The paper presents the damage model of German Research Unit 537 which was used as a working hypothesis for the development of a user‐friendly design model. Excerpts from the laboratory experiments and numerical calculations processed in project A of the research unit are presented here. The excerpts include the quantification of self‐corrosion, geometrical effects in the macrocell corrosion, development of corroding steel surface and pit depth as well as the quantification of the resistivity of the concrete and the corrosion of steel in cracked concrete.

In this paper investigations into the formation of specific corrosion products during the process of chloride induced corrosion of steel in concrete are presented. The extension of corrosion products within concrete was established by means of X-ray tomography analyses. Then a detailed analysis of the nature of corrosion products has been conducted by means of Raman micro-spectroscopy and energy dispersive spectroscopy. Results emphasize two different corrosion patterns. The first one is composed of shallow cavities, where mostly magnetite and goethite were identified, traducing aerated to moderate aerated conditions in these media. The second pattern was identified as deep, needle-like pits, where chlorinated-iron-oxides phases were present associated with more or less important chloride enrichments. The presence of these particular species is indicating low redox and low pH conditions within these pits.

This paper deals with the possible corrosion risk for steel rebars in cracked reinforced concrete structures by using acrylate gels for grouting. In the course of this project, 19 customary acrylate gels were analysed. The results of the conducted test procedures revealed that none of the tested acrylate gels can provide an active corrosion protection for the steel rebars due to their low electrolytic resistivity and low pH values. Just when applied in very thin layers (e.g., fine cracks) it seems to be possible that alkaline components of the surrounding concrete can penetrate through the gel to form a passive layer on the embedded steel rebar.

In this paper the development of a key parameter for the static evaluation of corroding steel reinforced concrete members is presented. Based on an extensive test series under defined laboratory conditions as well as outdoor exposure the time dependent morphology and thus the development of the residual cross section of reinforcement steel embedded in uncracked concrete with high chloride contents has been investigated. In order to reach that goal a cutting edge sensor system using the principle of optical triangulation has been applied. Based on the obtained results a so called Residual Cross Section Factor has been developed. Its value and time dependency is discussed linking it to further morphological key parameters such as the corroding surface area as well as the maximum pitting depth on the corroded steel probe. The applicability of the introduced factor in comparison to the well known pitting factor is presented and discussed.

Im folgenden Beitrag werden die Ergebnisse eines Gemeinschaftsprojektes zwischen dem Techion in Haifa, Israel und dem Institut für Bauforschung der RWTH Aachen (ibac) vorgestellt. Ziel des Projektes war es, den Einfluss der Kontaktzone auf den kritischen korrosionsauslösenden Chloridgehalt für unlegierten Stahl in Beton besser zu verstehen. Zu diesem Zweck wurden am ibac an insgesamt 15 Betonvariationen elektrochemische Untersuchungen zur Ermittlung des Depassivierungszeitpunktes sowie nasschemische Analysen zur Bestimmung des vorliegenden Gesamtchloridgehaltes auf Höhe der Bewehrung durchgeführt. Jede Betonvariation wurde mit “stehender” (parallel zur Betonierrichtung) sowie “liegender” (orthogonal zur Betonierrichtung) Bewehrungsführung hergestellt, um neben den betontechnologischen Aspekten auch baupraktisch relevante Einflüsse auf die Kontaktzone zu erfassen. Die Ergebnisse zeigen, dass betontechnologische Variationen einen starken Einfluss auf die Initiierungszeit ausüben. Hinsichtlich des festgestellten korrosionsauslösenden Chloridgehaltes dominiert jedoch der Einfluss der Bewehrungslage. Diesem Aspekt sollte daher bei der Entwicklung von Prüfverfahren unbedingt Rechnung getragen werden.Investigations Into the Time to Corrosion and Corrosion Initiating Chloride Contents for Steel in ConcreteThe present paper highlights the results of a German‐Israeli research project. The research work was conducted in order to improve the understanding for the influence of the interfacial transition zone (ITZ) between steel and concrete on the critical (corrosion inducing) chloride content for black steel in concrete. In order to reach that goal an extensive electrochemical test series covering 15 different concrete mixes was established aiming at initiation times and critical chloride contents. For each concrete mix a pair of test specimens with a vertical and a horizontal rebar arrangement with regard to the cast direction was investigated. In this way it was possible to consider not only the influence of mix variations but also of craftsmanship on the ITZ. The results show that mix variations have a measurable impact on the initiation time while the formation of the critical chloride content seems to be dominated by the rebar arrangement. It is emphasized that these aspects should be considered in any test procedure regarding the critical chloride content of black steel in concrete.