A NOVEL TYPE OF DISCRETE GALVANIC ZINC ANODES FOR THE PREVENTION OF INCIPIENT ANODES INDUCED BY PATCH REPAIR

摘要

Corrosion of steel reinforcement as a result of repair of concrete damages induced by reinforcing steel corrosion is a common and well documented result of "patch repairs". The corrosion is caused by the transformation of cathodic areas near the corroding steel reinforcement into "incipient anodes". Cathodic protection (CP) is one safe method to prevent the formation of incipient anodes. Very often, repairs have to be executed on locally limited areas where CP is not economical. Incipient anodes may be prevented by embedding discrete galvanic anodes into the patch repair close to the interface repair/old concrete, shifting the steel potentials of the passive steel towards sufficiently negative potentials to eliminate or at least minimize macro-cells. Considering the fact that the electrochemical potential of zinc is more negative than even the corrosion potentials of pits on reinforcement, discrete zinc anodes offer a thermodynamically sound possibility to prevent incipient anodes. Reports based on field tests of discrete galvanic anodes (e.g. A. A. Sagues 2009) yielded mixed results on the durability and reliability of the prevention of corrosion of steel reinforcement adjacent to patch repairs, proving that the thermodynamics is no guarantee that systems work in reality. The main issues regarding durability and reliability of galvanic zinc anodes are passivation of the zinc anode and the formation of anodically formed zinc hydroxide forming an ion-transport barrier. A novel type of discrete galvanic zinc anode will be presented that addresses and solves these issues. The novel discrete galvanic zinc anode system is composed of a novel type of composite zinc mesh embedded into a proprietary matrix that solidifies into an electrolyte with ion exchange properties. The combination of the novel composite zinc anode and the solid matrix containing additives that prevent passivation of the zinc anode assures high and durable galvanic activity of the discrete galvanic zinc anode.