EP0186334B1 - Cathodic protection system for reinforcing bars in concrete, a method of carrying out such protection and an anode for use in the method and system - Google Patents
Cathodic protection system for reinforcing bars in concrete, a method of carrying out such protection and an anode for use in the method and system Download PDFInfo
- Publication number
- EP0186334B1 EP0186334B1 EP85308692A EP85308692A EP0186334B1 EP 0186334 B1 EP0186334 B1 EP 0186334B1 EP 85308692 A EP85308692 A EP 85308692A EP 85308692 A EP85308692 A EP 85308692A EP 0186334 B1 EP0186334 B1 EP 0186334B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- cathodic protection
- concrete
- protection system
- anode
- strips
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Images
Classifications
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
- C23F13/00—Inhibiting corrosion of metals by anodic or cathodic protection
- C23F13/02—Inhibiting corrosion of metals by anodic or cathodic protection cathodic; Selection of conditions, parameters or procedures for cathodic protection, e.g. of electrical conditions
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
- C23F2201/00—Type of materials to be protected by cathodic protection
- C23F2201/02—Concrete, e.g. reinforced
Definitions
- This invention relates to cathodic protection systems and has particular reference to cathodic protection systems used to protect iron or steel reinforcement bars in concrete structures.
- Impressed current cathodic protection systems are well known in use to protect structures immersed in water, particularly sea water.
- the object to be protected is made a cathode whilst the counter electrode is made an anode.
- Negatively charged ion species are attracted towards the anode where they tend to concentrate, unless sufficient diffusion of ions occurs in the region of the anode to disperse them.
- free sea water the movement of the negatively charged ions occurs freely and readily, such that there is a minimal buildup of ions around the anode.
- Reinforced concrete essentially comprises a series of steel reinforcing bars (commonly referred to as rebars) surrounded by a concrete mixture.
- chloride contaminated concrete In the case of chloride contaminated concrete, a risk exists that chloride ions will enhance the corrosion of the steel.
- the resultant corrosion product formed by the enhanced reaction occupies a greater volume than the space occupied by components prior to chemical reaction, eventually creating intense local pressure that brings about cracking of the concrete and eventual spalling of the concrete cover to expose rebars directly to the atmosphere.
- Electrode potential mapping of the outside surface of concrete rebars is used as a means of assessing the state of corrosion of embedded rebars and by inference the depth of penetration and concentration of salt.
- the variation in electrode potential may be 0.5 volts or more. It might be logical to expect that salt contamination from the bridge roadway would leak onto the top surface of the cross beams and hence lead to more rapid penetration to rebars lying near the top surface than on the bottom surface, and this is exactly what is found.
- cathodic protection is meant the application of an electrolytic system whereby the electrode potential of the steel is depressed to a cathodic (negative) potential to stop or significantly decrease corrosion.
- cathodic protection of steel in concrete represents an especially challenging problem for application of cathodic protection for a variety of reasons.
- An obvious difference between cathodic protection in concrete and seawater is the difference in ionic mobility of species within the electrolyte.
- the level of diffusion between anode and cathode is many orders of magnitude lower than in the seawater case, and the distance between the anode and the cathode to be protected cannot usually exceed 15 to 30cms.
- the problem of cathodic protection of rebars in concrete is not the ability to arrest the corrosion of steel by depressing the electrode potential, but the problem of acidity surrounding anodes.
- the longevity of cathodic protection systems applied to concrete may well not be related to the durability of the electrode materials involved, but be related to the acid attack on concrete surrounding anodes.
- the cathodic protection of rebars in concrete is very different to cathodic protection of steel in seawater.
- US-A 4 255 241 describes a cathodic protection system for concrete structures which utilizes plati- nized niobium wire or like metal anodes positioned adjacent the concrete in a matrix of of conductive carbonaceous material.
- the wire anode can be installed directly in a conductive asphaltic coke breeze overlay or inserted into a slot cut directly into a concrete surface.
- EP-A 85 582 describes a cathodic protection system using conductive polymer concrete in which anodic materials are positioned adjacent a concrete surface. Polymers are described as desirable because of their resistance to acid attack.
- US-A 4 422 917 discloses an electrode material of the formula TiO x , wherein x is from 1.55 to 1.95. The material may be used in a cathodic protection system in which the material forms the anode.
- a cathodic protection system for the protection of iron or steel reinforcement bars in concrete which includes a source of electrical current connected to the reinforcement bars and to an anode, so that, in use, the reinforcement bars are connected as a cathode, wherein the anode is a hydraulically porous material permeable to water in the liquid state, which is bonded to the concrete so as to make electrical contact therewith and exposed to the environment over part of its surface area.
- a preferred material for the anode is porous TiO x where "x" is in the range 1.67 to 1.95. Preferably "x" is in the range of 1.75 to 1.8.
