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RE: Fly ash in concrete

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Gentlemen
Fly Ash is basically a pozzolana. And, pozzolanas have a long history of successful use & applications in both plain & reinforced concrete. A great number of research publications have also been made on the subject in the universities the world over. In the US alone it has been used extensively in the construction of dams. Because besides other qualities fly ash also help to contain concrete temperature ( resulting out of exothermic reaction in hydration process ) in mass concrete. Basic reasons fly ash ( or for that matter any other pozzolana ) is used are:
1. to improve workability & flowability of concrete.
2. for durability purposes as it is known to be very effective in providing resistance against corrosive actions of soil.
3. as mentioned above to control concrete temperature in mass concrete.
3 and, for economy reasons, that is for cement replacement.
a numbere of research publications have been also been published by ACI JOURNAL FOR MATERIALS dating as early as beginning of twentieth century. Known experts on the subject are:
1. Adam Neville
2. Mather
3.Murdock
The US Bureau of Reclamation, The US Corp. of Engineers have contributed a lot on the subject. You can also find good works done at the Asian Institute of Technology (AIT), Bangkok, THailand. As for your question, i think use of fly ash would serve the following purposes: 1. Slab-on-Grade are basically mass concrete. They are prone to cracking due to drying shrinkage. fly ash would help inhibit that. 2. use of fly ash would provide it extra durability quality to resist corrosive actions of soil with which it will come & remain in contact.
SYED FAIZ AHMAD
SENIOR STRUCTURAL ENGINEER
SAUDI OGER LTD. RIYADH, SAUDI ARABIA

From: Scott Maxwell <smaxwell(--nospam--at)engin.umich.edu>
Reply-To: seaint(--nospam--at)seaint.org
To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
Subject: RE: Fly ash in concrete
Date: Thu, 24 May 2001 18:39:16 -0400 (EDT)

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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