[GSBN] Steel mesh in clay plaster + earthquake safe fire shelters

martin hammer mfhammer at pacbell.net
Sun Aug 25 16:25:01 UTC 2013 

Classic Art ­ thank you.  Didn¹t know you were doing such testing.  Lot¹s of
good combinations.  Encouraging short term results, though in a relatively
dry climate.  Am interested to see when/if significant (performance
affecting) corrosion occurs.  I may not live that long for some of the
materials tested.  Great work.  (On the structural and fire fronts also.)

Martin


On 8/25/13 4:17 AM, "Art Ludwig" <oasis at oasisdesign.net> wrote:
> 
>  
>  Classic Derek--thank you; I will keep this incredibly informative response on
> file.
>  
>  Here's our (short term this far; 5 years±) anecdotal experience with metal
> and clay, followed by a preview of where we're going with this.
>  
>  ~~~~~~~~~~~~~~
>  
>  We have every possible permutation and combination of clay and steel under
> testing in dry (20" rain)  so cal:
>  
>  Cob, straw clay, heavy straw clay, earth plaster, lime plaster, aliz--
>  
>  in contact with:
>  
>  6-6-10-10 welded wire mesh, rebar and structural steel, all plain,
> unprotected-
>  plus heavy and light stainless steel meshes, various guages of galvanized
> mesh and lath, and painted structural steel.
>  
>  So far what I've observed is a high degree of initial corrosion in
> unprotected interior mesh caused by the sopping wet fresh mix, followed
> by...nothing much.
>  
>  I suspect that in this climate  that all this stuff is going to last for
> decades. Until something fails I'm not going to have much more to say about
> longevity.
>  
>  By far the most charmed combination for structural strength and ease of
> construction among those that we've tried is 6-6-10-10 (6x6" squares, 10
> guage) reinforcing mesh in cob. The configuration I'm most excited about is
> one in which there is a reinforcing layer just under both the inside and the
> outside surface of a classic compound curved, tapered wall cob building, with
> an integral cob floor and heavy straw clay ceiling.
>  
>  Where corrosion concern, the reinforcing could be galvanized, painted or
> slathered with local organic beach tar.
>  
>  Structurally, this would be both a monolithic fibercomposite, and a
> stress-skin structure. It is also suited for a base isolation footing. There
> could be zero cement in the structure in this case.
>  
>  The wrap-around several inches of earth would provide naturally extreme fire
> resistance. This would be coupled with fire safety details we've been working
> on, including metal framed cob doors and rooftop turbine ventilators. The idea
> here is to make a building that is without question more safe than a
> conventional building for structural and wildfire, with more than the required
> seismic safety. The initial application could be charming backyard cob
> playhouse/ impregnable fire bunkers, something that could be life-saving in
> this area.
>  
>  Misha and I plan to pursue seismic testing of such a structural system next
> fall, along with our best shot at an organic-only reinforced structure
> (bamboo, rope, jute...?) If anyone has suggestions about reinforcing or
> anything else please charm in. I feel like we're way more on top of the steel
> reinforcement than the organic reinforcement scenario (awaiting direction from
> Massey on this).
>  
>  Here's a slide show of our scale model testing
> <http://oasisdesign.net/shelter/cob/slideshow/> . The steel model totally
> rocked this test--the equivalent of taking 2.4 g's of lateral, though at 12:1
> there's plenty of error in the way it scales, this is encouraging. The
> orgainic-only model also did well--0.2 g's if memory serves, which used to be
> enough for California's old seismic standard and is also very encouraging for
> a first try.
>  
>  Yours,
>  
>  Art
>  
>  
>  
>    (Note: There's also bunch of ferrocement in more exposed locations; it
> seems to play well with cob and ferrocob).
>  
>  Quoting martin hammer <mfhammer at pacbell.net>:
>  
>>  > Hi Derek,
>>  >
>>  > A very thorough and thoughtful response, as always.  Thank you.
>>  >
>>  > Thoughts and information are welcome from others as well.
>>  >
>>  > Martin
>>  >
>>  >
>>  > On 8/24/13 5:51 PM, "Derek Roff" <derek at unm.edu> wrote:
>>  >
>>>  >> Hi, Martin,
>>>  >>
>>>  >> I will start with a quote from the site
>>>  >> http://www.cement.org/tech/cct_dur_corrosion.asp:  "Corrosion of
>>> reinforcing
>>>  >> steel and other embedded metals is the leading cause of deterioration in
>>>  >> concrete."  This page is a fairly concise, not too technical description
of
>>>  >> reinforcing steel corrosion in concrete.  The article points out
>>>  >> that concrete
>>>  >> contains all the ingredients necessary to cause corrosion in steel. 
