[Cob] Coblist Digest, Vol 7, Issue 45

[john fordice]

Ed,
i had a conversation with an engineer about straw length in cob.
He pointed out that in concrete construction the minimum length of  
rebar embedment needed to reach maximum strength of the rebar in  
concrete is called the "development length".   It has to do with the  
ability of the concrete to grip the rebar.  At any length of embedded  
rebar longer than the development length, there is no added strength  
benefit.
  He posited that the same may be true for straw in cob.  If we knew  
the ability of cob to grip the embedded straw, we would know at what  
length of straw, there would be no added benefit strength wise of  
having longer straw.  This is something worth knowing & will be one  
of the fields of study to be done be the CRI once the study of cob  
strength & structural performance gets going.
Regards,
john fordice - cob research institute

On Mar 5, 2009, at 12:08 PM, Henry Raduazo wrote:

> I always chop the straw. Laying out the flakes on the ground and
> running a mower across them and raking up the chopped straw is quick
> and easy. The only caveat is you must wear a n-95 or better dust mask
> and eye protectors. I do not live in an earth quake area, and I
> figure that even when using finely chopped straw the finished
> structure is many times stronger than adobe, and the application and
> sculpting of cob with chopped straw is much easier than with whole
> straw. This is particularly true when doing windows or any complex
> cob shape. Note, for example, the windows shown to the left of
> "WINDOWS, WINDOWS!" in The Sculpted House book. The windows mullions
> were made with finely chopped straw and I can not imagine trying to
> form these windows with whole straw. It would have been nearly
> impossible.
> Ed
>
>
> On Mar 5, 2009, at 3:02 AM, Robert Alcock wrote:
>
>>
>>> Date: Tue, 3 Mar 2009 12:28:24 -0800 (PST)
>>> From: Mitch Ventura <h_anpyp at yahoo.com>
>>> Subject: [Cob] Rototillers
>>> To: coblist at deatech.com
>>> Message-ID: <893907.81988.qm at web36808.mail.mud.yahoo.com>
>>> Content-Type: text/plain; charset=iso-8859-1
>>>
>>> Although there is no argument on my part as to the benefits of
>>> speed with the rototiller, as?I live in a seismic area I would
>>> question having to "chop" straw when using mechanical devices as
>>> that would seem to detract a bit of srength from the final
>>> product. Not saying that a rototiller produces an inferior cob,
>>> but rather it could be limited to more stable environments. Please
>>> correct me if I am in error.
>>> ?
>>> Saludos.
>>> ?
>>> Mitch
>>>
>>>
>>>
>>>
>> Mitch,
>>
>> I didn't chop the straw. The extra work of cleaning the straw from  
>> the
>> tines every so often is not that onerous - compared to chopping it in
>> the first place.
>> I would have chopped it if it was mixing cob plaster for instance.
>>
>> Robert
>>
>>
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>
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