- the porous TiO x material is preferably in the form of a tile grouted to the exterior of the concrete. A liquid mortar may be used as the grout.
- the porous TiO x material may have a thickness in the range 2-3 mm. The density of the material may be in the range 2.3 to 3.5.
- the porous TiO x material may be in the form of a tube passing into a hole in the concrete structure.
- the porous material may be graphite or porous magnetite, porous high silicon iron or porous sintered zinc, aluminium or magnesium sheet.
- the porous material may be in the form of a tile bonded to the concrete, the tile having a projecting ear to which electrical contact can be made.
- the ear may be provided with a hole or slot.
- the ear may be connected to a power supply cable having an electrically conducting core and a lead metal exterior in electrical contact with the core, the lead being deformed by the action of being pushed into the slot to make electrical contact therewith.
- the titanium may be anodically passivated and may be coloured.
- the anodically passivated layer may be removed where the titanium is in contact with the TiO x material anodes.
- the titanium may be in the form of strips having sections cut and bent out of the plane of the strips to form tabs to which the anodes are connected.
- the anodes may be connected to the titanium strips by nuts and bolts of titanium or by a titanium rivet.
- the strips may mechanically locate the anodes on the concrete.
- the strips may be provided with slots.
- the number of coulombs of electricity passed in seven days is 15,120 coulombs. Assuming 30% current efficiency for oxygen evolution, the reaction 2H 2 0 - 4e - 0 2 + 4H + will result in 0.047gH + ion generation. Hence it appears that a 25mA anode will produce between 0.05 to 0.1 gH + per week. At 1 mA/anode the corresponding figure would be 0.002 to 0.004gH + per week. At this rate it would take eighteen weeks to react all Ca(OH) 2 in 12cm 3 zone of concrete per week, and, of course, correspondingly longer time periods the lower the current passed or the volume of concrete affected.
- hydraulically porous T J4 0 7 material was used to divide the volume of a glass beaker into two approximately equal volumes.
- one side was placed sodium chloride solution and a titanium metal strip cathode.
- the other (representing the atmosphere side in the bridge deck) was put distilled water.
- acidity developed with time in the initially distilled water compartment. Such acidity develops in spite of the good diffusivity of H+ ions in the sodium chloride side, ie H + ions diffused in the "wrong" direction away from the cathode.
- FIG. 2 and 3 there is provided a mechanism for cathodically protecting the rebars in the structure 3.
- the rebars 7 (more clearly shown in Figure 3) are connected to a source of electrical current 8 as cathodes.
- a series of hydraulically porous TiOx tiles 9, 10 are grouted to the exterior of the concrete structure 3 and an electrical connection is made to the tiles in a suitable manner.
- the preferred value for x is 1.75, but tiles where x is predominantly in the range 1.75 to 1.8 are acceptable. Electrodes of this material are described in US Patent 4 422 917, the description of which patent is incorporated herein by way of reference.
- the TiOx material will conduct electricity as an anode it may be used to pass an electrical current through the moisture in the concrete into the rebars 7.
- anions such as CI- are attracted to the anodes and by using porous TiO x material the anions can diffuse through the TiO x to be oxidised by the air in the atmosphere or to be washed away by the irrigation of the anodes which will occur from rain water washing over the surface of the support structures, or by applied water irrigation.
- tubular anodes can be used. If necessary water could be directed through the anodes from gulleys on the road deck.
- FIG. 4 One method of connecting the anodes to the electrical conductor line is shown with reference to Figure 4.
- the anode plate 11 is provided with an upstanding ear 12 integral with the plate.
- FIG. 5 An alternative method of making a connection is illustrated in Figure 5.
- a tile 14 of circular or eliptical shape is provided in the centre with three up-standing ears 15, 16 and 17.
- the ears are provided with slots 18, 19 and 20. It will be seen with the slots 18 and 20 face in the opposite direction to the slot 19.
- a lead coated wire having a copper core is threaded around the ears 15, 16 and 17 and the slots are so positioned that tightening of the lead covered wire causes the wire to bite into the slots 18, 19 and 20 to make an electrical contact.
- An alternative mode of operation may be used containing TiOx as the electrical conducting constituent formed by packing powder into grooves in the concrete back-filled into grooves in the concrete.
- the current density which needs to be applied to the anodes is very low. Typically a current density of the order of 20 milliamps/m 2 will protect the steel rebars. Thus for concrete structure 11/ 2 m2 by 14 m long, a total current number across being 1-2 1 / 2 amps would be sufficient. Operating 15 cm x 15 cm tiles at 5 amps/m 2 would permit each tile to pass 0.1 amp so that 15-20 tiles per cross-beam would be sufficient.
- each anode would be electrically connected to the power source used for the impressed current cathodic protection system.
- the hydraulically porous TiO x material particularly material having a density in the range 2.3 to 3.5 g/cc is readily bonded by cement to concrete and has the distinctly advantageous property of not being effected by water freezing within the pores of the material.
