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RE: Portlands vs. Blended Hydraulics

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Flyash is generally categorized as a C or F ash.  The benefit of ash varies
from the C or F ashes.  The following responses are general in nature.
There are exceptions.

Durability:  Durability is a large topic (abrasion, sulfate resistance, ASR,
cavitation, cracks)  Indirectly it helps by partially replacing the cement
and lowering the initial heat of hydration and reducing the potential for
cracks, especially for thick concrete slabs.  If by durability you mean
resistance to abrasion, I am not aware of any benefit.  Type F ashes have
been demonstrated to help in sulfate and ASR resistance.

Workability:  It increases pumpabiltiy.

Crack resistance:  It helps reduce shrinkage cracks by moderating the heat
of hydration.  It has no effect on tensile strength.

Freeze thaw breakdown resistance:  I am aware of no effect.

Alkalinity improvement (reduce carbonation):  Alkalinity and carbonation are
two separate issues.  I do not believe that flyash has an effect on either

Finish:  It is stickier and some finishers do not like it.  Kalman flooring
uses laser screeds, and prefers it in many of their mixes.  Used in large
quantities in cold weather conditions, flyash can retard a mix.  You must be
at the upper range of water temperature, and/or heat the area.

When using flyash, one should study its properties in both the plastic and
hardened state.  If properly used, the addition of flyash can benefit
performance.  If there is a problem, the problem cause must be properly

Harold Sprague
The Neenan Company

-----Original Message-----
From: Dee Henrie [mailto:dee(--nospam--at)]
Sent: Sunday, June 06, 1999 2:27 PM
To: 'seaint(--nospam--at)'
Subject: RE: Portlands vs. Blended Hydraulics

Although I am in steel construction, I attend construction coordination
meeting regularly.  The question came up regarding the addition of fly ash
and why it was not allowed on this particular project.  The Owners Rep. had
had a bad experience with it and would not allow it and the Structural
Design Engineer said it was company policy not to allow it.  I can
understand the Owners rep comment, but the Engineers was interesting.  My
point before I ramble much farther and expose my ignorance is this.
	Does the addition of fly ash provide an improved Concrete, and in
what area's?
		In Durability
		Crack resistance
		Freeze thaw breakdown resistance
		Alkalinity improvement (reduce carbonation)
I look forward to the final word on this.

Dee Henrie
Adams & Smith Inc.