[01 ] This invention relates to improved methods of protecting steel in concrete using sacrificial (galvanic) anode assemblies, and, more specifically, to the use of compact discrete sacrificial anode assemblies installed within anode cavities in concrete exposed to the atmosphere.

Background

[02] The prior art is discussed within this section and problems with the prior art are disclosed. However such disclosure of these problems is not an admission that these problems are well known or appreciated within the prior art.

[03] Reinforced concrete structures sometimes suffer deterioration because the

reinforcing steel corrodes. This is often caused by chloride contamination or carbonation of the concrete.

[04] Sacrificial anodes are used to restrain the corrosion of steel in concrete.

Sacrificial anodes for reinforced concrete structures are split into surface applied anode assemblies and discrete anode assemblies. Surface applied anode assemblies differ from discrete anode assemblies in that they comprise thin sheets or a thin mesh of anode material (i.e. the sacrificial metal element) applied to the surface of a concrete structure. Surface applied sacrificial anodes include thermally sprayed zinc, adhesive lined zinc sheets and jacketed zinc mesh.

Adhesion to the concrete is the main problem affecting these surface applied systems.

[05] By contrast, discrete sacrificial anode assemblies are embedded in cavities in concrete. They will generally comprise a sacrificial metal element that is less noble than steel (electrochemically more negative than steel) such as zinc, an activator to maintain sacrificial metal activity, a backfill to accommodate the products of sacrificial metal dissolution and a metal conductor (connector) to connect the assembly to the steel or to a power supply.

[06] Compact discrete anode assemblies may be pre-assembled prior to installation.

Such assemblies may be installed in cavities in the concrete arising from steel corrosion damage. In cavities formed as the result of corrosion damage, a pre- assembled sacrificial anode and backfill assembly may be tied to the steel before substantially filling the cavity with a concrete repair material to restore the concrete properties and profile. ACI (American Concrete Institute) Repair Application Procedure 8, refers to this arrangement as a "Type 1 " arrangement. However, steel in a fresh concrete repair material is usually protected by the repair material, while protection current is mainly required by the steel in the adjacent physically sound but contaminated parent concrete. In addition the performance of the anode assembly is inversely proportional to the quality of the concrete repair material.

Alternatively, compact discrete anode assemblies may be installed within anode cavities. ACI Repair Application Procedure 8, refers to this arrangement as a "Type 2" arrangement. An anode cavity is formed to substantially accommodate one anode assembly. An anode cavity is a cavity that will be substantially filled with the assembly including its backfill. For example, a sacrificial metal element may be installed into, and embedded within, a backfill in a drilled hole within the concrete (WO/2007/039768). Anodes in anode cavities are targeted at protecting steel in undamaged concrete. The anode cavity may open into a larger cavity formed as the result of corrosion damage (WO/2010/043908).

Sacrificial anode assemblies are sometimes used with an external power supply to deliver an impressed current treatment (WO/2006/097770). This can be used to draw chloride ions present in the concrete to the sacrificial metal element to activate the anode assembly. In this case activation of the sacrificial metal element may be achieved only using the aggressive contaminants already present in the concrete that caused the corrosion problem in the first place.

Another form of activation employs the use of a catalytic activator. Examples of catalytic activators include halide ions and sulphate ions (WO/2006/0431 13). These ions render passive films on a sacrificial metal element unstable, but they are not substantially consumed in the process of oxidation of the sacrificial metal element. A problem with this form of activation is that these activators are also aggressive to the reinforcing steel.

