Performance of a Conductive-paint Anode in Cathodic Protection Systems for Inland Concrete Bridge Piers in Virginia

About the report:

As part of efforts to identify effective and durable anodes for use in cathodic protection (CP) of reinforced concrete members, a water-based, electrically conductive paint was evaluated for use as the secondary anode in CP systems for protecting inland concrete piers. In such piers, the concrete areas susceptible to rebar corrosion are not constantly wet as they are in marine environments. The paint was used in two CP systems, one 6 years old and the other 8 years old, that were designed to protect the concrete piers of two pairs of twin bridges in inland Virginia. Measurements of circuit current, circuit voltage, rebar potential, and 4-hour depolarization indicated that the two CP systems were operating as expected and providing more than sufficient protection to the rebars in the concrete piers. Paint deterioration, such as peeling, cracks, and stains, occurred in both systems. The extent of the deterioration was estimated with the use of a newly developed digital image analysis method, and the largest area of damage was 2.40 percent of the total coated concrete area of a pier protected by the older CP system. Since this unusually large area was restricted to the upstream-side footing of the pier, it was attributed to abrasion and damage caused by timber debris crashing against the footing as the result of recent severe flooding. Other than this area, the natural deterioration in the paint system ranged from only 0 to 0.37 percent. Similar deterioration in the second paint system ranged from only 0 to 0.14 percent. Most of the paint deterioration in both systems was at the ends of the pier caps, where the concrete was not sheltered from rain by the deck overhang. This suggests that even with inland concrete piers, deterioration of the conductive paint, albeit slow, can occur on any portion of the concrete that becomes wet intermittently, either by rainfall or drainage from the deck. Therefore, extra measures for avoiding this problem must be considered in the design of any CP system that uses the conductive paint as a secondary anode. Overall, the performance of the paint was better than expected, and its effectiveness can reasonably be expected to last for at least 15 years if minor deterioration is touched up as soon as possible. This type of conductive paint can, therefore, be considered a suitable secondary anode for use in CP of inland concrete piers.

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