Expansion joint questions

[ianinnj]

I am getting ready to pour my garage apron and driveway. The overall size is 40' deep x 50' wide and will be making 10' x 50' pours. Control joints will be cut on the 10'.
My question is do I need to be placing expansion strips between each 10' pour, every second one, or none are necessary?
Maybe I am just green, but I never really figured concrete to be something that has any significant amount of expanding properties. Blacktop, yes, I have seen expand and contract on a seasonal basis, but not with concrete.
Also I am intending to place rebar stubs to tie each 10 x 50 pour together, which thinking about it, would seriously compromise the 'expanding' slabs.
Any help or suggestions please would be appreciated.

[RobBase]

Put one expansion joint at the 20' joint. Standard distance for concrete expansion joints is every 30' so you will be well within that spec. Concrete expands and contracts like everything else.

When you order your concrete, tell them you want it "air-entrained." This is an additive that makes the concrete full of microscopic air bubbles which allows it to be a bit more "flexible", shall we say, to withstand the heat/freeze cycles that outdoor concrete is subjected to.

For the 10' and 30' joints, you can use rebar dowels to tie the slabs together. For the 20' joint, you will want to pour the slab edge with the rebars projecting just like for the 10 and 30 joint. After you strip that edge form, put your expansion joint against the concrete with holes drilled through your expansion material so the rebar projects through it. Then take some 30# roofing felt and roll some around the rebar so it's like a sleeve. You can also put some grease on the rebar before you put the felt around it. Then duct tape the felt so it stays on the dowel. Pour your next driveway segment against this. The felt/grease will allow the slabs to expand/contract against each other without tearing the concrete apart.

[Timothy Hampton]

Rob is correct in that all concrete subject to freeze/thaw cycles should be air entrained. It is also important that one side of your dowels have sleeves on them to allow for the expansion and contraction. Basically it is a "load transfer" as well as an expantion joint. Good luck with your project!