In WO94/29496, hydroxide is used as an activator for a zinc sacrificial metal element. Hydroxide is a consumed activator that forms a complex with zinc ions. A large quantity of hydroxide is required to sustain a pH at a level that maintain zinc activity because the oxidation of zinc consumes hydroxide. ] One problem with the use of hydroxide as an activator is the risk of human exposure to the activator. Another problem is that hydroxide is neutralised by carbon dioxide in the air rendering it inefficient as an activator. This limits the shelf life of an assembled assembly. A third problem is that it is consumed in the dissolution of the sacrificial metal element. An advantage is that it does not present a corrosion risk to steel. ] To bring the hydroxide activator, into contact with the zinc, it is generally located in a backfill that is cast around the zinc to form a pre-assembled unit. This contains the hydroxide in a porous solid and in an electrolyte in the porous solid making it safer to handle. Repair Application Procedure 8 published by the American Concrete Institute at www.concrete.org/general/RAP-8.pdf provides examples of such pre-assembled assemblies. However a problem with this pre- assembled arrangement is that the activator begins to react with the zinc when the anode assembly is assembled during manufacture. This sometimes causes a gap to form at the surface of the zinc and zinc is consumed affecting product shelf life and function. ] A further problem arises when a pre-assembled assembly is installed within an anode cavity (for example, a drilled or cored hole or cut chase). A pre-assembled assembly requires another embedding material to connect the anode assembly to the concrete. Thus the overall volume occupied by the assembly within concrete is increased because a second embedding (encapsulating) material is required to embed such a preassembled anode assembly within the anode cavity. For example, a larger hole has to be drilled into the concrete to accept the anode assembly. ] To overcome the above problems a hydroxide activator may be included in the backfill material that is used to embed the sacrificial metal element at the time of installation in an anode cavity on a construction site. However, a problem with this arrangement is hydroxide salts, such as lithium, potassium or sodium hydroxide or combinations thereof, present significant health and safety risks in the form of caustic burns to the installer. Furthermore, when such assemblies are installed on the underside of structures the caustic material may fall out of the cavity and make contact with the installer.

[15] In WO2007/101325 the activator is intermixed within the sacrificial metal element.

A problem with this arrangement is an activator located within the sacrificial metal element causes internal corrosion of the sacrificial metal element. This corrosion reduces the efficiency of the assembly by consuming the sacrificial element without producing a beneficial effect, and by cutting the electronically conductive paths within the sacrificial metal element. This prevents the whole of the sacrificial metal element from being utilised. The activator also displaces sacrificial metal, reducing the charge capacity of the assembly.

Disclosure of Invention

[16] An objective of the present invention is to overcome or alleviate at least one of the problems of the prior art.

[17] In summary, a method of using an activator in a compact discrete sacrificial

anode assembly that is assembled within an anode cavity in concrete is described. The method includes providing a sacrificial anode, and an activator to activate the sacrificial anode, and a backfill to embed the sacrificial anode and the activator in an anode cavity in the concrete. The activator is provided as a discrete contained unit. The activator disperses through or reacts with the backfill to at least in part deliver activator to surfaces of the sacrificial anode. The activator unit is preferably at least in part separated from surfaces of the sacrificial anode. The activator is separated from the backfill that is used to embed the sacrificial anode and the activator in an anode cavity prior to use. A surprising benefit results from a transient increase in the temperature of the assembly as a result of a reaction in which soluble activator is formed within the backfill.

[18] One advantageous embodiment provides an improved method of using an

activator. In particular a hydroxide activator may be introduced into sacrificial anode assemblies for reinforced concrete construction in a manner that reduces the risk of activator contact with the installer of the anode assembly. [19] Another advantageous embodiment increases the soluble activator content in a backfill in situ (an installed backfill) via a reaction between the backfill and another component introduced into the system.

[20] Another advantageous embodiment limits the effect of carbonation of a hydroxide activator in sacrificial anode assemblies for reinforced concrete construction.

[21 ] Another advantageous embodiment of the present invention provides a method of varying the quantity of activator during the installation of a sacrificial anode assembly to match the condition of a structure and the protection it requires.

[22] Another advantageous embodiment of the present invention limits the quantity of consumed activator (e.g. hydroxide) while maintaining anode activity.

