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RE: Admixtures for Concrete Clarifier Tank - further thoughts

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One other thing to note with the fly ash is you should take enough test
cylinders to do a 56 day break also. I have had some tests fail on 28
day breaks but did fine after 56 days. . I agree with 15% as a maximum
limit although I thought that was a 1:1 replacment by mass. I will have
to check with the supplier next time...

Kevin 

-----Original Message-----
From: Harold Sprague [mailto:spraguehope(--nospam--at)hotmail.com] 
Sent: Thursday, April 27, 2006 3:55 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Admixtures for Concrete Clarifier Tank - further thoughts

Dave,
By "Old School", I mean that there are many that trade out F ash at a 1
to 1 and don't limit the maximum to 15%.  I have just had good luck with
the 1.5 to 1 and 15% max.

I think that if you try these limitations with F ash, you will find that
you have better performance in the plastic state, setting, and the
hardened state.

Regards,
Harold Sprague





>From: "Dave Handy" <dhandy(--nospam--at)trg.ca>
>Reply-To: <seaint(--nospam--at)seaint.org>
>To: <seaint(--nospam--at)seaint.org>
>Subject: Re: Admixtures for Concrete Clarifier Tank - further thoughts
>Date: Thu, 27 Apr 2006 17:45:16 -0400
>
>Harold:
>
>----- Original Message ----- From: "Harold Sprague" 
><spraguehope(--nospam--at)hotmail.com>
>To: <seaint(--nospam--at)seaint.org>
>Sent: Thursday, April 27, 2006 4:19 PM
>Subject: Re: Admixtures for Concrete Clarifier Tank - further thoughts
>
>
>>Dave,
>>
>>I find it incredible that a concrete plant would opt to increase both 
>>cement and water to avoid super P.  That is like shooting ones self in

>>the foot and at 6" spacing up the ankle, leg, wallet, etc.
>
>This is what I thought as well. I am glad that I am not alone on this. 
>Maybe this is why he doesn't work at that concrete plant anymore. He 
>told me that it was cheaper for them to increase both than add the 
>chemicals. I had never thought about it until he made this statement 
>and I figured the w/c alone would address my concerns and they would 
>naturally add the super-p.
>
>>I would think that in lieu of using a slump limit (which is a very 
>>poor indicator of w/c ratio and workability) I would opt to put in a 
>>limit on the water.  This would by default limit the w/c ratio. You 
>>are still stuck with a slump for the target indicator of workability.
>
>For a 35MPa mix used for sewage/water treatment (or even a flat slab or

>slab on grade to minimize shrinkage) how would you spec the mix to 
>minimize shrinkage assuming there are no shrinkage compensating cements

>available. I have used the larger aggregates for floor slabs and that 
>seemed to work well. With the more heavily reinforced items I haven't 
>been straying from the 3/4" aggregate.
>
>>If I or one of my staff have authority to approve the mix design 
>>submittal, I don't have a problem in using F fly ash.  It can provide 
>>some benefits regarding density, lower heat of hydration, reactivity, 
>>reduced propensity for cracking, pumpability, etc.  But I limit the 
>>maximum amount of fly ash to 15% of the total cementitious materials 
>>and use a substitution rate of 1.5 pounds of fly ash for 1 pound of 
>>cement.  I know that that is old school, but I am a bit of a chicken.
>
>So has this produced a concrete strength consistently above your min
specs? 
>(and conversely not too high above your specs). When you say this is 
>old school..how old school is this? Do you know what the current 
>recommendations are regarding this?
>
>>Fly ash also gives me a LEED tree hugger atta-boy, but that is not 
>>high on my list of motivators.
>
>My motivation is always that I don't want any problems..on this 
>particular job that soured us the slumps were up and down and the 
>mobile concrete technicians (truck drivers) were adding water to the 
>mix on site after being repeatedly told that it was heading back to the

>plant if it didn't get to site properly batched.
>
>>Regards,
>>Harold Sprague
>
>Thanks
>Dave Handy
>

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