2.1. Measurement Principle Governing INESSCOM Sensor

Figure 1a depicts the corrosion measurement principle governing the INESSCOM sensor we have developed and whose possible use to determine concrete resistivity is explored hereunder. The system uses potential step voltammetry (PSV) to measure corrosion rate, as described elsewhere [29]. The technique is based on the intersection method, with the added advantage that as the Tafel slopes can be found in less time, the technique is less invasive than the original method. The circuit in Figure 1b proposed in earlier studies [27] is used to model the transient response of the steel-concrete system when the potential pulse sequence shown in Figure 1c was applied. In addition to corrosion rate, the model can be used to find parameters such as the electrical resistance of concrete (R_E-_PSV), based on circuit resistances R₁ and R₂ from Equation (1):

Embedded corrosion sensor for measuring the corrosion rate: (a) measuring cell used to apply PSV with the optional inclusion of a reference electrode (RE) to measure the E_CORR; (b) equivalent circuit used in PSV to model the transient response of the steel-concrete system; and (c) potential pulse sequence applied in PSV to polarize the system.

The sensor needs only two elements (Figure 1a) for conducting the PSV measurement, the working (WE) and counter (CE) electrodes. The advantage of such a two-electrode setup is that, unlike standard sensors, it does not require an embedded reference electrode (RE) whose uncertain long-term stability could affect sensor reliability. The sensor may, however, optionally bear a built-in RE to measure the corrosion potential (E_CORR) which, although a qualitative parameter, provides more complete analyses of reinforcement condition.

In the two-electrode PSV measurements (Figure 1a), the WE was a corrugated carbon steel bar with the same characteristics as the reinforcement of the structure to be monitored, but shorter and with the two ends sealed with epoxy resin to clearly delimit the working area. The CE, in turn, was the reinforcement itself of the structure to be monitored. The CE area was consequently much larger than the WE area, an arrangement shown in earlier studies [31] to be imperative for reliable two-electrode PSV measurement.