Concrete cover for reinforcement is required to protect the rebar against corrosion and to provide resistance against fire. The thickness of cover depends on environmental conditions and type of structural member.
The minimum thickness of reinforcement cover is indicated in the drawings, or shall be obtained from the relevant code of practice.
Minimum Concrete Cover for Reinforcement
Below are the specifications for reinforcement cover for different structural members in different conditions.
a) At each end of reinforcing bar, concrete cover not less that 25 mm or less than twice the diameter of the bar should be provided.
b) For a longitudinal reinforcing bar in a column, concrete cover not less than 40 mm not less than the diameter of such bar should be provided. In case of columns of minimum dimension of 20 cm or under, whose reinforcing bars do no not exceed 12 mm, concrete cover of 25 mm to be used for reinforcement.
c) For longitudinal reinforcing bars in a beam, not less than 30 mm or less than the diameter of the bar.
d) For tensile, compressive shear or other reinforcements in a slab or wall not less than 15 mm, not less that the diameter of such bar.
e) For any other reinforcement not less than 15 mm, concrete cover not less than the diameter of such bar.
f) For footings and other principal structural members in which the concrete is deposited directly against the ground, cover to the bottom reinforcement shall be 75 mm. If concrete is poured on a layer of lean concrete, the bottom cover maybe reduced to 50 mm.
g) For concrete surfaces exposed to the weather or the ground after removal of forms, such as retaining walls, grade beams, footing sides and top etc. cover should not be less than 50 mm.
h) Increased cover thickness shall be provided as indicated on the drawings, for surfaces exposed to the action of harmful chemicals (or exposed to earth contaminated by such chemicals), acid, alkali, saline atmosphere, sulphur, smoke etc.
i) For liquid retaining structures, the minimum cover to all steel shall be 40mm or the diameter of the main bar, whichever is greater. In the presence of sea water and oils and waters of a corrosive character the covers, shall be increased by 10 mm.
j) Protection to reinforcement in case of concrete exposed to harmful surroundings may also be given by providing a dense impermeable concrete with approved protective coatings. In such a case the extra cover mentioned in (b) & (i) above may be reduced.
k) The correct cover shall be maintained by cement mortar cubes (blocks) or other approved means. Reinforcements for footings, grade beams and slabs on a sub-grade shall be supported on precast concrete blocks as approved by EIC. The use of pebbles or stones shall not be permitted.
l) The minimum clear distance between reinforcing bars shall be in accordance with IS:456 – 2000 or as shown in drawing.