Existing corrosion protection methods (epoxy and zinc coatings, cathodic protection, stainless steel) for reinforced concrete structures are efficient, but in most cases are very expensive or have a short service life. This paper describes some new combined corrosion protection methods, which utilize cathodic protection together with other techniques, which decrease the corrosivity of the environment surrounding the reinforcing steel.
The equipment necessary to apply these methods can be incorporated into the structure during construction or retrofitted to existing structures (bridges, buildings, power stations, marine structures, docks, dams, storage tanks, etc.).
Coatings and cathodic protection systems (CPS) are routinely used in the science 1-12, and it is known that the electro-osmosis treatment method (ETM) will change the concentration of ions in the environment subjected to sufficient current to generate the electro-osmotic effect (EE). EE is the movement of ions in water along the surface of solid concrete particles in a concrete structure. This application is directed to a system which combines electro-osmotic removal of corrosive anions from concrete and the cathodic protection of metal members embedded in concrete (rebar), such as in footings of steel bridges, the bases of communications towers, and more particularly, to the protection of rebars in conventionally reinforced concrete structures. Such rebars are produced from mild steel. Removal of ions such as chlorides is well known12. An electric field is applied between the reinforcement and an electrolyte on the concrete surface with the reinforcement as the negative pole. The chloride ions migrate through the concrete and either reacts with the electrolyte or is oxidized at the anode to chlorine gas. Cathodic protection is typically effected either with sacrificial anodes, or impressed current with potential control or current control, the reinforcement being the reactive cathode and the anode being substantially inert (Figure 1a).
Typically, reinforced steel structures such as bridges, power stations, marine structures such as docks, and roadways, which are under construction, are the best candidates for cathodic protection with an impressed current. Existing structures, which are internally reinforced and pre-stressed concrete structures, which have been damaged due to chemical reaction with acidic elements, cannot be adequately protected without eliminating the source of the problem causing the damage. The problem of protecting aged reinforced concrete structures is very different from cathodic protection of embedded rebar and other metal members in a concrete structure.
A system is provided for controlling corrosion of reinforced concrete which is contaminated with atmospheric pollutants such as sulfur oxides, nitrogen oxides, hydrogen sulfide, and road treatment salts, sodium chloride and potassium chloride, all of which permeate the concrete structure and attack the steel rebar. Our method combines either electro-osmotic treatment with cathodic protection using a sacrificial or an impressed current anode (Figure 1b). The former removes ions detrimental to steel and reduces the corrosive environment surrounding the steel.
Since electro-osmosis depletes the concentration of ions in the concrete environment thus increasing the resistivity of the concrete, it would be logical to conclude that under such conditions the current required to maintain cathodic protection would increase; eventually the conductivity would be so low that the current density for cathodic current would be uneconomical and have to be discontinued. Therefore it was not evident that subjecting the reinforced concrete to