Re: [GBlist] Re: Big Green: High Fly Ash Concrete

["Richard McCabe" <rmccabe@alumni.princeton.edu>]

Didn't we have a discussion about the toxicity of fly ash recently?  I
wouldn't put it in any building after learning the details about fly ash.
Silica fume (another waste product.) is what I am looking at, but I think it
has gotten too expensive.  There are lots of other pozzolans to consider.

Another thing to consider is pumice.  There is a mine near the top of
California.  It is great stuff and has been used in lots of government
complexes etc. Glass Mountain Pumice. http://www.glassmtnpumice.com  All
chemistry info available online. Sales Manager is Russell Downie.
209.369.0657  Offices in Sacto. and Reno. Environmentally correct (for
concrete) since lava is a semi-renewable resource!  Lightweight and cheaper
than expanded shale.

I think the main reason to still use fly ash is to reduce the heat of
hydration on really thick pours, like dams.  For places where people might
be exposed to dust coming off the concrete, I would be very reluctant to use
fly ash.  At least you would want to buy it from a known-clean source.  If
you simply specify "fly ash" you could get some very nasty stuff in the mix.
(It does have a positive impact on strength, durability, porosity and
workability, but I wouldn't go above 25% as replacement for portland cement
in any case.)

Of course the best way to be green is to use less material, which is easily
accomplished using ferrocement techniques.  Check out the archives at
http://www.ferrocement.net/archives/search.html.  Do NOT use their search
engine.  It is a bad dog. Use Google's site search instead.  I recommend
downloading their very cool toolbar, but you can go to www.google.com and
enter terms using the following syntax: search terms
site:www.ferrocement.net. (Eg: +"laminated ferrocement"
site:www.ferrocement.net)

I would recommend Martin Iorns' laminated ferrocement techniques.  His
original patent from 1964 is now in the public domain.  He licensed it all
over the world for many projects.  It is simple and cheap and gives you flat
panels that you tilt up.  (Basically laminations of 3mm per layer of
super-mortar with expanded metal lath and welded wire mesh.) Those of us
fighting the gravel mining in the Russian River appreciate the fact that
this technique uses only sand and portland cement.  The final shell can be
as thin as 3/8 inch.  For greater strength, you simply add more laminate
layers.

Another technique that will save time, money and the environment that is
widely used on large projects is shotcrete against a one-sided form.  You
can save money on the formwork and use Dramix steel fibers (or PVA fibers)
and largely eliminate the need for rebar.(Big labor expense.)  Floors need
no rebar. No expansion joints needed with steel fibers.  And it is stronger
than traditional RC (reinforced concrete) to boot.  I talked to a contractor
in San Francisco building high rises like this.  He sprays against a form,
giving a smooth surface for the inside wall.  Then they put insulation and
siding over rough sprayed side.

What researchers have discovered is that the brittle cement matrix is strong
only in the vicinity of the reinforcement.  So you actually get a much
stronger product, and much thinner, but spreading the reinforcement around
with the hair-thin steel fibers.  This technique is used in tunnels, mines
and commercial uses worldwide.

Portland cement is energy intensive to create, but handled correctly, you
can make thin cement shells that will be maintenance free for hundreds of
years.  (Not to mention fireproof, rot-proof, rodent-proof, wind and flood
resistant, etc.)  If you use white cement, you can make it any color you
want.  If you don't like the color when you are done, just use pure portland
cement and a coloring agent and simply paint over the old coat!  (I just
made a curved spa privacy wall that is half an inch thick.  We tried three
shades before settling on a dark forest green.)

As for fiberglass, it can be used, but the highly alkaline cement
environment will attack and destroy fiberglass unless it is treated.  There
is zircon-treated fibers from Spain, but they are expensive and can be
destroyed by overmixing with aggregate.  Very delicate.  I believe that
matts are often used for commercial floors, but I am not informed on that
subject.  Simply going to synthetic rebar will add cost and be even less
green that metal rebar, which is, after all, recyclable.

Richard McCabe




----- Original Message -----
From: <billc_lists@greenbuilder.com>
To: <greenbuilding@crest.org>
Sent: Friday, July 26, 2002 9:23 PM
Subject: [GBlist] Re: Big Green: High Fly Ash Concrete


> >Hello:
> >
> >We are looking at specifying high fly ash concrete for a large
> >multi-family project in Seattle, WA.  A recent objection has come up
> >that high fly-ash promotes early corrosion of the reinforcing.  Has
> >anyone heard of anything to this effect or have any data?
>
> Despite the posts postulating the assumed reduction of corrosion,
> could you consider switching to fiberglass reinforcing?
>
> --
> Bill Christensen
> billc@greenbuilder.com
>
> Green Homes For Sale/Lease:  http://www.greenbuilder.com/realestate/
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>
> ______________________________________________________________________
> This greenbuilding dialogue is sponsored by REPP/CREST, creator of
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> ______________________________________________________________________
>


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This greenbuilding dialogue is sponsored by REPP/CREST, creator of
Solstice http://www.crest.org, and BuildingGreen, Inc., publisher of
Environmental Building News and GreenSpec http://www.BuildingGreen.com
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