Horizontal Joints in Water Tanks

[cjung]

Hi, I am working on new waste-water digester concrete tank construction. I am wondering if horizontal construction joints are allowed during the tank wall construction. It is 40ft diameter and 40 ft height circular shape concrete tank. I heard only vertical construction joints are permitted due to the leak of horizontal joints in the past. I am looking for any code or specification regarding the construction joint locations for above ground concrete water tank or waste-water digest tank. Please help me to locate the spec or book. I know you guys are the best.
Chris

 

[hokie66]

I assume you have a horizontal joint at the bottom of the wall. How do you deal with leakage there?

 

[cjung]

Hi HOKIE66:

Starter wall about 2-3" and horizontal keyed joint with water stop. After pressure water wash, I may use expandable water stop or PVC. I am not sure yet.
I am asking because at the bottom wall level, the concrete shrinkage could be managed well due to enough time between slab and wall pour. However, at intermediate wall height joints were prevented due to concrete shrinkage between the wall pour (short waiting time).
I am looking for some documentation to prove its statement.

 

[JedClampett]

Horizontal joints are allowed and common in water bearing tanks, especially for 40'-0" tall ones.
Separately, if you're using starter walls (good idea) don't use just expandable waterstop. Six inch PVC waterstop, 3/8 inch thick should be used at a minimum. If you want to add some hydrophilic waterstop, go ahead, it won't do any harm. But PVC waterstop buried in concrete is forever.
They're not going to pour a higher level that quickly. If you're worried, require a minimum pour back time, like 14 days.
If I can find my copy of ACI 350-89, it might have some language regarding joints. But if you're looking for permission to put in a horizontal joint, just tell them JedClampett says they're OK.

 

[hokie66]

I think cjung is concerned with vertical cracking in the upper portion due to restraint by the already cast lower section. That is a valid concern, and waiting longer between pours will make that worse.

Add some additional reinforcement just above the joint to attempt to control those cracks better. That applies at the bottom as well as at intermediate joints. But if you have about 0.6% Ag reinforcement, crack control will be good.

Agree with Jed...use PVC waterstops on the inside face.

 

[JedClampett]

hokie66, I agree about adding reinforcement above horizontal joints. I wished I would remember it more often. But in my digester experience, the horizontal reinforcing is usually so heavy that this cracking is not a problem. Even if the joint is at mid-height, you've got 20 feet of liquid pressure you're designing against.
But cjung, I think hokie and I would agree that adding 6 #8's (three each face) above the joint is cheap insurance.

 

[hokie66]

Yep, I do agree.