Protection of steel in concrete using galvanic and hybrid electrochemical treatments

In this study, data from galvanic and hybrid electrochemical treatments applied to structures is analysed. It is shown that the protection of steel in concrete using galvanic anodes finds theoretical support from a basis of improving the environment or maintaining a benign environment at the steel. Protection current output responds to the aggressive nature of the environment and, as a result, galvanic anodes have substantially longer lives than originally predicted. Monitoring is preferably focused on monitoring the effect of the protection on the condition of the structure and may be achieved by monitoring either steel corrosion rate and/or steel corrosion potential. Monitoring is preferably combined with a risk management option such as a facility to apply a temporary impressed current treatment to arrest active corrosion if a risk is identified. An allowance for new galvanic protection criteria has been made in the latest European standard on Cathodic Protection of Steel in Concrete

Monitoring the passivity of steel subject to galvanic protection

This work investigates the assessment of the passivity of steel in concrete subject to galvanic protection. Under atmospherically exposed conditions the kinetics of the cathodic reaction often exhibit activation controlled behaviour. It is shown that in these conditions the corrosion rates estimated from a large negative potential shift are very similar to those determined using the more widely accepted polarisation resistance method. The results are considered in the light of the potential decay cathodic protection criterion, and show how criteria based on potential shift may be improved to monitor steel passivity induced in a galvanic cathodic protection system. This provides the basis for an improved reinforced concrete acceptance criterion that is focussed on the condition of the structure and is included within the ISO standard cathodic protection when applied to galvanic systems

Long term assessment of a hybrid electrochemical treatment

Monitoring the performance of systems installed to protect against/halt the corrosion of reinforcing steel in concrete is essential in ensuring that the reinforcing bar (rebar) is adequately protected and remains in a non-corroding state. A chloride contaminated concrete test block containing a hybrid anode system has been periodically monitored over the past 4.5 years to assess the anode current output and thus, the protection offered to the steel. De-polarisation and impedance analysis data have been acquired to calculate steel corrosion rates. Both tests indicated that the steel was passive in the concrete environment and that the anode was able to protect all of the embedded steel despite the difficult geometry of the sample. It was also found that after 2 years it was still possible to drive a high current from the installed anod

Responsive behaviour of galvanic anodes in concrete and the basis for its utilisation

In this study, a unique concrete specimen was used to analyse the response of embedded sacrificial zinc and steel anodes to rainfall and fluctuations in temperature. Current from the zinc and steel anodes increased when the environment was aggressive, showing that the required protection current depends on the present level of corrosion risk. A basis for using the ‘responsive behaviour’ of galvanic anodes is provided by the protective effects of pit re-alkalisation and pH maintenance. By contrast, protection based on achieving adequate polarisation inhibits the use of responsive behaviour and galvanic anodes might only deliver adequate polarisation in aggressive environments