Steady-state polarization response of chloride-induced macrocell corrosion systems in steel reinforced concrete — numerical and experimental investigations

Statistical quantification of Tafel coefficients is investigated in this study for isolated steel rebar embedded in concrete. The survey is supported by a wide experimental campaign carried out earlier to characterize the passive and active states of carbonation‐induced corrosion of steel. Electrochemical measurements (polarization resistance, corrosion potential, Tafel coefficients) and gravimetric estimations of iron loss were regularly conducted over 417 days on 108 concrete specimens. The statistical analysis reveals that the mean value of Tafel coefficients, both cathodic and anodic, is higher under active corrosion, which seems to contradict the general tendency found for chloride‐induced corrosion, while their coefficient of variation is smaller. The statistical inference was based on the first step of distributions fitting the experimental data and then on the second step of goodness‐of‐fit tests. The most suitable of the distributions proposed were the Burr, Rayleigh, and Gamma distributions. A similar analysis was made for the corrosion potential and polarization resistance. The findings of the study will be valuable for probabilistic approaches to corrosion where probabilistic distributions are required.

E_{corr, A}

in active area is much lower than

E_{corr, P}

in passive area) the active area undergoes anodic polarization while the passive area undergoes cathodic polarization.…”

Section: Assessment Of the Tafel Coefficientsmentioning

confidence: 99%

“…As polarized steel surfaces generally have various extents, anodic and cathodic net currents are no longer balanced. According to Laurens et al, the corrosion current can be expressed as

j_{corr} = i_{m} / A_{A} + i_{micro} / A_{A} = j_{m} + j_{micro}

where

A_{A}

is the extent of the active area and

i_{micro}

is the residual microcell current intensity. Butler–Volmer equations apply for each area

j_{A} = j_{m} = j_{corr, A} true[exp true(\ln true(10 true) η_{A} / β_{a, A} true) - exp true(- \ln true(10 true) η_{A} / β_{c, A} true) true]

and

j_{P} = j_{corr, P} true[exp true(\ln true(10 true) η_{P} / β_{a, P} true) - exp true(- \ln true(10 true) η_{P} / β_{c, P} true) true]

where

η_{A} = E_{A} - E_{corr, A}

and

η_{P} = E_{P} ...

…”

Section: Assessment Of the Tafel Coefficientsmentioning

confidence: 99%

“…The residual microcell current results from the difference between the total anodic current and the net anodic current …”

Section: Assessment Of the Tafel Coefficientsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Quantification of Tafel coefficients according to passive/active state of steel carbonation‐induced corrosion in concrete

Duprat

Larrard

2019

Macrocell corrosion of steel in concrete: Characterization of anodic behavior in relation to the chloride content

Chalhoub

François

García

et al. 2020

This study presents the determination of electrochemical properties of active steel in mortar, based on inverse numerical modeling that focuses on their dependency on chloride content. An experimental campaign, consisting of galvanic coupling tests between anode samples contaminated with different chloride concentrations and cathode samples without chlorides, was carried out. Cathode polarization tests allowed for directly determining passive steel electrochemical parameters. Anode polarization tests coupled with a numerical optimization were then performed for quantifying active steel parameters and focusing on chloride's effect on the iron anodic Tafel coefficient. Furthermore, the steel electrochemical properties were successfully used as input parameters to model the galvanic experiments.

A new perspective on measuring the corrosion rate of localized corrosion

Angst

Büchler

2020

Many corrosion phenomena are nonuniform, which means that anodic and cathodic locations are spatially separated. An example is macrocell corrosion of steel in concrete. Under these conditions, determining the corrosion rate from polarization resistance measurements and using the Stern-Geary equation is fundamentally not possible. We present a novel theoretical approach for the interpretation of galvanostatic pulse measurements, to make them applicable as a method for corrosion rate measurements in situations of localized corrosion. Experiments show that it is important to consider that (a) only a fraction of the applied current flows through the anode of the macrocell, and (b) this current is not constant over time. We propose an approach to quantify and consider these two effects, based on information generally accessible in condition assessment of concrete structures. Our results show that galvanostatic pulse measurements are a robust method to determine the corrosion current. With the traditional empirical approach, the measurement error was generally below factor 3, and occasionally up to factor 10. With the novel approach, this error could be reduced to a factor of maximum 2 in all cases. K E Y W O R D Scorrosion rate, galvanic corrosion, localized corrosion, macrocell corrosion, test method