Long-term monitoring of galvanic anodes installed in reinforced concrete structures has provided the data required to better understand long-term anode performance. Detailed analysis of field and laboratory performance data has identified an aging pattern which follows an exponential decrease in current output similar to a ‘half-life’ principle where current is halved at constant periods of time. A predictive model has been developed to describe anode current output over time. The predictive model which includes an "aging-factor" can be determined for any galvanic anode. The aging-factor is primarily dependent on the activating chemistry of the anode. The aging-factor also depends on the relative surface area of the anode compared to the surface area of steel wherein the harder an anode works early on in its life the worse its aging-factor becomes.
The predictive model which is based on long-term field data allows galvanic anode systems to be designed to meet any desired performance criteria at any point in time. The model may also be used to design galvanic cathodic protection systems to provide specifiable long-term current density and more controlled polarization to the steel.
Galvanic anodes for mitigation of corrosion of steel in concrete have now been monitored to various degrees for up to 20 years. A large volume of data exists, which has enabled this detailed analysis. This in turn has allowed a much better understanding of long-term anode behavior and the development of predictive models.
A major finding of this analysis is that the long-term current of a particular anode diminishes in an approximately exponential manner that can be modelled by a "half-life" principle.1 This was shown by analysis of many sets of current output results which revealed repeated behavior of a slowly decreasing trend consistent with Equation 1.2
(equation) Eq. (1)
Where,
it = current density at time, t (mA/m2)
i0 = initial current density, (mA/m2)
