CONCRETE COVER IN REINFORCED CONCRETE STRUCTURES

Reinforced Concrete as the composite structural material of reinforcements and concrete is mostly popular construction material in the world due to its properties.

During construction of reinforced concrete structures, always reinforcements are not left exposed to the environment due to different factors, a concrete portion that keep reinforcements away from environmental exposure is what called concrete cover.

In construction of different of structures there is provision of concrete covers of different sizes (thickness), in this post we will look on concrete cover its purpose for application and how its size is desired.

Reasons for provision of concrete cover

1. Provision of thermal insulation and fire protection to reinforcements.

Concrete is one of materials forming reinforced concrete, is most highly fire resistive material in construction.

At high temperature that could be due to uncontrolled fire properties such as strength, modulus of elasticity of different materials are reduced.

At some extend of higher temperature concrete shows more stability than reinforcements (steel) on its properties, some kind of concrete shows their stability at a temperature up Concrete, while steel  cannot.

Although steel has high melting point, it shows  weakness to its properties such as ductility and strength at high temperatures.

This made engineers to provide concrete cover of certain size to protect reinforcements, where by extent of temperature (time of fire exposure) signifies the  size of Concrete cover.

2.  Protection from corrosive environments.

Steel reinforcements are more prone to corrosion attacks compared to Concrete, steel reinforcements are more prone to attacks from water (moisture), salts, acids and other chemicals compared to Concrete.

These corrosion attacks or processes reduce ductility property and strength of steel reinforcements which make unsuitable to be used in exposed environment.

Specifications for concrete cover

Concrete covers of different size or thickness are provided to different structures considering standard codes of different countries and regions.

Concrete cover provision under different standard codes are given considering both level of exposure to corrosive environment and time of fire exposure.

The following are few and popular standard code showing concrete covers thicknesses.

1. BS

BS specification concerning concrete cover

2. ACI

ACI standard minimum covers to reinforcements

How concrete covers are installed

Concrete cover installation and maintaining its size is very important which can be done by the following procedures.

1. Selection and preparation of precast cover spacer blocks or steel chairs of required size so as to position reinforcements at its required position.

Steel chairs raise reinforcements to its position

2. Installing them between shutter and reinforcements (formwork surface an reinforcements).

Cover spacer blocks provide cover to reinforcements

3. Concrete works proceeds on formwork system with cover spacer blocks or steel chairs and reinforcements.

Concrete works over reinforcements above steel chairs

Conclusion

Concrete cover provide thermal insulation (fire resistance) to reinforcements, which has great contribution in structure strength.

Considering above descriptions it seems that for construction of strong and durable reinforced concrete structures adequate concrete cover should be provided.