A platform for research: civil engineering, architecture and urbanism
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Zinc galvanic anodes, activated by a lithium hydroxide saturated mortar, were shown to be successful in providing adequate cathodic current to the steel reinforcement around the periphery of a patch repair for a period of 10 years. This ensured that no incipient anodes were formed on the steel adjacent to the repaired area and the repair as a whole remained intact and free from corrosion of the steel reinforcement. Extrapolation of the results also showed that a service life of between 24 years and 37 years can be expected from these 60 g zinc anodes. Depolarisation levels of the steel reinforcement after disconnection of the anodes for periods of either 4 h or 24h showed a diminishing trend over the first 112 days, rarely exceeding 50 mV around the periphery of the repair, but then increased to over 100 mV after 9 years. The 100 mV depolarisation criterion, which applies to cathodic protection systems, is unlikely therefore to apply for cathodic prevention systems of this type. An alternative more realistic criterion should be developed. It is suggested that the change in the rest potential of the steel, following periods of depolarisation over a constant time (4 h or 24 h), be considered as a criterion for establishing the performance of a corrosion prevention system. This can be aided by estimation of the corrosion current density of the steel from knowledge of the depolarised potential and the equivalent applied current density. In this particular case, it was seen that the steel rest potential gradually moved in a positive direction while the corrosion current density diminished to a very low level signifying improved passivity of the steel. Although the current output followed an overall decreasing trend, the driving power of each anode did not show any evidence of diminishing. To the contrary, the current output at switch-on, following a period of depolarisation, was seen to increase with time, possibly because the potential of the steel gradually moved in the positive direction thus increasing the 'drive voltage' between the anode and the steel. Lessons learned from this and other trials and from further research have enabled the production of enhanced performance anodes using a better surface area to volume ratio and improved chemical composition of the encasing mortar. Anodes with double or quadruple the current output capability have been used for a new trial at the same site. Early results confirm their higher capacity. The technology was shown to be very flexible and by utilising a distributed current-type anode set-up consisting of long anodes affixed along the steel reinforcement, it was possible to provide depolarisation levels exceeding 100 mV, and to achieve current densities compatible to conventional impressed current cathodic protection systems.
Zinc galvanic anodes, activated by a lithium hydroxide saturated mortar, were shown to be successful in providing adequate cathodic current to the steel reinforcement around the periphery of a patch repair for a period of 10 years. This ensured that no incipient anodes were formed on the steel adjacent to the repaired area and the repair as a whole remained intact and free from corrosion of the steel reinforcement. Extrapolation of the results also showed that a service life of between 24 years and 37 years can be expected from these 60 g zinc anodes. Depolarisation levels of the steel reinforcement after disconnection of the anodes for periods of either 4 h or 24h showed a diminishing trend over the first 112 days, rarely exceeding 50 mV around the periphery of the repair, but then increased to over 100 mV after 9 years. The 100 mV depolarisation criterion, which applies to cathodic protection systems, is unlikely therefore to apply for cathodic prevention systems of this type. An alternative more realistic criterion should be developed. It is suggested that the change in the rest potential of the steel, following periods of depolarisation over a constant time (4 h or 24 h), be considered as a criterion for establishing the performance of a corrosion prevention system. This can be aided by estimation of the corrosion current density of the steel from knowledge of the depolarised potential and the equivalent applied current density. In this particular case, it was seen that the steel rest potential gradually moved in a positive direction while the corrosion current density diminished to a very low level signifying improved passivity of the steel. Although the current output followed an overall decreasing trend, the driving power of each anode did not show any evidence of diminishing. To the contrary, the current output at switch-on, following a period of depolarisation, was seen to increase with time, possibly because the potential of the steel gradually moved in the positive direction thus increasing the 'drive voltage' between the anode and the steel. Lessons learned from this and other trials and from further research have enabled the production of enhanced performance anodes using a better surface area to volume ratio and improved chemical composition of the encasing mortar. Anodes with double or quadruple the current output capability have been used for a new trial at the same site. Early results confirm their higher capacity. The technology was shown to be very flexible and by utilising a distributed current-type anode set-up consisting of long anodes affixed along the steel reinforcement, it was possible to provide depolarisation levels exceeding 100 mV, and to achieve current densities compatible to conventional impressed current cathodic protection systems.
Ten-year results of galvanic sacrificial anodes in steel reinforced concrete
Zehnjahresresultate für galvanische Opferanoden in Stahlbeton
Sergi, G. (author)
Materials and Corrosion ; 62 ; 98-104
2011
7 Seiten, 14 Bilder, 2 Tabellen, 8 Quellen
Article (Journal)
English
TEN YEAR RESULTS OF GALVANIC SACRIFICIAL ANODES IN STEEL REINFORCED CONCRETE
| British Library Conference Proceedings | 2010
Ten-year results of galvanic sacrificial anodes in steel reinforced concrete
| British Library Online Contents | 2011