[23] Another advantageous embodiment of the present invention provides an

arrangement in which the activator displaces backfill in an assembly without changing the capacity of the sacrificial metal element in an assembly.

[24] Another advantageous embodiment of the present invention provides improved sacrificial cathodic protection to reinforced concrete structures by providing more than one of the above advantageous embodiments.

[25] In a first aspect, this invention provides a method of protecting steel in concrete, the method comprising the steps of:

providing

a sacrificial anode less noble than steel,

an activator to activate the sacrificial anode, and

a backfill to embed the sacrificial anode and the activator in an anode cavity in the concrete wherein

the sacrificial anode is a compact and discrete sacrificial anode for use in the anode cavity formed in the concrete; the activator is provided as a discrete contained unit which at least in part is separated from a surface of the sacrificial anode;

the activator is provided for dispersion through the backfill to the surface of the sacrificial anode;

the discrete contained activator unit is distinct from the sacrificial anode and the backfill; and the activator is separated from the backfill, forming the anode cavity in the concrete,

locating the activator in the anode cavity,

locating the sacrificial anode in the anode cavity,

locating the backfill in the anode cavity, wherein

the activator, sacrificial anode and backfill are brought into contact with each other in the anode cavity, and

passing a current from the sacrificial anode to the steel in the concrete to protect the steel in the concrete.

The advantages of this first aspect of the invention, in which the activator is provided as a discrete contained unit, include limiting corrosion of the sacrificial metal element prior to use, containment of the health and safety risk during installation and providing a facility to control the quantity of activator installed in a sacrificial anode assembly.

The sacrificial anode (or sacrificial metal element), activator and backfill are preferably provided as a kit prior to, and for, assembly and installation in an anode cavity. The activator is separated from the backfill in the kit prior to installation to avoid contact with any electrolyte that the backfill may contain. The activator is preferably located outside the exterior surface of the sacrificial metal element. The activator is preferably substantially separated from electrolyte in contact with the sacrificial metal element prior to the assembly of the sacrificial anode assembly in an anode cavity in concrete. The activator may be separated from the sacrificial metal element or alternatively may be connected to the sacrificial metal element.

The sacrificial anode is an electrode comprising a metal less noble than steel (electrochemically more active with a more negative potential than steel) with an exterior surface. The sacrificial metal element is preferably zinc or a zinc alloy.

Other sacrificial metals include aluminium, magnesium and alloys thereof.

Besides an exterior surface, it may also have interior surfaces such as the interior surfaces of a porous anode formed from a foamed metal or pressed powder. However the sacrificial metal element is preferably a non-porous unit. The sacrificial metal element is a discrete metal element sized for use in an anode cavity formed within the concrete. One example of an anode cavity is a cored or drilled hole up to 50 mm in diameter but preferably less than or equal to 40 mm in diameter and even more preferably less than or equal to 30 mm in diameter. Another example of an anode cavity is a chase cut into the concrete surface of up to 30 mm in width and up to 50 mm in depth.

The anode cavity is a cavity sized to accept the components of the assembly installed within the anode cavity. These components substantially fill the anode cavity. These components at least include the sacrificial metal element and the backfill and the activator. A space may be left at the opening to the cavity which can be plugged with a concrete repair mortar which hardens to separate the assembly from the external environment in which the concrete is located.

Alternatively the cavity may be covered by a concrete repair mortar or a sprayed concrete overlay or a membrane. As noted above, examples of the anode cavity include a cored hole, a drilled hole and a cut chase within the concrete.

The backfill is a material that is used to embed the sacrificial anode in a cavity in concrete. In use, the backfill contains an electrolyte connected to the sacrificial metal element. This electrolyte connects the sacrificial metal element to the surrounding concrete. Typically the backfill will also accommodate the products of sacrificial metal dissolution. The backfill is preferably provided as a pliable and viscous material containing an electrolyte and preferably remains pliable and viscous when stored. A pliable and viscous backfill preferably has a shelf life of at least 7 days and preferably more than one month. An example would be lime putty or lime mortar. Lime putty contains a substantial quantity of precipitated hydroxide which may be released by addition of a suitable salt to the lime putty.

