Electrochemical studies on the performance characteristics of solid metal–metal oxide reference sensor for concrete environments

Cylindrical titanium surface activated with mixed metal–metal oxides (MMO) (though similar to permanent impressed current titanium anodes used in cathodic protection) was used as a reference sensor for concrete environments. The performance characteristics were evaluated in a saturated calcium hydroxide solution (pH 12.5), a synthetic concrete pore solution (pH 13.5) and ordinary Portland cement (OPC) extracts (pH 13.0), which correspond to the concrete environments. The electrochemical stability of the MMO electrode was studied in the said concrete environments and in various buffer solutions (pH 4, 7 and 10) for an exposure period of 180 days. Simultaneous experiments were carried out to realize the performance of the MMO electrode in various solutions containing different concentration of chloride. The self-corrosion studies of the MMO electrode both in concrete environments and in other solutions with and without addition of chloride were carried out gravimetrically for an exposure period of 180 days. The polarization behavior of the MMO electrode in the concrete environments was carried out potentiodynamically with a progressive addition of chloride. All the studies revealed that the MMO was a suitable sensory electrode for concrete structures both in the absence and presence of chloride ions.