Bernard S. Covino

Corrosion prevention and remediation strategies for reinforced concrete coastal bridges

Abstract Oregons coastal highway includes over 120 bridges, most of which are reinforced concrete bridges. Twelve are historic structures. Over 40,000 m 2 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.

Field Test of High-Temperature Corrosion Sensors in a Waste-to-Energy Plant

Abstract Electrochemical probes originally designed for use in aqueous environments were shown to measure corrosion rates in a high-temperature gaseous environment where electrolyte consisted of conductive ashes and liquid slag. The field trial of the probes was conducted over a five-month period to monitor fireside corrosion in a waste-to-energy (WTE) plant. The three-electrode air-cooled corrosion sensors, each including a thermocouple to monitor sensor temperature, were installed in four different ports at approximately the same level of the WTE boiler. A total of 12 sensors were tested: six with electrodes using the carbon steel boiler tube material and six using the nickel-chromium alloy used for weld overlays for the electrodes. Corrosion rates and temperatures of the sensors were monitored continuously throughout the trial. Metallographic measurements of sensor thickness loss were used to calibrate the electrochemical corrosion rates. Air cooling of the sensors was found to be necessary to bring th...