CATHODIC PROTECTION FIGURE 1
Testing Old Cathodic Protection on Ohio Bridge Decks
This survey revealed minor patches of debonding on the wearing surface of the deck, suspected as a result of the original pour, as any noted spalling was due to cavitation rather than rebar corrosion. The ICCP system on the Jackson Street Bridge was tested in June 2011 and July 2011, more than 20 years after instal- lation. Table 1 shows the ICCP currents and voltages as recorded on June 21, June 30, and July 27, 2011. The currents shown in Table 1, equal to 1.30 to 1.45 mA/ft2 m2
(14.1 to 15.4 mA/ ) for the active zone, are considered Jackson Street Bridge. TABLE 1
Power supply data for Jackson Street Bridge Zone 2
Current (A)
06/21/11 7.85 06/30/11 8.35 07/27/11 8.55
Voltage (V)
5.43 5.89 5.77
Reference 1 (mV)
–0.259 –0.151 –0.200
–1.076 –1.176 –1.108
Reference 2 (mV)
Reference 3 (mV)
–1.150 –1.150 –0.949
FIGURE 2
typical. The voltages for this active zone are also considered typical. The poten- tials recorded by embedded Reference Electrode 1, however, are clearly in error. Silver/silver chloride (Ag/AgCl) refer- ence electrodes are usually embedded in the concrete to monitor the performance of the system. But it is not uncommon for such electrodes to fail from years of expo- sure to environmental conditions. The potentials recorded by Reference Elec- trode 1 are unusually positive, and are considered to be suspect. Reference Electrodes 2 and 3 are also suspect after review of the potential decay data. Reference Electrode 2 is Ag/AgCl and Reference Electrode 3 is an Elgard† reference cell.
Potential Decay Test, Jackson Street
The performance of an ICCP system
is determined by measuring the polariza- tion of the steel, which is the change of potential of the steel caused by the ap- plication of protective current. Interrupt- ing the current and measuring the decay of potential over a 4-h period is usually done to determine this polarization. Polarizations at the Jackson Street
Bridge were determined using the refer- ence electrodes embedded in Zone 2, and
Potential decay at Jackson Street Bridge. 32 MATERIALS PERFORMANCE November 2012
†Trade name. NACE International, Vol. 51, No. 11