Rebar clearance is a critical component in regards to reinforcing steel placement. If the reinforcing steel does not have proper clearance from the surface of the concrete, it will creates an increased oxygen and moisture rich environment. Oxygen and moisture are perfect for creating an environment for rust. As the rebar begins to rust, it will begin to corrode. This corrosion will lead to a decrease in tensile strength, which in turn affects the integrity of the structure.
Typically the clearance specifications are located on the project drawings and/or the project specifications. If not, you can refer to ACI 318 (Concrete protection for reinforcement – non-prestressed), which states the following:
- Concrete cast against earth and permanently exposed to earth: 3 inches
- Concrete exposed to earth or weather (No. 6 to No. 18): 2 inches
- Concrete exposed to earth or weather (No. 5 and smaller): 1.5 inches
- Concrete not exposed to earth or weather (No. 14 to No. 18): 1.5 inches
- Concrete not exposed to earth or weather (No. 11 and smaller): .75 inches
- Beams and Columns: Primary reinforcement, ties, stirrups, spirals: 1.5 inches
- Shells and folded plate members (No. 6 and Larger): .75 inches
- Shells and folded plate members (No. 5 and smaller): .5 inches
