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GSBN:re: Interesting test results

On Thu, 09 Dec 2004 13:07:52 -0500Chris Magwood

I was just giving a talk for the Engineering Department at Queen's
University in Kingston, Ontario last week. There is a prof/student
team there doing some testing work on bale walls, and I was able to
check out the results of what they've been doing. Very interesting...


To be honest, as a Canadian and someone with Queenâs Univ alumni in
the family, I was embarrassed for both when I saw this note.

Queenâs is a very good, globally-respected  university and I find it
hard to believe that they would put out anything like this.

I donât think that itâd be a stretch to say that any first year
engineering student by the end of first term, should know that as the
compression resistance of a material is lowered, its cross sectional
area (ie thickness) must be increased in order to carry the same load.

As such, it would make no sense for anyone  involved with a
university-level engineering faculty to make a statement such as :

   ã that the actual strength of the plaster had  much less effect on
the working strength of the plastered bale than did the thickness of
the plaster. So making a really strong  plaster is not as important
as putting it on the wall thickly ã

Second, anyone with a working knowledge of  mortars would know that a
mortar made with 75% lime (presumably bagged hydrated lime added
directly to the mortar mix instead of being slaked for a month or
more) and 25% Portland  would end up with a plaster that has the
strength and consistency of stale baking soda.

And anyone with a basic knowledge of lime plasters would know that
carbonation  (and hence, hardening) occurs over a period of years and
decades, not a mere 28 days.

So, to say that such a Îlime-richâ plaster (at 28 day strength of 1.7
MPa (247 psi)  is weaker than an earthen plaster sample ( whose
compression resistance was tested as being  in the range of 2.1 -2.4
MPa (305 Î 348 psi)  is pretty much meaningless to anyone who has a
basic understanding of  the mechanical properties of plasters.

(ie Type S  is the masonry cement typically used for Portland cement stucco.
Its compression resistance  is typically  in the range of 12.4 MPa (
1800 psi). )

So I have to wonder if maybe the Îtestingâ was being done by first
year students as one of their first exercises intended to familiarize
them with the structures lab and the results of which were not
intended as a scholarly contribution to the body of SB engineering
knowledge ?

    ~~~ * ~~~
    Robert W. Tom
 Kanata, Ontario, Canada
(winnow the chaff from my edress in your reply)Robert W. Tom

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