The backfill may alternatively be a preformed material encapsulating the sacrificial metal element of the assembly and supplied in this form prior to installation. Such a backfill will typically contain an electrolyte. Another possible backfill would be a powder that is mixed with water to produce a paste when required, an example of which would be a weak, cement mortar powder with an air entraining agent that can be mixed with water to produce an air entrained cement mortar paste. Such backfills typically harden within 1 day and are mixed with water as part of the anode assembly installation process. The activator is preferably an activator that is benign (not corrosive) to the steel such as a hydroxide consumed activator. A consumed activator forms a soluble complex with the sacrificial metal of the sacrificial metal element. Such activators include complexing agents. The activator preferably substantially comprises hydroxide. Examples include lithium, sodium and potassium hydroxide or combinations thereof. These materials are hazardous to humans but promote steel passivity. The inclusion of lithium hydroxide is preferred when there is an alkali - silica reaction risk in the concrete.

The activator may be located in the anode cavity before or after the backfill is located in the anode cavity, but is preferably located in the anode cavity after the backfill is located in the anode cavity. The activator is preferably installed into the backfill after the backfill has been installed within the anode cavity.

In one preferred example, the activator at least doubles the soluble hydroxide content of the backfill and more preferably increases the soluble hydroxide content of the backfill by a factor of ten when it is added to the backfill. For example the activator may double the concentration of hydroxide in the

electrolyte in the backfill or more preferably increase it by an order of magnitude.

It is preferable that the activator lowers the potential of the sacrificial metal element (shifts it to more negative values) by at least 100 mV as this will increase the current output from the sacrificial metal element. A solid activator may also dissolve in an endothermic reaction to produce heat when it is brought into contact with an electrolyte such as the electrolyte in a backfill. The heat may raise the temperature of the backfill by at least 5 C and more preferably by at least 10 C which further increases the current output of a sacrificial metal element. These features are surprising benefits discovered by dissolving solid lithium, sodium and potassium hydroxide activators in the electrolyte provided by a pliable and viscous lime putty backfill surrounding a sacrificial anode in testing undertaken in this work.

The activator is provided as a distinct contained unit for dispersion through a backfill to reach surfaces of the sacrificial anode not in contact with the activator. The activator is distinct from (i.e. not intermixed with) either the backfill or the sacrificial metal element. When it is provided as part of a kit that includes the sacrificial metal element for use as a sacrificial anode assembly, the activator unit at least in part separates the activator from a surface of the sacrificial metal element prior to the assembly and installation of the sacrificial anode assembly within the anode cavity. After installation, the activator at least in part disperses through the backfill to reach a surface of the sacrificial metal element.

The activator may be provided in a container which separates it from the backfill and sacrificial metal element. The activator unit will have dimensions and to facilitate handling of the unit its largest dimension is preferably at least 10 mm and more preferably at least 20 mm long. This largest dimension of the activator unit is also preferably less than 150 mm and more preferably less than 100 mm and even more preferably less than 80 mm in length to facilitate its use in an anode cavity.

The location of potentially harmful components is isolated as a consequence of the containment of the activator in the kit. The activator is preferably provided in combination with a benign (safe) backfill in the kit. When the kit is installed and assembled in a concrete structure, the activator disperses through the backfill (for example, by dissolving in and diffusing through an electrolyte within the backfill or by reacting with the backfill) after the backfill has been located within the concrete of the protected structure. As the activator disperses through the backfill, it makes contact with surfaces of the sacrificial metal element that were previously not in contact with the activator. The backfill is preferably secured within a cavity in the concrete prior to dispersing the activator through the backfill. This is particularly helpful when installing the assembly in a cavity that

unrestrained components may fall out of, such as in an anode cavity on the underside (soffit) of a concrete beam or slab.

