Q.: Why would you put reinforcing steel in sidewalks, driveways or other exterior flatwork where cracking is likely to occur? Won't the cracks expose the reinforcing steel and increase the probability of corrosion?
A.: Many engineers recommend the use of reinforcing steel at locations such as re-entrant corners, where cracking is likely. This steel helps to hold the crack faces together, maintaining load transfer through aggregate interlock. Reinforcing steel also helps to prevent faulting or relative vertical movement between adjoining portions of a cracked slab. But it doesn't prevent cracking.
Although a steel bar may corrode in regions near a crack, the crack usually is perpendicular to the bar, thus limiting the area exposed to corrosion.
When properly jointed driveways and sidewalks without re-entrant corners are built on a well-compacted subbase using good-quality concrete, reinforcing steel may not be needed. However, some builders use it to control the width of unexpected cracks.