Detecting critical chloride content in concrete using embedded ion selective electrodes - effect of liquid junction and membrane potentials

摘要

When studying critical chloride content in reinforced concrete, the amount of chloride dissolved in the pore solution is an important parameter. Ion selective electrodes offer the possibility of measuring the chloride ion concentration (activity) in the concrete pore solution non-destructively. However, the potentiometric measurement might be disturbed by, amongst others, diffusion potentials (liquid junction potentials and membrane potentials). Laboratory samples designed to find critical chloride contents often involve chloride ingress by capillary suction, diffusion or migration, and thus chloride and pH profiles are usually present. As a result of these concentration gradients, membrane potentials are established, which markedly affect the determination of the chloride concentration. In addition, liquid junction potentials at the interface of the concrete sample and the reference electrode contribute to the measured potential. Experimental observations in the present work illustrate the effect of liquid junction potentials on the application of ion selective electrodes in concrete. Moreover, the influence of internal membrane potentials has been estimated by a theoretical model.