In one preferred example, the activator is provided in the form of a pellet, such as a block or capsule in a kit. One or more activator pellets may be provided for use with each anode assembly. Examples of a pellet of activator include a block of crystalline activator, divided activator and binder formed into a block, and finely divided activator pressed into the shape of a block. The pellet may be coated with a degradable coating that, for example, disintegrates in the presence of water.

The pellet may be a loose powder contained in a capsule by such a coating. In this example, the activator pellet forms a contained block that at least includes the activator and is separate from the anode backfill. It is preferable that such a pellet is dry and substantially free from electrolyte.

[43] In use, such an activator pellet will be inserted into an anode cavity formed within the concrete of the protected structure. The activator pellet will preferably have a largest dimension that falls within the range of 10 mm to 120 mm in length. The activator pellet may be held in the cavity by, for example, locating a pliable and viscous backfill such as an ionically conductive putty in the cavity and then pressing the activator into the backfill in the cavity. The pellet of activator may also be attached to the sacrificial metal element by an appropriate clip, tie or band and the sacrificial metal element may then be inserted into and held within the anode cavity. In this arrangement, the pellet of activator is preferably substantially free from ionically conductive electrolyte. The activator and sacrificial metal element may then be surrounded with a pliable and viscous backfill. When the activator comes into contact with moisture within the backfill, the activator dissolves and disperses through the backfill to reach all surfaces of the sacrificial metal element in contact with the backfill.

[44] In another example, the activator is injected into the backfill after the backfill has been installed. In this arrangement, the activator may be contained in a cartridge for use with a cartridge gun to inject activator from the cartridge into the backfill. A cartridge gun may be supplied with the cartridge or the cartridge may be an integral part of a gun such as the case with guns that are used to dispense grease when servicing road vehicles (a grease gun). Another example of a cartridge is an integral part of a pump containing activator that may be used to inject the activator into the backfill. The activator may also be contained within a syringe and transferred into a syringed just prior to installation. In this case the activator is contained in a container and is prepared for injection into an installed backfill by at least transferring it to a cartridge prior to injection.

[45] An activator that is to be injected into the backfill may be supplied in the form of a fluid such as a paste, gel or liquid for injection. A wet paste, gel or liquid, as opposed to a dry fine powder, allows the activator to be more easily contained during installation and limits the risk of an installer inhaling the activator. On the other hand, an activator injected as a free flowing dry powder into a wet pliable and viscous backfill will dissolve and may heat the backfill. The activator may also be provided in the form of small pellets contained within a cartridge or syringe in the kit to improve containment and generate heat when installed. The activator may be injected as one or more pellets into a pliable and viscous backfill in an anode cavity when installing the anode assembly in a concrete structure.

In another example, a fluid activator is injected into the backfill of an installed anode assembly to enhance the activity of the sacrificial metal element. A fluid activator may be injected into a hardened backfill provided it is sufficiently porous. It can also be injected into a pliable and viscous backfill.

The backfill is preferably placed in the anode cavity and the sacrificial metal element and the activator is preferably inserted or pressed into the backfill in the anode cavity.

The sacrificial metal element may include a second activator and may be assembled with the second activator prior to embedment in the anode cavity.

The second activator is preferably a catalytic activator, an example being sodium chloride (e.g. common table salt). The second activating agent may, for example, be applied as a coating to the sacrificial metal element to limit the quantity of catalytic activator in the assembly. An activating coating will comprise a binder and the activating agent.

Coatings may only contain a limited quantity of activating agent and are therefore not particularly suitable for use with consumed activators. It is therefore

preferable to provide a consumed activator in a contained unit and a catalytic activator as a coating. After the consumed activator has been consumed, the catalytic activator will continue to maintain anode activity in conditions that might result in steel corrosion. In this way, the quantity of a consumed activator such as hydroxide in an assembly that presents a significant health and safety risk may be restricted.

