Rebar is not required for all concrete projects. The usual rule of thumb is that if you are pouring concrete that is deeper than 5 inches, you should generally add some rebar to assist support the entire building. Concrete is heavy and needs reinforcement to be strong.
The only time I would recommend against adding rebar to a project is if you have soil underneath that can resist pressure from the weight of the concrete. In this case, you would want to make sure that the soil is able to sustain any weight that might be placed on top of the slab. This could be in the form of foot traffic or as part of an architectural feature.
If you decide not to add rebar, here are a few things to consider when choosing what type of reinforcement to use:
The first thing to think about is whether you just want to ensure structural integrity or also want the concrete to look good. If you choose to add rebar but then also want the concrete to be colored or textured, it's easy enough to do. Just make sure that the type of rebar you select will work with your contractor's methods for coloring/texturing the concrete.
Next, you want to decide how much pressure the slab will be under.
When the concrete is being poured, rebar may slip out of position, resulting in inadequate covering. In general, rebar in residential construction requires 3 inches of concrete cover or separation from earth when placed against dirt, and 1 1/2 inches when poured against forms. The amount needed depends on the size of the bar, but about 18 inches long is a good starting point.
Rebar is used to provide structural strength in concrete buildings. It's usually made of steel, but some varieties of rebar are also made of other materials such as wood or plastic. The two main types of rebar are hollow and solid. Hollow rebar is usually $\ell$-shaped with one flat surface and a cylindrical section between $5$ and $20$ feet long. It can be used for tying together various elements of a building structure, including beams, columns, and slabs. Solid rebar is available in several shapes: round, square, and hexagonal. It can be used alone as a foundation reinforcement or in combination with other types of rebar. The depth of concrete coverage depends on the type of rebar used; for example, if solid rebar is to be buried completely under soil, at least $3$ inches must separate it from the ground.
The required length of rebar will vary depending on its use.
Wire mesh is becoming increasingly popular for projects such as residential driveways. Reinforcing concrete with rebar or wire mesh not only strengthens it, but it also reduces the amount of fractures that form in the concrete over time. These cracks allow water to seep into the surface and may eventually cause your driveway to fail.
The decision on whether or not to include rebar in your project will depend on several factors. The strength of your concrete, the type of reinforcement you select, the length of the bar, and the number of layers of reinforcement are all factors that may influence whether or not to include rebar in your project.
The first step in deciding how to reinforce your concrete driveway is to determine how strong it needs to be. Concrete strength is measured in pounds per square inch (psi). This means that if your concrete has 10 psi of strength, it can support 10 pounds per square inch of pressure. The higher the number, the stronger the concrete.
You should always use concrete with at least 6-8 inches (15-20 cm) of slump when pouring curbs, drives, or other structural components. This allows enough time for the cement to harden before any additional pressure is placed on it. If the concrete is too stiff, you will need to add more water to it or wait until it loses some strength before adding more concrete.