irons