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RE: Fly ash

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In addition to referring to ACI 232.2R, the August 2002 issue of Concrete
International had an article titled "Using Mineral and Chemical
Durability-Enhancing Admixtures in Structural Concrete" which may be
helpful. It discusses durability of high fly ash mixes and indicates that
there is little performance difference between concretes with between 35 to
40% fly ash and mixes with over 50% fly ash. It also indicates that greater
than 20% fly ash can increase carbonation at cracks, and ACI 301 doesn’t
permit greater than 25% fly ash for concrete exposed to deicing chemicals. 

I generally limit fly ash to 15 to 25% of cementitious content; however, I
do think that higher percentages up to 35 to 40% might be permissible in
some applications. I would recommend longer wet curing time with higher fly
ash contents. 

-----Original Message-----
From: Peder Golberg [mailto:peder(--nospam--at)]
Sent: Wednesday, August 28, 2002 4:09 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

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