CA2027711A1 - Inhibiting corrosion in reinforced concrete - Google Patents

Abstract

(57) Abstract There is disclosed apparatus of and a method for inhibiting corrosion of reinforcement in a reinforced structure wherein one or more anodes (3) are arranged adjacent a surface of the structure (1) to be protected and a body of ionically conductive ce-mentitious material (6) is arranged to suround the anodes and make contact with ionically conductive cementitious material of the structure (1), said body of ionically conductive cementitious material (6) being surrounded by a cover (4) of moisture resistant substantially non-porous material to maintain said material (6) in an ionically conducting condition. Said electrodes (3) and rein-for cement (2) within the body (1) can be electrically connected to cause a current to pass through said two sorts of ionically con-ductive cementitious material to protect the reinforcement (2) against electrolytic corrosion.

Description

WO 89/1043~ PCr/GB89/00404 ,:, r I ~ 7 ;~

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INE~IBITING CORROSION IN REINFORCED CONCRETE
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j ~his invention relates to a method ror inhi-biting corrosion of reinorcement in struc ures of masonry or cementitious material, especially (but not only) concrete, and includes apparatus ror àoing so, methods ~f installing such apparatus, assemblies for use in s~ch apparatus~ and methods of inhibiting corrosiGn using such apparatus.
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j Masonry or cementitious materials usually have compressive strength, but little tensile strength. It is therefore necessary when using concrete, for example, as a structural member to incorpora~e rein-forcing members (usually metal, Drererably steel) to impart the reauired tensile strength. The reinforcing members may be placed unàer tension to form ~pre-stressed" or "post-tensioned" concrete struc-tures.

If the reinforcement corrodes, it may expand and cause internal stresses within the concrete. This ultimately leads to cracking of the concrete which is then liable to start breaking up. The cracking also results in the reinforcement being further exposed to water and atmospheric oxygen, accelerating the corro-sion process.
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Rusting is a complex electrolytic process whereby ferrous metal is oxidised to the corresponding oxides and hydroxides of iron, generally by atmospheric oxygen in the presence of water. In fresh concrete the pH is typically in the range of 12-14, this high alkalinity bein~ a result of the formation of hydroxides of sodium, ~otassium and calcium, upon the hydration of ceme~t.
~1 i.,t~ Under such conditions steel is passive, this !~passivatiOn leading to long term stability and protec-~!; tion of the reinforcing member .rom corrosion.
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However, when such passivated reinrorcement is exposed to either a strong Lewis base e.g. chloride ions and/or a loss of pH to below 10, the passivation can be disrupted and the steel reinforcement subjected to corrosion. An example of the former is the intro-duction of chlorides into the concrete matrix by either road salt usage, exposure to the marine environment, or the use of salt-con~aminated aggregate or calcium chloride hardening accelerators in the ori-ginal mix.
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'These agents have caused widespread corrosion-related damaae in many structures including bridge piers, decXs, and crossheads, marine piers and harbour structures, and many pre-1970's pre-cast concrete ~lbuilding elements in which chloride-based accelerators 3were used to improve the economics of their manurac-l ture.

`lAnother cause of corrosion is carbonation or the ~concrete by penetrati~n of carbon dioxide from the WO X9/10435 PCI/S~ 8~/00~04 -:~
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atmosphere which reac~s With the p~re water in tne concrete to form car~onic acid which in turn neutrali-ses the soluble hydroxides and reacts with the calcium hydroxide present depositing calcium carbonate:
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(1) Ca(OH)2 + H2C03 ~ > CaC03 + 2H20 ~`

(2) CaC03 + CO2 + H20 ----> Ca(HCO3)2 `

Formation of the bicarbonate shown in the above reac-tion (2) enables additional CO2 made available by diffusion from the atmosphere to react with further calcium hydroxide in the cement.

Carbonated concrete exhibits a sufficiently low pH at which point steel passivation is not stable.

Carbonation takes place at a rate which depends upon a variety of factors such as the original cement content of the concrete, the water:cement ratio of the concrete, aggregate type and gradinq, density and com-paction, and the aspect and degree of protection afforded to the concrete surface. The net result of the carbonation process is however that ultimately the alkalinity which protects the metal from rusting is reduced and the rusting process will start. The reduction in alkalinity is further compounded by acid pollutants in the air such as oxides of sulphur and nitrogen.

In good quality concrete with correct placement of the reinforcement, problems of corrosion resulting from carbonation may not occur for fifty years or even longer. This period can be extended by the use of anti-carbonation coatings on the outer surface of the ,.. : . -3s PCI /G B89/00404 ~ ~ ~ r~, r~
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concrete which help to exclude carbon dioxide and other acidic atmospheric pollutants. There are however many structures where metal corrosion is ine-vitable and cannot easily be chec~ed. Surface ~;
coatings which restrict the entry of carbon dioxide are not as erfective if the carbonation depth prior to the application of .he coatinq has already reached or passed the rirst metal reinlorcements or if chloride ion is present in the concrete. `;
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It is well known to protect an elec~~ically con-ductive substrate from corrosion by ~stablishing a potential difference between the substrate and a spaced-apart electrode. The substrate and the electrode are connected to each other through a power suoply of constant sign tDC or rectified AC) and the circuit is comple~ed when electrolyte is present in the space between the substrate and the electrode. In most such impressed current systems, the substrate is the cathode (i.e. that electrode at which reduction reactions occur). However, with substrates which exhibit a stable passive state, e.g. Ni, Fe, Cr and Ti and their alloys, it is also sometimes possible to use impressed current systems in which the metal is the anode. In both cathodic and anodic systems, the substrate is often provided with a protective insu-lating coating; in this case the impressed current flows only through inherent porosity or accidentally exposed portions of the substrate, If the system is to have an adequate life, the electrode must not itself be corroded at a rate which necessitates its replacement; this is in contrast to the ~'sac.ificial anodes" which are used in galvanic protection systems.
The electrode mus,t also have a surface ~hich is not . ~ .. , . ~ .. . .. .

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i rendered ineffective Dy the C~lrrent passing through it or by the electochemical reactions taking place at its surface, such as the evolution of oxygen and possibly chlorine gas.
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Many conventional impressed current corrosion protection systems make use of a plurality of discrete '3 electrodes which are spaced apart at some distance ~i from the substrate. Typically, the anodes are rigid rods which are composed of ~a) graphite or (b) silicon iron or catalysed valve metals. Because of the distance between the electrodes and the substrate, large power supplies are often needed and interference I from other electrical systems (including other corro-i sion protection systems) is common. In addition, the high current density at the electrode can give rise to problems, e.g. in dispersing gases generated by electrochemical reactions at the surface of the eLectrode.

