Surface protection system

from Wikipedia, the free encyclopedia

Surface protection systems (OS) are often polymer-containing coatings that are mainly applied to the surfaces of reinforced concrete structures and are intended to protect the reinforced concrete from external damage mechanisms during its service life.

The selection of the surface protection is based on the one hand on the exposure classes of DIN 1045-2: 2008-08 and on the other hand on the special aging mechanisms of polymer materials. Preventing the diffusion of carbon dioxide CO 2 into the concrete and the penetration of chemical substances is of particular importance . Furthermore, a coating can protect against mechanical attack, for example from vehicle traffic.

Rules and definitions

The following guidelines and standards are in use in Germany and other European countries:

  • DAfStb guideline for the protection and repair of concrete components (repair guideline, Rili-SIB for short), October 2001
  • EN 1062: Coating materials - Coating materials and coating systems for mineral substrates and concrete in outdoor areas (several parts)
  • EN 1504-9: Products and systems for the protection and repair of concrete structures (several parts)
  • DIN 50035: Terms in the field of aging of materials - polymer materials
  • BASt Additional technical contract conditions and guidelines for civil engineering structures ZTV-ING

Definitions for the three basic procedures for the application of surface protection systems:

Water repellency
A water-repellent impregnation is a water-repellent coating that is easily absorbed into the surface. It only protects against the ingress of liquids and usually only slightly increases the diffusion resistance to CO 2 . It is particularly suitable for building materials with a large porosity , since a deep penetration of the impregnation is possible here. In the past u. a. Testalin applied.
sealing
A sealing impregnation provides protection against liquids or gases and represents a thin film-forming layer. The impregnation can only be mechanically stressed to a limited extent, but can serve as a primer for subsequent coatings.
Coating
Coatings are always film-forming and offer protection against mechanical and chemical attacks, weathering and, depending on their elasticity, contribute to bridging cracks.

Damage Mechanisms

Damage based on the exposure classes of DIN 1045-2: 2008-08:

Chemical attack (XA)
The resistance to chemical attack is increased by polymeric binders . Since polymers are more or less resistant to special chemical substances, the selection of the binder must be made according to the expected attacks. Acids , alkalis , solvents and fuels are the main damaging groups .
Mechanical wear (XM)
In order to achieve a high mechanical resistance of the surface protection system, a sufficient layer thickness and a certain elasticity (low modulus of elasticity ) must be achieved, as well as an appropriate preparation of the substrate. EP and PUR with the addition of quartz sand are usually used as polymeric binders .
Carbonation (XC)
A carbonation of the concrete by the absorption of carbon dioxide does not damage this immediately. However, the resulting increase in pH can lead to corrosion of the reinforcement. Surface protection systems should inhibit the diffusion of CO 2 by reducing the permeability . The diffusion resistance to CO 2 is expressed by the equivalent air layer thickness S d .
Chloride attack (XS and XD)
Coatings that increase the diffusion resistance of the concrete also reduce the absorption of chlorides.

Damage to the coating:

Embrittlement of the binder
UV radiation , the reaction with oxygen and high temperatures can split the CN bonds, causing the coating to lose its elasticity.
Chalk off the coating
The embrittlement of the binder leads to a loss of substance due to surface abrasion and chalking, the magnitude of which depends primarily on the type of polymer.

Durability of the surface protection systems

The durability of surface protection systems is mainly influenced by:

  • the underground liability
  • of polymer aging
  • mechanical abrasion

If the adhesive force anchors the coating sufficiently on the substrate, the service life of the coating depends on the aging and abrasion of the polymer.

The durability of surface protection systems cannot yet be predicted with sufficient certainty. The modeling of the damage mechanisms proves to be difficult. Simple probabilistic approaches using linear degradation in the sense of a resistance model can be developed relatively easily, but do not reflect the actual reduction in reliability.

The substrate adhesion is mainly determined by the roughness depth and adhesive tensile strength of the concrete surface. Common test methods for this are the sand surface method and the pull-off test . Required minimum and mean values ​​for the individual classes are given in Part 2 of the Rili-SIB.

The aging of the polymer can be compensated for with an appropriate layer thickness. Minimum and maximum values ​​as well as additional layer thicknesses for the corresponding coating classes are also specified in the Rili-SIB.

literature

  • Rolf P. Gieler, Andrea Dimmig-Osburg: Plastics for building protection and concrete repair . Birkhauser Verlag, Berlin, 2006, ISBN 3-7643-6345-2 .
  • Robert Engelfried: About the influence of layer thickness and aging on the effectiveness of surface protection systems for concrete components . Dissertation, University of Dortmund, 2000, ISBN 3-8265-8817-7 .
  • Michael Fiebrich: Plastic coatings on constantly damp concrete . Beuth Verlag, Berlin 1990, ISBN 3-410-65610-3 . (DAfStb booklet 410)
  • Michael Raupach: Preservation of concrete structures . Vieweg + Teubner Verlag, Wiesbaden, 2008, ISBN 978-3-8351-0120-3 .
  • Lars Wolff: Mechanisms of bubble formation in reaction resin coatings on concrete . Beuth Verlag, Berlin 2009, ISBN 978-3-410-65049-2 . (DAfStb booklet 576)