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Re: Testing Old Concrete

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Fellow engineers,

        Back in August I submitted the inquiry below regarding the testing 
of old concrete.  As I indicated below the problem with the testing is that 
 cores were not practical to retrieve due to crumbling of the concrete. 
The reason given by the testing expert is that the old concrete frequently 
was mixed using golf ball, and even baseball size aggregate with smooth, 
not crushed surfaces, hence the concrete often does not test well but 
usually performs well in practice.

        We, therefore, did some drilled and epoxied anchor pull-out and 
shear tests.  The test results were reasonably compatible with HILTI 
published values.  The ultimate values that I had assumed in my design were 
 about 70% to 75% of the measured test values.  I, therefore, decided not 
to change the design; after all, saving a few anchors doesn't seem a 
worthwhile saving in the construction of a $6,000,000 building.

        Since all of you read my request and two of you replied (and I 
thank both of you) I thought you deserved to know the final outcome.

Regards,

Daryl
  ----- Original Message -----
  From: h.d.richardson(--nospam--at)shaw.ca
  To: seaintlist
  Sent: Friday, August 16, 2013 6:43 PM
  Subject: Testing Old Concrete

  Fellow engineers,

          I have encountered a problem with some old concrete in foundation 
 walls.  The concrete is from about 1912.  The aggregate contains 1" to 1 
1/2" smooth river rock; no crushed aggregate.  Four cores were taken for 
testing; three of the four crumbled on removal; the testing company say 
that this is not uncommon for concrete of this age even though the concrete 
 is otherwise sound.

          The intent is to reuse the foundation which appears to be in 
excellent condition; the allowable soil bearing pressure is in  excess of 
7,000 p.s.f.  The new loading will come from W6x15.5 columns connected to 
the foundation walls with long vertical clip angles connected to the walls 
with 3/4" HILTI epoxy anchors and welded to the columns.  There is no 
seismic loading in Calgary (actually, it's Zone 1, after several decades of 
 being Zone 0).

          Load testing of a sample connection can be done.  Also, Schmidt 
Hammer testing can be done.  The first is expensive; the second may not be 
as reliable as desired.  Can anyone recommend any other testing?

          It is now Friday and I would like to be prepared to discuss this 
with the testing company Monday or Tuesday.

  Thank you for any help you can provide.

  Regards,

  Daryl

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