We are having a pool installed and when the deck is poured we are extending an existing Slab Patio by Approx. 4 Feet. I feel that that holes should be drilled horizontally into the existing edge and steel pins should be inserted to prevent Vertical movement between the old and new portions. The pool installer tells me its a waste of time.
I think I will do it anyway unless it would cause some other problems.
I recently had a room added and the contractor had to "connect" 2 sections of concrete footing. They did it with pins (not certain what they were made of) and a powerful adhesive called Rezi-weld. Hope that's helpful.