The minimum clear cover (in mm) for footing, according to IS 456 : 2000, shall bea)20b)25c)40d)50Correct answer is option 'D'. Can you explain this answer?

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Answer

Minimum Clear Cover for Footing as per IS 456:2000

The minimum clear cover for footing is specified in the Indian Standard code IS 456:2000, which provides guidelines for the design and construction of reinforced concrete structures. According to this code, the minimum clear cover for footings is 50 mm.

Reasons for Minimum Clear Cover

The clear cover refers to the distance between the outer surface of the reinforcement and the nearest surface of the concrete. It is essential to provide an adequate clear cover to ensure the durability and performance of the concrete structure. Here are some reasons why a minimum clear cover is required for footings:

Protection against corrosion: The primary purpose of providing a clear cover is to protect the reinforcement bars from corrosion. The concrete cover acts as a barrier and prevents the ingress of moisture, oxygen, and other corrosive agents that can lead to the corrosion of reinforcement. Corrosion can significantly reduce the strength and structural integrity of the footing.

Fire resistance: Adequate clear cover also provides fire resistance to the reinforcement bars. During a fire, the high temperatures can cause the steel to lose its strength. The clear cover acts as an insulating layer, reducing the rate of heat transfer to the reinforcement and protecting it from damage.

Bond strength: The clear cover plays a crucial role in ensuring proper bond between the reinforcement bars and the surrounding concrete. Sufficient cover allows for the development of bond stress between the reinforcement and the concrete, which is essential for transferring the applied loads to the reinforcement.

Workability and compaction: An adequate clear cover provides enough space for proper compaction of concrete around the reinforcement. It allows for the easy flow of concrete during placement and ensures that the reinforcement is properly embedded within the concrete.

Importance of Minimum Clear Cover

Adhering to the minimum clear cover requirements specified in the code is crucial to maintain the structural integrity and durability of the footing. The minimum clear cover of 50 mm ensures sufficient protection against corrosion, fire resistance, and proper bond strength. It also allows for proper workability and compaction of the concrete during construction.

It is important to note that the minimum clear cover specified in the code is the minimum requirement, and in practical scenarios, it is often recommended to provide a higher clear cover to enhance the durability and longevity of the footing. Factors such as exposure conditions, environmental considerations, and design requirements may necessitate the use of a higher clear cover than the minimum prescribed.

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