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RE: Fly ash in concrete

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Some documents of interest regarding the use of fly ash:

ACI 232.2R-96 (Use of Fly Ash in Concrete).  This report contains a
chapter on the effects of using fly ash in both hardened and plastic
concrte.

ACI 211.1-91 Reapproved 1997 (Standard Practice for Selecting Proportions
for Normal, Heavyweight, and Mass Concrete).  This documents provides more
general information for proportioning concrete, but does discuss some of
the issues relative to fly ash.

HTH

Scott


On Thu, 24 May 2001, Nicholas Blackburn wrote:

> Fly ash in concrete is typically used to reduce the per-yard cost of the
> concrete by reducing the quantity of cement while still producing the
> desired strength at 28days.  ACI recommends at least 15%replacement with an
> upper limit of 25% for normal mixtures.  Strength-gain for fly-ash
> containing concrete may be somewhat slower than for more conventional mixes
> depending on the dosage.  This could be seen as a problem if a specific
> finish is desired and that that finish might get degraded by the
> construction processes going on during the first 28 days.  I cannot conceive
> of this kind of problem for foundations.  
>  
> We have had some architectural resistance to the use of fly ash in
> slab-on-grade mixes in parking structures because of the perceived hardening
> issues.  However, it has been my experience the possible negative affects on
> the sweated swirl finish do not materialize and are far outweighed by the
> durability benefits.
>  
> Fly ash can also increase the finishability and pumpability of the concrete
> as it helps to fill in the grading sequence of the fine aggregates.
>  
> Nicholas Blackburn
> 
>  -----Original Message-----
> From: DWILLIAMSSEI(--nospam--at)aol.com [mailto:DWILLIAMSSEI(--nospam--at)aol.com]
> Sent: Thursday, May 24, 2001 9:25 AM
> To: seaint(--nospam--at)seaint.org
> Subject: Fly ash in concrete
> 
> 
> 
> Has anyone had negative experiences with using fly ash in concrete mixes? 
> 
> I'm working with an architect who doesn't want it used, but I'm not sure
> why. 
>  The spec's call for 3,500 psi 28 day strength concrete.  Fly ash is not 
> mentioned in the spec's, but a contractor has asked if it's permissible to 
> add it to the mix.  I understand that fly ash is used to improve flowability
> 
> of dry mixes.  I couldn't find much other information regarding the use of 
> fly ash in ACI 318 or any of my materials and concrete references. 
> 
> The application for the concrete in question is spread footings for steel 
> columns and perimeter footings for slab/brick masonry support for a 2-story 
> building. 
> 
> Thanks. 
> 
> David Williams, P.E. 
> Snyder Engineering, Inc. 
> Columbia, MO 
> 
> 



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