An Alternative Potentiometric Method for Determining Chloride Content in Concrete Samples from Reinforced-Concrete Bridges

About the report:

Analysis of chloride contents in ground concrete samples collected from reinforced concrete bridges and other structures exposed to deicing salts or seawater has become an important part of the inspection for such structures. Such an analysis provides important information for deciding what measures to implement to protect and rehabilitate such structures. As an alternative to the standard potentiometric-titration method of chloride analysis for concrete samples, which is time-consuming and expensive, this study developed and evaluated a new, simple, short method called internal calibration. With this method, cold digested solutions of concrete samples are spiked twice with a relatively small and precisely measured amount of a standard NaCl solution, and the chloride content of each sample is calculated from the potential readings before and after the spiking by an equation derived from the Nernst equation. A comparison of the results from analyses of concrete samples using the standard method and the new method showed that the chloride concentration determinations are lower with the new method. However, at chloride contents around the chloride corrosion threshold, i.e., 0.00 to 2.00 kg/m3, which is the range of most interest in decisions regarding rehabilitation, the differences between the methods were almost negligible. When the time and reagents required are considered, the cost of using the new method is relatively low, less than 25 percent of the cost of using the standard method. This does not include the indirect savings resulting from eliminating the need to use and properly dispose of potentially hazardous reagents and waste. Since the new method does not require the extensive glassware required with the standard method, and the digestion solution and standard NaCl solution can be prepackaged, concrete samples can be analyzed by trained field units.

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