In this article we share the all details of cover, such as what is concrete cover, why cover is important in RCC element, minimum cover requirement for different type of structure as per IS 456 and how structure engineers decide the cover for structural elements, etc.
So, read the article till the end, and if you get any valuable information from this article then please share it with friends. Let’s Start
Engineers, I think cover in reinforced cement concrete is most common and least important things for everyone specially for contractors who are not technically sound, and why not because it is one of the easiest things of the construction. Its not required any special consideration or calculation.
For many people, this is the minimum value fixed by the Indian Standards, not only this, if you give it less than the minimum, then what difference will it make, the reinforcement has to be covered, no one is going to see it. This is how people treat concrete cover during construction.
But, for Structural Engineers, Concrete Cover is the one of the most important things of the structure because they are subjected to the safety and durability of structure. and that’s why i am writing this blog to share the information of concrete cover, why it is one of the most important thing of the structure.
But before going to understand it, let’s understand what is concrete cover because their is lots of people who don’t know about it.
Table of Contents
What is Concrete Cover?
In RCC, cover is a protective layer of concrete which protect the reinforcement of member from environmental, chemical & fire effect to ensure the minimum durability of structure. It is the minimum value of concrete recommended by IS 456 from outer face of the reinforcement.
Now, lets come to the topic, why it is important?
Importance of Cover in Concrete
As per its definition, Concrete Cover is important,
- To protect reinforcement against corrosion
- To protect reinforcement from fire
- Act as a barrier to protect reinforcement from chemicals, moisture & other harmful elements.
Let’s I explain you with example,
For example our Body, A human body have nerve system and inner mussels which protected by layers of skin to protect it form environmental and external harmful elements.
Same way, Reinforced Cement Concrete (RCC) have reinforcements & core concrete which is like a nerve system and mussels of structural element. So it is very important to protect reinforcement from environmental, chemical and fire effects to prevent it from deterioration.
And here, it is necessary to provide protective layer of concrete which protect reinforcement from damage due to environmental, chemical and fire effects.
Here is the list of problems mostly occur due to insufficient cover.
- Reinforcement of concrete exposed to environment
- Corrosion of Reinforcement & Cracks in Concrete
- Rapid deterioration of concrete core & reinforcement due to chemical effect
- Reinforcement of concrete get melts/burn during fire
Minimum Requirement of Cover as per IS 456
As per IS 456, cover of concrete is depends on Exposure condition and fire rating hours. Table 16 of IS 456 Recommend the minimum value of concrete cover to meet the durability requirement.
Minimum Cover in Concrete based on Exposure Condition
As per Table – 16,
| Exposure Condition | Nominal Concrete Cover in MM Not Less Than |
|---|---|
| Mild | 20 |
| Moderate | 30 |
| Severe | 45 |
| Very Severe | 50 |
| Extreme | 75 |
Notes:
- For main reinforcement up to 12mm diameter bar for mild exposure the nominal cover may be reduced by 5mm.
- Unless specified otherwise, actual concrete cover should not deviate from the required nominal cover by +10mm.
- For exposure condition ‘severe’ and ‘very severe’, reduction of 5mm may be made, where concrete grade is M35 and above.
Minimum Cover in Concrete based on Fire Resistance
And, requirement of minimum nominal cover to meet specified period of fire resistance is given in Table 16A of IS 456:2000.
- However, As per clause 26.4.2.1 of IS 456, the minimum cover in column shall not be less than 40mm or a diameter of bar, In the case of column of minimum dimension of 200mm or under, whose reinforcing bars do not exceed 12mm, a nominal cover of 25mm may be used.
- For footings minimum cover shall be 50mm.
Here we listed the minimum cover for different RCC Member.
- Beam: 30mm
- Slab: 25mm
- Column: 40mm
- Isolated Footings: 50mm
- Combined/Raft Foundation: 50mm
- Lintel: 20mm
- RCC Band: 20mm
- Pile: 50mm
- Pile Cap: 50mm (Sides & top) & 75mm (bottom)
I hope this article is helpful for you. Also i recommend to visit our new latest article to get the engineering & construction details.