The circuit required to pass current from the sacrificial metal element to the steel in the concrete is well known. Typically a conductor (a connector) is attached to the sacrificial anode assembly. The conductor may be a steel, stainless steel or titanium wire, or an insulated copper core cable, and is preferably assembled with the sacrificial anode as a single unit. In one example, the sacrificial metal element is cast around a portion of the conductor. The conductor may be connected directly to the steel to deliver a galvanic current, or through an electric lead to the steel. It may also be connected through an external power supply to the steel to deliver an impressed current which in turn may precede a subsequent galvanic current. Alternatively a cell or battery may be included within the sacrificial anode assembly and the conductor may be attached to the negative terminal of the cell with the positive terminal of the cell being connected to the sacrificial metal element of the assembly.

In another aspect this invention provides a kit for assembly as a sacrificial anode assembly in concrete to protect steel in reinforced concrete, the steel reinforced concrete protector kit comprising

a sacrificial anode less noble than steel, and

an activator to activate the sacrificial anode, and

a backfill to embed the sacrificial anode and activator in an anode cavity in the concrete and connect the concrete and the sacrificial anode and the activator together, wherein

the sacrificial anode is a compact and discrete sacrificial anode for use in the anode cavity in concrete; and

the activator is a consumed activator provided as a discrete contained unit substantially separated from a surface of sacrificial anode; and

the activator is provided for dispersion through the backfill to the surface of the sacrificial anode; and

the activator is separated from said backfill in the kit.

The backfill to embed the sacrificial anode and activator in an anode cavity in the concrete and connect the sacrificial anode to the concrete may, for example, be provided as a powder that can be mixed with water to form a paste when installing the assembly. It may also be provided as a pre-formed pliable and viscous material containing an electrolyte.

In another aspect, this invention provides a method of protecting steel in concrete using a sacrificial metal element, and a backfill, and an activator separated from the backfill, the method comprising the steps of:

forming an anode cavity in the concrete for the purposes of installing a sacrificial anode assembly therein; locating the backfill in the anode cavity;

locating the activator in the anode cavity;

locating the sacrificial metal element in the anode cavity and

passing a current from the sacrificial metal element to the steel in the concrete to protect the steel in the concrete,

wherein

the backfill is a pliable and viscous backfill that provides an electrolyte to connect the sacrificial metal element to the concrete, and

the sacrificial metal element comprises a metal less noble than steel, and the activator is provided in a discrete contained unit selected from at least one of

a block,

a cartridge,

a syringe.

In another aspect, this invention provides a method of protecting reinforcing steel comprising the steps of:

providing a steel reinforced concrete structure containing a sacrificial anode less noble than steel and a backfill wherein the sacrificial metal element and the backfill are assembled within an anode cavity in the structure, and

injecting the activator into the backfill in the anode cavity, and

passing a current from the sacrificial metal element to the steel in the concrete to protect the steel in the concrete.

In the above arrangements the activator is contained within its own unit which is distinct from the sacrificial anode and the backfill and which is separated from the backfill. For example the activator is contained within a pellet or cartridge ready for use or within a carton or tub prior to placement in a syringe or cartridge. The activator only disperses through the backfill after the backfill has been located in the cavity in the concrete. The advantage of this is that it allows the risk associated with the use of an activator that is harmful to humans at the levels required for anode activation, to be contained. At the same time, a single more benign backfill may be used to connect the sacrificial metal element to the concrete. The activator may be readily separated from the air to prevent carbonation when stored on the shelf. The quantity of activator may be varied at the time of installation to take account of the conditions in which the assembly is to operate. The size of the assembly may be kept to a minimum by avoiding the need for an encapsulating material to encapsulate a pre-formed backfill in a cavity. The shelf life of the activator may be improved by separating it from the air. The utilization and efficiency of the sacrificial metal element is maximized through the use of either an activator that is outside the external surface of the sacrificial metal element and that is either substantially electrolyte free (dry) or separated from the sacrificial metal element prior to installation. By combining a hydroxide activator with a catalytic activator, the quantity of hydroxide activator within the assembly may be limited.