U.S~ Patent 4502929 describes advantageous ' electrodes whose electrically active outer surface is provided by an element which is composed of a conduc-tive polymer and which is at least S00 microns, pre-erably at least lQ00 microns, thick. The term "conductive polymer" is used herein to denote a com-position which comprises a polymer component and, dispersed in the polymer component, a particulate con-ductive filler which has good resistance to corrosion, for example catalytic titanium sponge particles as described in U.S. Patent 4454169, or especially carbon black or graphite.
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These advantageous electrodes may be incor-porated in a mas~ or reinforced concrete to impress a ~ - ~
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corrosion-resisting current on the reinforcement, or may be applied to a surface of the mass and covered by -a further layer of concrete as described in Published European Patent Application 0147977.
~ :-The present invention provides a corrosion pro-tection system which can be more conveniently applied to existing reinforced structures, avoiding the need to cover the surface with a further layer of concrete.
Such overlays are often unacceptable in view of weight 3 and space considerations in an existing building structure.

The invention accordingly provides apparatus for ` inhibiting corrosion of reinforcement in a reinforced I structure of masonry or cementitious material, comprising ta) one or more electrodes overlying a surface of the structure, (b) ionically conductive cementitious grouting material connecting the electrode(s) to the said surface, and (c) a ~ -~ moisture-resistant substantially non-porous cover overlying the electrode(s) and the grouting material, an edge portion of which cover extends partly around the electrode(s) and the grouting material towards the said surface -~
of the reinforced structure. .
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It will be understood that the term "grouting material" is applied herein ~o the ionically conduc-tive cementitious grouting material for covenient reference, and is hot intended to imply any limitation : ,. , . .,- .

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or that material .o ccmr~ositions known to De used for '~grouting~ in other circumstances or contexts. The term however specifically excludes flexible polymeric I gels, whose function ~hereinafter described) is unlike that of grouting. The ionic conductivity will pre-ferably result from the presence of water and mobile ¦ ions in the grouting material, rather than from any inherent conductivity of the solid masonry or cemen-titious components themselves. However, conductive fillers, for example carbon or graphite, which are -known as additives .o concrete and conventional grouting materials, can also be used and may enhance the performance of the anode in some cases.

The following description will refer, for simplicity, simply to concrete, but the invention is applicable generally to structures o masonry material, (e.g. natural or artificial stone, non- ;
cementitious "mortars" or "concretes" which set by reaction with atmosDheric carbon dioxide, or brickwork), as well as to cementitious material, é.g.
concrete, "microconcrete" (having no large aggregate~, mortars or renders.

Another aspect of the invention conveniently provides a pre-formed article fol application ~o the surface of a reinforceà structure to inhibit corrosion of the reinforcement therein, the article comprising ., . :
(a) one or more electrodes capable of serving as active anode(s) in operation, (b) ionically conductive grouting material in con-tact with the electrode(s) which grouting material is capable of permitting the t` ' '`',` ' : ~ -' ~ :' ' .
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WO89/10435 PCTtGB8g/00404 ,$~t1 .i~ .
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I electrochemical reactions necessary to inhibi~
corrosion, ' ( C) 2 moisture-resistant cover ext~nding partly around the electrode(s) and grouting material, ~-an edge portion of which cover will extend toward the surrace to which the article is to be applied in use, and optionally, (d) electrical connector(s) for connecting the -electrode(s) to a power supply and~or to each other in use, and/or optionally (e) means for mechanically attaching the cover to the reinforced structure.
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The connector(s) is or are preferably pre-installed as part of the article, but could be installed after or immediately before mounting of the remainder of the article on the surface of the struc-ture to be protected. Further grouting material may be applied between the article and the surface which it is mounted at the time of mounting, and this further grouting material may be the same as or dif-ferent from that pre-formed in the article itself.
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The form of the electrodets) is not critical, but it is preferable to use elongate electrodes of the advantageous kind described in the aforementioned U.S.
Patent 4502929, the disclosure of which is incor-porated herein by reference, preferably comprising a single conductor wire substantially concentrically surrounded by the conductive polymer composition.
Other forms of these electrode~s comprising one, two or more wires embedded in the conductive polymer com-position may also be used. Metal mesh or wire electrodes may also be useful in some circumstances.

WO~9/10435 PCT/~BB9/OOqO4 i iJ 7 1~ ~

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Electrodes may comprise titanlum or platinum wire, ~raphite rods, catalytic ceramic tiles, carbon fibre yarns, or val~Je metal wire coated oxide or an electrocatalytic coating for example a spinal ceramic or other conductive containing a noble metal catalyst, as described for example in published International Patent Applic:ations ~08500838 and WO8600158, US Patents 4517068 and 4402996, British Patent 1329855 or Canadian Patent 923069, the disclosures of all of which are incorporated herein by reference.

The moisture-resistant cover could be formed in situ, e.g. by coating the grouting material with O.l to 10 millimetres thic.~ness o~ suitable film-forming composition ~e.g. glass-reinforced polyepoxy or polyester curable composition) after fixing the electrode(s) and enveloping grouting material in place. In this connection, a pre-formed assembly of the electrode(s) and solid grouting material could conveniently be used. however, for physica1 robustness and convenience of installation it is preferred to use a pre-formed cover of suitably moisture-resistant material, for example extxuded or moulded plastics materials such as unplasticised polyvinyl chloride, polystyrene, polyethylene, polypropylene, polyamide (e.g. Nylon 6, Nylon 6,6, Nylon l1, Nylon 12), polyepoxy resin, or fibre-reinforced versions of these.
Glass or other) fibre-reinforced concrete may also be formed by extr~sion or moulding to act as the cover, one such material being Cell-line G.R.C. (Trade Mark) as supplied by Cellite Selfix Co.Ltd. A suitable finish will be applied to render such a cover substantially non-pcrous and water resistant.

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It will usually be preferable that at least part of the periphery of the cover is in contact with the said surface, thereby at least partly enclosing the electrode(s) and the grouting material. In most ;
cases, it is advantageous that the cover substantially completely encloses the electrode~s) and the grouting ~ material against the said surface.
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~ Although flat electrodes on the surface or a `;~ flat layer of the grouting material could be used, it is prererred that the grouting material at least partly surrounds the electrode(s). Preferably, the grouting material completely surrounds at least part of the electrode(s), in which case it is prefèrred that the surface of the electrode(s) furthest rom the said surface of the reinforced structure is covered by the grouting material to a depth of not more than 25 millimetres, preferably not more than lS mm, more pre-ferably not more than lO mm, and especially to a depth of L to S millimetres. Preferably the grouting mate~ial ~ubstantially îills the soace surrounding the electrode~s) between the cover and the said surface of ~` the reinforced structure.

