Monitoring the chloride concentration in the concrete pore solution by means of direct potentiometry

Determination of the chloride concentration at the depth of the rebar is important when studying the mechanisms of chloride-induced corrosion. It is generally assumed that only the chloride ions dissolved in the concrete pore solution can initiate corrosion, while those bound by the constituents of the cement paste are considered harmless. Attempts to use ion selective electrodes in concrete, to non-destructively monitor the free chloride concentration, have thus been made by several researchers. In the present work, results from laboratory experiments with such chloride sensors are presented. It was found that the presence of concentration gradients such as pH differences markedly influences the measurement of the sensor potential and thereby the accuracy of this chloride measurement technique. This has to be taken into account carefully when designing an experimental setup involving the use of ion selective electrodes.