Brief Description of Drawings

[57] This invention is now illustrated further with reference by way of example to the drawings in which:

[58] Figure 1 shows an assembly comprising a sacrificial anode, activator pellet and backfill in a cavity.

[59] Figure 2 shows an assembly comprising a sacrificial anode and backfill in a

cavity and the injection of an activator into the backfill.

[60] Figure 3 shows the use of activated sacrificial anode assemblies to protect steel in concrete.

[61 ] Figure 4 shows an injection device containing activator pellets for injecting the activator pellets into a pliable and viscous backfill.

[62] Figure 5 shows an anode assembly comprising a sacrificial metal element and activator pellets fastened onto the sacrificial metal element using clips.

[63] Figure 6 shows an anode assembly comprising a sacrificial metal element and activator pellets tied onto the sacrificial metal element.

[64] It will be appreciated that the combinations of features shown in individual figures and described with reference to specific examples below are purely exemplary. As those skilled in the art will readily understand, specific features of any of the examples described and shown may be used in combination with a feature, or a subset of features of any other specific examples to the extent that it is technically feasible.

Examples

[65] One arrangement of a sacrificial anode assembly in use is shown in Figure 1 . A sacrificial metal element 1 , backfill 2, and pellets 3 containing an activator, are located in a cavity 4 in concrete. The sacrificial metal element 1 (sacrificial anode), is typically a metal less noble than steel. It acts as an anode in that it supports an oxidation reaction. The principle oxidation reaction is the dissolution of the sacrificial metal element. If the element was used in an impressed current mode, another impressed current oxidation reaction that may occur, results in the generation of oxygen. The assembly includes a connector 5 to connect the sacrificial metal element to a power supply or to a protected metal section.

[66] The backfill 2, connects the sacrificial metal element 1 , to the wall of the cavity 4.

The backfill needs to be at least in part pliable and viscous at the time the assembly is assembled within the cavity to achieve such a connection with the cavity wall.

[67] The backfill 2 also needs to contain an electrolyte at the time of installation and provides an electrolytic connection between the sacrificial metal element and the cavity wall. The backfill may be provided with electrolyte or mixed with water at the time of installation to provide an electrolyte within the backfill.

[68] The pellets 3 in Figure 1 contain the activator as a distinct contained unit. The activator is provided as an item in a kit which is distinct and separate from the backfill in the kit. The activator pellet may be one or more of a crystalline solid activator, divided solid activator particles that stick together to form a unit or an encapsulated unit contained by an encapsulation material that disintegrates in use to release the activator. The pellet has a largest dimension that is preferably between 10 mm and 120 mm. The pellets 3 in Figure 1 have the shape of a bar with a round cross-section. Other possible bar cross-sections of a bar shaped pellet or block of activator include rectangular and triangular cross-sections. The activator is preferably a hydroxide activator.

[69] In one preferred method of assembling the assembly within the cavity, a pliable an viscous backfill is first located in the cavity and the sacrificial metal element and activator pellets are pressed into the backfill. The activator then dissolves within the electrolyte in the backfill and disperses through the backfill to the surface of the sacrificial metal element. The activator is preferably a hydroxide activator with a dissolution reaction that is endothermic in that it releases heat. The dissolution of the activator then warms the assembly and this increases the initial current output delivered by the assembly. It also increases the rate of activator dissolution and the dispersion of the activator through the backfill. The use of hydroxide as an activator increases the pH of the backfill and makes the potential of the sacrificial metal element more negative, thereby increasing the potential difference between the sacrificial metal element and the steel and therefore the current delivered by the assembly.