>>>  >> Concrete
>>>  >> itself can function as an electrolyte, and different locations in
>>>  >> reinforcing
>>>  >> steel can act as anode and cathode for inducing corrosion.  The
>>> electrical
>>>  >> conductivity of concrete is sufficient to support corrosion.  If
>>>  >> other metals,
>>>  >> such as aluminum or zinc (galvanized metal) are in contact with the
>>>  >> concrete,
>>>  >> this increases the rate of corrosion for the reinforcing steel.  On
>>>  >> the other
>>>  >> hand, in the galvanized metal itself, the zinc is a sacrificial layer,
>>> which
>>>  >> protects the steel, for as long as the zinc lasts.
>>>  >>
>>>  >> Concrete also contains one significant corrosion inhibitor- high pH, >>>
which
>>>  >> helps protect the steel, by aiding the formation of a thin, passivating
>>>  >> protective layer on the surface of the steel.  The author says that the
>>>  >> "corrosion rate [of steel with the passive film protective layer] is
>>>  >> typically
>>>  >> 0.1 µm per year. Without the passive film, the steel would corrode
>>>  >> at rates at
>>>  >> least 1,000 times higher [100 µm per year] (ACI222 2001)."  [If your >>>
mail
>>>  >> program isn't showing the special characters properly, the measurement
>>> units
>>>  >> are micro-meters per year, one millionth of a meter.]  Lime also has a
>>>  >> similarly high pH.
>>>  >>
>>>  >> The main causes of increased corrosion are salts in or applied to the
>>>  >> concrete, and decreased pH.  Salts may be common in the materials used
as
>>>  >> aggregate, in the water used for the mix, or may be introduced after the
>>>  >> concrete has solidified.  People add salts to concrete for ice removal
and
>>>  >> other reasons, and salts may also be introduced unintentionally by wind
and
>>>  >> water, in some locations.
>>>  >>
>>>  >> Decrease in pH can be the result of carbonation in the concrete, or
>>> acids in
>>>  >> the environment, both naturally occurring and applied intentionally. 
>>> Carbon
>>>  >> Dioxide in the air reacts with water vapor to produce carbonic acid, so
a
>>>  >> small acid source is always present.  Acid rain can introduce much
>>> stronger
>>>  >> acids in greater quantities.  Carbonation is usually slow for good, >>>
thick
>>>  >> concrete made with pure materials, but may occur much more quickly in
>>> less
>>>  >> pure concrete mixes and thinner applications, such as plasters. 
>>> Carbonation
>>>  >> is more rapid in lime mixes than in concrete.  Cracks in the
>>>  >> concrete or lime,
>>>  >> of course, increase the rate of corrosion.
>>>  >>
>>>  >> Clays are highly variable, but are unlikely to have the high pH that >>>
helps
>>>  >> form a protective layer on reinforcing steel in concrete and lime. 
>>>  >> I found a
>>>  >> statement that natural clays can vary between pH 2 and 10.  Within the
pH
>>>  >> range that is common for clays, neutral to slightly basic mixes will
>>>  >> have the
>>>  >> lowest corrosion rates, according to the websites that I checked.  On
the
>>>  >> other hand, many clays will not act as an electrolyte.  If an
>>> electrolyte is
>>>  >> lacking, the rate of corrosion will stay low.  This site
>>>  >> http://www.ncbi.nlm.nih.gov/pubmed/22200075 contains an abstract on
>>>  >> the use of
>>>  >> clays "to impart remarkable protection against corrosion to
>>>  >> galvanized steel."
>>>  >> Salts may or may not be present in the clay, depending on the local
>>>  >> conditions, water, geology, and the clay mix.  Clay is a much better
>>> buffer
>>>  >> for moisture than concrete is, which would usually help steel in clay
>>> resist
>>>  >> corrosion.  Clays are not subject to carbonation.  Lower temperatures
>>> will
>>>  >> reduce the rate of corrosion.
>>>  >>
>>>  >> The PDF freely downloadable at this site
>>>  >> 
>>> 
http://bookshop.europa.eu/en/corrosion-of-low-carbon-steel-in-clay-and-sea-sed
>>>  >> iments-pbCDNA10522/ contains several interesting quotes, which are
>>> somewhat
>>>  >> divergent from each other, and not identical to the conditions of
>>>  >> reinforcing
>>>  >> steel in clay plasters.  The authors were concerned about steel immersed
at
>>>  >> high temperatures (90 degrees C) in sea sediments.  While other sites
>>> have
>>>  >> suggested that more water increases the rates of corrosion, this
>>>  >> article finds
>>>  >> the reverse, which they attribute to the lack of dissolved oxygen in the
>>>  >> sediment zone they investigated.
>>>  >>
>>>  >> With no mention of the amount of water involved in the referenced
>>>  >> studies, the
>>>  >> authors say, "In literature, data can be found on corrosion of mild
>>> steel in
>>>  >> clay. Exposing ductile iron or carbon steel [H. Tas SCK/CEN Mol,
>>> Personal
>>>  >> communication] directly to clay at room temperature gives rise to
>>> general
>>>  >> corrosion rates ranging from 10 to 50 µm/yr."
>>>  >>
>>>  >> However, their tests and references show a much lower corrosion rate
>>>  >> of only 8
>>>  >> µm/yr in one study with steel in clay under unspecified conditions, and
>>> from
>>>  >> another study, 2-10 µm/yr at 25°C, in bentonite clay.
