As Most of the buildings are constructed by Reinforced Cement Concrete (RCC), RCC has become the most used material, but ever wondered what happens to the reinforcing bar which is embedded in concrete which is not visible, have you wondered why those reinforcing bars should not be visible for having healthy RCC structure. This article will give you insight to this concept and this concept is technically is known as “CONCRETE COVER”. In simple terms, Concrete Cover can be defined as the distance between the surfaces of the reinforcing bar to the outer surface of the concrete.
Concrete Cover is a very important term in the design of RCC Structures, structural engineer as well as site engineer should know the importance of concrete cover, all the RCC elements should be provided with nominal cover to the reinforcement. Concrete Cover should be provided for the following reasons:
Above picture shows cover blocks appropriately placed for a slab
- Concrete Cover will provide protection to the reinforcement from corrosion, if reinforcement bar is kept open in the atmosphere it tends to corrode due to the process called oxidation. Oxidation occurs when moisture and carbon dioxide penetrate in the concrete, rusting causes steel to expand in volume and thus resulting cracks in the RCC members. The more cover concrete the more time required for moisture and carbon dioxide for intrusion.
- Concrete Cover protects the reinforcement from fire, during sudden outbreak of fire the temperature may exceed 1500o F and at that temperature steel will lose more than 50% of the strength, therefore concrete cover is essential to keep reinforcing bars in relatively cooler temperature compared to outer surface temperature.
- Concrete Cover ensures good durability of the RCC element as it protects the reinforcing steel from various external agencies like rain, snow, wind, salts, chemicals etc.
- The main aim in RCC is to have good bond between concrete and steel and concrete cover is essential for ensuring good bond between reinforcing bars and concrete, increase in the depth of concrete cover also increases bond strength and slip resistance between both the materials.
Picture showing poor concrete cover resulting in rebar corrosion
As a designer we also have to be careful about how much cover we should provide because if you provide more cover irrespective of exposure conditions (all the design codes suggest to provide cover based on exposure conditions) the structure becomes unnecessarily heavy and also it results to bigger sections and this will lead to uneconomical structure.
Prof. Abhijeet Baikerikar
Founder,
All About Structural Analysis and Design
All About Civil Engineering (AACE)
Head of Civil Engineering Department,
KLS’s Shri Vasantrao Potdar Polytechnic, Belgaum
