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RE: Admixtures for Concrete Clarifier Tank

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You have received some good advice from others regarding the proposed mix. 
Regarding fly ash, it can have the following benefits: improved workability and impermeability.  May also improve sulfate resistance and ASR resistance.
I typically allow Class F fly ash to be used in the 15 to 25% range as an option.  Class C fly ash can be used but may require a closer look at properties.

William C. Sherman, PE
(Bill Sherman)
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)


From: Joe Grill [mailto:jgrill(--nospam--at)]
Sent: Tuesday, April 25, 2006 5:06 PM
To: seaint
Subject: Admixtures for Concrete Clarifier Tank

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 exposure?)

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