Why Cover Block is provided?

  Hi There, Welcome to  " The Civil Engineer",

    Cover Block, why it is called so because it covers some things. But actually, it does not help in the covering of the concrete around the steel by providing or creating a space between the formwork and the steel. Since it helps in the covering of concrete around the steel it is termed as simply cover block or concrete cover block.

Why does Steel need to be covered?

    When steel is exposed to an open atmosphere in the presence of water let's say rain then the steel oxidizes and forms rust.

    The chemical reaction in which iron (Fe) combines with oxygen (O2) to form rust, or iron oxide (Fe2O3). The equation for this reaction is 4Fe+ 3O2 → 2Fe2O3.

    To prevent this chemical reaction we need to avoid the exposure of steel or direct contact of steel with the atmosphere.

What happens when we use a cover block?

    When we use cover block, Steel is isolated from the atmosphere by a layer of concrete when we pour the concrete hence it prevents the corrosion of steel.

Minimum Cover Block provision in various Members of Concrete Structures

    Some minimum thicknesses need to be provided so that the water and the atmospheric air won't reach the steel. So the Condition of the surroundings determines the amount of cover that needs to be provided. Let's take 

    For example, Footing - footing is in direct contact with the ground all the time, and water molecules will always be in the soil at depth hence it is a severe condition so higher or maximum cover needs to be given.

Various Types of Cover Blocks Available in the market

1. Steel Cover Block
2. PVC Cover Block
3. Cement Cover Block
4. Aluminum Cover Block
5. Stone Cover Block

Structural Members and Their Minimum Cover Block

Member	Cover Block Thickness(mm)
Footing (Any type)	50-75
Column	40
Beam	25
Slab	15
Staircase	15
Retaining Wall	20/25
Water Retaining Structure	20/30