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RE: Flyash

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In my view, 50% fly ash is too much.  FWIW, the Corps of Engineers guide specification requires a minimum of 15% and a maximum of 35%.  Navy Guide specs allow up to 40%.  I normally reduce these maximums to 25%.
-----Original Message-----
From: Peder Golberg [mailto:peder(--nospam--at)] 
Sent: Wednesday, August 28, 2002 6:09 PM
To: seaint(--nospam--at)
Subject: Flyash

I have an architectural client who wants to use between 35% and 50% flyash to replace the cement content in a slab on grade (with a w/c ratio of 0.40).   The slab will be covered with flooring that is very moisture sensitive and this amount of flyash is being recommended to the architects by the "green" designers.    I have always thought 20% was the maximum recommended and any more than this makes the finish work and curing not practical along with strength issues.
Any have any good or bad experiences (or references) using this high amount of flyash content?   
Peder Golberg
Portland, Oregon