ECS : Assessment of electrochemical methods to study corrosion of steel in concrete
Deputy Chair: Prof. Dr. Ueli ANGST
Corrosion of steel in concrete is major reason for deterioration of concrete structures. The corrosion process of the reinforcement itself is of electrochemical nature. Therefore, electrochemical measurements are an essential tool in order to be able to assess and scientifically study the corrosion behaviour of metal-concrete-systems. These systems may vary with regard to the metal composition, concrete composition, metal-concrete-interface and environmental condition. Besides the assessment of the corrosion behaviour, electrochemical measurements form the basis to predict/ model the time of corrosion initiation and the propagation period. Consequently, the knowledge and detailed understanding about electrochemical techniques is crucial for the scientific study of corrosion mechanisms in concrete, the characterization of corrosion behaviour/performance of different materials, and the selection and combination of materials for given applications to ensure the designed service life of structures. In order to be able to assess the measurement performance fundamental knowledge of electrochemistry, metallurgy and the physical chemistry of interfaces is required.
There are very few standards (ASTM C876, ISO 12696) for electrochemical measurements of steel in concrete. In addition, a former RILEM technical committee, TC 154-EMC “Electrochemical techniques for measuring metallic corrosion” (started in 1992), set the fundaments for the measurement and interpretation of half-cell potentials, concrete resistivity, and polarization resistance of steel in concrete. All these measurements have in common that they can be applied in laboratory and on-site. Nevertheless, RILEM TC 154-EMC focussed only on i) a small selection of the broad array of possible electrochemical measurements, and ii) their on-site applicability. For the use of electrochemical techniques to scientifically study corrosion of steel in concrete – as opposed to the use of electrochemical techniques as “non-destructive test methods” or “inspection techniques” on structures – there is very limited documented guidance for scholars, researchers and practitioners from industry.
It should here also be mentioned that electrochemical techniques, common in corrosion science in general, cannot directly be applied to steel in concrete. This is because of the pronounced differences between a metal surrounded by a (often homogeneous) electrolyte or a conductive porous medium and the here relevant situation of steel embedded in a macroscopic, highly heterogeneous, resistive and non-inert porous medium. Thus, specific guidance for the application of electrochemical techniques to steel corrosion in concrete is needed, including the limitations on application and interpretation of performance not addressed in the TC 154-EMC.
The main objective of the proposed RILEM TC is to close the gap of documentation and to overcome the lack of guidance currently available for scholars, researchers and practitioners using electrochemical measurements as outlined above. To this aim, we will compile state of the art knowledge about electrochemical techniques for the quantification of corrosion processes of steel in concrete, with particular focus on latest advances of electrochemical techniques for scientific studies. The focus is on the assessment of sophisticated, electrochemical laboratory methods such as:
- potential measurements
- (linear, differential, …) polarization resistance measurements
- measurements of polarization curves
- IR-drop compensation
- (zero-resistance) corrosion current (galvanic current)
- electrochemical impedance spectroscopy (EIS)
- electrochemical noise
- coupled multi electrode array techniques
- AC techniques, e.g. harmonic analysis
- cyclic voltammetry
- galvanostatic pulse.
These measurement methods require fundamental background of electrochemistry and often, they are applied inappropriately due to lack of knowledge and experience. On the other hand, the available measurement devices become more and more user friendly and affordable for many laboratories that do not always have the needed background for the proper use of these techniques. There is a risk that erroneous measurements or inappropriate interpretation of data lead to biased conclusions.
Furthermore, there is no comprehensive lecture book available to teach and to train scholars working in the field of corrosion of steel in concrete, in particular civil engineers. As mentioned above, there exist only few standards/ specifications on how to perform and evaluate the above listed measurement methods. Nowadays, the knowledge on how to perform these measurements is transferred from one experienced researcher to the next generation orally and by training in the lab. However, the number of labs performing these measurements are limited worldwide and access to this knowledge is therefore difficult. Thus, the training process and its success may sometimes be random. There is no common agreement to ensure quality standards for these measurement methods.
Thus, the second objective is to make the state-of-the art knowledge available in a format suitable for education and use by scholars working in the field at different stages: graduate students (e.g. in the form of a RILEM PhD summer school/workshop or online tutorials organized by the TC), specific RILEM recommendations on some of the most commonly used techniques for the general scientific audience.
The corrosion condition assessment of laboratory specimen/ existing structures is out of scope for this proposed TC. The focus is on the measurement method itself and not on the system under investigation. This is because of the complexity of the electrochemical methods to be addressed in this TC and the limited time available. Thus, the proposed TC will focus on the measurement methods (i) until (vi) listed above. The consideration of the other electrochemical techniques (vii) – (xi) will be discussed during the first meetings within the TC. The applicability of some of these newer methods to structures / condition assessments may be left for further consideration in a potential follow-up TC later.
