By necessity, a concrete driveway must be sturdy to support cars and trucks that may drive over it. For a concrete driveway to last the life of your home, it must be well constructed. Concrete driveway slabs typically are 4 inches thick but can be up to 6 inches thick to provide additional support for large trucks and other heavy vehicle traffic. Ideally, the slab has some kind of reinforcement inside. One common building reinforcement material is rebar.
Rebar
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Rebar is the shortened name for a reinforcing bar. Rebar is made of steel and has been used for over 150 years to reinforce concrete construction. Concrete slabs are highly prone to cracking, and rebar helps prevent cracks from widening due to sections of cracked slabs moving apart.
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Rebar verses Mesh
One alternative to rebar for driveway reinforcement is welded wire mesh. The mesh consists of galvanized panels of welded wire. Heavy gague welded wire mesh panels can provide reinforcement for driveways that are not routinely driven on by heavy vehicles such as construction vehicles or industrial trucks. Mesh is typically used by contractors who pour driveway concrete to a thickness of 4 inches because it is a thinner reinforcement and less expensive than rebar. However, according to Tim Carter at Ask the Builder.com, if you can afford to have a thicker driveway poured, it's better to use number three rebar, which is 3/8 inches in diameter, for reinforcement.
Using Rebar
Rebar is best used in a driveway for which 5-6 inches of concrete can be poured. This is because rebar is comparatively thicker than galvanized mesh reinforcement. The proper way to use rebar reinforcement is to ensure that it is laid in the center or slightly above the center of the slab's thickness. To do this, concrete pros prop up the rebar grids on special metal or plastic supports, called "chairs." It's also possible to use bricks and other scrap material for supports, but this can create weak spots in the slab. Rebar grids are constructed by laying the pieces of bar in a perpendicular pattern, with even spacing. The bars are tied together at each intersection with metal wire. The edges of the grid should be kept at equal distances from all sides of the slab, and the minimum coverage of concrete must be maintained throughout the slab.