Development of an Embeddable Reference Electrode for Reinforced Concrete Structures

About the report:

There is a concern that none of the existing concrete-embeddable reference electrodes that are being used as a convenient means for monitoring the condition of the reinforcing steel in concrete bridges or the operation of cathodic protection systems for permanently halting steel corrosion in these structures may have sufficient stability of at least 25 years. This study examines the possibility of using stable-potential galvanic couples (SPGC), which rely on different rate constants between the component metals of each couple to maintain stable potentials, as a new concept for developing better concrete-embeddable reference electrodes. Each SPGC relies on the different rate constants between the component metals to maintain a characteristic stable potential and can be classified as either noble-noble, noble/active-passive, noble-active or active-active. The long-term and the short-term stability of the potentials of different galvanic couples (in saturated calcium hydroxide), relative to both a saturated calomel electrode and a commercial manganese dioxide electrode, were assessed. The cathode-to-anode area ratio aspects of some couples were also investigated and it was determined that the area ratio could be used to optimize couple stability. Mixed potential theory was used to characterize these electrodes and explain the stability behavior. Several potentially successful couples, that exhibited potential shifts of less than 10mV, were identified and embedded in concrete (both with and without added chloride) for further investigation. This resulted in the identification of three promising candidate couples (Cu-W, Ni-W, and Cu-Ni) that can be developed into very stable concrete-embeddable reference electrodes by optimizing the electrode design parameters such as anode-to-cathode area ratio and geometry.

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