How can you repair a reinforced concrete slab?

if it is a section of a pour. rent a walk behind masonry saw and cut a square. jack hammer out the bad section. drill the existing slab every 2 feet to accept the new re-bar. leave a foot of re-bar sticking out of every hole on both ends of the slabs.tie wire your new re-bar to these ends...re-pour slab with concrete matching the old specs...