[70] Another method of introducing the activator into the assembly is shown in Figure 2. In this example the sacrificial metal element 1 and backfill 2 are located in the cavity 4. The activator 7 is initially contained in a cartridge 8 of a syringe. The activator 7 is injected into the backfill through a nozzle 9 by depressing the plunger 10 of the syringe. The activator 7 is preferably a hydroxide activator and may be supplied as a solution. An activator provided as a solution may be injected into a hardened backfill 2, provided the backfill is sufficiently porous. In the alternative it may be injected into a pliable and viscous backfill.

[71 ] Figure 3 shows an arrangement of installed sacrificial anode assemblies

protecting a reinforcing steel bar in concrete. In this arrangement, sacrificial metal elements 1 , backfills 2 and activator pellets 3 are installed in anode cavities 4. The cavities may be formed by coring or drilling a hole into the underside (soffit) 15 of a concrete 16 structure. It is preferable to secure the backfill 2 in the anode cavity 4 as a pliable and viscous backfill. After it has been located in the cavity, the activator pellets 3 may be inserted into the backfill. The backfill then holds the activator pellets in place. The sacrificial metal element 1 may be inserted into the anode cavity at the same time as the activator pellets. Connectors 5 that are connected to the sacrificial metal element are attached to a second conductor 17 via a connection 18 that may, for example, be a clamp. The conductor 17 may in part be located in a slot cut into the concrete surface. The cavities 4 may be filled at their open ends by a cement mortar or concrete repair material. This material may also be used to fill any slots containing conductor 17. Sacrificial (galvanic) protection may then be delivered by connecting the conductor 17 to the steel 19. It is preferable to start the delivery of galvanic protection current to the steel as soon as the anodes have been activated. In the case of the use of one or more hydroxide activator pellets, the installation sequence could start with fitting the sacrificial metal elements in predrilled cavities in a dry condition with no electrolyte present and connecting them to the steel. The sacrificial metal elements could then be removed and refitted, one at a time after installing the backfill containing an electrolyte into the anode cavity. Hydroxide activator pellets could then also be installed into the backfill. As the pellet begins to dissolve in the electrolyte in the backfill it releases heat. The pH also increases and the potential of the sacrificial metal element shifts to more negative values. This increases the initial galvanic current output of the sacrificial metal element. To fully utilize the benefit of the increased temperature at the anode assembly, which will be a transient effect, the anode must be delivering current close to the time the activator dissolves in the backfill.

Figure 4 shows an example of a syringe for dispensing activator pellets into a pliable and viscous backfill. Activator pellets 21 are located in a cartridge 22 of a syringe. A plunger 23 is used to inject the pellets into a backfill. This arrangement may be used with small activator pellets that are hard to handle. It may also be used with powders.

One or more activator pellets may be attached to a sacrificial (galvanic) anode and inserted with the sacrificial anode into the backfill during installation. Figures 5 and 6 show two arrangements in which activator pellets 31 are attached to a sacrificial metal element 32. In Figure 5, the activator pellets 31 are attached by means of clips 33. These clips 33 hold the pellets in place while the sacrificial metal element and pellets are located in the cavity. The clips may be formed from a plastic or metal. The clips only need to hold the pellets in place until they are secured in place by a backfill in a cavity. Thus in one preferred example the clips are formed using a sacrificial metal to supplement the charge capacity of the anode.

In Figure 6 a band 34 is used to attach the pellets 31 to the sacrificial (galvanic) anode 32. The band may be made of any suitable material, it may be elastic or a cable tie and it may or may not be attached to the sacrificial metal element. [76] Other methods of attaching an activator, provided as a discrete contained unit for dispersion through the backfill to surfaces of a sacrificial anode, to the sacrificial anode include gluing the unit to the sacrificial anode and providing a recess in the sacrificial anode and locating the unit in the recess. In this last example, a unit that is dry is used to limit the risk of electrolyte making contact with both the unit and the sacrificial metal element.