Well, you could try welding a series of straps or bars parallel to the flutes to re-establish adequate tension area....
but...
The primary mode of failure for composite decking is shear-bond failure, not flexural failure. So with the rusting, I'd be concerned that you have lost some amount of bond (unknown quantity that's hard to test for) and thus, you could still have a failure...and an abrupt one at that.
I would think that if you have evidence of long term corrosion in the deck, that removal of the concrete would be warranted to allow complete inspection of the extent of damage. You would then be in a position to re-splice/weld on new deck sections and replace with fresh concrete to re-establish the deck to an original condition.