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CATHODIC PROTECTION Testing Old Cathodic Protection on Ohio Bridge Decks Tests were conducted on the surface of the curb concrete using a portable SCE. Tests were done at four spots located 4 in (101 mm) from the driving lane, and at four spots located 12 in (305 mm) from the driving lane. The results of these tests prove conclu- sively that the curb area adjacent to the protected southbound lanes was receiving protective current from the ICCP system, and that current was polarizing the steel within the curb area. Steel located 4 in from the driving lane was polarized an average of 64 mV, while steel located 12 in from the lane was polarized an average of 36 mV. Although this polarization was short of the 100 mV needed to meet NACE criteria for complete protection, Q\ _I[ KTMIZTa XZW^QLQVO [WUM JMVMÅ\ In order to further investigate the ef- fects of the ICCP system on the curb ar- eas, the ICCP system was shut off for a period of 13 days. This allowed the steel in the curbs to completely depolarize. A complete potential survey was then con- ducted on the curbs according to the procedures in ASTM C876-093 using an SCE. According to this procedure, loca- tions with potentials more negative than –276 mV (when using an SCE) have a >90% probability of corrosion activity at the time of measurement, whereas loca- tions with potentials less negative than –126 mV have a >90% probability of no corrosion activity. Potentials between these two values indicate an uncertain state of corrosion. Table 4 shows the re- sults of this survey. The potential survey results clearly indicate a higher state of corrosion in the unprotected curbs. Why would this be so, since the ICCP system was shut off at the time of measurement? This happens be- cause ICCP current causes chloride ions to migrate away from steel surfaces, and also causes hydroxide ions to accumulate on the surface. This results in a lower chloride/hydroxide ratio, and a lower 36 MATERIALS PERFORMANCE November 2012 state of corrosion, which persists long after ICCP current is interrupted. In order to further support this conten- tion, rate-of-corrosion measurements were taken on both curbs 13 days after the interruption of CP current. Rate-of- corrosion, also known as three-electrode linear polarization (3LP), is determined by applying a small current to the steel and measuring the resulting polarization. Corrosion rate can then be calculated by application of the Stern-Geary Equation.4 Results of the 3LP tests also show a lower state of corrosion in the protected curbs as a result of the application of ICCP current. From the results discussed above, the application of ICCP effectively mitigated damage due to corrosion at the Columbia Road Bridge. But the possibility still ex- isted that the corrosion damage observed on the unprotected curb could have been due to higher chloride contamination. To investigate this possibility, powder sam- ples were taken at two locations on the protected curb, and at two locations on the unprotected curb. Samples were taken 80 ft (25 m) and 190 ft (60 m) from the north end of the bridge, and from 0- to 1-in (0- to 76-mm) deep and from 1- to 2-in (127-mm) deep at each test location. Total acid-soluble chloride content was determined on each sample using the Germann Instruments† Rapid Chloride Test. Results of analysis show chloride con- tent to be very high in all samples. The average chloride content for samples from the unprotected side was 0.333%, or 12.8 lb/yd3 (7.6 kg/m3 (8.9 kg/m3 chloride content for samples taken from the protected side was 0.391%, or 15.0 lb/yd3 typically assumed to be ~0.04%, or ~1.1 lb/yd3 (0.7 kg/m3 ). In the absence of protective current, the chloride content at these test locations would cause exten- sive damage in only a few years. Differ- ences in chloride content therefore can- not be used to explain greater observed damage on the unprotected curb. Conclusions z The ICCP systems, installed on the Columbia Road, Jackson Street, and Westway Boulevard Bridges over 23, 20, and 16 years ago respectively, were still operating properly. z All potential decay tests conducted on the driving lanes showed the steel was being polarized >100 mV, in- dicating complete protection from corrosion. z Visual inspection revealed that the curb adjacent to the protected deck of the Columbia Road Bridge had very little damage due to corrosion, whereas the curb adjacent to the unprotected deck showed extensive damage, even though these areas were not directly protected. z Further tests on the curb areas showed that the curb adjacent to the protected deck was receiving protec- tive current. Potential survey, cor- rosion rate, and chloride analyses LI\I KWVÅZUML \PI\ \PM 1++8 [a[- tem had protected the curb from damage due to corrosion. ). The average ), slightly higher than the unprotected side. The minimum total chloride ion content that can lead to cor- rosion of embedded reinforcing steel is †Trade name. Acknowledgments The authors thank Richard J. Lesiecki, P.E., City Engineer, City of Painesville, Ohio Department of Engineering, for his assistance with the study. References 1 "Cathodic Protection of Reinforced Concrete Bridge Elements: A State-of- the-Art Report," National Research NACE International, Vol. 51, No. 11