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RE: concrete of forty years old

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Rpuebla,

Daryl put the question which I also wanted to put.

As, I understand from your description (ur english is far better than my
Spanish/Portugues is?), you have two parts of ur question:

    1. Do oncrete deteriorate in terms of its
       compressive strengths over a period of forty
       years?

    2. The Code requirements for design of columns
       were not the same as it is now?

My response to your first question is the compressive strengths of concrete
continue to progressively increase as the time period elapse; for an idea, a
365 day strength becomes approximately 1.56 times its 28-day strength.

But having said that, you must understand that this is the progressive
increase in compressive strenghts which is because of the reason that
HYDRATION PROCESS (chemical reaction b/w cement & water) which continues to
go on for an indefinite period. But at the same time if things do not work
well there could be deterioration of concrete due to exposure to aggressive
environments; the greater the severity of aggressiveness of the exposed
environment, the greater the deterioration . This deterioratio of concrete
could be spalling of concrete due to Corrosion of rebars or just cracks &
rupture due to alkali-silica reaction, so on  & so forth.

But the fact remains that the strength of concrete do continue to
progressively increase with the passage of time.

As for the second question; yes you are absolutely right Codal provisions
have changed considerably over last forty years. Earlier the column sections
used to be thick & robust (due to working stress design probably & poor
analytical tools!?...) and now the sections are slimmer comparatively. Also
there is a minimum/maximum steel ratio requirement which should be different
from those forty years ago.

So, if you are into a problem of analysing the capacity of the column
section my advise to you is:

   -  you can safely assume that the strenghts
      have increased since then; in case of doubt
      you can go for some samples of core tests.

   -  for column section & its reinforcement, i
      don't know what Codes of Practice is
      applicable in your country; if it were
      ACI-318, you can certainly assume it was
      based on ACI-318/63.

   -  Just in case you do not know it already,
      please be informed 1963 was the year which
      saw the TRANSITION from the Working Stress
      method of Design to the modern day Strength
      Design. That is why this Code is basically a
      Code based on woking Stress Theory & has an
      appendix on the Strength Design methods as
      well.

I hope I have been of some help to you & now over to our friend Daryl.

Regards,


SYED FAIZ AHMAD; MENGG, MASCE
SENIOR STRUCTURAL ENGINEER
SAUDI OGER LTD
RIYADH, SAUDI ARABIA.


From: rpuebla <rpuebla(--nospam--at)cee.gov.ec>
Reply-To: <seaint(--nospam--at)seaint.org>
To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
Subject: RE: concrete of forty years old
Date: Fri, 8 Mar 2002 08:40:50 -0500



Dear Daryl

Excuse but my English is not good.
I will  to clarify the idea.
It is wanted to a structure of reinforcement concrete had built for forty
years to make him an amplification. that which generates that the
solicitation increases on the structural elements. My question is this that
properties have deteriorated or as considering the age of the concrete in
the calculations.
I believe that   columns you necessary to reinforce because the
requirements 40 years ago are not the same ones that the current. Also as
aditional information for you the construction is in a region classified
with a Z=0.4
I wait to have clarified the idea


Regards,

-----Mensaje original-----
De: Daryl Richardson [mailto:h.d.richardson(--nospam--at)shaw.ca]
Enviado el: Thursday, March 07, 2002 11:57 AM
Para: seaint(--nospam--at)seaint.org
Asunto: Re: concrete of forty years old

Marino,

	Sorry, I don't understand the question.  Please try again and
provide
more detail as to what you want to know.

				Regards,

				H. Daryl Richardson

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SYED FAIZ AHMAD; MENGG, MASCE
SENIOR STRUCTURAL ENGINEER
SAUDI OGER LTD
RIYADH, SAUDI ARABIA.


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