What is the typical minimum cover for reinforcing steel in exterior slabs to protect against corrosion?

• A. Generally 2 inches minimum; larger bars or harsher exposure may require more (3 inches).
• B. 1 inch
• C. 3 inches
• D. 4 inches

Answer: (D)

Durability of reinforced concrete hinges on keeping moisture and chlorides away from the steel, and the concrete cover over the bars is the barrier that slows their ingress. In exterior slabs, where the steel is exposed to weather, rain, freeze‑thaw, and possibly deicing salts, a thicker cover protects the rebar longer and helps prevent corrosion over the structure’s life. Four inches of concrete cover is a common, practical minimum for exterior slabs to provide reliable corrosion protection. Smaller covers might be used in interior or less aggressive environments, or if conditions are milder, but for exterior slabs the extra thickness is a standard safeguard. If the exposure is particularly harsh or the bars are large, even more cover can be specified, but four inches is the typical minimum in this context.