- As the material is hydraulically porous water as a liquid (rather than merely as a vapour) can pass through it; for example material of 3 mm thickness with a head of water of 30 cm will pass one litre of water per 5 cm 2 of exposed surface area per day.
- titanium strips may be used instead of using lead coated wires as connectors.
- the titanium strips may themselves have a coating to restrict corrosion of the strips in which case an oxide film formed by ano- dising is preferred. This arrangement is shown more clearly in Figures 6 to 13.
- this shows the concrete cross beam 3 supported on the pillars 1, 2.
- the beam is a conventional steel rebar reinforced concrete structure.
- the pillars 1 and 2 are also conventional concrete with steel rebars.
- Extending along the length of the beam 3 is a titanium strip 21 and extending vertically from the strip is a plurality of strips, two of which are shown at 22, 23. The entire length of the concrete beam 1 will be covered by strips 22, 23.
- the strips 5, 6 are spot welded, riveted, bolted or otherwise connected to the strip 21 and a vertical strip 24 is connected to the strip 21.
- Strip 24 is connected to a suitable source of electrical current as an anode and a suitable connection is made to the steel reinforcement within the beam 3 as a cathode.
- the tabs can be formed as connectors for adjacent strips 31, 32 and also to connect in an anode 33.
- the anodes are secured by means of titanium nuts and bolts 34.
- the anodes may be embedded into holes drilled into the concrete and are grouted into position as shown in Figure 11.
- the anode 35 is surrounded by grout 36 located in the concrete structure 37.
- the anode is bolted to titanium strip 38.
- the permanently connected anodes can be distributed over the surface of the beam 3 and of course, if required, over the surface of the upright pillars 1, 2. Any other structure can simultaneously be protected.
- the concrete grout securing the anodes may well become weak during operation, even if it is one chosen for its acid resistance such as a high alumina cement, it is probably desirable to use mechanical means to hold the anodes in situ in addition to the grout.
- the titanium strips can carry out both functions of supplying current to the anodes and holding the anodes in situ.
- slotted strips 39 Figures 12 and 13 can be used. To install such a system, initially the position of the shear (longitudinal) rebars in the material is located, marked out with chalk, and thus enabling the location of the hydraulically porous tile anodes to be marked in approximate position.
- the hydraulically porous tile used measured 50 mm x 50 mm and had a hole drilled in one location to take a titanium metal nut 40 and bolt 41.
- the connector strip 39 of slotted titanium had a width of 20 mm and was 0.5 mm thickness.
- the strip is located at its upper end, leaving slot locations for the anode and defining positions for the self tapping holding screws 42. Because of large aggregate in the concrete cover, it is difficult to drill holes exactly in the concrete, thus the use of the slots facilitated installation. Then the anode tiles are grouted at locations down the strip and the titanium nuts 40 screwed loosely in position and the self tapping screws 42 screwed into position while the acid resisting cement is still soft. This sequence is progressed along the side of the beam.
- the horizontal connector will also be attached to the concrete structure, but only after all other positioning had been completed.
- the system can then be used to protect the rebars.
- cathodic protection system could be used to protect rebars in concrete in any situation, for example car parks, foundations, marine structures etc.
- the system can be installed on the underside of the bridge deck itself to protect the bridge deck. This installation can be done without interfering with the traffic flow.
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Prevention Of Electric Corrosion (AREA)
- Particle Accelerators (AREA)
- Cable Accessories (AREA)
- Laying Of Electric Cables Or Lines Outside (AREA)
Abstract
Description
- This invention relates to cathodic protection systems and has particular reference to cathodic protection systems used to protect iron or steel reinforcement bars in concrete structures.
- Impressed current cathodic protection systems are well known in use to protect structures immersed in water, particularly sea water. In such a system the object to be protected is made a cathode whilst the counter electrode is made an anode. Negatively charged ion species are attracted towards the anode where they tend to concentrate, unless sufficient diffusion of ions occurs in the region of the anode to disperse them. In free sea water, the movement of the negatively charged ions occurs freely and readily, such that there is a minimal buildup of ions around the anode.
- Reinforced concrete essentially comprises a series of steel reinforcing bars (commonly referred to as rebars) surrounded by a concrete mixture.
- It is well known that steels are not corroded in alkaline media. Reinforcing bars are very frequently covered with an adherent "rust" layer when embedded in concrete, which experience has shown improves the adhesion between concrete and steel. With time, as may be shown by removing the concrete cover, the rust changes chemically allowing the formation of a dark, protective, film well adherent to concrete. This is the very satisfactory usual situation that exists.