Preferably, the dimensions of the electrodes,~;~
the body of grouting material and the cover will be selected to enhance the maintenance of electrical con-tact between the electrode and the reinforcement.
x This ~ay, for example, involve keeping a necessary minimum moisture content in the grouting material around the electrodes and in ~he underlying reinforced structure. To this end, it may be desirable that the width or the individual electrode(s) lying substan- -~
tially parallel to the said surface of the reinforced ~5 :
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structur~ is not greater than the thickness o~ the grouting material between said surface and the surface of the electrode(s) closest thereto. However, electrodes may for example be 0.1 to 10 mm in width and the grout 1 to 25 mm in thickness. The ratio of the electrode width to the thickness of the grouting material should thus preferably be within the range from 1:0.1 to 1:250, more preferably from 1:1 to 1:100. The grout thickness referred to here does not include any further grouting material which may be ~`
applied during installation as aforesaid.

It may also be desirable that the cover extends beyond the electrode(s) to a distance at least 0.5 times and up to 100 times the electrode width.
Prererably, the cover will extend beyond the two outermost electrodes (when two or more are enclosed) to a distance within the range rrom 0.1 to 100 times the minimum distance between adjacent electrodes, pre-rerably 0.5 to 50, and more pre~erably 1 to 10 times that inter-electrode distance.

The grouting material is ionically conductive and preferably contains water. It preferably includes at least one hygroscopic (or deliquescent) material to assist in maintaining a desirable moisture content and ;
hence a desirable level of electrical conductivity.
Such materials include for example calcium chloride, or premixed commercially available materials such as- ;
the grout Thora CP (Trade Mark) supplied by the Thora Company. The ionic electrica~ conductivity as deter-mined by the four pin probe method (described in a paper presented by R.P.Brown at "Corrosion 83"
Symposium, Anaheim, Calrornia, U.S.A. during 18-22 ~ WO89/l0435 PCT/GB89/00404 . .
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:3 April 1983 incorporated herein by reference) is pre-ferably within the range from 10-5 to 0.02 S cm~l, more preferably 4 x 10-5 to 0.02 Scm~l, and especially 6.6 x 10-5 to 0~02 scm-l. Examples o. potentially suitable grouting materials include a mixture of .~portland cement and fine aggregate mixed with water to produce a pouring consistency without segregation of the constituents.

The type of cement is chosen f~om those shown in Table 1, to suit the particular working environment of the anode assembly.
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Portland Cement Types and Basic Composition Portland Cement ~ype Compound 1 2 3 4 5 C3S 53.7 58 62.3 53.6 42~0 C2S 19.9 16.212.5 17.2 28.8 C3A 11.4 7.12.8 14.0 14.0 C4AF 8.8 11.914.9 8.8 8.8 For example type 5 cement would be selected in .~
those instances in which the anode assembly would be : ~:
asked to work in a high sulphate containing environ- :
ment.

Further to the above, inclusion or pozzolanic materials in the cement can be considered, for example the use of type IP cement which contains pozzolan to 7 7 ~ ~
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between 1~ and 40~ by weici~t of the total cemen~.
Pozzolan is derined as a siiiceous or siliceous-and-r aluminous material which in i.self possesses little or no cementitious value, but which in finely divided form will react with calcium hydroxide in the presence .~ of moisture.

Use of this type of grout material will have the added value that a degree of acid resistance is imparted to the grout, this being useful around the anode due to the electrochemically generated acidic by-products of normal ooeration.

other examples of grouting materials include ~ polymer-modified cement mortars, ror example the com-'`¦ mercially available materials such as: Sika Grout, Icement 503, ES08 and 508 as supplied by Si.~a InterCol; Excem as supplied by Celtite Selfix Ltd; and ~3 calcium sulphate based plasters, e.g. plaster of paris. Preferred are those which are ini.ially flowable, for convenient introduction into the appara-tus, and then tend to solidify.
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The moisture-resistant cover is pre-erably substantially moisture-imDerviOuS, for example fibre-reinforced concrete or Dolymeric material having a moisture vapour transmission rate of less than 104, preferably less than 103, more preferably less than 102, and especially less than 10, g mil per m2 per 24 hours. The electrode(s) may, for covenience, be mechanically attached to the cover, which may for example be in the form of an elongate channel overlying at least one elonaate electrode.
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i~ In an espec1ally useful form of the apparatus ~;~ according to this invention, (a) the cover channel ; overlies two or more electrodes each comprising a single wire substantially concentrically covered with one or more electrically conductive polymer com-positions, each electrode having a finished diameter of 2 to 15 millimetres, ~b) the electrodes are spaced apart by a distance of 0.3 to 5 c~ (depending on the diameter of the electrodes), (c) the electrodes are ,3 surrounded by the grouting material with a thickness of 0.1 to 1 cm of grouting material between the said surface of the reinrorced structure and the pàrt of the electrode surface closest thereto and a thickness of 0.1 to 2.5 c~ of grouting material between the part of the electrode surface furthest from the said sur-face of the reinforced structure and the cover, and (d) the cover e.Ytends laterally beyond the electrodes by O.S to 10 cm, prererably by 1 to 5 cm. `

The invention has particular advantages when the ;
cover is attached to the said surface of the rein-s forced structure independently of any attachment by way of the grouting material. Such independent attachment gives rise to an advantaqeous method of installation (which is another aspect of this invention), wherein the prerormed cover is attached to the said surface of the reinforced structure so as to enclose the electrode(s) between the cover and the said surface, and the grouting material is therearter introduced into the space enclosed between the cover and the said surface. In this case, the grouting material will preferably be flowable, at least ini-tially, and will ~referably become less flowable or non-flowable after, introduction into the cover.

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~ WO89/1043~ PCT/GB89/004n4 .~ ~ 2 ~ 7 ~1 ,,, It may be desirabl~, especially where there are surface irregularities ~e.g. caused by poor shuttering leaving surface indentations and ridges in the har-, dened concrete surface) which may interfere with the electrical continuity of the system, to use an addi-tional layer of ionically conductive material ~ assisting the establishment and maintenance of 3 electrical contact between the electrode(s) and the ~ said surface of the reinforced structure. The addi-`i tional layer may be present at the interface between the grouting material and the reinforced structure, and/or at the interface between the grouting material and the electrode~s), and will preferably comprise a conformable ionically conductive composition, for example a soft cementitious mortar or a flexible ioni-cally conductive gel.

