Expansion joint in 2'-8" foundation slab?

[whymrg]

I am working on a project with a pump station and water tanks sitting below grade. Due to buoyancy, I need 2'-8" thick base slab. Due to length of structures, I need 1 inch expansion joint in this slab. I will use PVC waterstop.

I just can not find any ideas or info on how to leave this 1 inch open under the waterstop. If I use any filler, it will be smashed by the concrete during pour.

Any ideas?

 

[kayah]

I'm curious why you need a 1" expansion joint if this is below grade?

 

[whymrg]

Top of tanks and pump station is above grade and with winter-summer temperature changes it will move or brake.

 

[Focht3]

Where is your site?



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.

 

[whymrg]

OK, I talked to void forms people and they said that they may provide 1 1/2 inch void form. So I will use 1 1/2 inch joint.

Thanks.

 

[JedClampett]

We use a sponge rubber or asphaltic filler, a round backer rod at the top of the joint, a bond breaker and caulk the joint with a two-part polyurethane sealer. The concrete will not crush the filler. Don't forget, you're only talking about 32 inches of liquid concrete "head" and these filler are pretty stiff.
You want to make sure that stuff doesn't get in the joint and restrict the movement. Hence the backer rod and caulk. If the void forms you're talking about are the same I'm familiar with, they'll deteriorate and you'll be left with an open gap. This will quickly foul with grit and dirt and stop the joint from closing.
See ACI 224.3R Chapter 9 for some examples.

 

[ishvaaag]

We have made foundation (cellar) mats for buildings over 1 m thick and 120 m long (also of lesser thickness and horizontal dimension) without any special provision for joints in the mat and has not caused any problem. Underground vases may or may not require the joints. Walls use to be far more critical than the mats. In any case, engineered joints shouldn't cause any problem either and with proper consideration of what ongoing may be from required to simply part of a better designed structure.