- Concrete, by various mechanisms, is porous to water, albeit very slowly, and even after so called full curing, will allow a slow uptake with some kind of equilibrium being established with the surrounding environment. This again is a normal situation. However, if salt water is present on the surface, then the salt and its contained chloride ions may penetrate into the concrete. It is not immediately obvious why salt contamination is more of a problem to some concrete than others, because concrete is widely used as a constructional material for use in seawater. The design of the concrete structure and thickness of the outer concrete layer may be particularly important.
- In the case of chloride contaminated concrete, a risk exists that chloride ions will enhance the corrosion of the steel. The resultant corrosion product formed by the enhanced reaction occupies a greater volume than the space occupied by components prior to chemical reaction, eventually creating intense local pressure that brings about cracking of the concrete and eventual spalling of the concrete cover to expose rebars directly to the atmosphere.
- A great deal of reinforced concrete has been used in building and in road construction and particularly in the fabrication of support pillars, cross beams and road decks for bridges. Over the years increasing amounts of common salt, sodium chloride, has been used in winter to prevent ice formation on the road. The melted snow or ice and sodium chloride solution tends to seep down into the concrete, and it has been found that the presence of the chloride ion penetrating to the rebars can give rise to corrosion. In some cases, calcium chloride has been added to the concrete as a setting agent, or the water used to make the concrete contained naturally high levels of chloride ions and this also increases the rate of corrosion of the rebars. Further, some structures are exposed to salt-laden atmospheres, particularly in marine locations.
- Electrode potential mapping of the outside surface of concrete rebars is used as a means of assessing the state of corrosion of embedded rebars and by inference the depth of penetration and concentration of salt. Around a concrete cross bar to a motorway bridge, the variation in electrode potential may be 0.5 volts or more. It might be logical to expect that salt contamination from the bridge roadway would leak onto the top surface of the cross beams and hence lead to more rapid penetration to rebars lying near the top surface than on the bottom surface, and this is exactly what is found.
- The problem of corrosion of the rebars in bridges has become so significant that much effort is being expended in an attempt to slow down or halt the corrosion before the concrete structures in the bridges fail.
- By cathodic protection is meant the application of an electrolytic system whereby the electrode potential of the steel is depressed to a cathodic (negative) potential to stop or significantly decrease corrosion.
- The cathodic protection of steel in concrete represents an especially challenging problem for application of cathodic protection for a variety of reasons. An obvious difference between cathodic protection in concrete and seawater is the difference in ionic mobility of species within the electrolyte. Although there is an electrolytic path in concrete, otherwise application of cathodic protection would be impractical, nevertheless the level of diffusion between anode and cathode is many orders of magnitude lower than in the seawater case, and the distance between the anode and the cathode to be protected cannot usually exceed 15 to 30cms.
- Another difference between the seawater and concrete example relates to the change in pH surrounding the electrodes. It is well known that media surrounding a cathode will tend to alkalinity, and around an anode will tend to acidity. Alkalinity around a rebar in concrete, which is already alkaline, is no problem. Indeed additional alkalinity could be helpful towards the stabilisation of the steel from corrosion.
- The formation of acidity around anodes in concrete is a major issue. Acidity cannot readily diffuse away from the anode either by diffusion under a concentration gradient, or by field transport to the cathode (ie H+ to the cathode) brought about by the applied cell voltage. Concrete is readily attacked by acid, even at very low levels of acidity. Attack is significant at pH 6, and while some concretes may be more acid resisting than others, attack at pH's down to 2 or 1 (common in some cathodic protection situations) is extremely rapid.
- Hence in practical terms, the problem of cathodic protection of rebars in concrete is not the ability to arrest the corrosion of steel by depressing the electrode potential, but the problem of acidity surrounding anodes. Indeed the longevity of cathodic protection systems applied to concrete may well not be related to the durability of the electrode materials involved, but be related to the acid attack on concrete surrounding anodes. In this respect the cathodic protection of rebars in concrete is very different to cathodic protection of steel in seawater.
- US-A 4 255 241 describes a cathodic protection system for concrete structures which utilizes plati- nized niobium wire or like metal anodes positioned adjacent the concrete in a matrix of of conductive carbonaceous material. In this system the wire anode can be installed directly in a conductive asphaltic coke breeze overlay or inserted into a slot cut directly into a concrete surface. Likewise EP-A 85 582 describes a cathodic protection system using conductive polymer concrete in which anodic materials are positioned adjacent a concrete surface. Polymers are described as desirable because of their resistance to acid attack. US-A 4 422 917 discloses an electrode material of the formula TiOx, wherein x is from 1.55 to 1.95. The material may be used in a cathodic protection system in which the material forms the anode.
- By the present invention there is provided a cathodic protection system for the protection of iron or steel reinforcement bars in concrete which includes a source of electrical current connected to the reinforcement bars and to an anode, so that, in use, the reinforcement bars are connected as a cathode, wherein the anode is a hydraulically porous material permeable to water in the liquid state, which is bonded to the concrete so as to make electrical contact therewith and exposed to the environment over part of its surface area.
