[Ferro List] Reinforcement / Martin's Post

[Bo Atkinson]

(Please see my present comment and Martin's older post below)

On Mar 29, 2008, at 2:00 PM, list-request at ferrocement.net wrote:
>
> Hi Bo,
>
> There is no perfect mesh, they all have potential drawbacks  
> depending on
> how they are used.
>
> I am not sure what kind of lath you are referring to when you say  
> "...lath
> type FC demolition and saw large pieces of cement flake off 1/2"  
> mesh." If
> you are comparing hand applied mortar to sprayed mortar [as in LFC]  
> that
> could account for less adhesion with the hand applied mortar.
>
> Martin liked lath because the layers would tend to nest together  
> during
> the LFC method. Another reason he used lath was the high volume of  
> steel
> in a sheet of reinfocement that thin. This allowed him to get a lot of
> steel, 5 layers of 3.4 pound lath, in a 3/4" thickness. And finally  
> Martin
> liked lath because it came in flat sheets and held a bend well without
> springing back too much. Compared with meshes this simplified the  
> layout
> when the lath was pressed into place inside of a mold.
>
> Martin did use wire mesh in the construction of the bulkheads and in
> combination with lath in the deck. I'm not sure about the navy tests.
> Perhaps Colin King will jump in here as he read those tests about a  
> month
> ago.
> Paul

Hi Paul,

This is indeed a wide subject and i should not have included too many  
subheadings in one post. I believe these are Martin's own words on the  
facts of which particular mesh was used in the Navy test (Just found a  
quote in your archive. I believe this was Martin's post which follows  
below my long paragraph)--  Demolition teaches many subtitles about  
construction-- Weak sand, (due to soft sand component particles  
weakens the "mortar to mortar" bond which also weakens the mortar to  
steel bond. Still, one can learn much about shearing dynamics with  
weak mortar and weak bonds. Naturally demolition hammers are much  
stronger than any mortar we can buy today because they are solid and  
hardened steel. I would be the last person to disparage FC and hope  
that it will not be taken that way. I have used a lot of expanded lath  
but am intrigued that thin, un-welded wires, tend to hang on longer  
during catastrophic demolition in part due to greater flexibility and  
in part to dispersed leverage points during failure events.   The  
subheading i though very interesting to add was that catastrophic  
failure of FC can allow just a little more time to evacuate a  
crumbling building which presents a different sort of advantage than  
in boat destruction. Significant gashes in a boat hull could sink a  
boat with no opportunity to salvage anything.  Martin points to  
surface area or bond area of the reinforcement. I take that point  
tangentially and ask (myself) why then not increase the surface area  
or bond area by using smaller diameter wire? Martin pointed out the  
fact that expanded lath with square edges provides more surface area  
or bond area  than would a round wire mesh of the same general size,  
but did not necessarily contend that all expanded metal lath is  
identical or that all round wire mesh is identical.  More total  
surface area of steel can otherwise be achieved with smaller diameter  
wires and this aspects has not been addressed in testing as far as i  
know.  Also, how can varied failure modes affect product users?  I  
think a person can easily experiment with these ideas. Make up some  
small samples with the same mortar mix, but using scraps of  these  
differing reinforcement materials. After a good cure, smash them up  
with a hammer, to see if some reinforcement configurations take more  
"measured" blows to break away from the cured mortar.  (I think  
MxSteve pointed to a way to achieve measured blows: Use the same  
falling rock, from the same height, his "meteor test"). To see if  
smaller wire like reinforcement tends to remain attached to mortar  
pieces longer. To see if sharp-square  edges in the reinforcement  
might affect mortar tenacity. To see if high tensile steel  
reinforcement affects the demolition strength as compared to softer  
steel reinforcements.... (As far as i know, high tensile steel  
srtrength is made by drawing out wire and i do not think punching  
expanded lath allows this level of strength-development nor does  
welding wire provide the best high tensile levels).  When clumps of  
mortar manage to remain loosely wired together during catastrophic  
failure, a greater opportunity exists for building occupants to safely  
escape. There are more points to consider here and one can benefit  
from each context (of quotes)  to avoid what can otherwise seem  
contradictory. Ultimately, one has to consider and perhaps personally  
test the reinforcement and sand qualities, to say nothing of additive  
qualities and types. By sharing experiences, we might derive the  
needed stamina to push through many of these issues and personally  
administered tests ;-)

Bo Atkinson

On Dec 11, 2002, at 7:15 PM, MARTIN IORNS wrote:
>
>
> The all-mesh used by the Navy was hardware cloth and validated only my
> all-mesh system. Other Navy tests showed the optimum opening for crack
> control was between 6 and 10 millimeters. The opening in expanded  
> metal
> plaster lath fall within this range and the rectangular cross  
> section of its
> strands has more bond area than wire mesh, which is circular in
> cross-section. The greater the bond area the better the ability to  
> resist
> strain without cracking. So in our own test, we substituted lath for  
> wire
> mesh and got much better ductility and impact resistance than in our  
> wire
> mesh samples. Impact resistance is the most important criteria for  
> boat
> hulls.
>
> Martin
>
> ----- Original Message -----
> From: "Scott Knudsen" <s.knudsen at sasktel.net>
> To: <ferro-users at ferrocement.net>
> Sent: Saturday, December 07, 2002 8:00 PM
> Subject: [Ferro Cement] Re: What's "Expanded Metal"
>
>
> In 1969 the US Navy explored the use of ferrocement for high- 
> performance,
> 40-knot patrol boats.  The Materials Laboratory at Annapolis built  
> test
> hulls based on the systems used by the three leading commercial.   
> Two hulls
> used the traditional rod-and-mesh systems of Samson (British  
> Columbia) and
> Windboats (United Kingdom).  The third test hull used the all-mesh
> construction developed in California.
>
> The all-mesh boat was the only one to survive the high-speed tests  
> in choppy
> seas.  The investigators found that rods were an inefficient used of  
> the
> included steel because they were not loaded to take advantage of their
> strength, their spacing created areas of unreinforced mortar that
> contributed to weight but not to strength, and they acted as stress
> concentrators.  They concluded that a "remarkable increase in
> strength-to-weight" ratio was obtained by the use of mesh only.
>
>
>
> Dinsenbacher, A.L. and Brauer, F.E., "Material Development, Design,
> Construction and Evaluation of a Ferrocement Planing Boat," Marine
> Technology (SNAME), July 1984, pp. 277-296.
>
>
>> It's metal that was slit and then pulled and the slits became  
>> spaces. I
>> believe it was the US navy that did tests with it being used in ferro
>> boats, and found that under stress it would ack like and accordian  
>> and
>> cause structural damage, so in other words, not the best stuff to  
>> use in
>> boats.
>>
>> Scott
>