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The critical chloride content C(crit) is an indicator for the corrosion resistance of reinforcing steels in concrete. In this article, several experimental methods for determining the critical chloride content C(crit) of mild and an alloyed (12% Cr) steel in cementitious materials are compared. The methods used include accelerated polarization tests and tests using more natural (unpolarized) conditions in which chloride ingress occurs by diffusion and capillary uptake. The advantages and disadvantages of the methods are discussed, in particular, with the objective of reaching a compromise between applicability to practice and feasibility in laboratory testing.
This work presents machine learning-inspired data fusion approaches to improve the non-destructive testing of reinforced concrete. The principal effects that are used for data fusion are shown theoretically. Their effectiveness is tested in case studies carried out on largescale concrete specimens with built-in chloride-induced rebar corrosion. The dataset consists of half-cell potential mapping, Wenner resistivity, microwave moisture and ground penetrating radar measurements. Data fusion is based on the logistic Regression algorithm.
It learns an optimal linear decision boundary from multivariate labeled training data, to separate intact and defect areas. The training data are generated in an experiment that simulates the entire life cycle of chloride-exposed concrete building parts. The unique possibility to monitor the deterioration, and targeted corrosion initiation, allows data labeling.
The results exhibit an improved sensitivity of the data fusion with logistic regression compared to the best individual method half-cell potential.
Literature data on the influence of concrete cracks on corrosion propagation of reinforcing steel are contradictory. This might be due to very different exposure and test conditions but also to a lack of time-resolved data in cyclic wetting–drying exposure. Here, the influence of the environmental conditions on the corrosion rates in cracked concrete is studied experimentally. The results show that the corrosion rate in cracked concrete depends on the duration of wetting and drying phases and the relative humidity (RH) during the drying phase. The lower the ambient RH in the drying phase, the faster the cracks dry, which depresses the corrosion rate in the periods between the wetting events. A model is proposed to estimate corrosion rates in cracked concrete cyclic wetting/drying exposure.
Chloride contents at the steel–mortar interface that initiate steel corrosion were determined for carbon steel in alkali‐activated fly ash mortar for three different exposure conditions: exposure to 1 M NaCl solution; leaching in deionized water and then exposure to 1 M NaCl solution; and leaching in deionized water, aging in air at 20°C and natural CO2 concentration, and then exposure to 1 M NaCl solution. For comparison, a Portland cement mortar, exposed to 1 M NaCl solution, was studied. The median values of the corrosion‐initiating chloride contents (average over the full length of the rebar) in the alkali‐activated fly ash mortar varied between 0.35 and 1.05 wt% Cl with respect to binder, consistently lower than what was obtained for the Portland cement mortar, but with no clear trend regarding the exposure conditions. For most of the alkali‐activated fly ash mortar specimens, preferential corrosion at the connection between the working electrode and the external measurement setup was observed, while preferential corrosion did not occur for the Portland cement mortar. Scanning electron microscopy and auxiliary experiments in synthetic solutions indicated that this behavior was caused by inhomogeneities at the steel–mortar interface in the alkali‐activated mortar, likely due to its peculiar rheological properties in the fresh state.
Corrosion monitoring of reinforced concrete structures:The DGZfP specification B12 Collaboration
(2023)
Corrosion monitoring of reinforced or prestressed concrete structures has becomeincreasingly important in recent years. Areas of application include componentsthat are no longer accessible after completion or where potential fieldmeasurements cannot be carried out due to existing coatings. Corrosion monitoringcan also be used to monitor the progress of corrosion in corroding systems, e.g. to prove the success of repair measures according to repair principle 8 in accordancewith EN 1504‐9 or repair method 8.3 in accordance with the DIBt repair guideline.It also could be used to prove the functionality of cathodic corrosion protectionsystems in accordance with ISO 12696. Despite the increasing importance ofcorrosion monitoring, no guidelines orrecommendations existed until 2018. Thisgap was closed by the English version of specification B12,“Corrosion Monitoringof Reinforced and Prestressed Concrete Structures,”of the German Society for Non‐Destructive Testing, which was published in 2021. This article introducesspecification B12 by explaining the basicmeasurement principles and illustratingthe potential of corrosion monitoring in new and existing buildings.
