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RE: Admixtures for Concrete Clarifier Tank

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You have several good suggestions already.  I will add a few more.

I like to suggest polycarboxylate super plasticizers. I have had a lot of good luck with that particular type of high range water reducer.

Consider requiring a uniformly graded aggregate. Jim Shilstone is the expert in that area. This will reduce the amount of cement paste and total cement quantity. Thus there will be less shrinkage and less heat of hydration.

Require a wet / fog cure.

In your neck of the woods concrete will often be placed at night shortly after the sun goes down. The super P results in a set time cut in half. That way you are done finishing the flat work and the cruing is on before the sun comes up.

You already got the note on maximizing the large aggregate and bumping your rebar to control shrinkage cracks.

I think you are good to go. Oh yeah, be on site and get the trip tickets to assure that you are getting what you specify.

Harold Sprague

From: "Joe Grill" <jgrill(--nospam--at)>
Reply-To: <seaint(--nospam--at)>
To: "seaint" <seaint(--nospam--at)>
Subject: Admixtures for Concrete Clarifier Tank
Date: Tue, 25 Apr 2006 16:06:19 -0700

I?m trying to finish the design and detailing for a circular concrete
clarifier tank for wastewater treatment.

I guess I would like to get a little verification for a couple of items.
The tank is in an area where there is no frost of freezing concerns,
therefore I am considering the following:

No calcium chloride admixtures

Maximum water/cement ratio .45 (ACI 350 table 4.2.2)

Minimum f?c= 4000psi (ACI 350 table 4.2.2)

Type II cement ( will ask that ?owner to provide soils evaluation of sulfate

¾? maximum aggregate (ACI 350 table 4.2.1 even though no frost problems)

5% air content (ACI 350 table 4.2.1 even though no frost problems)

4? maximum slump

Tank is not covered, therefore no protective coatings

Are there any advantages/disadvantages to the use of fly ash?  I was not
going to spec. it, but if it is advantageous, what kind and how much?
Hopefully, that isn?t asking for too much information.  I need to do a
little more reading about fly ash.  ACI 350 seems to suggest the use (and
provides tables for % of weight of cementitious materials) of fly ash where
there is exposure to deicing chemicals, but there shouldn?t be any of that
in use here (Southwest desert).

I appreciate any help or other suggestions that may be given here.

Joe Grill

Joseph R. Grill, P.E. (Structural)

Shephard - Wesnitzer, Inc.

Civil Engineering and Surveying

P.O. Box 3924

Sedona, AZ  86340

PHONE (928) 282-1061

FAX (928) 282-2058




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