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 PREVENTION REPAIR
  Prevention

The corrosion of a reinforcement mainly depends on the geometrical (cover thickness) and physical (porosity) of the covering concrete. It also depends on the aggressiveness of its environment, particularly when those geometrical or physical properties do not meet the requirements.

A reinforced concrete structures is designed and built for a given service life, which is defined by the designer and is controlled by the manufacturer.  For this period of time, the structure should not be so deteriorated that it does not fulfill any more its functions.

The deterioration of reinforced concrete is mainly due to reinforcement corrosion The mechanism of this deterioration is to be reminded. Reinforcements corrode when they are in contact with a high amount of aggressive agents. This is the reason why, the prevention of reinforcement corrosion, in structures to be built, is obtained mainly by controlling the thickness and the quality of the concrete cover.

The most important parameters, which induce reinforcement corrosion, are the cover thickness and the quality of concrete, as well as the aggressiveness of the environment.

Concrete properties

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Cover thickness

Cover thickness is the distance between concrete surface and the reinforcement, which is the nearest to this surface. It is determined after taking into account the required mechanical properties. According to some regulations, its minimum value depends on the exposure class and on the type of structure (structure class)..

Most often, steel corrosion occurs when the cover thickness is too thin.


Corrosion of reinforcement under a too thin concrete cover

Design and placing of concrete

Concrete is characterized first by the cement (or equivalent binder) content, then by the wter-to-cement ratio, which strongly influences concrete porosity.

Concrete placing is important, as it can be the origin of local defects.

In every case, the quality of covering concrete, and particularly its physico-chemical properties (mainly compactness), is of a first importance for yielding protection. The techniques applied must continuously lead to a good quality, from concrete production to its placing.

Aggressiveness of the environment

This aggressiveness is of course an important parameter, which accelerates corrosion, when covering concrete is not satisfactory.

The European standards EN 206 EN1992-1.1 and EN1992-1.2 give the requirements concerning the environment classes, which must be taken into account for determining concrete thickness and quality.


Exposure class XC4 XS3 XD3
Carbonation
Alternate wetting
and drying
Chlorides in seawater. Tidal zones, splash areas Chlorides not due to marine environment. Alternate wetting and drying.
Examples Façades exposed to rains, superstructures of bridges
Bridges and buildings on seashore, marine structures.
Car parks under deicing salts or with frequent water leakagess.
 

Some applications of the here above standards are shown in the following table, concerning structures with a predicted lifetime of 50 years.

Exposure class XC4 XS3 XD3
Carbonation
Chlorides in seawater Chlorides from non marine origin
 C. thickness Cmin, dur 30 mm
45 mm
45 mm
water eff / cement ratio 0,60 0,50 0,50
Minimum of strength class C25/30
C35/45
C35/45
Minimum dosage of binder
(binder equivalent kg/m³
280 350
350
- «watereff »is the mass per unit volume of water available for cement hardening.
- The mass (binder equivalent) of equivalent binder, for a unit volume is that of ordinary Portland cement, For other cements it is calculated according to special formulas.
- The minimum strength class is in MPa.


A new concrete can be coated either for cosmetic reasons or for a protection against corrosion. It also can be impregnated.

Special metallic reinforcements

Reinforcements in concrete can be in plain carbon steel and have either an organic coatings or a metallic coating,for example by hot-dip galvanizing.These coatings must be adherent to steel even when it is bent, and yield a good bonding between reinforcement and concrete.

Reinforcements made of stainless steel are available. Their grades are chosen depending on the environment of the reinforced concrete.



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 Repair, rehabilitation
   

A reinforced concrete structure is repaired when its material is apparently damaged. The European standards EN 1504 describe the repair methods for concrete. Rehabilitation concerns a material, which seems sound, but in which steel is corroding.

Différentes méthodes de réparations et de réhabilitations peuvent être associées sur le même ouvrage à traiter. D’une façon générale, les phases d’une réparation d’armatures dégradées par la corrosion, dépendent de la forme de dégradation observée.

Various methods of repair and rehabilitation, can be applied on the same structure to be treated. For example, after a chloride extraction treatment, the concrete surface can be coated.

Highly cracked, delaminated concrete cover


When reinforcements are strongly corroded, their corrosion products can expand, and deteriorate the concrete cover, by cracking, delamination and spalling.

Then, the first action to be undertaken is to eliminate these geometrical defects, by replacing concrete cover, or sometimes by injecting cracks.

As this first action relates to only the zones under high corrosion, the close zones, where corrosion can appear in a short term, must be treated by other methods.


Concrete cover physically sound, but polluted
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In some cases, concrete reinforcement. are already corroding or will corrode shortly. Its concrete cover seems physically satisfactory and has neither crack or delamination. But, it is then convenient to slow down this corrosion rate, even to stop it.

The methods which can be proposed are either concrete impregnation with water-proof products (sealants) or corrosion inhibitors, or an electrochemical treatment : cathodic protection, re-alkalization or chloride extraction.

Sound concrete cover

When reinforcement is embedded in a sound cover and if its corrosion is likely initiated only in short or long term, it can be useful to protect them either by coating or by impregnation concrete cover.

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 Références
   

 A general guide line on the rehabilitation of reinforced concrete damaged by steel corrosion, has been published by CEFRACOR and AFGC.
Download 1906 Ko


On corrosion prevention

Some technical information on materials usable to prevent steel corrosion is given on line for , :

-
Epoxy-coated reinforcement : www.astm.org/Standards/A775
- Galvanized steel reinforcement : www.galvanizedrebar.com
- Stainless steel   www.nidi.org , www.idinox.com


On repair

Some guidelines on repair works have been published, in various countries, by :

- Syndicat des travaux de réparation et de renforcement de structure (France) : www.strres.org
- Concrete Repair Association (Royaume-Uni) : http://concreterepair.org.uk
- International Concrete Repair Institute (USA, Canada) : www.icri.org
- Australian Concrete Repair Association (Australie) www.acrassoc.com.aug

For more information, contact
info@concretecorrosion.net

 
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