Stray current, arising from direct current electrified traction systems, further circulating in nearby reinforced concrete structures may initiate corrosion or accelerate existing corrosion processes on the steel reinforcement. In some extreme conditions, corrosion of the embedded steel will occur at very early stage. One of the significant consequences is loss of bond strength and premature failure of the steel-matrix interface. This plays an important role for the integrity of a structure during its designed service life.

In this work, the level of stray current was set at 0.3 mA/cm2, applied as an external DC electrical field. This level of stray current was chosen based on preliminary calculations on expected corrosion damage, i.e., in view of material loss at the level of 10% weight loss of the steel rebar (analytically calculated via Faraday’s law). The investigated reinforced mortar specimens were cured for 24 h only and then conditioned in chloride-free and chloride-containing environment. The evolution of steel electrochemical response in rest (no stray current) and under current conditions was monitored for approx. 240 days via OCP (Open Circuit Potential), LPR (Linear Polarization Resistance), EIS (Electrochemical Impedance Spectroscopy) and PDP (Potentio-dynamic Polarization).

The results show that the effect of stray current on concrete bulk matrix properties, together with steel corrosion response, is significantly determined by the external environment, as well as by the level of maturity of the cement-based bulk matrix.

For chloride-free environment the effect of the chosen stray current level was not significant, although lower corrosion resistance of the steel rebars was recorded after longer exposure of ~240 days, compared to control conditions. In fact, even positive effects of the stray current were observed in the early stages, i.e., until 28 days of age: stray current flow through a fresh (non-mature) cement matrix led to enhanced water and ion transport due to migration. The result was enhanced cement hydration, consequently environment, assisting a more rapid stabilization of pore solution and steel/cement paste interface. In chloride-containing external medium, steel corrosion was a synergetic effect of both de-passivation due to chloride ions in the medium and stray current effects. Corrosion acceleration solely due to the stray current flow in chloride-containing medium cannot be claimed for the chosen current density levels and the duration and conditions of the experiment.

What can be concluded is that the effect of stray current for both chloride-free and chloride-containing conditions is predominantly positive in the initial stages of this test. The expected negative influence towards corrosion acceleration was observed after a prolonged treatment, when a stable maturity level of the cement-based matrix was at hand. This also means that the properties of the cementitious material in reinforced cement-based system are of significant importance and largely determine the electrochemical state of the steel reinforcement.
Original languageEnglish
Title of host publicationConcrete Durability
Subtitle of host publicationCementitious Materials and Reinforced Concrete Properties, Behavior and Corrosion Resistance
EditorsLuis Emilio Rendon Diaz Miron, Dessi A. Koleva
Place of PublicationCham, Switzerland
PublisherSpringer
Pages83-108
VolumeVIII
Edition1
ISBN (Electronic)978-3-319-55463-1
ISBN (Print)978-3-319-55461-7
DOIs
Publication statusPublished - 2017

    Research areas

  • Stray current, Steel corrosion, Mortar, Electrochemical tests

ID: 18066951