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Re: GSBN:Cemento (combined responses)

At 10:53 AM 7/5/2007, Derek Roff wrote:
What are some examples of using less Portland cement to do the same job?

        These may not be along the lines you're thinking (and are
generally much smaller in individual scope than what John Straube
addressed, and may fall outside of code), but for instance, dry-laid
or lime-mortared stone stemwall foundations on rubble trenches in
non-seismic areas; earthen plasters with non-portland stabilizers;
natural stone pavers or gravel paths instead of sidewalks where ADA
compliance isn't an issue; wooden or stone steps rather than
concrete. That is, choosing alternatives that don't use portland
cement at all when those choices make sense.

        Again with the Eisenberg: we were in an underground train
station in Washington D.C. some scant years ago and I asked him what
he thought about the huge amounts of concrete around us. He said, "I
think it's great."

Rob Tom advocated the development of an inside out insulated
concrete form, where the concrete skins would be on the outside, and
the foam in the middle.

        Those exist; see
<a  target="_blank" href="http://www.tridipanel.com/";>http://www.tridipanel.com/</a>
<a  target="_blank" href="http://www.greensandwichtech.com/";>http://www.greensandwichtech.com/</a>
for examples. I seem to recall that there are insulating-core precast
panels as well. And VariantHouse offers ICFs with imbalanced levels
of insulation from one side to the other - a step in the right direction.

Rene and maybe Lars talked about using a small amount of cement, to
cement seashells together, with lots of air gaps. Living near
volcanoes, pumice-crete uses the same idea, with a little cement and
a lot of pumice.

        For what uses?

        The website www.pumicecrete.com says that they use "under 3
sacks of portland cement for every cubic yard of aggregate" for a 400
psi product. That's about half the cement of a typical 3000 psi
concrete mix, but might not make a code-compliant grade beam.

        If it's for an insulative wall system, the climate may
suggest that it's an idea worth considering (thinking of Martin
Oehlmann's weather-exposed wall by the sea). But if the shell or
pumice system is so friable and / or so air-gappy that it requires
protection from the elements (like wind-blown rain), or from people
and animals, that an additional coating or covering layer is needed,
the whole thing might want yet another reconsideration.

A cement grade beam on a rubble trench saves a lot of concrete, with
potentially superior performance.

        To be fair, I guess we also have to say that a full-depth
concrete foundation offers potentially superior performance to a
rubble trench with a grade beam, too. It just depends.

Other examples and techniques?

        I was on the phone with the guy from GCS Radiant earlier,
and he said they're using ground-up windshield dust as a
portland-replacing pozzolon in their product. (He claimed that it
partially replaces their portland and isn't just filler. But they
also have fly ash content, so who knows.)

        Precast components can achieve optimal strength through
controlled curing, reducing material consumption by opening the doors
to optimized design for the materials so that field pours aren't
overdesigned. There's also less waste in precast vs fieldcast (no
overage dumping), and there can actually be less transportation
energy since the moisture in a wet mix isn't being transported as well.


--On Wednesday, July 4, 2007 9:39 PM -0400 John Straube
jfstraub@... wrote:
I also think one has to consider that cement is just one material
that is used. It is used an awful lot, and this is part of its
environmental footprint. However, the reason it is used a lot is that
it is made of clay and limestone (available most places in quantity)
and results in a very durable and low dollar cost product. I am all
for reducing cement use, and changing cement manafucturing to
dramatically reduce CO2 and other emissions. however, if the
replacement for the apartment buildings in China is, for example,
steel, then the CO2 emissions will rise dramatically as steel will
use more energy and CO2 for the same beam or column. Lots of cement
is used in heavy civil works like roads, and sewers, curbs and
sidewalks. There are some replacements, but few work as well.
At the end of the day, I think cement is one of many materials that
we need to use more wisely and hence less of, but for many purposes,
it is hard to find an equally durable, non-combustible material that
has less impact.
One of the clear substitutions is wood framed housing instead of
concrete. This works in some places, like where they have trees, but
there are limits to height, fire resistance, and durability that are
quite practical. For most other applications, like basements,bridges,
sewer pipes etc, I think we can gain more by be smarter in its use
(optimally designed structures) and dramatically improve is
production (e.g. there is little reason why a coal-fired cement plant
could not use carbon sequestration.

Mark Piepkorn

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