[Cob] Basalt Rebar

[Rob Hayes]

With rebar made from basalt there's no problem with rusting and the coefficient of 
contraction/expansion is similar to masonry so it could prove ideal for those bond beams.
It's light too, maybe some "alpha builders" have had some experiences to share?
I'm thinking of those future 400 year lifespan bridges or thin shell roofing which contain basalt rebar and reinforcements unaffected by alkali, salt and moisture even in marine environments.  Is this going to be the perfect rebar?  The basalt mesh substituted for steel EWL could even be somewhat exposed in finish plastering without being compromised by rust - allowing thinner coverage or skill levels, suitable for water harvesting roofs and without iron contamination.  Lightweight and larger overhangs might be more likely.  Tie those designed planters and other stuff to the basalt wall elements too without compromising them to unsightly corrosion failures?  Lighter boat hulls?  Boggles the imagination.

http://www.monolithic.com/stories/basalt-fiber-rebar
http://www.monolithic.com/stories/basalt-fiber-rebar/photos
http://www.basalt-rebar.com/
for example:
Thin concrete with basalt rebar 
http://www.youtube.com/watch?v=sNB5T3714xI

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Message: 3
Date: Mon, 25 Jun 2012 20:46:51 -0400
From: Henry Raduazo <raduazo at cox.net>
To: Anthony Novelli <anthony.novelli at gmail.com>
Cc: coblist at deatech.com,    "dhowell at pickensprogressonline.com"
    <dhowell at pickensprogressonline.com>
Subject: Re: [Cob] rebar
Message-ID: <E32CEE6A-9950-47E9-AFF2-23A60F41723C at cox.net>
Content-Type: text/plain; charset=us-ascii

    Alpha testers are the pioneers and scientists of the world they try things that have never been done before in order to advance building technology, Often they suffer the consequences of failure. Anyone putting steel in cob is an alpha tester. An alpha test of this type should run at least 10 years at a minimum and possibly 30 years to be meaningful.  Why so long? Buildings are designed to last for many years and the problems might not show up in short term testing. 
    A first problem that might occur is "popping". Have you ever attached something like a board to a cob wall with long screws. If you have a nice long screw and slowly tighten it on a board the head of the screw will start taking up tensile forces even imbedding its self into the board until you reach the limit of the cob and then the screw will pop loose of the cob and begin turning freely in the hole. No amount of additional turning will get the screw to engage the cob wall. Something similar to this might happen when you install a 10 or 15 foot piece of rebar in a cob wall. As the weather gets hotter the steel will expand faster than the cob putting the cob around the rebar under tension. As the weather gets cooler the steel will shrink more then the cob causing the cob around the steel bar to be under compression. The question is: Will the steel bar pop free of the cob wall and just slide free relative to the cob as it expands and contracts? If
 it does then the steel bar will not reinforce cob.
    A second problem is in-situ disintegration of the steel. Will steel rebar rust out over time? At what rate will it rust? How much holding power will the rusted steel have? Even if the steel is rust proofed will chemicals in the earth attack the rust proof coating? 
    The knurling on rebar is plenty adequate for concrete is it adequate for cob or should we use a more extreme knurling to give the bar more grabbing power?
    The only way to answer these questions is for some adventurous Alpha tester to try them out.
    I do alpha testing on buildings that I do not care about. My wood shed for example has three alpha teats running at the same time. 
    1) I have a steel dead man anchor, a wood dead man with a galvanized steel wire and an all wood deadman held together with galvanized screws. These anchors attach a 7 foot by 32 foot shed roof to three short cob wall segments
    2) I also have sections of the shed wall built with wood fiber cob instead of straw fiber cob. 
    3) The roof its self is made of a bamboo mat covered with paper/clay/sand plaster and waterproofed with boiled linseed oil on one section and driveway sealer on another.
    I may come out some day after a big storm or hurricane and find the roof of my shed laying in my back yard, and that will give me a chance to analyze how and why the roof failed. 
    People who use steel rebar in cob walls should be aware that they are Alpha testers and they should also be ready to accept the fact that their experiment may fail.

Ed

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