~ The localised or patterned application of the ! electrode~s), grouting material and cover to a rein-orced structure provides benefits in terms of weight saving and efficient installation com~ared with metbods requiring application of concrete or other overlayers over the whcle surface of the structure to be protected. This aspect of the invention accor-dingly provides apparatus for inhibiting corrosion of reinforcement in a reinforced structure of masonry or cementitious material, comprising .
(a) a pattern of one or more electrodes overlying a surface of the structure, (b) a layer of ionically conductive grouting material arranged in a pattern corresponding with the pa,ttern of the electrode(s) and, con-necting th~ electrodes to the said surface, ~ -~ WO89/1V435 PCT/GB89/00404 7 ~ 1 :
.:~' ~c) a moisture resistant substantially non-porous cover arranged in a pattern corresponding to `~ that of the electrode(s) and the grouting :~
material and overlying the same, and . (d) means for connecting the electrode(s) to an electrical power source (e.g. as hereinafter described).
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Although a "pattern" of only one assembly of electrode(s), grouting material and cover is not ~::
excluded, there will usually be two or more assemblies ~:
of the electrode(s~, grouting material and cover on the surface of the reinforced structure~

¦ The invention includes a method of inhibiting jl corrosion of reinforcement in a reinforced structure ~:
¦ of masonry or cementitious material, comprising :`
applying cathodic protection current to the structure ~-by means of apparatus as described above. ~
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For some commercial uses, it may also be con-venient to provide self-supporting assemblies of the electrode(s), grouting material and cover ready for installation, preferably including means for con-necting the electrode(s) to those of other such assemblies to form an electrically linked group of such assemblies. The connection means could comprise suitable male/female connections at opposite ends of the assemblies, allowing butt fitting of the ends of the assemblies against one another, or could comprise wires and clamps or other conne~tors where small spa-ces between the ends of the assemblies are acceptable.
The connection meansimay be constructed so as to faci-litate correct alignment of the channel and electrode ~y ~- ~ r~ 7 i ~

, sections with one another. Such assemblies render possible a quick method of installation by simply attaching one or more such assemblies to the surface of a reinforced structure to be protected so as to establish electrical contact between the surface and electrode(s), preferably including the step of applying a conformable ionically conductive com-position to the surface of the reinforced structure and/or to the surface or the grouting material before attaching the assembly or assemblies to the said sur-face.

A highly advantageous aspect of the present invention is that wherein the grouting materiàl is additionally used to repair or replace damaqed or missing parts of the underlying concrete of the rein-forced structure, in addition to ionically connecting it to the protective electrodes. For example, the frequently damaged edges and corners of reinforced concrete bridge sections, pylons, or road joints may be repaired and protected against further corrosion of the reinforcement by (l) removing any existing covers or joint casings, (2) trimming the concrete to remove unsound material and/or provide room for the protec~
tive electrodes, (3) applying the electrodes and covers generally of the kinds hereinbefore described, and (4) filling the space between the cover and the concrete with the grouting material, in this case pre-ferably a high strength cementitious compound, for example the aforementioned Excem.

Specific embodiments of the invention will now be described by w~ay of example with reference to the accompanying drawings, wherein:

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, Figure 1 shows schematically in perspective a section of steel-reinrorced concrete with covered electrodes constituting apparatus according to this invention;
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~ Figure 2 shows in cross-sectiOn a prererred form i~ of electrode for the apparatus of Figure 1;
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3 Figure 3 shows in schematic perspective a self-supporting assembly of electrodes, grouting material and cover for the apparatus of Figure l; and ~] Figure 4 shows schematically in cross-se~tion a cover with attached electrodes; and .' Figure 5 shows schematically the stages of repairi,ng damaged edges of a concrete road or floor joint.

Referring to Figure 1, a section of concrete 1 can be seen with embedded steel reinforcement rods 2, which,might represent, for e~ample, a floor in a rein-forced concrete building. Electrodes 3 are enclosed against the underside (or "soffit") of the concrete section by channel-shaped cove~s 4 of extruded ABS
plastics material, which are filled with electrically conductive water-containing grouting material (omitted for clarity) which surrounds the electrodes and con-nects them to the surface of the reinforced concrete.
As shown schematically, in operation a D.C. voltage of 3 to 12 volts (prererably about 6 volts) is applied between the electrodes 3 as anode and the reinforcing rods 2 as cathode, the resulting ionic current flow counteracting the tendency for the reinrorcing rods to ~ WO89/10~3~ PCT/GB89/00404 , ~
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.~ , - !9 corrode. The channels 4 extend laterally beyond the electrodeS to an extent (b) which retards drying of the grout and the concrete underlying the electrodes, thus maintaining the eLectrical connection between electrodeS and reinforcement. The thickness (a) of grouting material between the electrodes 3 a~d the concrete is greater than the width of the electrodes 3 lying parallel with the concrete surface, which width in this example equals the diameter of the substan-tially circular cross-section of the electrodes. The channel covers 4 are attached to the concrete by suitable fasteners (not shown), for example masonry nails driven through the edge flanges 5 of the covers.
The electrodes 3 may be appropriately spaced from the cover and the concrete by means of "spiders" made of any suitable material, preferably insulating plastics material, or may be attached to the cover for examole as shown in Figure 4. Flowable arouting material is then introduced to fill the channels enclosed by the covers, the viscosity or the grouting material oeing, or rapidly becoming, sufficiently high to p~event it from flowing out again.

The preferred electrode shown in Figure 2 comprises a conductive metal wirè 10 surrounded by an adherent layer 11 of a carbon-filled electrically con-ductive polymeric composition, whi~ch constitutes the electrolytically active surface of the electrode. The wire 10 thus advantageously plays no part in the electrolytic processes of corrosion protection. A
woven braid 12 is shown surrounding the conductive polymeric layer 11, but this br~id may be omitted i~
Dractice.

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Figure 3 shows a self-supporting assembly or channel cover 4, electrodes 3, and substantially solid grouting material 6, which may be attached to the concrete surface by fasteners inserted through the holes 7 in the edge flanges 5. An ionically conduc-tive gel or other material (not shown) may be applied to the surface 8 of the grouting material 6 to help establish electrical contact with the concrete and to compens`ate for any surface irregularities.

It will be understood that a sufficiently coherent grouting material 6 could be used to enable the cover 4 to be supplied separately or formed in situ after attachment of the assembly of the electro-des and grouting material alone to the concrete sur~
face.
' '' Figure 4 shows a self-supporting assembly of a channel cover 4 with the electrodes 3 attached thereto by webs 9 formed intearally with the Dlastics body of the cover.

In Figure SA, a damaged bridge roadway joint is shown schematically comprising reinrorced concrete sections 30 with rebars 31 and recessed jointing mem-bers 32, the edges of the sections having begun to crack. The jointing members 32 are removed and the concrete cut bac.~ to a profile shown in Fig. SB, leaving room for the electrodes and covers and grouting material to form the intended profile for a new joint as indicated by the broken lines. Figure 5C
shows the installed covers in two parts 20A and 20B, with the electrodes 22 attached thereto by means omitted for clarity. The space between the covers and j ~VO~9/l0435 PCT/GB89/00404 `'1 `'a4 ~J~ 7 J ~ ~.
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the road sec'ions is f:illed with high strength Excem grout 23 under pressure, and a new joint cover 25 is provided. On connection of the electrodes to a suitable power source, cathodic protection is applied to the rebars 31. Similarly, repairs could be made to bridge columns or piers with the cover surrounding the damaged parts and filled wlth strong grout.

