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.

Claims

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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] One embodiment of the invention will now be described in conjunction with the accompanying drawings in which:

[0054] FIG. 1 is a front elevational view of a column including the application to the column of a first embodiment method of corrosion protection according to the present invention.

[0055] FIG. 2 is an enlarged view of the of the junction box of the embodiment of FIG. 1.

[0056] FIG. 3 is a rear elevational view of the jacket section of the embodiment of FIG. 1.

[0057] FIG. 4 is an isometric view of the jacket section of the embodiment of FIG. 1.

[0058] FIG. 5 is a top plan view of the jacket section of the embodiment of FIG. 1.

[0059] FIG. 6 is a transverse cross-sectional view through a column including the application to the column of a second embodiment of corrosion protection according to the present invention.

[0060] FIG. 7 is a longitudinal cross-sectional view through a column including the application to the column of a third embodiment of corrosion protection according to the present invention.

[0061] FIG. 8 is a longitudinal cross-sectional view through a column including the application to the column of a further embodiment of corrosion protection according to the present invention including an activator for maintaining the activity of the inner anode.

[0062] FIG. 9 is a longitudinal cross-sectional view through a column including the application to the column of a yet further embodiment of corrosion protection according to the present invention including an activator within the grout and where the bulk anode 431 is mounted on the column independently of the covering jacket material.

[0063] FIG. 10 is a longitudinal cross-sectional view through a column including the application to the column of a further embodiment of corrosion protection according to the present invention where the covering material acts as an initial formwork for the grout and is then removed during operation and where the bulk anode is mounted on the column independently of the covering jacket material.

DETAILED DESCRIPTION

[0064] In FIG. 1 is shown a conventional reinforced concrete column mounted in water 9 so that the column 10 has a bottom end generally indicated at 11 mounted on a suitable support in the water with the upper end 12 arranged to carry a structure to be supported by the column. Typical columns of this type are formed of a concrete body 13 within which are steel reinforcing members generally indicated at 14. These include vertical longitudinal members 15 and transverse or peripheral hoops or ties 16. The steel reinforcement is located inside the column just under the outside surface 17 of the column.

[0065] The column is illustrated as being mounted so that a part of the length of the column is located in the inter-tidal zone generally indicated at 20 with a low tide mark indicated at 21 and a high tide mark indicated at 22. Above the high tide mark is a splash zone. It will of course be appreciated that the tides vary and the amount of splash height varies but in general the area between the low tide mark 21 and the top of the splash zone provides an area of the column which is subject to repeated wetting and drying depending upon the height of the water surrounding the column at any time.

[0066] This zone and the area extending upwards from this zone of the concrete column is particularly subject to corrosion since the steel is exposed to moisture, chlorides and oxygen which act to break down the steel and form corrosion products. These corrosion products may cause expansion sufficient to crack the concrete. In addition to this cracking, the corrosion of the steel may also result in loss of structural capacity.

[0067] The technique of the present invention is primarily intended as a repair technique for the column but it can also be used in new constructions.

[0068] The construction of the present method comprises a surrounding impermeable layer or jacket 30 which is attached to the column at a position outward of the outer surface 17 of the column. The jacket 30 may be formed of an impermeable material such as resin, plastics, fiber reinforced plastics or stainless steel. The jacket may be reinforced to provide structural strength to assist resisting movement of the concrete or the jacket may be fabric, or a stretchable or flexible material without such structural reinforcement so that it simply moves with any movement of the concrete. Where reinforced, it may be reinforced by fibres such as glass, plastics, carbon fibers or other materials well known to a person skilled in the art. In the embodiment as shown in FIGS. 1 to 5, the impermeable layer or jacket 30 is formed in pieces 30A and 30B which are connected at a joint 30C. In one embodiment the joint is a butting flange joint where two projecting flanges of the two parts of the jacket butt and are clamped together by bolts or screws with a layer of a sealing material between the two butting flanges. This ensures that the jacket is fully sealed around the column at the connections between the parts of the jacket to form a sealed sleeve around the column from a top edge 31 of the jacket to a bottom edge 32 of the jacket. Other methods of sealing the joints are also possible such as tongue and groove joints, lap splice joints and self-locking mechanical connectors.

[0069] Inside the jacket is filled with a cementitious or polymer grout or other filler material 33 to form a band of the material around the column within the jacket. In most cases the jacket is used as a form for applying the grout to the column. Prior to application, repairs can be made to any cracked portions by excavation or removal of damaged concrete materials so that the finished jacket is filled with material surrounding the column and filling any indentations, cracks or excavated portions of the concrete column. The grout is commonly Portland cement based which cures and bonds to the outside surface of the column and acts as an effective filler material. Other types of filler materials including other organic and inorganic based materials may be used.

