The benefits of using half-cell potential measurements in condition surveys of concrete bridge decks were examined using data collected from several decks by visual inspection, sounding with chain draggings, and measurement of half-cell potentials. Half-cell potentials on a deck were found to fluctuate from survey to survey, likely in response to seasonal fluctuations of temperature, oxygen, chloride, and moisture content in the concrete. Consequently, in contrast to ASTM interpretation guidelines (ASTM C-876), the numerical value of each measured half-cell potential by itself would be a poor indicator of the condition of rebars. Instead, the potential measured at each location should be considered relative to potentials measured in the surrounding concrete. When the potentials were plotted on an iso-potential contour map, the locations of active rebar corrosion and corrosion-induced damage in the concrete were associated with high negative potential gradients. Because of the localised nature of rebar corrosion, the recommended grid spacing of 4.0 ft (ASTM C-876) for surveys of bridge decks was found to be too large to allow location of existing active corrosion and the associated damage to concrete. It was determined that a grid spacing of no more than 2.0 ft should be used. If a half-cell potential survey is performed on a sufficiently small grid and the collected measurements are plotted on contour maps of iso-potential lines, the locations of existing active rebar corrosion and corrosion-induced damage in the concrete will be indicated with a high degree of accuracy by areas of relatively high potential gradients. When combined with the other inspection techniques, such a survey would be extremely useful in estimating necessary repair. (Author/publisher)
Abstract