- A preferred material for the anode is porous TiOx where "x" is in the range 1.67 to 1.95. Preferably "x" is in the range of 1.75 to 1.8. The porous TiOx material is preferably in the form of a tile grouted to the exterior of the concrete. A liquid mortar may be used as the grout. The porous TiOx material may have a thickness in the range 2-3 mm. The density of the material may be in the range 2.3 to 3.5. The porous TiOx material may be in the form of a tube passing into a hole in the concrete structure.
- The porous material may be graphite or porous magnetite, porous high silicon iron or porous sintered zinc, aluminium or magnesium sheet.
- The porous material may be in the form of a tile bonded to the concrete, the tile having a projecting ear to which electrical contact can be made. The ear may be provided with a hole or slot. The ear may be connected to a power supply cable having an electrically conducting core and a lead metal exterior in electrical contact with the core, the lead being deformed by the action of being pushed into the slot to make electrical contact therewith.
- The titanium may be anodically passivated and may be coloured. The anodically passivated layer may be removed where the titanium is in contact with the TiOx material anodes.
- The titanium may be in the form of strips having sections cut and bent out of the plane of the strips to form tabs to which the anodes are connected. The anodes may be connected to the titanium strips by nuts and bolts of titanium or by a titanium rivet. The strips may mechanically locate the anodes on the concrete. The strips may be provided with slots.
- There may be a plurality of strips with the strips being bolted, riveted, welded or otherwise electrically joined together.
- By way of example embodiments of the present invention will now be described with reference to the accompanying drawings, of which:
- Figure 1 is a schematic view in section of a road bridge;
- Figure 2 is a schematic view of a support member of a bridge wired with a series of anodes;
- Figure 3 is a cross-section of a support member showing anodes and reinforcement bars;
- Figure 4 is a perspective view of one form of anode;
- Figure 5 is a perspective view of an alternative form of anode;
- Figure 6 is a schematic view of a concrete cross beam and pillars;
- -- Figure 7 is a schematic perspective view of an anode connected to a portion of a strip;
- Figures 8 and 9 are schematic views of tabs formed in titanium strip;
- Figure 10 is a schematic view of a connection between two titanium strips incorporating an anode at the connection;
- Figure 11 is a plan view of a strip with an anode embedded in concrete;
- Figure 12 is a perspective view of an anode and strip; and
- Figure 13 is a sectional view of an anode and strip.
- It is necessary to understand the causes of acidity to understand the present invention. In any electrolytic system involving anodes and cathodes, the overall reaction is the summation of component parts, which includes specific electrochemical reactions at both electrodes. In the case of an anode in concrete, the predominating reactions, albeit at very slow rate compared with most cathodic protection systems, is either the oxidation of chloride ions to release chlorine gas, or the oxidation of water to release oxygen and leave behind H+ ions. This latter reaction is the particularly important one, 2H20 - 4e → O2 + 4H+.
- For every 96,540 coulombs of electricity passed involving this reaction, 1g H+ will be produced. Such H+ concentration (which is, of course, acidic) will react with concrete, in a volume depending upon the available calcium hydroxide accessibility within the concrete. Thus a simple model can be considered. Hydrogen ions generated by the reaction set out above may:
- a) react with all the calcium compounds in the volume of concrete immediately surrounding the anode;
- b) depress the pH of the surrounding concrete to a low pH;
- c) migrate towards the OH- near the cathode;
- d) pass through the porous anode to be oxidised by the air; or
- e) pass through the porous anode and be diluted by the moisture from the atmosphere or rainwater.
- Short term (seven day) practical tests with a single anode passing 25mA suggests that the volume of concrete attacked will be 12cm3, and the pH depressed to a value of O. Assuming normal porosity, density and Ca(OH)2 content of concrete, the amount of H+ ion produced required to react with 12cm3 of concrete will be 0.036gH+.
- At a pH of O the H+ concentration will be 1 g/I H+ so that the H+ requirement to depress the pH of available moisture will be 0.012gH+. Therefore the total H+ generated to the anode over seven days would approximate to 0.036 + 0.012 = 0.048gH+.
- The number of coulombs of electricity passed in seven days is 15,120 coulombs. Assuming 30% current efficiency for oxygen evolution, the reaction 2H20 - 4e - 02 + 4H+ will result in 0.047gH+ ion generation. Hence it appears that a 25mA anode will produce between 0.05 to 0.1 gH+ per week. At 1 mA/anode the corresponding figure would be 0.002 to 0.004gH+ per week. At this rate it would take eighteen weeks to react all Ca(OH)2 in 12cm3 zone of concrete per week, and, of course, correspondingly longer time periods the lower the current passed or the volume of concrete affected.
- The calculations involved are approximate but while advanced at no detriment to the claims of the patent, are advanced as an indication of the magnitude of the problem of acid attack around anodes in concrete.