[0070] During filling of the jacket, the bottom edge 32 of the jacket may be closed by a forming structure or platform 35 to hold the grout material in place until it is set. After the setting of the grout, the bottom form may be removed so that the bottom surface 34 of the grout is exposed. However it may also be left in place. At the top 31 of the jacket, after filling, an upper surface 305 of the grout is generally exposed.

[0071] The anode for the cathodic protection system comprises a sheet anode 42 surrounding the column under the jacket 30. The anode 42 is connected to the reinforcing steel by an electrical conductor or wire 45 which is connected to the steel reinforcement within the column as explained hereinafter. If necessary, additional connections can be provided to other parts of the reinforcing steel depending upon the electrical continuity of the steel reinforcement bars. The conductor wire 45 is brazed or soldered to the zinc mesh at locations 451 to provide an effective connection even after some corrosion has occurred. The conductor wire may be cast into the anode material directly The wire 45 is connected to a junction box 452. The junction box can also receive connecting wires from other anode sections, for example when the jacket is formed from separate components as explained hereinafter.

[0072] Thus the cathodic protection system includes the bulk anode 43 and optionally the inner anode 42 provided by the sacrificial anode material, the reinforcing steel 14, the electrical connection 45 from the anode to the steel and an ionic connection from the anode through ionically conductive material which may include the grout and the concrete to the steel to provide cathodic protection of the steel while effecting sacrificial corrosion of the anode.

[0073] The sacrificial anode may be provided as a sheet or layer extending fully around the column adjacent the outer surface of the concrete so that ionic current passes through the grout layer to the concrete. The sacrificial anode is preferably and typically formed as a zinc mesh of expanded metal or other perforated sheet. Alternatively, the sacrificial anode may be provided in the form of a solid sheet or as rods, strips or discrete pieces. A suitable known enhancement material may be provided at the anode as part of its structure or in a next adjacent layer such as the grout.

[0074] The sacrificial anode forms the sheet inside the jacket so that this also includes at least a part located above the water line or surface of the water indicated at 91 and part below the water line 91.

[0075] In order to provide an efficient manner of assembly of the construction for operation of the method above, the bulk anode and the jacket 30, together with the inner anode optionally, form an assembled structure for common application to the concrete structure. That is the two layers can be supplied together as a wrapping to engage around the column or otherwise to be applied to the surface of the concrete. This common assembly or pre-assembled structure can also include the junction box 452.

[0076] More preferably the covering layer 30, and the sacrificial anode or anodes all form an assembled structure for common application as an assembled structure on to the concrete structure with the covering layer covering the sacrificial anode. Thus the outer jacket 30 has the sacrificial anode formed as a layer inside the outer jacket. In this way this structure can be simply applied onto the column as a tight wrapping or as a form for grout to be poured into the jacket.

[0077] The impermeable sleeve 30 around the steel within the jacket prevents escape of moisture from the jacket during the time that the concrete is exposed to the air and thus is otherwise free to dry. The sleeve also prevents diffusion of oxygen to the steel.

[0078] As an alternative, the jacket can be formed as a single part which is wrapped around the column and a single overlap seal can be provided.

[0079] The jacket can be wrapped around the column and applied directly to the outside surface of the concrete. In this arrangement, therefore, there is provided no additional grout apart from possibly grout provided to fill cracks or holes within the concrete of the column. The intention is therefore that a simple sleeve is wrapped around the column in the inter-tidal and splash zone. If there is no necessity for repair, the jacket 30 is applied directly onto the column without any grout at all. In this arrangement the jacket can be provided by a fibreglass lay-up process formed on site simply by applying or wrapping fiber glass sheet material and a resin onto the outside surface of the column.

[0080] Other suitable plastic, rubber, organic or inorganic materials can be used as the sheet.

[0081] The bulk anode 43 of a sacrificial material such as zinc, or an alloy predominantly of zinc, generates a galvanic current to the steel reinforcement in the concrete structure, where the bulk anode 43 is positioned outside the covering layer or jacket 30 at or adjacent the bottom edge 32 so as to be located and below the surface 91 of the water 9.

[0082] The jacket may also carry at least a part of the inner anode 42 on the inner surface of the jacket and at least one panel of the jacket carries the bulk anode 43 on the outer surface.

[0083] Where the jacket is formed as separate panels connected together as shown in FIGS. 1 to 4, at least one panel carries both at least a part of the inner anode 42 on the inner surface, if provided as part of the assembly as shown, and the bulk anode on the outer surface. In the embodiment shown, both panels carry both the inner anode and a bulk anode so that the combined quantity of anode material of each of the inner anode and the bulk anode from both panels can be used to provide the required life of protection.

