[Ferro List] FERROCEMENT-AERATED CONCRETE SANDWICH BLOCKS

[steve garner]

----- Original Message ----- 
From: "Doug Lacy" <douglacy77 at hotmail.com>
To: "Ferrocement Discussion List" <list at ferrocement.net>
Sent: Wednesday, April 09, 2008 1:22 AM
Subject: Re: [Ferro List] FERROCEMENT-AERATED CONCRETE SANDWICH BLOCKS


>
>
> That technical paper about the ferrocement encased aerated concrete is
simular to what I am doing in a few ways but very different for the most
part.  The final mode of failure in their samples during compression were
delamination.  That couldn't happen using the Parabolic Stress Skin Process
because of the evenly spaced cross ties of steel bonded to both surface
shells.  Maybe it could happen in some manner due to some state of
hypothetical outerspace decay but it would be on the list of stuff not
likely to happen on earth because of the tight bond between the mortar and
the lath due to the low-shrink mix and the tight bond between the lath and
the internal welded wire cubical structure that also reinforces the 30 pcf
600 psi closed cell neat cellular concrete fill that occupies a 12 inch
thick cavity.
>  Some interesting thing about that paper is that:  They showed that even
after failure, these hybrid ferro and cast aerated maintened 20 percent of
their strength in thier semi squashed form.
>  They had an interesting mix for the aerated fill, complete with
blastfurnace slag, sifted sand, super P, very specific dry material to water
ratio, and only 20 percent aeration, all for a wimpy 1100 psi mix. But when
it came to describing the ferrocement mortar paste, it was just reffered to
as a 1 to 2 binder and an adjusted water binder ratio and and .2 percent
super P. to achieve a certain flowability. No water to binder ratio stated
and not too many other specifics revealed there. And then after going on
about where the ferrocement mortar cube's  psi was tested and how much they
weighed, they forgot to include that psi data so we have to do surface area
calculations based on their shell area and aerated area to figure that out
to make a guess at how their mortar augments compression before the
inclusion of any steel.
> They seem really excited about the 1100 psi 20 percent aerated mix for the
inside of their sandwich because one of the reasons sited for using a
ferrocement surface is to protect this precious and complex aerated mix from
moisture because  the aerated cement can absorb a lot of moisture.  This is
true of their mix because they used powdered alluminum as an aerating agent
which produces open cell aeration -open pores.  Closed cell aeration, from
aerating compounds like Cellucon and Mearlcell 3532, blocks moisture
intrusion.  My own test cylinders held under water for days were dry in the
center region.
> It is a great paper in that they are making some basic testing about
hybrid materials and showing some significant strength increases with the
inclussion of FC and some important information about how ferro encased
low-density mixes fail. This is some needed data.
>  If their studies are pursued I will bet that their focus will shift from
the aerated fill to the composite surface shells as it did for me. They may
not make it all the way to using wine bottles as an internal fill any time
soon, but who knows.
> Doug
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