The concrete cover is important for protecting the reinforcement steel from aggressive chemicals such as chloride and melting due to fire. A concrete block will be used to maintain the required cover. Concrete blocks should have the same strength of the concrete used for casting members. Concrete blocks with lesser strength will form a weak point, and it may reduce the structural strength and durability.
Concrete cover playing an important role in protecting structures when a fire occurs. When a fire occurs and if the concrete cover is shallow. The temperature of rebar will increase due to fire. In general, the steel loses half of its strength when the temperature rises 550C. As the temperature rise, the steel will lose more of it is strength. This will lead to structure deflection and failure in some cases.
Increasing the concrete cover more than the required can adversely affect the structural members. Increasing the concrete cover will affect the size of the cracks. The distance between longitudinal bars and the point under consideration will control the size of cracks.
The widely spaced bars with a larger cover that will result in bigger cracks. Increasing the concrete cover will increase the dead weight of the structure. This can be critical in the design of structures such as floating ships and platforms where the self-weight is important in the design. Increase the concrete cover for the same member depth will reduce the lever arm of internal resisting forces, and this means reducing the structure capacity.