The space between the surface of steel and concrete of an RCC (Reinforcement cement concrete) member is the concrete cover.
Typically, concrete cover also called “clear cover” or “minimum concrete cover” in usual speaking on construction site. The minimum concrete cover between steel and concrete shall be in match with IS:456 – 2000 code of practice.
Table of Contents
- 1 Concrete cover:
- 2 Nominal Cover:
- 3 Why Do We Provide Concrete Cover?
- 4 Share this:
In this article we will discuss what is concrete cover and why it is provided in structural members and also the thickness of concrete cover will be describing in this post. Let’s start.
Cover is the small space between the outside of the concrete surface to the steel inserted inside of that RCC structure.
Generally, the thickness of the steel bar cover is specify in the drawing of structure, or it shall be get from a code of practice of Concrete cover for steel bar or it shall be get from a thumb rules.
Why Do We Provide Concrete Cover?
It is used in Reinforced construction to protect steel from outside severe environment. typically, PH value of concrete is more than 11 because of this a protective core is formed over steel giving it safety. The cracks create chloride, Sulphur carbon and some other acidic gases may enter concrete and attack that alkaline protective cover over steel and thus giving a way of rusting it by lowering PH value. Mostly in slab concrete cover is 0.75″. in beam and columns, it is 1.5″ while in foundation it is 3″.
Steel is used to bear the tension force and concrete is used to bear the compression force. Now, steel bar can damage because of corrosion and it required to bond with reinforcing bar to work as a combine.
Importance of Concrete Cover:
The importance of concrete cover in structure is given below:
- Concrete cover needs to maintain long life of the RCC (Reinforced cement concrete) structure,
- Concrete Cover prevent steels to corrode because of weather’s awful effect.
- In case of fire, it works as a thermal protector of steel to protect it.
- Concrete cover gives sufficient place to steel to enable them to be stressed without losing grip.
The thickness of concrete cover is depending on the environmental condition and type of different members of structure. Concrete cover thickness can be get from the code of practice.
Concrete Cover for different Members:
The concrete cover or clear cover for different members in structure is given below:
|S. No||Member of structure||Concrete cover in (mm)|
|5||Raft foundation Sides||75|
|7||Raft foundation bottom||75|
|8||Water retaining structures||25|
|12||Raft foundation top||50|
Concrete Cover for Beams:
The thickness of Concrete cover or clear cover normally ranges between 25mm to 35 mm depending on the environmental circumstances. The 25 mm thickness of concrete cover apply to a dry region and the 35 mm to a water side area.
The concrete cover used in the beam at the bottom and also with the side face of beam. clear cover of Plastic also used in place of concrete cover, as per to its thickness of use.
Concrete Cover for Beam
Clear cover with circular shapes is better, when using the cage of stirrup to put the connecting steel to maintain their position at the time of concreting.
Concrete Cover for Columns:
The thickness of Concrete cover or clear cover normally ranges between 25 to 40 mm depending on the environmental condition. The 25 mm thickness of concrete cover apply to a dry region and the 40 mm to a water side area. The concrete cover used in the column at the side face of column.
Clear cover with circular shapes is better, when using the cage of ties to put the connecting steel to maintain their position at the time of concreting.
Clear Cover for Slabs:
When steel rust or corrode, because of corrosion of steel concrete is throwing from slab and therefore the cracking of the plaster.
Huge rusting affects the life of structure and affects the safety of residents structures. The clear cover for the slab steel usually between 15 and 25 mm it is depending on the environmental condition.
Concrete Cover for Slab
The required clear cover is maintained only with the help of a specific structure called spacers. Slab will not be unaffected by rusting if clear cover is provided every 1 m spacing.
Clear cover for footings:
Footing structure is directly contact on ground or soil, or sometimes , the PCC (plain cement concrete) layer is provided to level surface for mesh prepared by steel bars.
This mesh stays on clear cover to maintain space between soil or steel to filled concrete in it, thus usually concrete covered is provided 50 mm to 75 mm.
The required concrete cover in the foundation steel is 40 mm for the foundation set on a concrete layer and 75 mm for the foundation, which comes in contact with soil.
Permissible Clear Cover for steel in all type of structure:
The terms for concrete cover for different types of structural members in different condition is given below:
According to codes, the min size of concrete cover should be 25 mm, or less than twofold of the diameter of the steel should be used. Concrete cover should be put at the end of the steel.
In beam, the size of longitudinal steel shall not less than 30 mm or lesser compared to the diameter of the steel.
In column, the size of clear cover must not be less than 40 mm
In the concreting of PCC (plain cement concrete) layer, the size of clear cover will be decreased up to 50 mm.
The concrete cover between steel is explain in IS: 456 – 2000.
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- Types of Concrete and their Uses, Classification and Properties
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