Cover to reinforcement in columns, beams, foundations, etc. is
required for the following reasons:- To protect the steel against corrosion.
- To provide sufficient bond or adhesion between steel and concrete.
- To ensure sufficient protection of the steel in a fire (see Note).
If the cover is insufficient, concrete will spall away from the steel.
Minimum cover ~ never less than the maximum size of aggregate in the
concrete, or the largest reinforcement bar size (take greater value).
Guidance on minimum cover for particular locations:Below ground ~- Foundations,retainingwalls,basements,etc.,40 mm,binders25 mm.
- Marine structures, 65 mm, binders 50 mm.
- Uneven earth and fill 75 mm, blinding 40 mm.
Above ground ~ - Ends of reinforcing bars, not less than 25 mm nor less than 2 ¾ bar
diameter. - Column longitudinal reinforcement 40 mm, binders 20 mm.
- Columns <190 mm min. dimension with bars <12 mm dia., 25 mm.
- Beams 25 mm, binders 20 mm.
- Slabs 20 mm (15 mm where max. aggregate size is <15 mm).
Note: Minimum cover for corrosion protection and bond may not
be sufficient for fire protection and severe exposure situations.
For details of fire protection see ~
Building Regulations, Approved Document B: Fire safety.
BS 8110-2: Structural use of concrete. Code of practice for special
circumstances and BS EN 1992-1-2: Design of concrete structures.
General rules. Structural fire design.
For general applications, including exposure situations, see next
page.Concrete Cover to Reinforcing Steel