[0084] The bulk anode 43 mounted on the exterior of the jacket comprises a portion of metal which may have two end flanges 431 shown in FIG. 5 which are fastened by bolts 432 through the jacket and into a connection plate 433 on the interior so as to effectively support the heavy bulk anode on the exterior without tearing or distortion of the jacket.

[0085] The pre-assembled structure further comprises an electrical connection wire or conductor 434 from the bulk anode 43 for connection eventually to the steel reinforcement in the concrete structure. The wire 434 is connected to the plate 433 on the inside of the jacket and extends to the junction box 452.

[0086] The pre-assembled structure thus further comprises the electrical junction box 452 which has connection terminals 453 for connection to the electrical connection or connections 45 from the inner anode 42 and terminals 454 for connection to the electrical connection from the bulk anode.

[0087] The electrical junction box 452 is carried on the pre-assembled structure inside the covering layer and is accessible from outside the covering layer by removal of a covering plate 456. This allows the terminals to be disconnected if required and also provides access to the terminals for measuring current and/or voltage by suitable probes.

[0088] The arrangement herein can thus be used in a method of cathodic protection of a steel reinforcement in a concrete structure located in an ionically conductive medium where 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 includes providing the covering layer or jacket 30 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.

[0089] The method optionally further includes providing the inner anode 42 of a sacrificial material for generating a galvanic current to the steel reinforcement with the inner anode positioned between the inside surface of the covering material 30 and the outer surface 13 of the concrete structure 11.

[0090] The jacket, prior to its application to the structure carries the bulk anode and optionally the inner anode as a pre-assembled structure and is then attached to the concrete structure so as to attach both the bulk anode and optionally the inner anode carried thereby to the concrete structure. The electrical connections between the inner anode and the steel reinforcement and between the bulk anode and the steel reinforcement are also provided simply and automatically by their connection to the junction box. In this way a single connection from the junction box to the steel can be provided. Alternatively if the steel is not sufficiently integrally connected, additional coupling wires can be taken from the junction box to selected locations on the steel.

[0091] In FIG. 6 is shown very schematically an arrangement where the jacket is formed from a plurality of separate panels 311 and 312 and the method includes connecting the panels by suitable side connecting arrangements 313 to form an assembly which engages at least two surfaces of the concrete structure and typically wraps around the concrete in the form of the jacket.

[0092] The separate panels include a plurality of flat panels 312 and a plurality of corner panels 311 for connecting together to form the square or rectangular jacket. Separate flat panels can be provided, coupled together and flexed to surround a circular column.

[0093] At least one of the components or panels 312 carries at least a part of the bulk anode 43 and optionally at least one panel carries at least part of the inner anode 42 as a pre-assembled structure. The panels are then fastened together so that the competed jacket carries the bulk anode and optionally both the inner and bulk anodes.

[0094] As previously described, the covering layer or jacket may include a bottom closure member 35 at the bottom end 32 for preventing escape of the grout when poured into the forming mould defined by the jacket.

[0095] The lower part of the jacket carries and supports the bulk anode 43 at or adjacent the lower end 32, when the covering layer is attached, at a height below the surface of the water. In this way, the bulk anode 43 is supported relative to the concrete surface solely by the connection of the bulk anode to the covering layer without any necessity for the bulk anode to be separately attached to the column below the water.

[0096] Additionally a reinforcing member 435 shown in FIG. 5 may be attached directly or indirectly to the bulk anode or its connection plate to provide additional reinforcing and support to the bulk anode into the grout when the grout is poured and sets. The reinforcement thus extends from the inside surface of the covering layer toward the surface of the concrete to be buried when the grout is poured.

[0097] The inner anode can be pre-attached. However as an alternative, particularly for strip and rod anodes and for modular jackets, the inner anodes can be supplied separately. They can be thus installed on the face of the column and wiring is connected without the jacket being in the way whereupon the jacket is applied later onto the inner anode and the column.

[0098] The bulk anode 43 is preferably formed from Aluminum, or an alloy predominantly of aluminum, as discussed above but can also be of zinc, or an alloy predominantly of zinc, when the potential toxicity is not relevant.

[0099] Turning now to the arrangement shown in FIG. 8, an activator is provided at or adjacent the inner anode to maintain the ionic current flow. In this embodiment the activator is provided by a layer 50 of a water transport medium different from concrete which carries the ionically conductive medium, that is the sea water, to a position at or adjacent the inner anode.