>>>  >>
>>>  >> "Tests in deaerated substitute seawater were conducted at Harwell at >>>
90°C
>>>  >> [G.P. Marsh et al. - Corrosion assessment of metal operpacks for
>>> radioactive
>>>  >> waste disposal - European Appi. Res. Rept. - Nucí. Sc. Technol., vol. 5,
pp.
>>>  >> 223-52 (1983)] which give, after a stabilization period of about 2.000 h
a
>>>  >> corrosion rate of about 8 µm/yr. Another series of tests was per­formed
in
>>>  >> which low carbon steel sample were embedded in bentonite saturated with
a
>>>  >> basic synthetic granite groundwater at 90, 50°C and at room
>>>  >> temperature [K.J.
>>>  >> Taylor, I.D. Blaid, C.C. Naish, G.P. Marsh - Corrosion stu­ dies on
>>>  >> Containment Materials for vitrified Heat Generating Nu­clear waste AERE
G -
>>>  >> 3217 (1984)]. After a stabilization period a corrosion rate ranging
>>> between
>>>  >> 20-37 µm/yr at 90, 9-32 µm/yr at 50 and 2-10 µm/yr at 25°C was
>>> apparent."
>>>  >>
>>>  >> Based on the references that I could find, the rate of corrosion for
>>>  >> steel in
>>>  >> clay is substantially less variable than for steel in concrete.  (I >>>
can't
>>>  >> think of another example where a property of clay is less variable than
an
>>>  >> industrial product.)  Steel deeply imbedded in excellent concrete, and
>>>  >> protected by a passivating layer, will have a corrosion rate that is a
>>> tenth
>>>  >> or less of that for steel in clay, according to the figures that I
>>> found.
>>>  >> Steel imbedded in an average Portland cement plaster with some cracks,
in
>>>  >> which the passivating layer is absent or compromised, might have a
>>> corrosion
>>>  >> rate fifty times higher than steel in a clay plaster.
>>>  >>
>>>  >> As with so many things in building, since testing reveals such a range
of
>>>  >> potential variability, it would be useful to test the materials under
>>> local
>>>  >> conditions.
>>>  >>
>>>  >> I hope this is of some help.
>>>  >>
>>>  >> Derek
>>>  >>
>>>  >> On Aug 24, 2013, at 4:39 PM, martin hammer wrote:
>>>  >>
>>>>  >>> Steel mesh in clay plaster (?)
>>>>  >>> Hello all,
>>>>  >>>
>>>>  >>> Can anyone weigh in on the use of steel mesh in clay plaster, in terms
of
>>>>  >>> corrosion of the steel?  In particular if it is susceptible to a
>>>>  >>> higher rate
>>>>  >>> of corrosion than steel mesh in lime or cement plaster (or what an
>>>> expected
>>>>  >>> service life might be).  Laboratory tested evidence is especially
>>>> welcome,
>>>>  >>> but so is anecdotal evidence (pro or con).
>>>>  >>>
>>>>  >>> I know there has been concern expressed about this for many years. 
I?ve
>>>>  >>> heard theory, but I haven?t seen hard evidence that it is actually
>>>>  >>> a problem.
>>>>  >>>
>>>>  >>> I ask this in the context of a Strawbale Tutorial I am co-authoring
>>>> for the
>>>>  >>> World Housing Encyclopedia.  The tutorial is meant as guide for
>>>>  >>> constructing
>>>>  >>> small houses in seismically active regions of the developing world.
>>>>  >>>  Thus the
>>>>  >>> desire for a reinforced clay plaster as the in-plane lateral resisting
>>>>  >>> system.  Darcey Donovan has used nylon fishing net in her system
>>>>  >>> with PAKSBAB
>>>>  >>> in Pakistan (which was shake table tested) but I am looking to use
>>>>  >>> other mesh
>>>>  >>> materials where such fishing net might not be available.  Metal
>>>>  >>> mesh seems to
>>>>  >>> be readily available in most of the developing world. (We are also
>>>>  >>> considering natural fiber mesh, but these may have strength and
>>>> degradation
>>>>  >>> problems).
>>>>  >>>
>>>>  >>> Thanks!
>>>>  >>>
>>>>  >>> Martin
>>>>  >>>
>>>>  >>> PS ? I?ve copied my colleague, Dmitry Ozeryansky, PE
>>>>  >>> _______________________________________________
>>>>  >>> GSBN mailing list
>>>>  >>> GSBN at sustainablesources.com
>>>>  >>> http://sustainablesources.com/mailman/listinfo.cgi/GSBN
>>>  >>
>>>  >> Derek Roff
>>>  >> derek at unm.edu
>>>  >>
>>>  >>
>>>  >>
>>>  >>
>>>  >> _______________________________________________
>>>  >> GSBN mailing list
>>>  >> GSBN at sustainablesources.com
>>>  >> http://sustainablesources.com/mailman/listinfo.cgi/GSBN
>>  >
>>  >
>  
>  
>  
> 
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