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The steel–concrete interface (SCI) is known to influence corrosion of steel in concrete. However, due to the numerous factors affecting the SCI—including steel properties, concrete properties, execution, and exposure conditions—it remains unclear which factors have the most dominant impact on the susceptibility of reinforced concrete to corrosion. In this literature review, prepared by members of RILEM technical committee 262-SCI, an attempt is made to elucidate the effect of numerous SCI characteristics on chloride-induced corrosion initiation of steel in concrete. We use a method to quantify and normalize the effect of individual SCI characteristics based on different literature results, which allows comparing them in a comprehensive context. It is found that the different SCI characteristics have received highly unbalanced research attention. Parameters such as w/b ratio and cement type have been studied most extensively. Interestingly, however, literature consistently indicates that those parameters have merely a moderate effect on the corrosion susceptibility of steel in concrete. Considerably more pronounced effects were identified for (1) steel properties, including metallurgy, presence of mill scale or rust layers, and surface roughness, and (2) the moisture state. Unfortunately, however, these aspects have received comparatively little research attention. Due to their apparently strong influence, future corrosion studies as well as developments towards predicting corrosion initiation in concrete would benefit from considering those aspects. Particularly the working mechanisms related to the moisture conditions in microscopic and macroscopic voids at the SCI is complex and presents major opportunities for further research in corrosion of steel in concrete.
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.
During their life span, concrete structures interact with many kinds of external mechanical loads. Most of these loads are considered in advance and result in reversible deformations. Nevertheless, some of the loads cause irreversible, sometimes unnoticed changes below the macroscopic scale depending on the type and dimension of the impact. As the functionality of concrete structures is often relevant to safety and society, their condition must be known and, therefore, assessed on a regular basis. Out of the spectrum of non-destructive monitoring methods, Coda Wave Interferometry using embedded ultrasonic sensors is one particularly sensitive technique to evaluate changes to heterogeneous media. However, there are various influences on Coda waves in concrete, and the interpretation of their superimposed effect is ambiguous. In this study, we quantify the relations of uniaxial compression and uniaxial tension on Coda waves propagating in normal concrete. We found that both the signal correlation of ultrasonic signals as well as their velocity variation directly reflect the stress change in concrete structures in a laboratory environment. For the linear elastic range up to 30% of the strength, we calculated a velocity variation of −0.97‰/MPa for compression and 0.33%/MPa for tension using linear regression. In addition, these parameters revealed even weak irreversible changes after removal of the load. Furthermore, we show the time-dependent effects of shrinkage and creep on Coda waves by providing the development of the signal parameters over time during half a year together with creep recovery. Our observations showed that time-dependent material changes must be taken into account for any comparison of ultrasonic signals that are far apart in time. The study’s results demonstrate how Coda Wave Interferometry is capable of monitoring stress changes and detecting even small-size microstructural changes. By indicating the stated relations and their separation from further impacts, e.g., temperature and moisture, we anticipate our study to contribute to the qualification of Coda Wave Interferometry for its application as an early-warning system for concrete structures.