For the purposes of the present invention, it is generally preferred that the size of the cover and gas permeability of the grouting material are such that gases evolved at the electrodes in operation can escape sufficiently quickly to avoid unacceptable pressure build-up by diffusion through the grout to the edges of the enclosure formed by the cover. This tends to limit the size of cover and volume of grout.
Such limitation of size is fortunately in keeping with another feature of the present invention, which pre-ferably involves leaving enough of the concrete sur-face uncovered to permit wetting to replenish the absorbed water used up by electrochemical reactions or lost by evaporation.
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Operating curxent, rate of gas evolution, cover size, volume and porosity of grout, spacing between ...
covers, and the other spatial relationships already referred to can be brought into a harmonious working relationship by simple calculations based on the characteristics of the materials concerned in any spe-cific application of the invention.

The invention is further illustra~ed by the `~
following specific Examples, in which reference is ~`
made to Figures 6 to 10 of the accompanying drawings.

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EXAkSPLE 1 :.
Employing an unplastised poly vinyl chloride (PVC) polymer exhibiting the properties shown in Table 1, a channel profile as portrayed in (4) Fig.6 was melt extruded. This channel had a wall section thickness of 1 mm and an internal width (d) of 80 mm and an internal depth of (c) 18 mm.
Table 1 Water Vapour Transmission Rate @ 40 C = 1 x 10 -4 kg,im/M2, 24 hrs ~olume Resistivity = 1013 ohm cm Following extrusion the channel section produced ~`
was cut into 1000 mm lengths, these forming the outer `-section of the anode assembly of this invention.

To the internal surface of the channel section small UPVC clips were affixed in three parallel lines at 200 ~m centres. These clips were attached on the back surface in order that an anode spacing of 20 mm (e) ~ig.6 results.

Conductive polymer anode as described by US4502929 with an external diameter of 8 mm, sold under the trade name Ferex 100, was cut into 900 mm lengths.
~.
Three such anode lengths were then bussed together at one end to a 500 mm length of high molecu-lar weight polyethylene insulated 12 AWG lead wire, such that the anodes were connected in ~arallel. Over :; . -,. . . .
.
: ~ . , ,:, ~ . ~ ~ : ' ':"' ' WO89/10435 PCT/GB89/0~404 ~i:
7 :~ 1 : j this electrical connection a water impervious seal was 1 produced by injection moulding. This was done using i medium density polyethylene resin and such that the l bussed connection was completely encapsulated. The ;~ finished thickness of the encapsulated section was 12 mm and width 46 mm, the encapsulation extending 20 mm down the polymeric anode.
: . .
-The completed parallel anode assembly was then ~' clipped into the prepared PVC channel ~y means of the small clips previously described. At the other cut end of each of the three anode sections, an environ-mental seal was provided employing 50 mm lengths of an adhesive lined heat shrinkable polyolefine tubing. It is necessary to seal both ends of the anode cut sec-tions in order to prevent the copper core becoming anodically active. The separation (a) Fig.6 of the anode to the PVC channel lower edge was 7 mm.
'~ After assembly of the anode/channel element, the inside was filled with a cementitious mortar, encap-sulating the anode along its entire length. This was 3~ done employing a vibration table in order that good void filling was achieved.
.
` The cementitious mortar adopted in this proce-dure was as shown in Table 2. A small amount of chopped polypropylene fibre sold under the trade name of Fibremesh as sold by Fibremesh Ltd, Europe, was added to enhance the flexural strength of this cured mortar. The depth of the cementitious Iill was 16 mm.
.:
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~ WO89/l0435 PCT/GB89/00404 .. . .

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24 ~

~ Table 2 ;~
.
Type IV cement 1 part Sand (fine) 3 parts Polypropylene f ibre 0.1 % note 1 Sulphonated aryl alkylene 1.0 % note 1 superplasticiser -, (ICI Mighty 150) '".
Water added to provide a 0.3 water cement ratio of :~ ;'''';'`
Note 1: Percentage vaLues shown are percent by weight of cement content.

After loading the channel the cementitious fill was allowed to cure for 28 days at 100 ~ R~ and 21C
3 prior to use.

i~Anode sections described above were attached to a prepared soffit of a 3000 mm x 1000 mm test slab.
This test slab was produced such that a standard two ;ilayer steel reinforcement cage comprising 20 mm diameter bars was configured with a cover of 35 mm top and bottom, this centrally located in a slab section thickness of 250 mm.

Salt (NaCL) solution 3 ~ by weight of water was applied periodically to the upper sur~ace of the test slab over a 6 month period, this was done in order to engineer the existance of a corrosion macro cell on ~j ~ WO89/10435 PCr~GB89tO0404 :~; jJ 'i 1 ' ~ 7 ~ ;~

~ - 25 ,,i , the reinforcement. Native potentials as measured by a surface mounted copper/copper sulphate electrode -~ (CSE), were prior to salt application - 190 mV and after 6 months -487 mV.
'.~
The attacnment or the anode assembly comprised a ~-~' 3 - 5 mm thick cement mortar to the cured cementitious fill surface, then pushing this against the slab sof-fit. Mechanical plastic fastners 6 were passed `
,~ through pre-drilled holes in the anode assembly and i hammered into correspondingly smaller holes in the iJ slab section. Fig.6 (6). Prior to anode attachment latents and sur~~ace dirt was removed from the slab `~
soffit by means of a needle gun and high pressure water washing.
", Anode sections were applied to the surface at 300 mm spacing and in oarallel across the slabs 100 mm width. Following a 7 day cure period for the bonding mortar, the anode sections were interconnected to a common buss lead by means of their respective lead wires. The buss wire was in turn connected to a DC
transformer rectirier capable of operating under constant voltage conditions. The steel reinforcement was connected to the negative terminal of the rec-tifier unit, so completing the electrical circuit.
Prior to conducting this last step, the electrical continuity of the reinrorcement was established and shown to exhibit a < 0.5 DC resistance between all points on the cage.

After powering the cathodic protection arrange-ment described the electrode potentials recorded on the reinforcement with time were as shown in TabLe 3.

~ ~3 .~`i WO89/10435 PCT/GB89/00404 .~
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6 - :

.! ~hese indicate clearly that the reinforcement is .: indeed cathodically protected with a good measure of . ~::
.~ .cathodic polarisation on the steel throughout the test ,. perlod.

