The requirements for the concrete protective layer for the protection of reinforcement are given in clause 3.5 and section 10.3 of the joint venture 63.13330.2012 (SP 63.13330.2018)[Russian building standarts] Concrete and reinforced concrete structures. The main provisions. Updated edition of SNiP 52-01-2003.
The concrete protective layer is the thickness of the concrete layer from the face of the element to the nearest surface of the reinforcing bar.
Why a protective layer of concrete is needed:
- ensuring the joint work of reinforcement with concrete;
- ensuring the possibility of a joint of reinforcing elements and anchoring of reinforcement in concrete;
- safety of valves from environmental influences, including aggressive influences;
- ensuring fire resistance of structures.
According to clause 10.3.2 and table 10.1 (SP 63.13330.2012, SP 63.13330.2018), the thickness of the minimum protective layer of concrete should be:
- Indoors with normal and low humidity of at least 20 mm.
- Indoors with high humidity (in the absence of additional protective measures) at least 25 mm.
- In the open air (in the absence of additional protective measures) at least 30 mm.
- In the ground (in the absence of additional protective measures), in the foundations in the presence of concrete preparation of at least 40 mm.
Important notes!
1. The thickness of the concrete protective layer should be taken not less than the diameter of the reinforcement bar and not less than 10 mm.
2. For structural reinforcement (not working), it is permissible to reduce the thickness of the protective layer of concrete by 5 mm (compared with those required for working reinforcement).
3. For prefabricated elements (prefabricated floor and cover slabs, beams, etc.), the thickness of the protective concrete layer of the working reinforcement is reduced by 5 mm.
4. In single-layer cellular concrete structures, the thickness of the protective layer in all cases is taken to be at least 25 mm.
5. In single-layer constructions made of light and porous concrete of classes B7.5 and below, the thickness of the protective layer should be at least 20 mm, and for external wall panels (without a textured layer) at least 25 mm.
6. The thickness of the concrete protective layer at the ends of prestressed elements along the length of the stress transfer zone should be at least 3d and at least 40 mm for bar reinforcement and at least 20 mm for reinforcing ropes.
7. It is allowed to take the protective layer of concrete of the section at the support for prestressed reinforcement with and without anchors the same as for the section in the span for prestressed elements with concentrated transmission of supporting forces in the presence of a steel supporting part and indirect reinforcement (welded transverse grids or covering longitudinal reinforcement clamps).
8. In elements with tensioned longitudinal reinforcement stretched on concrete and located in the channels, the distance from the surface of the element to the channel surface should be taken at least 40 mm and at least the width (diameter) of the channel, and to the side faces at least half the height (diameter ) channel.
9. When the prestressed reinforcement is located in the grooves or outside the section of the element, the thickness of the concrete protective layer formed by subsequent shotcrete or in any other way should be taken not less than 20 mm.