Terms of reference
The estimated activity period of the TC is 4 years. The focus is on literature review and expert compilation of expertise. Round Robin tests are not intended to be part of the RILEM TC. However, if considered useful in the course of the work, Round Robin tests may be anticipated.
Confirmed and prospective partners represent several countries (Germany, Switzerland, Australia, India, Slovenia, Spain, USA, etc.).
Detailed working programme
The objective is to establish an agreement on electrochemical techniques for the study of corrosion of steel in concrete by
- discussing the setting parameters (including laboratory setup and specimen design)
- comparing the needed calibration measurement(s),
- agreeing on data representation and finally
- agreeing on data evaluation/ post-processing protocols.
The TC work consists of 4 work packages (WP):
- WP1: Influencing factors on electrochemical measurement methods - settings
- WP2: Measurement procedures
- WP3: Data evaluation and post-processing
- WP4: Preparation of educational material
The first step is the compilation of the influence of the setting parameters on the electrochemical measurements of steel in concrete based on published data. Secondly, basic requirements (settings, calibration) on the electrochemical measurement are set after the discussion on the acceptable noise-to-response ratio. The last step deals with the post-processing of the electrochemical data by evaluating the boundary conditions, which allow a further evaluation of the electrochemical data. The outcome of this TC are recommendations on how to perform and to process electrochemical measurements of steel in concrete appropriately.
The following milestones (MS) are associated to the work packages:
- MS 1: Second year - State-of-the-art paper:
- Identification of factors affecting electrochemical measurements of corrosion of steel in concrete in laboratory setups.
- Quantification of these effects
- How to control the influencing factors – Minimizing their effect
- MS 2/3: Third/ Fourth year - Recommendation on how to design, perform, and post-process electrochemical measurements
- Paper on, e.g. potential, current, polarization, IR-drop measurements
- Paper on, e.g. EIS, electrochemical noise
- MS 4: Fourth year - Organization and execution of a PhD summer school on electrochemical techniques for steel in concrete.
Furthermore, the successful performance of electrochemical measurement methods is dependent on the design of the test specimens, especially the electrode arrangement. Thus, the recommendations will include advice on how to design test specimens if necessary, even though, it is not in the direct scope of this TC.
The last RILEM TC dealing with electrochemical measurements was RILEM TC 154-EMC “Electrochemical techniques for measuring metallic corrosion” more than 20 years ago. Their objective was the detection of corrosion and quantification of corrosion rates of steel in concrete, basically, with three selected methods (potential, polarization resistance, resistivity). The focus was on the use of these methods for “inspection” of structures. This proposed RILEM TC will focus on the scientific study of mechanisms of corrosion of steel in concrete.
This TC interacts to other former and current TC’s such as:
- 262-SCI: Characteristics of the steel/concrete interface and their effect on initiation of chloride induced reinforcement corrosion
- 281-CCC: Carbonation of concrete with supplementary cementitious materials, especially WG 5
- 283-CAM: Chloride transport in alkali-activated materials
- FTC: Durability and service life of concrete under the influence of freeze-thaw cycles combined with chloride penetration
- TMS: Test method for concrete durability under combined role of sulphate and chloride ions.
The TC will provide the following achievements:
- State-of-the-art report addressing the influencing factors on performing electrochemical measurement of steel in concrete
- Recommendations on how to prepare and perform an accurate measurement and on how to evaluate and post-process data from selected electrochemical test methods
- Preparation of educational material on electrochemical measurements to study corrosion of steel in concrete
- Organization of a summer school for graduate students researching in the field of corrosion of steel in concrete
- Establishment of a network among the laboratories performing electrochemical measurements of steel in concrete
The proposed TC evaluates common, electrochemical laboratory test methods and provides support for their interpretation. However, this proposed TC will not publish any thresholds for corrosion assessment.
Group of users
Academics, graduate students, testing laboratories, industry, practitioners and technical bodies of standardization committees.
Specific use of the results
The outcome of this TC contributes primarily to academia and testing laboratories. The published reports will serve as recommendation for the application of electrochemical measurement methods in concrete. Thus, industry and practitioners will benefit from these findings as well. Furthermore, the recommendation will provide the basis for quality control of electrochemical data to assess the corrosion risk of steel/ metal interaction with concrete.
Additionally, the knowledge of the application of electrochemical methods is crucial, especially to assess corrosion behaviour of new metal-concrete systems such as self-healed concrete, additive manufactured concrete, supplementary cementitious materials, alkali-activated systems or other alternative metallic reinforcements (as galvanised, stainless steel) etc.
Consequently, this RILEM TC intends to compile the current knowledge on electrochemical methods for steel in concrete and make it available to the next generation of corrosion scientist in civil engineering. Thus, the objective is in line with the pioneers in corrosion science:
“However, in corrosion research the most valuable investment is not an instrument, but the brain of a researcher: a good corrosionist without a potentiostat is to be preferred to a bad one with a potentiostat”
Marcel Pourbaix, 1971