- Some indication of the effect of porous anodes in removing acidity has been obtained from laboratory experiments in which porous anodes were cemented to a reinforced concrete block and were kept saturated with water artificially by means of a surrounding shallow rim. With application of current to rebars within the concrete, acidity develops on the outer surface of the porous anode and after five hours of operation at 80mA at 8 volts the pH of the distilled water fell to 2.7.
- It should be noted that H+ ions generated at the anode/concrete interface diffused away from the cathode into water to the outer side of the anode, presumably because of the favourable concentration gradient.
- In a further experiment, hydraulically porous TJ407 material was used to divide the volume of a glass beaker into two approximately equal volumes. In one side was placed sodium chloride solution and a titanium metal strip cathode. In the other (representing the atmosphere side in the bridge deck) was put distilled water. With the hydraulically porous Ti407 separator connected as an anode and anodically polarised with respect to the titanium cathode, acidity developed with time in the initially distilled water compartment. Such acidity develops in spite of the good diffusivity of H+ ions in the sodium chloride side, ie H+ ions diffused in the "wrong" direction away from the cathode.
- Referring now to the drawings, as illustrated schematically in Figure 1, many road bridges are based on a series of upstanding pillars 1, 2 supporting a
cross member 3.Members 1, 2 and 3 are formed of reinforced concrete. Thecross members 3 carry a plurality of substantially rectangular section steel girders 4, 5 which carry the actual road bed 6. - As shown in Figures 2 and 3 there is provided a mechanism for cathodically protecting the rebars in the
structure 3. The rebars 7 (more clearly shown in Figure 3) are connected to a source of electrical current 8 as cathodes. A series of hydraulically porousTiOx tiles 9, 10 are grouted to the exterior of theconcrete structure 3 and an electrical connection is made to the tiles in a suitable manner. The preferred value for x is 1.75, but tiles where x is predominantly in the range 1.75 to 1.8 are acceptable. Electrodes of this material are described in US Patent 4 422 917, the description of which patent is incorporated herein by way of reference. - As the TiOx material will conduct electricity as an anode it may be used to pass an electrical current through the moisture in the concrete into the rebars 7. During operation anions such as CI- are attracted to the anodes and by using porous TiOx material the anions can diffuse through the TiOx to be oxidised by the air in the atmosphere or to be washed away by the irrigation of the anodes which will occur from rain water washing over the surface of the support structures, or by applied water irrigation.
- It will be appreciated that tubular anodes can be used. If necessary water could be directed through the anodes from gulleys on the road deck.
- By irrigating the anodes, excessive anion buildup in the concrete can be reduced.
- One method of connecting the anodes to the electrical conductor line is shown with reference to Figure 4. In Figure 4 the anode plate 11 is provided with an
upstanding ear 12 integral with the plate. Ahole 13 exposed through theear 12. Electrical contact is made by bolting or clamping a suitable wire through theaperture 13. - An alternative method of making a connection is illustrated in Figure 5. In the design of Figure 5 a
tile 14 of circular or eliptical shape is provided in the centre with three up-standingears slots slots slot 19. - A lead coated wire having a copper core is threaded around the
ears slots - An alternative mode of operation may be used containing TiOx as the electrical conducting constituent formed by packing powder into grooves in the concrete back-filled into grooves in the concrete.
- The current density which needs to be applied to the anodes is very low. Typically a current density of the order of 20 milliamps/m2 will protect the steel rebars. Thus for concrete structure 11/2 m2 by 14 m long, a total current number across being 1-21/2 amps would be sufficient. Operating 15 cm x 15 cm tiles at 5 amps/m2 would permit each tile to pass 0.1 amp so that 15-20 tiles per cross-beam would be sufficient.
- It will be appreciated that the number of tiles used would be determined by the required cathodic protection throwing power. Each anode would be electrically connected to the power source used for the impressed current cathodic protection system.
- The hydraulically porous TiOx material, particularly material having a density in the range 2.3 to 3.5 g/cc is readily bonded by cement to concrete and has the distinctly advantageous property of not being effected by water freezing within the pores of the material. As the material is hydraulically porous water as a liquid (rather than merely as a vapour) can pass through it; for example material of 3 mm thickness with a head of water of 30 cm will pass one litre of water per 5 cm2 of exposed surface area per day.
- Instead of using lead coated wires as connectors titanium strips may be used. The titanium strips may themselves have a coating to restrict corrosion of the strips in which case an oxide film formed by ano- dising is preferred. This arrangement is shown more clearly in Figures 6 to 13.
