Concrete cover
As a concrete cover, partly concrete cover in reinforced concrete construction, the distance between the concrete surface and the outer edge of an enveloped by the concrete reinforcing steel is called.
A sufficient rebar cover, commonly referred to in Germany as concrete cover is required in reinforced concrete structures to ensure the necessary bond between concrete and reinforcement, a sufficient durability of the component and a corresponding fire resistance. To establish the requisite composite reinforcement overlap should be at least the rebar diameter. From the environmental conditions ( exposure classes ) (also carbonation (concrete ) see ) results after Euro Code 2 taking into account national annexes for the required durability of the necessary concrete cover over the reinforcing steel. The values described herein are based on a useful life of at least 50 years under ordinary maintenance expense from. Less than 15 mm, it should not be the usual 20 to 50 mm. The concrete cover is ensured by spacers and support brackets and baskets. Support brackets are usually made in accordance with bent rebar and are mainly used for the upper reinforcement layer of plates. Spacers are used, however, to ensure the distance between reinforcement and formwork. These are available in different variations. It may be, among other little boxes or snakes made of concrete or fiber cement, besides also blocks, strips or rings made of plastic are common. Metal spacers are rather uncommon today because they can lead to rust spots in the concrete surface.
The purpose of the concrete cover
- Protection of the reinforcing steel against environmental influences, in particular against oxygen and water to prevent corrosion.
- Protection of reinforcement against the effects of fire
- Ensure the interconnection between concrete and reinforcement (fixed integration of the steel in the concrete)
Guidelines
The concrete cover depends on the environmental factors that are expected at each location. You are in Europe regulated after exposure classes in the Euro Code 2 and the following concrete cover required there at requirement class S3 for the different corrosion -timer:
Depending on whether the ensure the interconnection or corrosion protection shall prevail, the values in the table must be increased by 10 to 15 mm, so there are nominal dimensions ( cnom ) of 20 to 55 mm.
Other national building standards write to the local climate in different minimum concrete cover before:
Paradox
Large concrete cover (50 to 60 mm) are needed to protect the reinforcement against corrosion in aggressive environments, but large surpluses also lead to large crack widths. Larger crack widths than 0.3 mm can perform ingress of moisture and oxygen to the corrosion of the reinforcement, which in turn has the spalling of concrete results in which the reinforcement is exposed. These contradictory effects may, for example, by the use of stainless reinforcement with lower concrete cover or by a non -rusting, fine fiber reinforcement (skin reinforcement) with good possible composite example be agreed galvanized steel, stainless steel, fiberglass reinforcement, textile or fiber composite within the concrete cover.
Methods to comply with the coverage
- Down free surface (eg ceiling ): on the flat formwork spacers in the form of little feet made of plastic, fiber cement are set.
- Vertical surface (eg walls ) with elongated and partially wavy spacer made of fiber cement or plastic are firmly bound to the outside of the reinforcement.
- To top free surface (eg ceiling ): As the formwork is open at the top, adhering to the overlap of the upper reinforcement is ensured by supporting baskets.