[PSUBS-MAILIST] concrete

Sat Apr 12 22:27:07 EDT 2014

Why not? But again you're talking about pouring, which means you are 
limiting yourself to very thick walls. Okay for a homebrew bathyscaphe, 
I guess...

It would be fun to test this on a small scale, though...

Marc

On 4/13/2014 8:06 AM, Sean T. Stevenson wrote:
> I wasn't thinking about fine mesh as in the sort of backing you would
> use as a shotcrete / gunnite form, but rather a large (e.g. 3-4") wire
> mesh just to discourage cracking.  In any case, interesting about the
> reinforcement actually working against you.  I wouldn't have expected
> that, but then I know only enough about concrete to be dangerous.
> ;-)    I had another thought - could you use two concentric steel
> spheres of relatively light gauge, that could be spun without too much
> regard for perfect roundness or shape control, as forms for your
> concrete, that would remain in place after the pour - the outer one
> serving as impact protection, and the inner one serving as a base to
> weld your interior fixtures to?
>
> Sean
>
>
> On 2014-04-12 17:13, Marc de Piolenc wrote:
>> Fiber-reinforced mortar is very difficult to apply to reinforcement
>> consisting of fine mesh. It's been a subject of discussion on the
>> Ferrocement forum for some time - people wanting the benefit of
>> distributed fiber reinforcement while retaining the advantage of
>> multiple layers of mesh - namely the ability to dispense completely
>> with molds.
>>
>> As for rebar, it has only one function in a ferrocement structure,
>> namely giving the bare armature enough stiffness and strength to hold
>> the weight of the uncured mortar without distortion. In the final
>> structure it actually causes stress concentrations. The US Navy
>> compared FC structures with and without rebar years ago and the latter
>> won hands down in terms of structural efficiency and durability.
>>
>> If you have a mold - male or female - you don't need the rebar. Plain
>> mesh works just fine. Martin Iorns' laminated ferrocement technique
>> also works just fine. In that technique, instead of forcing mortar
>> into multiple layers of mesh, mesh and mortar layers are applied in
>> alternation. And if you have fiber-reinforced mortar and some way to
>> hold it in place while curing, you don't need mesh (though you can
>> still use it, with Iorns' technique)!
>>
>> But with FC we're not talking about pouring the matrix - the panels
>> are too thin to do that reliably, vibrator or no vibrator. Instead,
>> plastering technique has to be used. This is not entirely a bad thing,
>> since it allows half the mold to be dispensed with and gives the
>> applicators a good view of their work, so that they can catch voids
>> and sand pockets in the making and correct them.
>>
>> Marc
>>
>> On 4/12/2014 9:37 PM, Sean T. Stevenson wrote:
>>> Build a geodesic dome out of rebar, cover it in mesh, and pour a sphere
>>> of ultra high strength (no aggregate) fiber reinforced concrete around
>>> it, vibrating the hell out of it to eliminate bubbles. The shape might
>>> be a bit strange, given that your openings need be reinforced with a pad
>>> sufficent to replace the material missing in the opening, and your
>>> concrete shell is quite thick. You'd have to build a bunch of them,
>>> strain gauge them all, and lower them over the side until failure.
>>>
>>> Sean
>>>
>>>
>>>
>>> On April 12, 2014 6:40:53 AM MDT, hank pronk <hanker_20032000 at yahoo.ca>
>>> wrote:
>>>
>>>      Hi Sean,
>>>      Thank you for the calculation. That figure is quite interesting,
>>> considering it is only 30mpa.  I wonder if re-enforcement is
>>> beneficial given the sphere shape.
>>>      Imagine if you could figure out a safe way to make an opening in
>>> the sphere for ports and hatch, you could build a hull for under
>>> 1,000 dollars.  Amazing!
>>>      Hank
>>>
>>> ------------------------------------------------------------------------
>>>
>>>      On Fri, 4/11/14, Sean T. Stevenson <cast55 at telus.net> wrote:
>>>
>>>        Subject: Re: [PSUBS-MAILIST] concrete
>>>        To: "Personal Submersibles General Discussion"
>>> <personal_submersibles at psubs.org>
>>>        Received: Friday, April 11, 2014, 10:34 PM
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>            Hank,
>>>
>>>
>>>
>>>              There are countless varieties of concrete, all with
>>>        different
>>>              mechanical properties, so it is difficult to make an
>>>        effective
>>>              comparison, but just for fun, I ran your scenario
>>>        (6' OD, 4in
>>>
>>>      thick shell) with average material properties for
>>>        ordinary
>>>              concrete, and it turns out it's good to over 1000
>>>        fsw!  See below.
>>>
>>>
>>>
>>>              Sean
>
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