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Organisationseinheit der BAM
- 7.6 Korrosion und Korrosionsschutz (14) (entfernen)
This specification describes how corrosion monitoring is used to check the condition of reinforced and prestressed concrete members. In this specification, the term "corrosion monitoring" covers all methods in which it is possible to continuously track corrosion-relevant variables in the area of stationary, built-in sensors. This specification does not cover other possible methods, such as potential field measurements, involving the use of mobile, portable sensors that are placed temporarily on the membersurface to take measurements.
Due to the large number of stainless steels with different chemical composition and different microstructure the selection of the suitable material represents a huge challenge. In order to facilitate the appropriate grade selection, in the current European standard EN 1993-1-4 a procedure is defined based on the use of a look-up table considering the key variables that influence the selection of stainless steels. The table uses descriptions that competent designers should be able to readily understand or define without prior knowledge. The output from the look-up table is used to select alloys based on a Corrosion Resistance Class (CRC) from I to V. The advantage of this approach is that the designer simply specifies the relevant CRC and does not need to consider in detail which of the many (very similar) alloys to specify.
Die Potentialmessung kann zum Auffinden korrosionsaktiver Bereiche neben Stahlbetonbauwerken auch bei Spannbetonbauwerken angewandt werden, die mit Spannstählen im direkten Verbund hergestellt werden. Bei Vorspannsystemen mit metallischen Hüllrohren im nachträglichen Verbund ist eine Aussage über den Korrosionszustand des Hüllrohrs, nicht aber des Spannstahls möglich. Messungen an Spannbetonbauteilen erfordern grundsätzlich die besonderen Kenntnisse eines Spezialisten.
Nine different stainless steel alloys were exposed for 5 years under marine environment and their corrosion behaviour was compared and assessed. The investigation of four different surface finishes for all alloys tested further enabled to consider industry-specific features of the surface finish for the material comparison. The results of the exposure tests yield conclusions regarding the influence of alloy composition, surface finish and exposure duration under marine environment. The three duplex stainless steels revealed excellent corrosion resistance even in case of crevices during the 5 years of exposure under the given exposure conditions. Also the molybdenum-alloyed ferritic steel 1.4521 showed good corrosion resistance comparable to the classical austenitic materials 1.4301 and 1.4404.
Alkali-activated fly ash mortars were studied with regard to durability-relevant transport coefficients and the electrochemical behaviour of embedded carbon steel bars on exposure of the mortars to leaching, carbonation and chloride penetration environments. The transport coefficients differed considerably between different formulations, being lowest for a mortar with BFS addition, but still acceptable for one of the purely fly ash-based mortars. Leaching over a period of ~300 days in de-ionized water did not lead to observable corrosion of the embedded steel, as shown by the electrochemical data and visual inspection of the steel. Exposure to 100 % CO2 atmosphere caused steel depassivation within approx. two weeks; in addition, indications of a deterioration of the mortar were observed. The results are discussed in the context of the different reaction products expected in high- and low-Ca alkali-activated binders, and the alterations caused by leaching and carbonation.
The salinization and contamination of metal surfaces by chloride-containing aerosols is of great importance with regard to corrosion phenomena of damaged coated metal surfaces and stainless steels in the maritime sector and in offshore applications. Detailed questions have to be answered to clarify whether and to what extent salinization of the surface has an influence on the adhesion and durability of coatings in repairing applications and on pitting occurrence on stainless steels under atmospheric conditions. The questions arise which degree of salinization is reached after which period of time and how a defined and reproducible salinization can be simulated in the laboratory for further systematic investigations. The article is dedicated to these questions. Results of a field trial on the Island of Heligoland are presented and a simple procedure for a defined loading of metal surfaces with chlorides at a laboratory scale using a design of experiments (DoE) approach is introduced.
The corrosion resistance of aluminium surfaces is closely linked to the surfacecstate after a grinding process. For years, iron‐containing abrasive materials were suspected to lead to increased corrosion susceptibility after processing of aluminium surfaces. To prove a possible correlation between the iron content of an abrasive and the corrosion behaviour of aluminium components, scientific investigations and experimentally practical corrosion tests are necessary.
For the current investigation, specimens of a technical Al‐Si alloy from the same batch were used. The test specimens were mechanically ground with various resin‐bonded model abrasives containing different iron contents. The performed corrosion tests did not reveal a negative influence of the different iron‐containing abrasives on the corrosion behaviour of the Al–Si alloy.
However, the most sensitive measuring method (electrochemical noise)
showed differences in the surface activity depending on the type of abrasive.
Electrochemical potential mapping according to guideline B3 of DGZfP (German Society for Nondestructive Testing) is a recognized technique for the localization of corroding reinforcing steels. In reinforced concrete structures the measured potentials are not necessarily directly linked to the corrosion likelihood of the reinforcing steel. The measured values may be significantly affected, different from, e.g., stress measurement, by different influences on the potential formation at the phase boundary metal/concrete itself as well as the acquisition procedure. Due to the complexity of influencing factors there is a risk that the results are misinterpreted. Therefore, in a training concept firstly the theoretical basics of the test method should be imparted. Then, frequently occurring practical situations of various influencing factors will be made accessible to the participants by a model object specially designed for this purpose. The aim is to impart profound knowledge concerning the characteristics of potential mapping for detecting corrosion of reinforcing steel in order to apply this technique in practice as reliable and economical test method.
Während das Instandsetzungsprinzip W bei carbonatisierungsinduzierter Korrosion seit vielen Jahren als Standardverfahren etabliert ist, wird seine Anwendbarkeit bei chloridinduzierter Korrosion (W-Cl) in der Fachwelt bis heute kontrovers diskutiert. Zwar ergeben sich aus seiner Anwendung gegenüber anderen Instandsetzungsverfahren auf den ersten Blick u. U. deutliche wirtschaftliche Vorteile, allerdings besteht bei diesem Verfahren ein deutlich höheres Risiko, dass das Instandsetzungsziel nicht erreicht wird.
Im vorliegenden Beitrag werden die technischen Grundlagen des Instandsetzungsprinzips W-Cl sowie der aktuelle Kenntnisstand - sowohl für den gerissenen als auch für den ungerissenen Beton - dargestellt und baurechtliche Konsequenzen, die sich aus dem erhöhten Ausführungsrisiko ergeben, diskutiert.
Korrosionsmonitoring als Element zum Nachweis des Instandsetzungserfolgs bei Anwendung des Prinzips W-Cl wird vorgestellt.
Anhand von Anwendungsbeispielen werden sowohl die Risiken, die mit dem Verfahren verbunden sind, als auch das Potenzial bei erfolgreicher Anwendung veranschaulicht.