Details about concrete cover in reinforcement

Concrete cover means the minimum distance among the surface of implanted reinforcement and the exterior surface of the concrete according to ACI 130 code. The concrete cover depth is calculated with a cover meter.

The purpose of the concrete cover is to safeguard the reinforcement.

While making design of reinforced concrete structures, the reinforcement already arranged is implanted in the concrete up to a specific distance from the face of the member due to the following grounds:

• To safeguard the reinforcement against corrosion.
• To make reinforcement as a good fire resistant.
• To arrange adequate entrenched depth in order to provide necessary stress to reinforcement.

This distance is calculated in several methods and recognized with various names:

1. Clear cover: It stands for the distance from the face of the member to the most exterior face of the reinforcement along with shear or torsion Stirrups or links.

2. Nominal cover: It has similarity as clear cover though with a dissimilar name. This term is applied with the code. It belongs to the distance calculated from the face of the member to the most exterior face of the reinforcement along with Stirrups or links. It is the dimension demonstrated in drawings and detailing.

3. Effective cover: It is the distance calculated from the face of the member to the center of area of the main reinforcement i.e. the tension or compression reinforcement. It refers to the dimension generally applied for design calculations.

Effective cover = Clear cover + (Dia of Stirrups/links) + 0.5 * (Dia of main reinforcement bars).

Also,
Effective cover = Overall depth – effective depth.

At each end of reinforcing bar, concrete cover should not be under 25 mm or less than twice the diameter of the bar.

For a longitudinal reinforcing bar in a column, concrete cover should not be under 40 mm or under the diameter of such bar. In case of columns with least dimension of 20 cm or under, whose reinforcing bars do no not goes beyond 12 mm, concrete cover of 25 mm should be applied for reinforcement.

For longitudinal reinforcing bars in a beam, the concrete cover should not be under 30 mm or less than the diameter of the bar.

For tensile, compressive shear or other reinforcements in a slab or wall, the cover should not remain under 15 mm or under the diameter of such bar.

For footings and other major structural members in which the concrete is arranged directly against the ground, cover to the bottom reinforcement should remain 75 mm. If concrete is poured on a layer of lean concrete, the bottom cover should be minimized to 50 mm.

Details about concrete cover in reinforcement