[PSUBS-MAILIST] concrete

Sat Apr 12 22:28:26 EDT 2014

Amazing. You don't get any segregation of the aggregate?

Marc

On 4/13/2014 8:43 AM, hank pronk wrote:
> I would make a mould and pour the concrete.  We pump concrete into Styrofoam forms all the time and they are plumb full of re-bar.  The local batch plant and I experimented to find a perfect mix.  They deliver a 4in slump 35mpa mix with 3/8 aggregate and lots of flyash.  When the truck arrives we add plasticizer to make the mix into a 6in slump,and it flows like water and does not plug up the 2in line.  The plasticizer lasts for 20 min and does not weaken the mix like adding water would.  Building a sphere mold would be easy peezy.
> Hank
> --------------------------------------------
> On Sat, 4/12/14, Sean T. Stevenson <cast55 at telus.net> wrote:
>
>   Subject: Re: [PSUBS-MAILIST] concrete
>   To: "Personal Submersibles General Discussion" <personal_submersibles at psubs.org>
>   Received: Saturday, April 12, 2014, 8:06 PM
>
>   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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