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Admixtures for Concrete Clarifier Tank

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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

jgrill(--nospam--at)swiaz.com