Benefits of Measuring Half-cell Potentials and Rebar Corrosion Rates in Condition Surveys of Concrete Bridge Decks

About the report:

The practice of conducting a half-cell potential survey during the assessment of the condition of a concrete deck was reexamined with the objective of eliminating some of the doubts concerning its benefits. It was found that the survey grid size of 4.0 ft recommended in ASTM C 876 had partly contributed to the uncertainty because this spacing is too large to allow complete detection of all the rebar corrosion and the associated concrete delamination that may exist in a deck. It was shown that the effect of rebar corrosion on the potential of the concrete was relatively localized; thus, a grid size of no more than 2.0 ft should be used. Another contributing factor was that the half-cell potential at any location on a concrete deck can fluctuate normally with temperature and other factors. Consequently, in contrast to the interpretation guidelines suggested in ASTM C 876, the numerical value of the potential measured at each location (by itself) would be an imprecise indicator of the condition of the rebar and/or concrete at the location. Instead, the actively corroding rebars are manifested on the concrete surface in large potential gradients that can be readily located in iso-potential contour maps made from the survey results. It was found that the 3LP device provides a simple but time-consuming means for measuring the corrosion rates of rebars, which correlate reasonably well with the metal losses observed in the rebars. However, since corrosion rate also fluctuates with location on a concrete deck and time, the benefit of such a survey would not be fully realized until an appropriate method for determining the representative rebar corrosion rate for a deck and for relating such to remaining service life has been developed.

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