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.
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.
Although zinc and zinc coatings have been widely used for corrosion protection for decades new zinc coatings are constantly being developed. Characterizing the corrosion protectiveness of these new coatings, however, should not be underestimated. While exposure tests are time intensive, cyclic tests can only be used for a very limited field of application. Thus, electrochemical measurements provide both an efficient and an effective alternative. Conventional aqueous bulk electrolytes influence the surface layers of a tested zinc coating and are therefore not reliable. Gel electrolytes, however, have evolved over the last few years, are minimally invasive and provide reliable results.
This work describes experiments with gel electrolytes made of agar. Unlike previous work, it proposes a composition of gel electrolyte for minimally invasive description of the protective power of naturally formed oxide layers on zinc and zinc coatings. Therefore, as a first part, the gel electrolyte made of agar is verified as a method for zinc and zinc-coated samples. Afterwards, this paper introduces the corrosion product layer resistance RL as a promising parameter to evaluate the protective power of zinc coatings. Results are verified with EIS and FTIR measurements. An example on a representative zinc coating demonstrates the practical application.
The corrosion behavior of galvanized steels and zinc components under atmospheric exposure depends mostly on the corrosion product‐based cover layer formation under the prevailing conditions. The use of agar‐based gel electrolytes makes it possible to use electrochemical methods to obtain a characteristic value from these cover layers that describe their current and future protective capacity. It is shown here that different states of galvanized steel can be distinguished very well under laboratory conditions and that this method is also suitable for use under practical conditions. Based on the characteristic values and assuming future time of wetness, it is very easy to draw up a forecast for the future corrosion rate, which provides plausible values.
Bei der Brücke Altstädter Bahnhof handelte es sich um eine große Spannbetonkonstruktion, die einen elementaren Verkehrsknotenpunkt in der Stadt Brandenburg an der Havel bildete. Entgegen üblichen Spannbetonkonstruktionen mit kleinen Bündelspanngliedern kamen beim Haupttragwerk in Längsrichtung großformatige Spannblockspannglieder zum Einsatz. Im Fall der vorliegenden Brücke setzte sich das Spannglied aus 392 ovalen Einzeldrähten aus Hennigsdorfer Produktion zusammen, welche als spannungsrisskorrosionsgefährdet gelten. Bei Bauwerkserkundungen wurde ein hoher Versprödungsgrad der Spannstähle festgestellt, sodass die Brücke am 19.05.2021 gesprengt werden musste. Zuvor traten im Bereich detektierter Spanndrahtbrüche von außen erkennbare Längsrisse in den Stegen anstatt von üblicherweise quer gerichteten Biegerissen an der gezogenen Randfaser auf. Die abweichende Schadensäußerung im Falle einer Spannstahlschädigung brachte das Bundesministerium für Digitales und Verkehr (BMDV) dazu, weitergehende Untersuchungen durchzuführen. In Zusammenarbeit mit dem Landesbetrieb Straßenwesen Brandenburg, der Hochschule für Technik und Wirtschaft Dresden sowie der Bundesanstalt für Materialforschung und prüfung (BAM) wurden experimentelle Untersuchungen insitu konzipiert und durchgeführt. Im Konkreten wurde an zwei Messstellen eine gezielte Schädigung des großformatigen Spannglieds vorgenommen, um das zuvor vorgefundene Schadensbild nachzuvoll ziehen und validieren zu können. Konzept, Ergebnisse aus den Untersuchungen und Erkenntnisse für gleichartig ausgeführte Bauwerke sind Gegenstand des ersten Beitrags (Teil 1). Der zweite Teil [1] wird sich im Schwerpunkt den verwendeten Messverfahren und Monitoringsystemen widmen, welche die Durchführung des Versuchs begleiteten.