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RE: Fly Ash

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Todd
As I understand from your response your objective for using fly ash in light weight concrete is:
i) for improving workability &
ii) for partial replacement of cement.
Well, in my opinion the w/c ratio normally used in light weight concrete makes it quite a workable concrete already so you don't really need fly ash for the purpose, unless there is an special requirement. For the purpose of partial replacement of cement(to effect cost), in my opinion, there is no harm in using fly ash in your particular case. But I must caution you here. Fly ash (like any other pozzolana) is known for low strength gain in the early ages, especially at 3 & 7 days as compared to normal concrete. The strength gain at 28 days is also low (as compared to normal concrete) but is comparable. However, at 56 days & beyond, fly ash concrete is known to surpass the strength gain of normal cocrete. So, you need to provide:
i) extended period of curing.
ii) extended period of propping before stripping.
Otherwise, it is quite safe to use fly ash, infact it provides a better durability to concrete.
Hope that explains. Best regards.
SYED FAIZ AHMAD. MENGG, Mem ASCE.
SENIOR STRUCTURAL ENGINEER
SAUDI OGER LTD
RIYADH, SAUDI ARABIA.


From: Todd Hill <thill(--nospam--at)tkarch.com>
Reply-To: seaint(--nospam--at)seaint.org
To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
Subject: RE: Fly Ash
Date: Thu, 14 Jun 2001 10:08:13 -0500

I suppose the concrete supplier uses it for all the reasons you stated
below.
Probably 1 & 3 mostly.
The lightweight concrete is structural.
I use the lightweight concrete on a composite metal deck for lighter floors.


-----Original Message-----
From: syed faiz ahmad [mailto:syedfaiz23(--nospam--at)hotmail.com]
Sent: Wednesday, June 13, 2001 4:41 PM
To: seaint(--nospam--at)seaint.org
Cc: thill(--nospam--at)tkarch.com
Subject: Re: Fly Ash


Gentlemen
Fly ash is a Pozzolana. It has a  long  trusted history of uses as:
- as an agent for better workability
- as a water reducer agent in concrete
- as an agent to replace Cement partially, so as to effect cost
  economics of concrete.
- as an agent to control temperature cracks in mass concrete, resulting
  out of exothermic reaction due to hydration process.
- as an agent to fight against sulphates & chlorides in soil
- so on & so forth.
My question is:
      - why you want to use fly ash in light weight concrete? In simple
        what is the objective of using it?
      - Is the light weight concrete STRUCTURAL or NON-STRUCTURAL?
Unless this is answered, it will be difficult to defend your case for use of

fly ash in the concrete perse.

>From: Todd Hill <thill(--nospam--at)tkarch.com>
>Reply-To: seaint(--nospam--at)seaint.org
>To: "SEAINT (E-mail)" <SEAINT(--nospam--at)SEAINT.ORG>
>Subject: Fly Ash
>Date: Wed, 13 Jun 2001 11:49:57 -0500
>
>Is there any reason why fly ash should not be used in Lightweight concrete? >We've had a colored concrete manufacturer say their product won't work with
>fly ash.
>But, I was wondering if there was another reason.
>
>Todd Hill, P.E.
>TK Architects, Inc.
>816-842-7552 ext. 233
>
>
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