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Kiko Denzer on Art

[Cob] straw in cob or concrete?

Ocean Liff-Anderson ocean at
Fri Aug 15 15:51:21 CDT 2008

Hey down there Lance,

Bridge failures during the Santa Cruz earthquakes were determined to  
be due to rebar failure - especially in the maritime environment of  
the Bay area.  Many lives were lost.  I saw them rebuilding the Bay  
Bridge several years back, making huge cages of epoxy coated rebar to  
for the pillars.

Her in Oregon ODOT just electroplated the entire concrete Newport Bay  
bridge, placing a negative electrical charge to draw the salt ions  
away from the rebar - trying to save a beautiful architectural  
landmark from the elements.  Waldport Bridge was demolished and  
replaced with a new, epoxy coated rebar bridge.

Sure, epoxy is only needed where exposure to salt is likely.  My  
concern about straw is in the actual mixing process, where the  
concrete is strongly caustic.  Have you left concrete on your hands  
without washing it off immediately?So you found a chunk of wood in  
old concrete - was it structural?  Give the caustic effect I wouldn't  
want to depend on thin fibers of straw for structural reinforcement.

I never said concrete didn't work well for all the wonderful  
industrial applications.

But mixing straw in as an experiment seems ill-advised.  Instead of  
asking the coblist, why not float the idea to the concrete people -  
builders, contractors, cement delivery people - they'd probably laugh  
their asses off...

Ocean Liff-Anderson
FireWorks Restaurant
Corvallis Oregon

On Aug 14, 2008, at 2:06 PM, Lance Collins wrote:

>> Have you ever gotten concrete on your hands?  It is highly caustic,
>> dissolving all carbon straw doesn't have a chance!
> I've found wood pieces in old concrete still in excellent condition.
>> Concrete guys will throw in bags of loose poly-fibers (plastic) which
>> are supposed to prevent cracking in slabs...
> It does work.  The people on the ferro-cement list are very positive
> about PVA fibres.
>> But rebar even doesn't hold out forever, because concrete acts as a
>> wick, drawing whatever moisture hits it straight in - rusting the
>> rebar and causing collapses of bridges, etc...
> This only happens to poorly built structures or those attacked by
> de-icing chemicals.
> I've broken old weather-exposed concrete where the rebar was as shiny
> as the day the concrete was poured.
>> Now they coat the rebar
>> with epoxy or plastic, then pour the concrete over it.
> Thst's safer but unnecessary if you get the concrete mix right.
> The above comments on concrete are analogous to saying that cob
> building can't work because the cob will turn to mud when it rains.
> Lance
> (in Aus)
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