;!
. Table 3 :-~
,~
~e ~¢~DC E~3~i~-e~r~e Es~n~eR~a~s(~) OE~m~l~ 4hr . .".
O O O 0 ~7 0 24 ~s 3.2 42 ~ 2 ~
1 ~ Z) 3.2 42 -~0 ~ ~o :.
3 llu~ 2.8 32 6 m~ 2.8 30 ~0 -~ L~
12mo~s 2.a ~ q l ., ~1 Note 1: "Instant Off" potential Note 2: Following this measurement applied voltage ~¦ reduced to 2.8 volts D.C. .:

~ ~ploying the channel as described in E~ample 1, i the conductive polymer anode strand was replaced with 3 mm dlameter Irridium catalysed titanium wire (34) Fig.7. Four 900 mm long sections of the titanium anode were welded together at~both ends to provide an assembly as shown in Fig.7. Spacing between the indi-vidual anode wire,elements was 12 mm.

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The titanium anoae assembly was located and held into position by the small PVC clips previously -~
described. After rixing, the anode was 9 mm from the channel lower edge portion this corresponding to dimension (a) Fig.6. The bent section (32) Fig.6 of the titanium anode, was positioned such as to exlt the channel via a pre-drllled hole in the side wall. This .. ..
it is intended will be used in the finished ar~icle to ~ provide the means of electrical interconnection of the ~
;~ anode element to the power supply. `
'j ,.
Into the channel so encapsulating the titanium anode, a cementitious mor~ar was compacted and vibrated into place. The formulation in this instance of the cementitious mortar being shown in Table 4. In this example calcium aluminate cement is adopted, this being done since upon hydration no calcium hydroxide !3 is Eormed. This reature distinguishes it ~rom the portland cements and imoroves the acid resistance or the cured material.
i ......

, W O 89/1043~ PC~r/GB89/00404 ',,~'.
! - 28 . ',~
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Table 4 Calcium Aluminate Cement l part ~ ;

Fine sand 2.5 parts `
'':
Polyproplylene fibre 0.1 ~ Note 1, Table 2 ~-Naphthalene ~ormaldehyde 0.25 % Note 1, Table 2 condensate "Lomar D" ;
Diamond Shamroc.~

Water added to provide a 0.35 water:cement ratio After filling of the channel section fully void filliny around the anode elements, the mortar was cured at lOO ~ R~ and 21C for 28 days. The finished mortar section thickness was 16 mm.

Anode elements were attached to the vertical face of a precast reinforced concrete wall section the characteristics of which are shown in Table 5.

The anode sections were attached to the prepared surface 2S previously described employing a cement mortar based upon calcium aluminate cement. Anode spacing adopted on the wall section due to the light reinforcement present was 400 mm between anode sec-tions.

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~ WO~9/10435 PCT/CB89/00404 v i~

Table 5 Reinforcement density 0.68 sq m steel surface sq metre of concrete ~-surface Reinforcement diameter lO mm -`~
:' 2 Chloride content (Cl-) 2.8 % by weight of cement Carbonation depth 7 mm Volume resistivity (average) 26000 ohm cm ¦ Cover over steel (average) 25 mm ~ative potential (avera~e) -360mV silver/silver chloride Into ~he slab section, prior to conducting the trial silver/silver chloride ref electrodes were posi-tioned at the depth of the steel reinforcement. These were cast into excavated holes and cast in an OPC mor-tar containing an equivalent chloride ion content as the surrounding concrete.

With the steel reinrorcement connected to the negative terminal of a constant voltage DC transformer rectifier and the anodes to the other terminal. In this instance the individual anode elements were all interconnected in parall~l. Results of this experi-ment with time as,shown in Table 6, from this it can be seen that the,reinforcement is adequately cathodi-cally orotected.

~ WO89/10435 PCT/GB89/00404 !, :
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~ - 30 "',, ~ TabLe 6 ` .

~e ~ dCC EE3~i~-eA~e ~ x~ R*s~s(l) ~;
¦ ~ts ~n q~o~ent S~ ~*e~
m3~ OEF ~ 4 ~ d3~t~n 2.8 ~ _oo 1 3 mu~s(2~ 2.8 50 ~2 8 m~ 2.
1 ~3r 2.60 ~ ~31 147 .

Note 1: Silver Chloride electrode potentials Note 2: Voltage applied reduced to 2.6 volts A PVC channel was extruded as ror Example 1.
However, a further elongated compartment running along one edge was incorporated, This had a width of 20 mm and was the same depth as the channel section. :
Following extrusion, the channel was cut into 1000 mm lengths and as in ~xample 1, small PVC cable clips attached to the inside surface of main channel sec-tion.

Inside the channel a titanium catalysed anode array was attached, as described in F.xample 2.
However, a 100 mm section or one of the titanium ano-des was removed at the central position along its length, the two cut ends being supported in clips. ;:

' ~: . . ... . :

.,1, WO89/10435 PCTtGB89/00404 ' `~.3 .~

.
Within this area a 10 mm diameter silver-silver chloride reference electrode WE10 type supplied by Silvion Ltd, was ~ttached. The whoie assembly of anode and reference elect:rode was then encapsulated in a cementitious mortar of the type shown in Table 5.

The reference electrode lead wire was exited 3 through the partition between the main channel and the elongate compartment, through a pre-drilled hole.
.~ This wire was held in position along the compartment by push fit PVC cable clips and terminated at the end ~ of the channel that had the bent portion of titanium ¦ anode (32) Fig.7. ~oth the titanium anode section (32), the reference electrode lead wire, and an addi-! tionaL black 14 AWG lead wire, were then connected to a three pin plug, this adhesively connected to the PVC
channel séction side wall. The additional black wire I to be used as the reference electrode negative, for attachment to the reinforcement, also being clipped into the elongate CoMpartment, the latter now acting as an integral wire conduit within the anode assemblY
and total system.

The finished anode assem~ly it is intended would be used in conjunction with similar sections not con-taining reference electrodes, hence, providing the array with an integral means of system monitoring.
All wires for the system being contained within the integral conduit and matching PVC cover over the plug and soc.~et attachments on the channel. This enhancing the aesthetics, important when~used in building appli-cations open to the public. Inherent in this example also in the additional safety of havins all electrical wires within rigid conduits.

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~3 i~ - .32 , A glass fi~re reinforced concrete (G~C) section ~`
was produced of section, size and configuration shown in (36~ Fig.8. The cement mortar adopted in the pro-duction of this section being as shown on Table 7. `

Manuracture of the GRC element was conducted by hand spraying the mix into a plastic coated mould.
The slurry beinq prepared prior to spraying on a Tumac T~B-lC0 high speed mortar-mixer. After spraying to produce the desired section thickness of 15 mm, the mould was positioned on a vacuum table to vacuum dewater the section. This increases the density of the matrix and removes excess water from the section.

