Cathodic corrosion protection to enhance the long term performance of concrete bridges Najif Ismail Senior Lecturer, School of Architecture, Building and Engineering Otago Polytechnic, Private Bag 1910 Dunedin 9054, New Zealand. Fax: +64 3 479 6191 E-mail: najif.ismail@op.ac.nz Abstract The use of Cathodic protection (CP) in bridges took off in 1970’s and since then attracted reasonable attention from practicing engineers and academia for protecting structural steel reinforcement in bridges against corrosion. The problem is further magnified when the bridge is exposed to high chloride contamination and humidity. CP is deemed to be a cost effective protection technique in such corrosive environment, thus reducing bridge deterioration and helping to uphold the structural integrity of the bridge for a longer period of time. In this article, several corrosion protection techniques are highlighted and a state-of-the-art on electrochemical corrosion protection techniques is presented, followed by an overview of a case study on state highway bridge 44 (also known as Brighton Road Bridge) located in Otago, New Zealand. The case study investigates the key factors involved in the selection of a corrosion protection technique along with a discussion of several aspects of the design process, the installation process and the performance monitoring of the selected solution. The project involves design, installation, and monitoring of an impressed current CP system for the bridge 44, where the installation has been completed to date within 32 weeks from the kick off date and well within budget equaling to one third of the cost estimated to replace the bridge. 1. INTRODUCTION The solid we know as rust or iron oxide (Fe2O3) is actually a dehydrated iron hydroxide (Fe2(OH)3), which is formed as a result of a series of reactions between free iron ions (present nearly in all ferrous metals), water and oxygen. This reaction is able to occur in the presence of water (H 2 O) on the surface of ferrous metal and oxygen (O 2 ) present in the surrounding environment, where the water reacts with the inherent non-bonded carbon in most irons or steels to create a carbonic acid. The carbonic acid creates galvanic cells like batteries that allow a reduction and oxidation (RedOx) reaction to occur to both the oxygen and iron, while other contaminants such as salts and chlorides (e.g., NaCl) act as electrolytes and make the process faster and more damaging to the overall structure of the steel. Figure 1 show the chemical reactions involved in the rusting process, where the physical state of each compound is written within the braces. Several protection techniques have been used in the past to avoid corrosion of steel reinforcement in concrete structures by creating a protective coating around the surface of the steel reinforcement that breaks the path of electronic flow and thus avoids RedOx reaction to occur. These include biofilm coating, electroplating, galvanization, painting, and powder coating. Biofilm protection is a relatively new type of protection which uses a thin coat of around 0.2 - 10 μm thick of biofilm coating. Electroplating is the