Method and apparatus for cathodic protection of steel in a concrete structure located in an ionically conductive liquid

Abstract

Cathodic protection of steel in a concrete column in sea water is simplified by providing a pre-assembled unit including a jacket to surround the column carrying a bulk sacrificial anode outside the jacket and optionally an inner sacrificial anode with a cast grout inside the jacket. The jacket can also include a pre-assembled junction box and couplings to connect to the steel. The jacket is attached to the surface of the column at the water line so that the bulk anode is located below the surface of the water. The bulk anode can be formed of aluminum so as to be less toxic in sea water. An activator is applied inside the jacket either as a wicking layer or as a chemical activating material. The jacket can act only as a form work which is then removed after casting of the grout.

1 . A method of cathodic protection of a steel reinforcement in a concrete structure located in an ionically conductive medium so that a first part of the concrete structure is in contact with the medium below a surface of the medium and a second part of the concrete structure, continuous with the first part, is above the surface of the medium, the concrete structure having the steel reinforcement in both the first part and the second part, the method comprising:
 providing a covering layer arranged to cover at least part of at least one outer surface of the concrete structure so that an inside surface of the covering layer is located adjacent said at least one outer surface;   providing an inner anode of a sacrificial material for generating a galvanic current to the steel reinforcement, the inner anode being arranged so as to be positioned between the inside surface of the covering material and said at least one outer surface of the concrete structure;   providing a bulk anode of a sacrificial material for generating a galvanic current to the steel reinforcement in the concrete structure, the bulk anode being arranged so as to be positioned outside the covering layer and below the surface of the medium;   attaching the covering layer to the concrete structure;   and providing electrical connections between the inner anode and the steel reinforcement and between the bulk anode and the steel reinforcement such that an ionic current flows between the inner and bulk anodes and the steel reinforcement tending to inhibit corrosion thereof;   wherein the bulk anode comprises aluminum.   
     
     
         2 . The method according to  claim 1  wherein an activator is provided at or adjacent the inner anode to maintain the ionic current flow. 
     
     
         3 . The method according to  claim 2  wherein the activator is provided by a layer of a water transport medium different from concrete which carries the ionically conductive medium to a position at or adjacent the inner anode. 
     
     
         4 . The method according to  claim 3  wherein the layer of water transport medium is located such that a bottom part of the layer of water transport medium contacts the ionically conductive medium and the layer of water transport medium extends to a position above the level of the ionically conductive medium. 
     
     
         5 . The method according to  claim 4  wherein the covering layer, the inner anode construction and the layer of water transport medium comprise an assembled structure for common application to the concrete structure. 
     
     
         6 . The method according to  claim 2  wherein the activator is carried by the inner anode. 
     
     
         7 . The method according to  claim 2  wherein the activator comprises a chemical activation material carried with the covering layer. 
     
     
         8 . The method according to  claim 1  wherein the covering layer defines a form spaced from the surface for receiving grout material which is cast between the covering layer and the surface and wherein the activator provided in the grout. 
     
     
         9 . The method according to  claim 1  wherein the covering layer, prior to application to said at least part of at least one outer surface of the structure for covering thereof, carries both the inner anode and the bulk anode and attaching the covering layer to the concrete structure so as to attach both the inner anode and the bulk anode carried thereby to the concrete structure. 
     
     
         10 . The method according to  claim 1  wherein the covering layer comprises a plurality of separate panels and the method includes connecting the panels to form an assembly which engages at least two surfaces of the concrete structure. 
     
     
         11 . The method according to  claim 10  wherein at least one panel carries at least a part of the inner anode on an inner surface and at least one panel carries the bulk anode on an outer surface. 
     
     
         12 . The method according to  claim 1  wherein the concrete structure comprises a column and the covering layer when attached forms a jacket surrounding the column. 
     
     
         13 . The method according to  claim 1  wherein the covering layer comprises a plurality of separate components which when attached together form a jacket and wherein at least one of the components carries at least a part of the inner anode as a pre-assembled structure. 
     
     
         14 . The method according to  claim 1  wherein the covering layer comprises a plurality of separate components which when attached together form a jacket and wherein at least one of the components carries at least a part of the bulk anode as a pre-assembled structure. 
     
     
         15 . The method according to  claim 1  wherein the covering layer includes an electrical junction box including connection terminals for electrical connection to the inner anode and the bulk anode. 
     
     
         16 . The method according to  claim 1  wherein the inner anode comprises aluminum. 
     
     
         17 . The method according to  claim 1  wherein the inner anode comprises zinc. 
     
     
         18 . The method according to  claim 1  wherein the covering layer defines a form spaced from the surface for receiving a grout material which is cast between the covering layer and the surface. 
     
     
         19 . The method according to  claim 18  wherein the covering layer is removed leaving the inner anode and the bulk anode in place after the grout material is cast so that the grout material is exposed.