Monitoring chloride ion penetration in concrete with different mineral admixtures based on embedded chloride ion selective electrodes

- Monitoring of free Cl− content in concrete by embedded Cl− selective sensors.
- The Cl− content in various concrete types followed the Fick's second law.
- The relationships between free Cl− and bound as well as total Cl− contents were investigated.
- Lower total and larger locked porosities were found out for modified concrete.

In this paper the development of free Cl− content in various types of concrete was monitored by means of the embedded Ag/AgCl electrode. Moreover, the bound as well as total Cl− contents were determined through volumetric method. Besides, these mechanisms about the Cl− diffusion in different types of concrete are analyzed and discussed. Results revealed that real-time monitoring of free Cl− concentration in concrete was achieved based on the measurements of potentials of embedded electrodes and the diffusion law of free Cl− content followed Fick's second law. In addition, the Freundlich isotherm was recommended to describe these relationships between free Cl− content and bound as well as total Cl− concentrations. As for the types of concrete with the addition of mineral admixture, lower total porosity and larger locked porosity have been found out. However, much more efforts should be paid to develop low-cost, robustness and long-term reliable Cl− selective sensors in order to achieve the wide application in concrete environment.