In-situ monitoring of pH and Cl− concentration and rebar corrosion at the rebar/mortar interface

Abstract

This study performed in-situ monitoring of pH and [Cl−] in pore water near the rebar/mortar interface using embedded electrochemical sensors (i.e., IrOx and Ag/AgCl electrodes). Membrane potential (Emembrane), which is the potential difference across the mortar/bulk electrolyte interface, was found to bring significant errors in determining pH and [Cl−]. These errors could be eliminated by measuring the potential of the sensors against the home-made-embedded reference electrode. In a long-term immersion experiment, the corrosion of steel rebar was recorded using electrochemical impedance spectroscopy. Results showed that over the 75 days of immersion experiment, [Cl−] in pore water near the rebar/mortar interface increased from 0.005 mol∙L−1 (at day 2) to 1.37 mol∙L−1, while pH decreased from 13.4 to 11.5. With the evolution of [Cl−] and pH, the corrosion of steel surface was accelerated due to passive film breakdown. The “passive to active” transition occurred when [Cl−] was ≥0.25 mol∙L−1 and pH was ≤12.1.