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RE: ASR Repair

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Mark,

Stopping the effects of ASR is not too much of a problem in theory, but in
practice may be another issue.

The ingredients of the ASR problem are alkali, reactive silica and moisture.
To start the concrete deterioration process in ASR concrete takes a relative
humidity of about 80% at 70 degrees F.  You can't remove the alkali or the
reactive silica, but you can reduce the humidity.

Hopefully, by now you have had the petrographic and microscopic studies to
determine:
1.	What is the frequency of the yet-to-react aggregate.
2.	What is the true source of the observed deterioration.  Often times
ASR can lead to freeze thaw damage.  The small cracking may be able to
accommodate additional future expansion of the alkali-silica gel.

If there is a potential for future damage (unreacted aggregate) you may wish
to apply a breathable waterproofing material.  If most of the aggregate has
reacted, repair what needs to be repaired with patching materials and call
it a day.

I would suspect that a building constructed in the 60's has maxed out the
reactive aggregate.

If the deterioration is slight, just repair the local areas.  If it is more
significant, do the repairs and apply the breathable membrane.  If it is
really bombed out, rebuild it with non ASR concrete.  

If the structure is small, it may not warrant a microscopic or petrograpic
study.  You might be able to do the repairs for the cost of the study.  It
is the old lesson of don't use a sledge hammer on thumb tacks.

There was an article about ASR repair in Concrete International, January
1993, p. 74, by Dean Kofoed of Concrete Microscopy, Inc. 612-521-5186.

Regards,
Harold Sprague
The Neenan Company


-----Original Message-----
From: Mark Rodgers [mailto:MarkR(--nospam--at)dpsabq.com]
Sent: Tuesday, September 07, 1999 3:40 PM
To: seaint(--nospam--at)seaint.org
Subject: ASR Repair


I am working on a remodel and addition to a retail store.  The concrete
parapets exhibit signs of Alkali Silica Reactivity (ASR).  The concrete has
been tested and ASR is present.  The building was built in the 60's in
Albuquerque, NM.

I am wondering if anyone has any ideas on the repair of concrete with ASR?

Thanks in Advance,

Mark Rodgers. EIT
Dekker / Perich / Sabatini
architecture  interiors  planning  engineering
505 761.9700
fax 761.4222