Algorithm for Extracting Corrosion Parameters from the Response of the Steel-Concrete System to a Current Pulse

Abstract

The transient response to a current pulse applied to steel reinforcement bars in concrete has been analyzed by means of a new computational algorithm based on discretised approximation of the fractional difference operator. An optimization strategy has been designed to obtain a set of optimal values for the characteristic corrosion parameters from the information contained in the potential-time transient ͑specially, in the decaying part of the trace͒. The method compares the experimental response with the simulated response in the time domain obtained from an electrical circuit model which includes the effects of a constant-phase element and diffusion coupled with charge transfer. The practical possibilities of this method for extracting corrosion parameters ͑in particular, the charge-transfer resistance͒ have been demonstrated with steel reinforcements embedded in concrete in the presence and absence of chloride additions.The literature contains many references to work that seeks to obtain information about the corrosion rate of reinforcement bars embedded in concrete from the responses in the time and frequency domains to different electrical signals. 1-10 In general, electrochemical impedance spectroscopy ͑EIS͒ is a powerful tool for studying the mechanism of the corrosion processes, but with a system as complex and peculiar as the steel-concrete interface, it suffers from certain limitations. 10-16 Badly defined impedance diagrams are a rather common occurrence in reinforced concrete. The response for the passive steel in concrete is essentially capacitive, and the Nyquist plots show very open and incomplete arcs, while the form of the plots for the active steel suggests a phenomenon much more complicated than a purely charge-transfer controlled one. Another problem of EIS is the long time required to complete the measurements, which makes it impracticable to carry out a large number of tests, and which allows the corrosion potential to drift, distorting the Nyquist plots.On the other hand, in the time domain, transient methods have shown some promise in determining the corrosion rate of steel in concrete, in both the laboratory and the field. 4,5,11-21 Compared with the EIS measurements they have the advantages of being obtained more rapidly and with less sophisticated instruments. The development of portable time-domain data acquisition equipment has greatly facilitated the in situ measurements. A number of workers have studied the response curves to potentiostatic transients 19,20 and, in particular to galvanostatic transients. 4,5,12,13,16,18,[21][22][23] Unlike laboratory studies with small specimens, on large concrete structures a complication can arise if the potential is position dependent, as when macrocells are present. 24,25 In practice, polarization measurements have been used successfully by many workers on a wide range of reinforced concrete structures, small likelywood because microcell corrosion is often the predominant mode of corrosion and small errors caused by the presence of some macrocel...

Corrosion performance of reinforced mortar in the presence of polymeric nano-aggregates: electrochemical behavior, surface analysis, and properties of the steel/cement paste interface

“…The elements of the equivalent circuit present the following physical meanings: R el?b is the mortar resistance, including the contribution of the electrolyte resistance; the first time constant (R pn and Q pn ) is attributed to the properties of the bulk matrix in terms of connected pore network; the second time constant (Q ct and R ct ) is normally used to evaluate charge transfer process in combination with mass transport process. When there are no mass transport limitations, R ct equals the global polarization resistance R p [35,45] and is related to the electrochemical reaction on the steel surface (widely accepted for reinforced cement-based materials is to use constant phase element (Q) instead of pure capacitance to account for steel surface, product layers, and bulk matrix heterogeneity [49,50]). …”

Electrochemical Behavior, Microstructural Analysis, and Morphological Observations in Reinforced Mortar Subjected to Chloride Ingress

“…The electrochemical behavior of steel reinforcement has been extensively studied and outcomes are reported in literature. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] The intention of this work is to see how well different electrochemical techniques agree for reinforced cement-based materials rather than obtaining absolute quantitative parameters ͑such as corrosion rate for example͒ and, further, to correlate results with structural and morphological observations of the bulk matrix and the steel/cement paste interface, thus setting up a combination of techniques for the assessment of corrosion and protection in reinforced concrete. …”

Rebar corrosion due to chlorides in synergy with sodium, potassium, and magnesium

“…Randles type circuit is useful in modelling the structure of the concrete/steel interface. This is characterised by the combined polarisation resistance (R p ) and the diffusion resistance (R D ) in parallel with a non-ideal double layer capacitance (C dl ), which is in series with the concrete (Ohmic) resistance (R O ) [8][9][10][11][12] as shown in Fig. 1.…”

“…The corrosion properties at the concrete/steel interface can be analysed using short galvanostatic pulse method [8][9][10][11][12][13]. It has been shown that the application of a small magnitude of current pulse (<100 mC/cm 2 ) eliminates the diffusion effects in the system [8,9,14,15], allowing the system to be analysed using the equivalent electrical circuit in Fig.…”

“…It has been shown that the application of a small magnitude of current pulse (<100 mC/cm 2 ) eliminates the diffusion effects in the system [8,9,14,15], allowing the system to be analysed using the equivalent electrical circuit in Fig. 1 without consideration of R D .…”