Reinforcement coverage is a key factor taken into consideration during planning and construction. It is directly related to the durability of the structure.
Providing the required reinforcement cross-section, using the correct quality of concrete and correct cross-section sizing does not always mean the construction is complete.
For successful structural design and a durable structure that will last at least its lifetime, it is essential to select the correct concrete coating based on exposure conditions and fire safety requirements.
The durability and design life of a structure directly depend on the coverage of the reinforcement, especially for structures built in corrosive environments. BS 8110 does not provide much information for design compared to Eurocode 2.
The Eurocode prescribes comprehensive information and selection methods to cover reinforcement.
BS 8110 provides a guideline for the selection of reinforcing covering based on fire resistance and the environment (loading condition) to which the structure will be exposed.
The coverage for reinforcement must in no case be less than the nominal coverage minus 5 mm. Nominal coverage is determined taking into account the following factors.
- Based on recommended bar sizes and aggregate sizes
- Protecting steel from corrosion
- Protecting steel from fire
- Allows surface treatments such as hammering
There are six exposure conditions that cover the different conditions a structure may be exposed to. The following table from BS 8110 contains information for each category.
Exposure conditions are selected depending on the location of the structure being erected. Reinforcement coverage can be selected from different tables listed in the same guideline depending on the quality of the concrete. For concrete with quality below C30, there is no requirement for cover selection.
A coverage can be selected from the table above for each exposure class, and a coverage can be selected from the table below based on fire safety requirements.
When designing a structure, the above procedure is generally followed to select the covering for the reinforcements. However, if structures are built in special locations such as the sea, more attention should be paid. In these situations, it is necessary to pay more attention to durability, since the structure is exposed to adverse environmental conditions.
BS 8500-1 provides further information on durability aspects. Specifying higher grades of concrete could be done by changing the exposure conditions to severe conditions. The quality of concrete is based on durability aspects. Thus, the selection of concrete quality could also be based on the exposure class and coverage selected, which is achieved by taking other aspects into account.