.
~ Table 7 `I
~? Sulphate resistant Portland Cement 30 kg '1 Zone 4 sana 10 kg Expanded Perlite (250 kg/cm3 2 kg : .
Glass (added at the gun nozzle) 2.5 kg 2.6 gm/cm3 density 80 G Pa modulus Naphthalene sulphate air 1.0 ~ Note entrainment agent ?
? Water added to achieve a water cement 0.4 ratio ~-Cure or the section produced was conducted at ,.` ~ ~ ... . . .

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~ WO89~1043~ PCT/GB8~/0040~ ~
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mental chamber. Properties o~ the finished curea sec-tion as measured on test s~ecimens made at the same 3 time, and cured under identical conditions were as shown in Table 8.

Table 8 '~
j Modulus on Rupture N/mm2 42 Ultimate Tensile Strength N/mm2 15 Young's .~odulus KN/MM2 21.4 Impact Strength 120 D (Nmm/mm2) 22,5 Following the 2a day cure period polypropylene cable clips were used to attach a conductive polymer anode strand ~35) Fig.8 or 8 mm diameter, similar to that used in Example 1. The anode strand was con-figurated in a serpentine arrangement running up and down the length of the GRC section (36) Fig.8. On the two cut ends of the anode strand two 14 AWG high mole-cular weight polyethylene insulated wires were attached by crimping onto the copper core of the anode. Over this crimped connection a heat shrinkable adhesive coated 100 mm long tube was thermally reco-vered to environmentally protect the connection. The two lead wires were then taken out through a pre-drilled hole in the GRC (37) Fig.8 and connected to a socket assembly. This socket assembly was in turn attached to the GRC outer sur~ace through the use of an epoxy based adhesive.

With the anode and electrical socket in posi-.: , : ~ ;

; -: .::: ~ - . : :. .. , :, . :

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tion, a two component polyepoxy coating was sprayed on 3 to the outer GRC surface. ~'he coating thic~ness arter several spray applications was ~easured to the 0.8 mm, ~ the general properties of the coating being as shown f~ in Table 9.
'l Table 9 r~
.. , :
Water vapour tranmission rate 1.041 ~g, cm/m2 24 hr Elongation to fracture 3.8 ~

Tensile strength 50 MPa : :
Volume resistivity 5 x 102 ohm cm ,~
~ .vertical building column exhibiting extensive chloride induced corrosion based deterioratian was repaired as follows. All the crac.~ed and delaminating concrete was removed from the structure using a pneumatic tool. After removal of this, concrete exposed steel was cleaned by grit blasting to a clean metal finish. All other concrete surface was treated with a needle gun to remove the outer l - 2 mm, exposing aggregate to provide a good mechanical key for the repair mortar. The structure was then finally washed with high pressure water to remove dust and other debris.
, , .
On two of the exposed steel reinforcement sec-tions, cathode connections ~ere ~ade employing the ~ thermite brazing technique. At these locations two f WE100 Silvion reference electrodes were also located, , held in position by nylon cable ties to the steel i. :

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`~ WO89/10435 PCT/GB89/00404 j77~ ~
.~
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, - 35 :~' ' , .rein~orcement. To each of the rererence electroae locations a corresponding negative connection was made to provide the complet:e monitoring circuit.
" ~ :
With the column preparation completed, tWQ or the above described G~C elements were arranged around ~ the column and fixed into position with plastic coated :~ screws. The annular gap between column concrete sur-face and that of the inside surface of the GRC was 3S
i mm. On the two vertical joints of the GRC sections a :-! polysulphide calking compound was applied, this turn coated with a thick fast cure epoxy adhesive.
. ,.~, Upon cure of the two joint sections a free flowing microconcrete was poured into the gap between the GRC and column. This concrete providing the repalr around exposed steel, the electrolyte or operation of the CP system and means of bonding the GRC to the column in the long term. The GRC in this instance provides not only an intearal component of the anode assembly but architecturally acceptable per-manent framework for the concrete repair.
'.'' ~' -, Cure of the microconcrete was effected for a 28 day period prior to envisaging the GP system. With the system under power oDerating at 2.9 volts constant -~
voltage condition, the 4 hour depolorisation value ;~
after 3 months of operation was recorded as 167 mV and 182 mV on the two reference electrodes. This J demonstrating a good measure of cathodic activity on -~
the steel reinforcement.

, ~" .~ . . . ~ . .

~ WO 89/1043~ PCT/G889/00404 , ;~.
J

1 - :6 ~ X r M _ _ _ -;

~ m~iovinq ~he G~C -z~r ~ o~. ~aC.nLCUe aesc~ oec in ~xam~le -, ~2-- ions ~a r9 ~ace =n2_ --_-ss?onae~ e ou~ 9r ~ a o a ~i ~oac J oin_ -o_ _ siaD' sec-ion ~ ness ~ 0 ~m. ~z_n ,ide o a -oin_ ~eing -om~osea o -wo ~C S9C- ' ons, ( 20r ) anc 20~) ?ic SC.

o ~;ne -1red insiae sUr'~Zce ^_ ~na G~C _ ~i=a~
ni~ me~2l mes.. anoae soi~ ance- ~ne _~aaa ?.ame o_ 1GC-- 210, _his ~einc ?1Z_:~.~m _~ vsec.
At_zc~e~ent o~ _he anode ln _his ~ns_~nc~ oeinc suc;.
~hz_ a = 2 mm ca~ exis~s De~een _:~e anode and _:ne G~C. ~lat ~ mm x 1 mm catzivseà ~ __nium s~- ?s ara r'ln ~~a lenc-h or the G~C anc ~elaec ~c ~he mesh a~
200 ~ in~ervz~s.

.~s wi_:~ e anoae ieac wi-_s ~ zm-ie ', _~ 5 =-~~~''~ s~-`? wzs Den~ an~ ?assed~ _..--uc.. _ne ~-~C ar.~
~e ~...z~ea in z soc.~e~ -onnec=o_. ~a= 3C C_ _ne ou -siaa s~~_zce wi=:~ an er?ox~r ga~ -oc_ _- z _.i-~ness o 0.6 ~.. comoie~es ~;~e anode asse~ol~.

G~C sec~ions o_ _;~is ~ e ?rc~-:~e a "52-'' WZ~
o --ovidinc ?e~manen~ or~wor.c anc -a~noci_ ?ro~ac-_ior. :c Dridge ioinr sec~ion _e?z_-s, zs _~~=ne~
i'` s=-a.ec ir. aesc-i?=:~Je ~ic~~es 5 zr.~ C.

