What is Cover Blocks?

A cover block is essentially a spacer that is used to lift the rebar mesh off the ground so that concrete may flow under the rebar.

Size Used in Construction Field.

In order to prevent corrosion of the rebar, it needs to be fully embedded in concrete. By code, it usually needs about 20 mm to 75 mm of coverage on all sides depends upon structure type. So, the cover block lifts the rebar up by about 20 mm to 75 mm and becomes a permanent and integral part of the poured concrete, ensuring that no part of the rebar sags and minimizes the required concrete coverage during the pouring of concrete.

Difference Between Clear Cover, Nominal Cover and Effective cover

Clear Cover

1. The clear cover is the distance from the bottom of fibre to the bottom level of the reinforcement.
2. In other words, the clear cover is the distance between concrete extreme fibre and the bottom edge of a stirrup.

Nominal Cover

1. This is the same thing as a clear cover with a different name. This term is introduced in IS Code 456:2000.
2. According to IS Code 456:200 section 26.4.1 Nominal cover is the design depth of concrete cover to all-steel reinforcements, including links (stirrups). It is the dimension used in the design and indicated in the drawings.
3. It shall be not less than the diameter of the bar.
4. Nominal cover means a clear distance between the face of concrete and the face of the main outer rebar.
5. So Nominal cover < effective cover.

Effective Cover

1. The effective cover is the distance from the bottom of the fibre of the beam to the centre of reinforcement.
2. According IS Code 456:2000 effective cover is given as follows-

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

 

What is Effective depth?

Effective depth = overall depth-effective cover

Type of Cover Blocks?

There are different types of covering blocks based on the type of material used: –

1. Steel cover block.
2. PVC Block.
3. Cement masonry cover block.
4. Aluminium cover block.
5. Stone cover block.

 

Why Cover Blocks Are Used In Reinforcement?

Cover blocks are used for the many following reasons:

1. Maintain a specified distance between the rebar and the shuttering.
2. To protect the steel reinforcement bars from environmental effects to prevent their corrosion.
3. Provide thermal insulation, which protects the reinforcement bars from fire.
4. Give reinforcing bars sufficient embedding to enable them to be stressed without slipping.

Cover Block in Different Structure and Different Size of Cover Block.

1. RAFT FOUNDATION BOTTOM/SIDES : 50mm – 75 mm
2. STRAP BEAM : 35 mm
3. SLAB : 20 mm
4. COLUMN : 40 mm
5. SHEAR WALL : 25 mm
6. BEAMS : 25 mm
7. SLABS : 15 mm
8. FLAT SLAB : 20 mm
9. STAIRCASE : 15 mm
10. RET. WALL : 20/ 25 mm on earth
11. WATER RETAINING STRUCTURES : 20/30 mm

 

For a Better Experience Watch These Videos.

  Making Of Cover Block Site Must Watch.

 

Better Understand about Cover block Watch this Video.

All Type cover 

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