Construction Joints in a water containing structures

[Schneidly]

I am in charge of the construction management of a 35ft x 111ft water containing structure. The bottom slab is 43.5ft x 119.33ft with 2 keyed, water stopped construction joints at third points of the length. The client wants a continuous poured slab. He states they did an aeration basin in a continuous pour and thinks there will be more leakage with jointed slab. I have always done “square pours” with joints spaced at 50ft or so. I have been look at code recommendations and the older codes give more strict recommendations than the more current ones. Does anyone have a reference I can refer to when I say “because I am the engineer and I say so”?

attached is a plan view and a couple sections

 

[JedClampett]

Well, actually that should be enough. If the client wants to seal the drawings, he can change the design.
ACI 350 used to have more guidance on joint spacing and they said to space contraction joints at 30 ft. We've always used 30 ft. for our default spacing for construction joints, so your 50 ft. spacing is actually pretty long.
You don't say how thick your slab is. But I'd make them install joints. AND to rub it in, I'd make them wait seven days between adjoining pours.

 

[apsix]

Fewer joints means more reinforcement (generally); it will need a redesign.

 

[hokie66]

Jed, he has two joints in the 111', so the sections are about square.

The client has a point...the joints are often where most leaks occur, but that is because they are not done right. But as apsix says, if you need to restrict the width of cracks in a longer slab, more reinforcement is required.

 

[JedClampett]

I could live with the 50 ft. joints, even though they're kind of widely spaced. I wouldn't like 119 ft without a joint.
Another issue, it's a good idea to have a wall joint at the same location as the slab joint. That's because the wall cracks tend to transmit to the slab. But if the joint locations you show are the only wall joints, you're going to have cracks in the walls. And these will continue into the slab.

 

[dik]

Can you use a bentonite 'rod' in the joint.... works like a charm at stopping water... and I'd definitely put in joints... for the width, depending on thickness of walls and slab, 50' seems like a reasonable maximum spacing.

Curing and low slump is critical...

Dik

 

[HeavyCivil]

I think bentonite isn't used much anymore in tanks. The ones I have done and seen all use PVC waterstops.

Building the bulkhead for the PVC is certainly more time consuming, and will require a couple people, a saw and many many pieces of dimensional lumber, but if done right It's going to be pretty tight.

 

[dik]

I still 'glue' bentonite rod in place for most of my waterproof containers... it goes right in the keyway, adjacent to any dowels... as far as PVC joint, I typically use the type that bridges the joint and is attached directly to the outside formwork. I've had too much difficulty with the PVC joints that are mid wall thickness.

Dik

 

[nilaypathak]

I have used waterstop c/w centerbulb and have riglet 25mm x 25mm on both sides and both faces. Fill riglet at the end with Sika SS/NS grout. It shold work.

 

[Schneidly]

dik and nilaypathak,

How do you space the joints? I use vinyl waterstops as nilapathak describes at new construction and bentonite at new to existing.

Thanks for your input!

 

[redsouther]

I recently did an aeration basin in a WWTP that was close to this size without any CJ's (though we did have a couple of expansion joints). However, as others have pointed out, ACI 350 requires a much tighter bar spacing for such a condition, so you'd have to redesign your slab.