Corrosion prevention and remediation strategies for reinforced concrete coastal bridges
Oregon's coastal highway includes over 120 bridges, most of which are reinforced concrete bridges. Twelve are historic structures. Over of bridge surface has been repaired and is protected from further corrosion damage using thermal-sprayed zinc anodes in impressed current and galvanic cathodic protection (CP) systems. In addition, thermal-sprayed titanium, thermal-sprayed Al–12Zn–0.2In, and zinc-hydrogel anodes are being evaluated in demonstration projects on coastal bridges. Thermal-sprayed zinc anodes are estimated to have a service life exceeding 25 yr but exhibit increasing anode polarization with electrochemical age. Humectants such as lithium nitrate and lithium bromide can reduce anode polarization and extend anode service life. Catalyzed thermal-sprayed titanium anodes develop no significant anode polarization and exhibit stable long-term performance. Zinc-hydrogel galvanic anodes produce a stable protection current with no evidence of aging effects. One of the more powerful and economical tools available for assessing potential corrosion problems in a structure and for characterizing the corrosivity of bridge microclimates is chloride profiling. Current Oregon DOT specifications call for the use of stainless steel reinforcing bar in deck, beams, and precast prestressed girders, and of microsilica concrete in all future coastal bridge construction. Stainless steel bar adds a 10% premium to total project cost compared to black iron bar but is expected to reduce cumulative costs by 50% over the 120+ yr bridge life.