- Referring to Figure 6 this shows the
concrete cross beam 3 supported on the pillars 1, 2. The beam is a conventional steel rebar reinforced concrete structure. The pillars 1 and 2 are also conventional concrete with steel rebars. Extending along the length of thebeam 3 is atitanium strip 21 and extending vertically from the strip is a plurality of strips, two of which are shown at 22, 23. The entire length of the concrete beam 1 will be covered bystrips strip 21 and avertical strip 24 is connected to thestrip 21.Strip 24 is connected to a suitable source of electrical current as an anode and a suitable connection is made to the steel reinforcement within thebeam 3 as a cathode. Thus electricity can be conducted alongstrips strips anode 25 are of a ceramic-like material and are bolted to tabs formed integrally in thestrip 26. The tabs are shown in more detail as 27 and 28 in thestrips - As can be seen in Figure 10 the tabs can be formed as connectors for
adjacent strips anode 33. The anodes are secured by means of titanium nuts andbolts 34. - The anodes may be embedded into holes drilled into the concrete and are grouted into position as shown in Figure 11. The
anode 35 is surrounded bygrout 36 located in theconcrete structure 37. The anode is bolted totitanium strip 38. - By this system the permanently connected anodes can be distributed over the surface of the
beam 3 and of course, if required, over the surface of the upright pillars 1, 2. Any other structure can simultaneously be protected. - Because the concrete grout securing the anodes may well become weak during operation, even if it is one chosen for its acid resistance such as a high alumina cement, it is probably desirable to use mechanical means to hold the anodes in situ in addition to the grout. The titanium strips can carry out both functions of supplying current to the anodes and holding the anodes in situ. When such a system is used, slotted strips 39 (Figures 12 and 13) can be used. To install such a system, initially the position of the shear (longitudinal) rebars in the material is located, marked out with chalk, and thus enabling the location of the hydraulically porous tile anodes to be marked in approximate position. The hydraulically porous tile used measured 50 mm x 50 mm and had a hole drilled in one location to take a
titanium metal nut 40 andbolt 41. Theconnector strip 39 of slotted titanium had a width of 20 mm and was 0.5 mm thickness. By means of a self tapping screw, the strip is located at its upper end, leaving slot locations for the anode and defining positions for the self tapping holding screws 42. Because of large aggregate in the concrete cover, it is difficult to drill holes exactly in the concrete, thus the use of the slots facilitated installation. Then the anode tiles are grouted at locations down the strip and thetitanium nuts 40 screwed loosely in position and the self tapping screws 42 screwed into position while the acid resisting cement is still soft. This sequence is progressed along the side of the beam. - When the electrically conducting and chemically resistant grout has hardened, the nuts to the anodes are tightened, and a horizontal linking titanium strip connector applied.
- The horizontal connector will also be attached to the concrete structure, but only after all other positioning had been completed. The system can then be used to protect the rebars.
- Obviously the cathodic protection system could be used to protect rebars in concrete in any situation, for example car parks, foundations, marine structures etc. In the case of bridges the system can be installed on the underside of the bridge deck itself to protect the bridge deck. This installation can be done without interfering with the traffic flow.
Claims (17)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AT85308692T ATE50291T1 (en) | 1984-12-15 | 1985-11-29 | CATHODIC PROTECTION SYSTEM FOR BARS IN REINFORCED CONCRETE, METHOD OF IMPLEMENTING SUCH PROTECTION AND AN ANODE FOR USE IN THE METHOD AND SYSTEM. |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB848431714A GB8431714D0 (en) | 1984-12-15 | 1984-12-15 | Cathodic protection system |
GB8431714 | 1984-12-15 |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0186334A1 EP0186334A1 (en) | 1986-07-02 |
EP0186334B1 true EP0186334B1 (en) | 1990-02-07 |
Family
ID=10571253
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP85308692A Expired - Lifetime EP0186334B1 (en) | 1984-12-15 | 1985-11-29 | Cathodic protection system for reinforcing bars in concrete, a method of carrying out such protection and an anode for use in the method and system |
Country Status (6)
Country | Link |
---|---|
EP (1) | EP0186334B1 (en) |
JP (1) | JPS61186487A (en) |
AT (1) | ATE50291T1 (en) |
CA (1) | CA1279606C (en) |
DE (1) | DE3575953D1 (en) |
GB (1) | GB8431714D0 (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN103205755A (en) * | 2013-04-16 | 2013-07-17 | 深圳大学 | Cathode protection method and cathode protection device for reinforced concrete adopting CFRP (carbon fibre reinforced plastics) embedded anode |
