Circular Water Tank Control Joint Spacing

[joshmaughan]

I have designed a circular water tank that is appoximately 150 feet in diameter and 16' tall. It has a concrete lid with interior columns. I have specified construction/control joints, with water stops at approximately 60 feet on center in the floor and lid. And vertical construction/control joints in the walls at approximately 60 feet o/c. This is the only recommendation I could find in the PCA Circular Concrete Tank manual for such spacing. Ths contractor has asked if he can pour the entire floor in one pour, with no joints. Then the walls in one pour with no joints, and the lid in one pour with no joints. CAn anyone advise me on whether this would be okay or not...........and direct me to any supporting code sections. Also, all concrete in this tank will have XYPEX admixture to provide additional waterproofing of any cracks.

Thanks!!

 

[ATSE]

Josh,
Probably not okay unless you have real high reinf ratios.
I am assuming you used ACI 350 for the tank design (ACI 318 is not adequate for this application), and you are not using shrinkage-compensating concrete. ACI 350 has recommendations re: joint spacing.

Do not pour the lid or the walls in a single pour. 60' is about the max single day pour length if you have at least 0.005% horiz steel in your walls (Table 7.12.2.1). Xypex will not close cracks that spiders can crawl thru.

By using construction joints ("cold joints"), you reduce the amount of strain in your concrete due to initial shrinkage.
Also, ACI 224.1 and 224.3 has a lot of useful info on joints.

 

[joshmaughan]

ATSE:

Thanks. Yes I did use ACI 350 in the design, so I do have at least .oo5% horiz. steel. I'm actually about .007% at my worst case (top of the wall). Sounds like I could stretch the 60' a little bit, but not too much. The XYPEX should help in the joints, along with the PVC water stops.

Any other input would be helpful. I don't have ACI 224

 

[JedClampett]

I wouldn't let him pour the slab in one pour. It's going to crack and leak. I would split the tank slabs into 12 pours. At the outside, the joints are about 45 ft. apart. Same for the walls. Make him pour the slabs in an alternating pattern with about seven days pourback time. That way you get most of the shrinkage out of the way before you pour the adjacent slabs. Not a big fan of Xypex or any other magic medicine. If the concrete leaks, it's usually due to poor workmanship and the Xypex won't help. It densifies the surface, but if there's cracks, it's not going to do as much good. We require epoxy injection of leaking cracks, if there are any. Or if the leaks are bad, you can divers in with dye wands and expanding hydrophilic material.
Do you have a leak test criteria? For a tank that size (~2,000,000 gallons) you shouldn't lose any more than .1% of the volume or about 2000 gallons per day.
Above all, don't give in to the contractor. It's your name on the drawings, not his.

 

[hokie66]

.005 = 0.5%. The Xypex salesmen must have been active in your area. The thing is, if you follow the complete Xypex specification for reinforcement, curing, etc., then the additive is unnecessary.

 

[joshmaughan]

Thanks ! You have all been helpful!