WHAT IS CORROSION?
Corrosion is a physical deterioration process associated with metals. The process involves the gradual destruction by electrochemical oxidation of metal in reaction with an oxidant such as oxygen.
Rusting is the formation of iron oxide which is an example of electrochemical corrosion.
Other materials also physically deteriorate, such as polymers or composites (GFRP), although the term “degradation” is more applicable.
As a consequence of corrosion and degradation, the useful properties of materials such as strength will be reduced, ultimately affecting the viability of structures.
THE CORROSION PROCESS / CYCLE
Typically, metal corrosion involves different types of rebar in a concrete structure connected electrochemically by an electrolytic solution of a chemical (salt) and water. The less passive bar is the anode while the more resistant bar is the cathode.
Under normal circumstances, the less passive metal (anode) oxidizes, or deteriorates, producing electrons which can be consumed by the more passive metal (the cathode). This process is known as a cathode reduction chemical reaction.
To avoid oxidation of the anode, the surface passivity of the cathode must be greatly increased or the electrolyte eliminated.
As such, the “kinetics” of the corrosion process, that is, the flow of electrons to a highly passivated cathode, will not occur therefore preventing the initiation of the corrosion cycle.