[0100] That is, in addition to the concrete, the grout and the anode within the jacket 30 is provided a layer 50 of a water transport medium. This is located adjacent to the sacrificial anode layer and preferably extends from a position below the water line 91 so as to be in contact with the water to a position above the water line. As shown therefore the layer 50 extends from a bottom portion 502 exposed beyond the bottom of the jacket to a top portion 502 exposed above the top of the jacket. This layer acts to provide additional wetting with the water from below the water line of the structure at least at parts of the concrete above the water line so as to provide additional water in the grout, at the sacrificial anode and inside the jacket to enhance the creation of the ionic current.

[0101] The water transport medium also acts to provide an improved, low resistance, ionic path between the sacrificial anode and the steel. In situations where the water transport medium is exposed to salt water, the improvement in ionic conduction is further improved. The resistance through the concrete between the sacrificial anode and the steel is reduced and the current is increased. As a result, steel which is close to the anode is better protected and sufficient current to protect the steel is able to travel a greater distance such that the protected area is increased.

[0102] Further details of the water transport or wicking layer can be found in U.S. Pat. No. 9,447,506 issued Sep. 20, 2016 to inventor Whitmore, the disclosure of which is incorporated herein by reference.

[0103] Thus the layer 50 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 may extend to a position above the level of the ionically conductive medium. The covering layer, the inner anode construction and the layer of water transport medium can preferably comprise a pre-assembled structure for common application to the concrete structure. However alternatively the elements of the structure can be applied individually. The location of the wicking layer 50 is preferably at the anode either on one or both sides and may be located at the jacket so as to be carried thereby.

[0104] The water transport layer or wicking material may also provide the benefit that it may act as a separator between the anode and the concrete or grout. This benefit is not limited to above the water line.

[0105] Turning now to the arrangement shown in FIG. 9, in this arrangement the activator or enhancement material comprises a chemical activation material 60 carried in the grout or filler material 33 inside the covering layer or jacket 30. That is, the jacket 30 defines a form spaced from the surface of the column for receiving the grout material 33 which is cast between the jacket and the surface and the activator 60 is provided in the grout.

[0106] As described in U.S. Pat. No. 7,520,974 cited above, the anode and jacket therefore may carry enhancement material.

[0107] For example, the level of the pH and the presence of a humectant enhances the maintenance of the current so that the current can be maintained for an extended period of time in a range 5 to 20 years.

[0108] In addition to the above materials, there is also applied into the mortar material, or into the anode body itself a humectant or deliquescent material. Suitable materials include Ca(NO3)2, CaCl2), LiNO3, CaNO2, MgCl2, Na2SO4 and many others well known to one skilled in the art. Such humectants are basically in solid or powder form but can be dissolved to form an aqueous solution. Alkali material arranged to maintain the pH greater than 12 can also be used. Further details of such materials and the humectants are disclosed in other patents of the present inventor Whitmore or the assignees of that inventor including the present applicant.

[0109] The presence of the humectant material acts to absorb sufficient moisture to maintain conductivity around the anode to ensure that sufficient output current is maintained during the life of the anode and to keep the anode/filler interface electrochemically active. The presence also increases the amount of the current. Even though the mortar material 21 is not exposed to the atmosphere as it is buried within the jacket, and even though the humectant material is bound in fixed form into the mortar material, it has been found that absorption of moisture into the humectant material is sufficient to enhance the maintenance of the current output and to prevent premature reduction of output current over an extended period of operation and before the anode is consumed.

[0110] The bulk anode 43 generally does not provide or require such enhancement materials since it is located in the aggressive action provided by the sea water both in view of the high conduction through the sea water and the chlorides which are present. However such enhancement materials or activators can be provided if required.

[0111] For example, the activator can be carried by the inner anode.

[0112] For example, the activator comprises a chemical activation material which can be carried with the covering layer.

[0113] As previously described, the covering layer, prior to application, carries both the inner anode and the bulk anode and the covering layer is attached to the concrete structure so as to attach both the inner anode and the bulk anode carried thereby to the concrete structure. Also 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.

[0114] Turning now to FIG. 10 there is shown an alternative arrangement in which the covering layer or jacket 30 is removed after casting leaving the inner anode and the cast grout in place so that the grout material is exposed. In this case the bulk anode 43 is attached to the column separately and remains in place after the grout material is cast and the jacket removed. In this case the inner anode 42 is preferably spaced from the jacket when the grout is cast so that the anode is spaced from an outer surface of the case grout leaving the cast grout surface exposed and unencumbered. This arrangement may be preferred in some installations so that the exterior surface is visible to expose its condition rather than being hidden under the jacket.