minor repair of slab concrete under rusted metal form deck

[AskTooMuch]

I have a non-composite form deck that has some areas rusting. You can see the concrete in these areas and some has spalled. It will be repaired by patching with cement grout.

The question is what to do with the metal form deck on this areas? Do you usually do a bigger cut of the form deck around the concrete patch?

 

[phamENG]

That would depend on what the metal deck is supposed to be doing. If non-composite deck is galvanized or properly painted, it is permissible to design it to carry the slab dead load and the slab itself to carry only the live loads. So you need to see if, once repaired, the slab alone can carry itself and the live loads. If not, and you need the deck, I'd be very cautious about removing more than is absolutely necessary, and of course finding a way to restore it as well. Cutting the form deck will probably damage the slab, so if you don't have to do it to get to sound concrete, I wouldn't.

 

[AskTooMuch]

Slab has both top and bottom reinforcement #4 @ 12". Slab can carry it's own DL and LL.

 

[AskTooMuch]

Do I just leave the deck alone with those jagged edges at the opening instead of having it cut clean?

 

[JAE]

You could either sand-blast, shot-blast or hand-tool the rusted deck areas away.

The remaining concrete should be sounded to find hidden delaminated areas and allow for its removal and replacement.

Another thing to consider - if the deck has had exposure to chlorides, you might have some "sick" concrete with a low pH (acidic) where this condition will continue to rust the reinforcement.
The low pH might also tell you that the concrete matrix may be damaged such that your assumption of a normal f'c concrete strength isn't valid.

You can at the least take some cores and verify in-situ compressive strength. Further efforts would be to send cores off to a lab that can analyze the concrete.