perlite cement core

I've been investigating building both a house and a sailboat, and surprisingly, appear that lightweight concrete, e.g. perlite concrete, is a good solution.
The latest "foam sandwhich" looks like just a much more expensive (ok lighter, but not THAT lighter) way of doing the same thing.
I'm not taking "ferrocement", and the perlite core would not have ferro init,
just like poly foam doesn't either.

So what I'm a missing here? Have you seen the "concrete canoe" builds?

 

Do your weight study and get back to us. I think (okay, I know) you'll find that even light weight concrete is heavy, which will require considerable concessions in hull form. I'm not sure what foam core designs you've looked at, but a well designed foam core hull shell will be half the weight of a concrete hull, which is considerably different then

Lastly, you do realize that light weight concrete isn't self supporting and must have a reinforcement, which typically adds considerable complexity and weight to the shell. Naturally, a fair bit of engineering will be necessary to take advantage of the physical properties of each material employed, while attempting to compensate for their draw backs. So, what's your engineering background, because something like this can't be "winged" on the fly with a reasonable expectation of success.

I recently purchased a 65' sloop that is 23,000 pounds of foam and 'glass. Of this about 9,000 pounds is in a ballast casting, so the hull shell is quite light. Again, I'm not sure what foam cored designs you're looking at, but you can't come remotely close to this with lava rock (okay it's actually glass) and concrete.

 

a quick review shows perlite concrete can vary its density and strength depending on how much cement is used.

http://www.perlite.com/concretemixdesigns.PDF
indicates 22 lbs per cubic foot for 80 lb per square inch compressive strength,
and up to 36 lbs for 300.

This reference, http://www.rfcafe.com/references/general/balsa-weight-sheet.htm
Basla wood varies from 4 lbs per cubic foot for 75 lb per square inch compressive strength
to 12 lbs for 175.

http://www.uscomposites.com/foam.html
Expanded Urethane Foam is available in a few densities,
3 lbs for 70 lb/in to 16 lbs for 580 lb/in

So perlite concrete is significantly heavier than balsa or foam, roughly 4x to 8x heavier,
however, it seems to be about the same as Spruce or marine plywood.

If you look at what each costs, a 4x8x1/2 sheet of balsa or foam is in the hundreds of dollars, marine plywood, is what hundred or so? perlite cement is probably 1/10th.
So perhaps with a big enough boat the cost becomes a major consideration, e.g. $50k vs $500k, I think I could live with a 4x heavier boat.

 

Displacement can weigh in favor of other materials, but the term "strength" can mean many things and needs definition. You're not the first with this idea, but generally we look toward materials with a high weight to strength, stiffness, etc. in it's physical properties before consideration. Starting with a heavy material, forces your hand in several categories of the design perimeters. Of course cost is a consideration too, but mash potatoes as a composite core, many be economical, but this is only one of the many variables you must study.

I believe you're one of the very few that could tolerate this concession. Weight directly translates into build and operation costs. A heavier boat requires heavier gear, equipment, propulsion, etc., which naturally you have to build, install, purchase, repair, maintain and live with.

 

nimble,

I researched cement as a boat material several months ago to find that it has a lot of potential for advancement, however, it is not quite there as a general boat hull material. The chemistry of cement is complex, which creates challenges as well as opportunity.

You might find this thread of interest.
http://www.boatdesign.net/forums/materials/poraver-new-35743.html

~ Michael

 

Thank you michael, that was a great thread, just what I was hoping to find. It didn't have the word perlite in it, it didn't come up in a search.
Perlite seems to be similiar to Poraver. But I thought perlite was a closed cell structure? I've been experimenting with it. I have a piece I made soaking in water for 2 days, it is doesn't appear to be absorbing any, it is certainly still floating. If covered in expoxy it would seem to me the be similiar to marine plywood or other woods, but very inexpensive and moldable.
Have you pursued it? I'm making a model boat out of it currently. --jack

 

I believe Perlite is similar to Poraver. The Poraver starts as recycled glass, and then soaked in some caustic (alkaline) proprietary solution. The trick is that they get the glass to absorb water. When this water soaked glass is put in a high temp kiln, it explodes like popcorn. So, it is definitely not closed cell. It is highly spherical, thus lends itself to encapsulation which would form closed cells in a composite.

I keep the idea in mind and have several possible uses in mind. I have some of the Poraver and intend to do some experimentation with it, but not likely to be in the near future. So, I have not pursued it very far.