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':.'j `~ W O 89/10435 PC~r/GB89/00404 . "
- 37 - i''J ~

various modifications can be made .o _he foregoing wi.hou. departing from the scope of the in-.-ention.
For example, the cover aforesaid can be constructed from a plurality of cover sections. These cover sections can be connectable one to the other by means of an overlapping connection, a push-fi. connection, or any other convenient means of interconnecting one section to another. In order that a continuous length of apparatus .
of the invention can be provided to ex=end over any convenient desired surface of structure to ~e protected, the cover or the apparatus can be cons,-uc_ed in various components, for example in-line connecting pieces, right angle or elbow pieces, T-pieces or cross-pieces and various other pieces which allow changes in direction and from one plane to'another plane, for e~ample a piece of covex extending along the underside or a beam could be provided with an external corner sec.ion _o allow it to proceed up the outer surface of the beam. Many other types of cover section can be provided.
The invention is, or course, applicable to electrodes of any convenient metal or o~he- conductor or partial conductor.
Metal anodes used in the apparatus of the invention can be joined together by any convenient means which will proviae electrical continuity. As examples there can be wel~ing, for example spot welding, crimping, clam?ing . ' ~,.i - 38 - ~h~ 7 with terminals, or the like.
The pre-formed components of the cover can include compartments specifically designed to allow the incorporation of reference cells at desired locations in order that monitoring of the components and other system can be carried out in situ and conveniently without having to make physical or electrical special entry into the system.
In order that supply and monitoring cabling can be conveniently accommodated close to the apparatus of the invention, the cover can include means for arranging for said cable to be disposed close to the cover. For .
¦ example, the cover can include one or more integral conduits. The or eac~ conduit can be closable to protect the cabling. Clips may be included to secure the cabling ~ to the covering material.
1 Instead of the covering material being pre-formed, it can, if desired, be formed in situ. For example, one or more members could be secured to basic concrete of structure to be protected and then a covering sheet arranged to extend between that strip and the material of the concrete or between two such strips adhered to the concrete to form the cover which encloses the anodes within the cementitious material.

Desirably, in applying the apparatus of the invention to concrete to be protected, the anodes are ~,WO89/10435 PCT/GB89/00404 - 3 9 ~

inltially embedded ln a firs. portion of ionically conductive cementitious material upon or within the cover and, during installation of the apparatus a second portion of ionically conductive cementitious grouting :
material is applied to the structure to be protected and/or to the first portion and that second portion sandwiched between the first portion and the structure, the cover being urged towards the structure, as by fasteners such as bolts of non-conductive material, to compress said second portion to ensure a continuous layer of ionically conductive cementitious material between the anodes and the surrace of the structure to be protected.
Many other variations are possible within the scope of the Eollowing claims. ~ :

Claims (18)

1. A reinforced structure of masonry or cementitious material having apparatus for inhibiting corrosion of reinforcement thereof, comprising a pattern of two or more assemblies located on a surface of the structure, each of which comprises:
(a) one or more electrodes overlaying a surface of the structure (b) ionically conductive cementitious grouting material connecting the electrode(s) to the said surface; and (c) a moisture-resistant cover having a moisture vapour transmission rate of less than 103g mil per m2 per 24 hours overlying the electrode(s) and the grouting material, an edge portion of which cover extends at least partly around the electrode(s) and the grouting material towards the said surface of the reinforced structure.

2. A structure as claimed in claim 1, wherein the cover substantially completely encloses the electrode(s) and the grouting material against the said surface.

3. A structure as claimed in claims 1 or 2, wherein the grouting material completely surrounds at least part of the electrode(s).

4. A structure as claimed in claim 3, wherein the surface of the electrode(s) furthest from the said surface of the reinforced structure is covered by the grouting material to a depth of not more than 25, preferably not more than 15 millimetres.

5. A structure as claimed in any preceding claim, wherein the electrode(s) comprise(s) one or more electrical conductor wires embedded in an electrically conductive polymeric composition, or valve metal wire coated with an electrocatalytic coating.

6. A structure as claimed in any preceding claim, wherein the width of the individual electrode(s) lying substantially parallel to the said surface of the reinforced structure is not greater than the thickness of the grouting material between the said surface and the surface of the electrode(s) closest thereto.

7. A structure as claimed in any preceding claim, wherein the cover extends beyond the electrode(s) to a distance at least 0.5 times and up to 100 times the width of the individual electrode(s).

8. A structure as claimed in any preceding claim, wherein the grouting material also serves to repair or replace portions of the underlying concrete structure.

9. A structure as claimed in any preceding claim, wherein the electrode(s) is or are mechanically attached to the cover by means other than the grouting material.

10. A structure as claimed in any preceding claim, wherein the cover is attached to the said surface of the reinforced structure independently of any attachment by way of the grouting material.

11. A structure as claimed in any preceding claim, comprising an additional layer of ionically conductive material assisting the establishment and maintenance of electrical contact between the electrode(s) and the said surface of the reinforced structure.

12. A structure as claimed in any preceding claim, wherein electrical connection means are incorporated in the said cover.

13. A structure as claimed in any preceding claim, wherein the cover comprises an elongate channel capable of holding electrical wires separately from the grouting material and electrode(s).

14. A method of inhibiting corrosion of reinforcement in a reinforced structure of masonry or cementitious material, comprising applying cathodic protection current to the structure by means of apparatus according to any of claims 1 to 13

15. A method of repairing a reinforced structure of masonry or cementitious material and providing it with a cathodic protection system, comprising:
(a) removing any unsound masonry or cementitious material and if necessary trimming the remaining structure to provide a profile suitable for the following steps, (b) attaching to the a surface of the structure at least one assembly which comprises at least one electrode and a preformed cover having a moisture vapour transmission rate of less than 103 g mil per m2 per 24 hours so as substantially to enclose the electrode(s) between the cover and the said structure, (c) introducing ionically conductive masonry or cementitious grouting material into the space enclosed between the cover and the said structure, and (d) causing or allowing the grouting material to harden; thereby connecting the electrode(s) to the said structure and repairing or replacing portions of the said structure.

16. A method as claimed in claim 14, wherein the cover is pre-formed.

17. Apparatus as claimed in any of claimss 1 to 13 wherein said cover includes in-line sections, right angle sections, and sections which allow changes in direction from one plane to another.

18. A pre-formed article for application to the surface of a reinforced structure to inhibit corrosion of the reinforcement therein, the article comprising:
(a) one or more electrodes capable of serving as active anode(s) in operation, (b) ionically conductive grouting material in contact with the elctrode(s) which grouting material is capable of permitting the electrochemical reactions necessary to inhibit corrosion.
(c) a moisture-resistant cover having a moisture vapour transmission rate of less than 103 g mil per m2 per 24 hours extending at least partly around the electrode(s) and grouting material, an edge portion of which cover will extend towards the surface to which the article is to be applied in use, and optionally, (d) electrical connector(s) for connecting the electrode(s) to a power supply and/or to each other in use, and (e) means for mechanically attaching the cover to the reinforced structure.