[PSUBS-MAILIST] concrete

[Sean T. Stevenson]

I ran that same 6' diameter 4" shell, but using an ultra high-performace
concrete with no aggregate, but with steel fiber reinforcement.  Working
pressure came out to more than 1700 m.  That said, while the compressive
strength of this stuff is 160 MPa, the tensile is only 8 MPa, so you
absolutely have to avoid putting this stuff in tension.  Sphere may not
be an issue, but a cylindrical hull would probably require some sort of
pretensioned reinforcement.  Results:




On 2014-04-12 21:52, Marc de Piolenc wrote:
> I had forgotten about the lubricant/plasticizer properties of fly ash.
>
> Marc
>
> On 4/13/2014 10:55 AM, hank pronk wrote:
>> Marc,
>> We don't get segregation at all, when pumping it we fill the wall and
>> then let it flow, I call it "ride the wave"
>> Also pumping the concrete helps hold the concrete together, it stays
>> in a cylinder shape until it hits the wave. We must use fly ash
>> because the aggregate and sand is washed so well there are no fines
>> left.  The jagged sand won't flow through the hose.  Fly ash is like
>> little ball bearings and makes it flow through the hose.  These are
>> the things that make me think a mold  is the way to go.  Four inches
>> wall thickness would be a breeze for this mix.
>> That makes sense that the rock is a cheap filler.  I would still use
>> the pea gravel mix, I have made a test panel and I drove my bob-cat
>> over a 2in thick 4by4 panel with no breakage.  I know, very
>> scientific .lol
>>
>> Hank
>> --------------------------------------------
>> On Sat, 4/12/14, Marc de Piolenc <piolenc at archivale.com> wrote:
>>
>>   Subject: Re: [PSUBS-MAILIST] concrete
>>   To: personal_submersibles at psubs.org
>>   Received: Saturday, April 12, 2014, 10:40 PM
>>
>>   Actually, all else being equal, using
>>   only fine aggregate (sand) will give a stronger mix. Coarse
>>   aggregate is needed mainly to make the mix affordable - as
>>   bulk filler, in other words - and also for decorative effect
>>   in some applications where the fresh concrete is brushed to
>>   show off the aggregate.
>>
>>   You have to be careful, in very high-strength applications,
>>   to make sure that the coarse aggregate is chemically inert
>>   with respect to the cement matrix. Some siliceous aggregate
>>   will weaken the concrete in the long term by reacting slowly
>>   with the matrix long after cure.
>>
>>   Confusingly, very fine silica incorporated in the form of
>>   fly ash, rice husk ash or silica fume can give a
>>   super-HIGH-strength mix. The reason for the effect is that
>>   the very fine silica reacts with the alkali formed DURING
>>   cure and actually strengthens the cement matrix.
>>   Unfortunately, much of the fly-ash and volcanic ash cement
>>   on the market is too coarsely ground to harness this
>>   effect.
>>
>>   Best,
>>   Marc de Piolenc
>>   Ferrocement freak

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