Research is being conducted in use of cathodic protection of highly stressed steel tendons, both prestressed and posttensioned, embedded in concrete bridge structures. these tendons are subject to embrittlement by hydrogen generated by cathodic protection under certain conditions. research indicates that hydrogen penetrates steel and causes ductility reduction at potentials equal to or more negative than those normally considered necessary for the thermodynamic stability of iron. other criteria commonly proposed for protection of steel reinforcement produce potentials considerably less negative than the potential required to generate hydrogen at the steel-concrete interface. because of the critical dependence of hydrogen evolution on potential, cathodic protection must be potential controlled and the detection circuit must be free of ir effects. the use of freely corroding iron as a reference is suggested. ongoing research includes studies on cathodic protection to answer questions about surface anodebehavior, current distribution within bridge members, and use of cathodic protection on posttensioned and segmented bridge construction. this paper appears in transportation research record no. 1304, highway maintenance operations and research 1991.
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