Swiss Society for Corrosion Protection

Zurich, Switzerland

Swiss Society for Corrosion Protection

Zurich, Switzerland
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Angst U.M.,ETH Zurich | Angst U.M.,Swiss Society for Corrosion Protection
Concrete Solutions - Proceedings of Concrete Solutions, 6th International Conference on Concrete Repair, 2016 | Year: 2016

This paper reviews the established conceptual approach of predicting initiation of chloride induced corrosion of reinforcing steel in concrete. The low predictive power of the current approach is illustrated with help of recent field data for the chloride threshold value. Limitations and particular gaps of knowledge are highlighted, and issues urgently needing further research are identified. This includes the production process and the resulting microstructure of the reinforcing steel. Most of our practical long-term experience from real structures relates to systems where cold worked steel and Portland cement were used. During the last few decades, however, a transition to thermomechanically strengthened reinforcing steels and to blended cements occurred. There is indication that this drastically affects the corrosion behaviour. © 2016 Taylor & Francis Group, London.

Angst U.M.,Swiss Society for Corrosion Protection | Buchler M.,Swiss Society for Corrosion Protection
Proceedings of the 4th International Conference on Concrete Repair, Rehabilitation and Retrofitting, ICCRRR 2015 | Year: 2016

The rate at which steel corrosion occurs in reinforced concrete is an essential parameter for assessing the residual service life of a structure and thus for maintenance planning. However, determining corrosion rates reliably, particularly on site, is not straightforward. In principle, there exist a variety of experimental methods to determine the corrosion rate such as electrochemical procedures, gravimetric (weight loss) measurements or other approaches (McCafferty, 2010). For reinforcement steel embedded in concrete, only electrochemical methods permit non-destructive measurements of instantaneous corrosion rates. These are typically based on applying an external polarization current to excite the system and recording the system response. The by far most common method is the so-called Linear Polarization Resistance (LPR) method. © 2016 Taylor & Francis Group, London.

Jansen S.,Deltares | Van Burgel M.,DNV GL Oil and Gas | Gerritse J.,Deltares | Buchler M.,Swiss Society for Corrosion Protection
NACE - International Corrosion Conference Series | Year: 2017

Uncertainties are present about the mechanisms of cathodic protection (CP) and its effectiveness to limit or completely stop Microbiologically Influenced Corrosion (MIC). The goal of this research was to improve the understanding of the mechanisms of CP by determining the interactions between corrosion and local chemical parameters, such as pH, under varying CP conditions, both in the absence and presence of MIC. Electrical resistance (ER) probes, covered with a biofilm of sulphate-reducing microorganisms, were subjected to a series of CP potentials. In some cases MIC could not be stopped by CP, even at very negative potentials. The application of CP potentials resulted in an increase of the pH near the steel surface. In the absence of a biofilm CP could raise the pH above 13, whereas the pH remained below 8 in the presence of an active MIC biofilm. These findings show that MIC biofilms can reduce the effectiveness of CP by maintaining a mild pH, supporting their activity. Once biofilms have established, it may be very hard or even impossible to stop MIC with CP, irrespective of the potential applied. This suggests that CP strategies should be aimed at preventing MIC biofilms to develop from the start. © 2017 by NACE International.

Hornbostel K.,Norwegian University of Science and Technology | Elsener B.,ETH Zurich | Angst U.M.,Swiss Society for Corrosion Protection | Larsen C.K.,Norwegian University of Science and Technology | Geiker M.R.,Norwegian University of Science and Technology
Structural Concrete | Year: 2017

An experimental setup was designed to study the impact of concrete bulk resistivity on the rate of chloride-induced reinforcement corrosion. Small pieces of mild steel were used to simulate pits (anodes) that form when chlorides come into contact with the reinforcement. The galvanic current was measured between the simulated anodes and a large cathode network. Comparisons were made between the corrosion rates calculated from the galvanic currents and the bulk resistivity. The bulk resistivity was varied using two mortar mixes (made of plain Portland cement and a Portland cement-fly ash blend), which were exposed in different temperature and moisture conditions. Despite a high scatter in the results, it was clear that the relationship between bulk resistivity and corrosion rate depended on the mortars tested. The findings presented in this article and the accompanying work strongly indicate that bulk resistivity alone does not provide sufficient information for assessment of the corrosion rate for chloride-induced macro-cell corrosion. © 2017 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin.

