Research ArticleAPPLIED SCIENCES AND ENGINEERING

The size effect in corrosion greatly influences the predicted life span of concrete infrastructures

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Science Advances  02 Aug 2017:
Vol. 3, no. 8, e1700751
DOI: 10.1126/sciadv.1700751
  • Fig. 1 Effect of specimen size on the chloride concentration needed for corrosion initiation of carbon steel in concrete.

    (A) Setup for corrosion tests of reinforced concrete specimens under chloride exposure with three different exposed lengths, labeled L (100 cm), M (10 cm), and S (1 cm). The number of tested specimens is also indicated. (B) Box plots of measured Ccrit (black) shown for the different Lexp (whiskers, min/max; red box plot, prediction for size L) based on the probabilistic model and on the results for M (compare discussion section for details). (C) Cumulative probability for corrosion initiation as a function of the chloride concentration. Dots represent individual measurements, the dashed lines are fits assuming a log-normal distribution, and the red line is the prediction based on the probabilistic model. μ and σ are the first two moments of the log-normal distributions. The smallest specimens (Lexp = 1-cm exposed length) did not corrode even at a chloride concentration of 2.38%.

  • Fig. 2 Inhomogeneities at the SCI.

    (A) Representative image of a split concrete specimen after removal of the steel bar, showing dark corrosion products at the location of corrosion initiation, surrounded by a rim of red/brown deposited rust and the presence of a coarse air void at the steel surface (free from corrosion). (B) Image of a section perpendicular through the steel bar in concrete with a coarse air void at the SCI. (C) Backscattered electron (BSE) micrograph of a polished section perpendicular to the steel bar of an epoxy-impregnated specimen illustrating the transition of the SCI morphology from zone A (steel in contact with concrete) to zone B (at coarse air void, where the steel is covered with a thin layer of cement paste). (D) SEM micrograph of a carbon-coated section perpendicular to the steel bar showing the presence of a cement-paste layer on the steel surface that is interspersed with small air voids.

  • Fig. 3 Corrosion morphology.

    (A) Close-up image of a steel bar after removal from the concrete and after chemical cleaning showing several sites of localized corrosion within an area of <1 cm2. (B) BSE micrograph of the section indicated in (A) showing two shallow corrosion pits, a and b. Pit b is covered with a crust of chloride containing iron complexes, underneath which branched corrosion attack extends into the steel. The dark spots in the steel are inclusions (MnO, SiO2, and FeO). (C) Light optical micrograph of the etched section of the framed portion of (B) showing the ferritic-pearlitic microstructure and the preferential corrosion attack of the pearlite phase of the Mn-Si oxide inclusions and along grain boundaries.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/8/e1700751/DC1

    fig. S1. Examples of coarse air voids at the SCI.

    fig. S2. Morphology of the corrosion attack.

    fig. S3. Example of prediction of time to corrosion initiation.

    fig. S4. Reinforced concrete slabs cast in the laboratory.

    fig. S5. Preparation of specimens of different sizes based on the slabs shown in fig. S4.

    fig. S6. Detail of end-shielding of the steel bars.

    table S1. Detailed results of measured chloride threshold values Ccrit for corrosion initiation.

    table S2. Nominal concrete mix proportions.

    table S3. Wetting/drying exposure and sampling times after corrosion initiation for the individual specimens.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Examples of coarse air voids at the SCI.
    • fig. S2. Morphology of the corrosion attack.
    • fig. S3. Example of prediction of time to corrosion initiation.
    • fig. S4. Reinforced concrete slabs cast in the laboratory.
    • fig. S5. Preparation of specimens of different sizes based on the slabs shown in fig. S4.
    • fig. S6. Detail of end-shielding of the steel bars.
    • table S1. Detailed results of measured chloride threshold values Ccrit for corrosion initiation.
    • table S2. Nominal concrete mix proportions.
    • table S3. Wetting/drying exposure and sampling times after corrosion initiation for the individual specimens.

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    Files in this Data Supplement:

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