Steel bar designed to be placed in concrete for reinforcement. Concrete has compression strength; reinforcing bar adds resistance to breaking when other types of forces are applied. The bars have a patterned, or textured exterior, which allows them to bond or interlock with the concrete mix. They come in a variety of sizes, starting at � inch diameter and increasing in size in increments of 1/8 inch. Also called rebar. BlueHeat snow melting cables or other radiant heating cables or tubing are often tied down to rebar for support and proper spacing.