Boschmann Kathler C.,ETH Zurich | Angst U.M.,ETH Zurich | Angst U.M.,Swiss Society for Corrosion Protection | Wagner M.,Tecnotest AG | And 2 more authors.
Cement and Concrete Research | Year: 2017

The chloride content Ccl expressed as %Cl by weight of cement is important in condition assessment of reinforced concrete structures. Whereas standardized procedures determine Ccl in concrete powder, the cement content Cm is generally assumed equal to the mix design or an experience-based constant value. This work shows in concrete with maximal aggregate diameter 32 mm, Cm exhibits significant variability in 50 mm diameter cores, because the specimens are too small to be representative of bulk concrete. In such specimens, Cm might differ from the bulk cement content by a factor of up to 2. Thus, a reliable determination of Ccl in terms of %Cl by weight of cement requires the analysis of both Ccl and Cm in a concrete specimen. A procedure based on colouring the cement paste, scanning the specimen surface, and image analysis allows the practically non-destructive determination of Cm with good accuracy. © 2017 Elsevier Ltd

Angst U.M.,ETH Zurich | Angst U.M.,Swiss Society for Corrosion Protection | Polder R.,TNO | Polder R.,Technical University of Delft
Cement and Concrete Research | Year: 2014

The concept of variability is increasingly considered in service life predictions. This paper reports experimental data on the spatial distribution of chloride in uncracked concrete subjected to homogeneous exposure. Chloride concentrations were measured with potentiometric sensors embedded in concrete exposed to chloride ingress by cyclic wetting and drying. The sensors allow highly localised, non-destructive measurements. Six different concrete mixes were tested, each with more than 20 sensors embedded within a plane at constant depth. The resulting dataset is discussed with respect to causes for the observed spatial variability of chloride as well as implications for service life predictions and experimental methods. It is concluded that the observed spatial chloride variability is a true property of chloride penetration into concrete and not an uncertainty arising from limited measurement precision. The primary cause was identified to be the presence of coarse aggregates rather than w/c ratio, cement type or exposure conditions. © 2013 Elsevier Ltd. All rights reserved.

Angst U.M.,Swiss Society for Corrosion Protection | Buchler M.,Swiss Society for Corrosion Protection | Schlumpf J.,Sika Services AG | Marazzani B.,Sika Technology AG
Materials and Structures/Materiaux et Constructions | Year: 2015

Long-term, well documented field experience with organic corrosion-inhibiting admixtures for reinforced concrete is scarce. The present paper contributes to closing this gap of knowledge by reporting 18 years of field performance of a proprietary inhibitor formulation based on alkanolamines (Sika FerroGard 901). Reinforced concrete elements were exposed to chloride-bearing splash water at a road in the Swiss Alps. Periodically, chloride profiles were determined and the specimens were monitored by galvanic current measurements, potential mapping, and electrical concrete resistance measurements. After 18 years, additional electrochemical measurements were undertaken on-site and selected zones of reinforcement steel were visually inspected. While in the reference concrete, corrosion initiated after approx. 8–9 years at a cover depth of 15 mm, the reinforcing steel in the concrete with inhibitor was after 18 years still essentially free from corrosion (at identical cover depth). Thus, under the conditions of the present work, the corrosion inhibitor increased the time to initiation of chloride-induced reinforcing steel corrosion by a factor of approx. 2. © 2015 RILEM

Buchler M.,Swiss Society for Corrosion Protection
Materials Performance | Year: 2015

According to ISO 15589-1, the effectiveness of cathodic protection (CP) for a buried steel structure is demonstrated by measuring the IR-free potential of the steel-to-soil interface. The physical-chemical significance of this criterion is discussed by means of theoretical considerations, numerical simulation, and comparisons with field data. The importance of mass transport at the steel surface is also considered. It is hoped this perspective will stimulate further discussion on the true nature of CP.

Buchler M.,Swiss Society for Corrosion Protection
Australasian Corrosion Association Annual Conference: Corrosion and Prevention 2015, ACA 2015 | Year: 2015

Cathodic protection has proved to be an efficient way to control corrosion and increase the service life of pipelines. While there is general agreement on the effectiveness of cathodic protection, there is a widespread discussion with respect to the mechanism of protection, the significance of the protection criteria, the methodology of their assessment and their interpretation. Moreover, there are significant differences in the application of these criteria, despite AS2832.1 and ISO 15589-1 that describe clear and strict requirements. The physical-chemical meaning of the protection criteria is discussed and a model for the mechanisms involved in cathodic protection is proposed. The fundamental applicability of the model concept is validated based on the comparison with extensive field data. The extension of the concept allows explaining the mechanisms involved in a.c. and d.c. interference. The consequences on protection criteria under these conditions are elaborated and compared to experimental data. Based on this analysis a possible explanation for the failure of cathodically protected structures is presented and a new methodology for assessing protection is proposed.

Based on laboratory studies and model concepts, a profound understanding of the involved processes in ac corrosion and the required limits has been obtained in the last years. But there was no information whether these thresholds can be effectively applied to pipelines or whether operational constraints make their implementation impossible. Therefore, an extensive field test was carried out. Thereby, the relevance of the laboratory tests for field application could be demonstrated and all threshold values were confirmed. Detailed analysis made it possible to explain the observed threshold values based on thermodynamic and kinetic considerations. The results summarized in the present work are the basis for the normative work defining the thresholds for the operation conditions of cathodically protected pipelines. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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