Since the early 1980?s cathodic protection technology has been increasingly applied to reinforced concrete structures. Various anode materials in various configurations have been used. In this study an effort was made to document the long-term field performance of nineteen impressed current systems installed on fourteen bridge structures and one tunnel located in ten states of the United States of America and one Province of Canada over a period of five years. The cathodic protection systems evaluated in this study utilized zinc, titanium with mixed metal oxide coating, conductive coating, conductive polymer, and coke asphalt based anode materials. These systems were installed on bridge decks, super and substructure elements of bridge structures and a deck of a tunnel in various environmental conditions. At the end of the study the age of the systems varied from thirteen months to twelve years. As the ability of the cathodic protection system to stop corrosion is well established, the focus of this effort was to ascertain the effectiveness of each anode material and configuration to serve as a cathodic protection anode on reinforced concrete structures. This paper documents the findings of this study.
Cathodic protection (CP) is a technology used to mitigate corrosion of metals and has been used on ships and pipelines for many decades. The first use of this technology on a bridge deck dates back to 19731. Based on extensive government and private industry research, the Federal Highway Administration (FHWA) concluded that CP is the only rehabilitation technique that has proven to stop corrosion in salt-contaminated bridge decks regardless of the chloride content in the concrete2. This technology is based on the principle of applying an external source of current to counteract the internal corrosion current produced in reinforced concrete components. During cathodic protection, current flows from an auxiliary anode material through the electrolyte (concrete) to the surface of the reinforcing steel.
Various materials in various configurations are used as auxiliary anodes for cathodic protection resulting in various types of cathodic protection systems. The selection of the anode material and its configuration is paramount to the success of the system. The primary objective of this study was to determine the effectiveness of various materials and configurations when used as auxiliary anodes on highway structures through a long-term evaluation.
A total of fifteen highway structures (fourteen bridges and one tunnel) protected by one or more CP system(s) were included in this study. The structures were located in ten states of the United States of America and one Province of Canada. These structures were protected by a total of nineteen impressed current CP systems using the following anode materials and were monitored for a period of five years:
a) Arc Sprayed Zinc
b) Zinc Stripes
c) Titanium Mesh Coated With Precious Metal Oxide
d) Titanium Ribbon Coated With Precious Metal Oxide
e) Arch Sprayed Titanium followed by an Application of Precious Metal Oxide
f) Conductive Coating
g) Conductive Polymer Placed in slots
h) Conductive Polymer Placed in mounds
i) Conductive Coke Asphalt
Based on the age of the system, two to six evaluations were conducted. Most of the structures were selected by FHWA based on previous studies performed under the Strategic Highway Research Program (SHRP). Additional structures were added to the program as they became known to the research team. Structures that could not be properly evaluated were deleted from the study.
During each evaluation, visual and delamination surveys were