Abstract
Recent studies have suggested that residual protection is afforded to structures following the application of impressed current cathodic protection (ICCP), in some cases for significant periods of time, while others for periods of only a few days. This study reported the findings of the de-activation of a 20 year old ICCP system installed on a 50 year old structure. The ICCP was de-activated for 84 days and the steel potentials at locations on the front pile cap and front wall were monitored via the installed reference electrodes. An adjacent water anode system was also de-activated for 48 hours during the initial de-activation period to observe the impact on the steel potentials. The results showed that out of 42 reference electrodes, 17 achieved a 100 mv decay within 24 hours and 10 had more positive instant off potentials than -150 mV. Furthermore, all displayed a positive shift in potential following deactivation of the ICCP system for a period of time, indicative of residual protection, with 22 displaying this positive shift for the whole 94 days of the trial.
Highlights
Reinforced concrete is one of the most widely employed construction materials, being utilized for structures including bridges, dams, high rise blocks, power plants, docks etc
Questions remain concerning the effects, causes and duration of residual protection from impressed current cathodic protection (ICCP) systems. This is of particular importance with many systems reaching the end of their design lifetimes. To further investigate these effects, this paper reports a study on a reinforced concrete wharf constructed in 1969 in southern Australia with an ICCP system that was installed in 1999
A potential decay over a maximum of 72 hours of at least 100 mV from the instantaneous off potential subject to a continuing decay and the use of reference electrodes for the measurement extended beyond 24 hours
Summary
Reinforced concrete is one of the most widely employed construction materials, being utilized for structures including bridges, dams, high rise blocks, power plants, docks etc. The reinforcing steel is normally passive in concrete due to the high pH environment provided by the Portlandite, sodium and potassium hydroxides and C-SH gel formed by the hydration of the cement [1]. This leads to the formation of iron oxides and hydroxides on the steel surface which prevent the oxidation of the reinforcing steel, and in doing so create a passive oxide layer on the steel which prevents corrosion [2]. Chloride induced corrosion of reinforced concrete structures is one of the major causes of deterioration worldwide, with repair and maintenance costs of billions of dollars required to maintain the operation of these critical parts of the infrastructure
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