Families Citing this family (12)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0264421B1 (en) * | 1986-05-02 | 1992-08-26 | Norwegian Concrete Technologies A.S. | Electrochemical re-alkalization of concrete |
US4912286A (en) * | 1988-08-16 | 1990-03-27 | Ebonex Technologies Inc. | Electrical conductors formed of sub-oxides of titanium |
GB2309978A (en) * | 1996-02-09 | 1997-08-13 | Atraverda Ltd | Titanium suboxide electrode; cathodic protection |
US6217742B1 (en) * | 1996-10-11 | 2001-04-17 | Jack E. Bennett | Cathodic protection system |
GB9802805D0 (en) * | 1998-02-10 | 1998-04-08 | Atraverda Ltd | Electrochemical treatment of reinforced concrete |
US8999137B2 (en) | 2004-10-20 | 2015-04-07 | Gareth Kevin Glass | Sacrificial anode and treatment of concrete |
US8211289B2 (en) | 2005-03-16 | 2012-07-03 | Gareth Kevin Glass | Sacrificial anode and treatment of concrete |
GB0505353D0 (en) | 2005-03-16 | 2005-04-20 | Chem Technologies Ltd E | Treatment process for concrete |
GB0604545D0 (en) * | 2006-03-07 | 2006-04-19 | Roberts Adrian C | Electrical connection |
JP4978861B2 (en) * | 2008-02-01 | 2012-07-18 | 株式会社ピーエス三菱 | Electrocorrosion protection method for existing PC girder ends |
JP5461093B2 (en) * | 2009-07-27 | 2014-04-02 | 国立大学法人九州大学 | Sacrificial anode panel and anticorrosion method using sacrificial anode panel |
EP2918568B1 (en) | 2014-03-14 | 2016-08-17 | Sociedad Anónima Minera Catalano-Aragonesa | Ceramic compositions and method of manufacture of ceramic electrodes comprising said compositions |
Family Cites Families (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4255241A (en) * | 1979-05-10 | 1981-03-10 | Kroon David H | Cathodic protection apparatus and method for steel reinforced concrete structures |
US4422917A (en) * | 1980-09-10 | 1983-12-27 | Imi Marston Limited | Electrode material, electrode and electrochemical cell |
EP0085582A1 (en) * | 1982-02-05 | 1983-08-10 | Harco Corporation | Cathodic protection using conductive polymer concrete |
-
1984
- 1984-12-15 GB GB848431714A patent/GB8431714D0/en active Pending
-
1985
- 1985-11-29 EP EP85308692A patent/EP0186334B1/en not_active Expired - Lifetime
- 1985-11-29 AT AT85308692T patent/ATE50291T1/en active
- 1985-11-29 DE DE8585308692T patent/DE3575953D1/en not_active Expired - Lifetime
- 1985-12-06 CA CA000497082A patent/CA1279606C/en not_active Expired - Fee Related
- 1985-12-16 JP JP60282706A patent/JPS61186487A/en active Pending
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN103205755A (en) * | 2013-04-16 | 2013-07-17 | 深圳大学 | Cathode protection method and cathode protection device for reinforced concrete adopting CFRP (carbon fibre reinforced plastics) embedded anode |
CN103205755B (en) * | 2013-04-16 | 2015-11-18 | 深圳大学 | CFRP is adopted to embed protecting reinforced concrete cathode method and the device of anode |
Also Published As
Publication number | Publication date |
---|---|
CA1279606C (en) | 1991-01-29 |
GB8431714D0 (en) | 1985-01-30 |
DE3575953D1 (en) | 1990-03-15 |
ATE50291T1 (en) | 1990-02-15 |
JPS61186487A (en) | 1986-08-20 |
EP0186334A1 (en) | 1986-07-02 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
Pedeferri | Cathodic protection and cathodic prevention | |
AU680694B2 (en) | Ionically conductive agent, system for cathodic protection of galvanically active metals, and method and apparatus for using same | |
EP0186334B1 (en) | Cathodic protection system for reinforcing bars in concrete, a method of carrying out such protection and an anode for use in the method and system | |
CA2880235C (en) | Galvanic anode and method of corrosion protection | |
US6358397B1 (en) | Doubly-protected reinforcing members in concrete | |
CA2426289C (en) | Cathodic protection of steel in reinforced concrete with electroosmotic treatment | |
US20150167178A1 (en) | Galvanic anode and method of corrosion protection | |
US5639358A (en) | Cathodic protection system for a steel-reinforced concrete structure | |
JPS62263986A (en) | Cathodic anti-corrosion of reinforced concrete contacted with conductive liquid | |
EP0222829B2 (en) | Cathodic protection system for a steel-reinforced concrete structure and method of installation | |
GB2271123A (en) | Electrochemical stabilisation of mineral masses such as concrete,and electrode arrangements therefor | |
CA1314518C (en) | Cathodic protection system for reinforced concrete including anode of valve metal mesh | |
US7338591B2 (en) | Method for the cathodic prevention of reinforcement corrosion on damp and wet marine structures | |
EP4139499B1 (en) | Anode assembly for corrosion control of steel reinforced concrete structures | |
Hayfield et al. | Titanium based mesh anode in the catholic protection of reinforcing bars in concrete | |
Bennett | Corrosion of reinforcing steel in concrete and its prevention by cathodic protection | |
Polder et al. | A multi-element approach for cathodic protection of reinforced concrete | |
van den Hondel et al. | Long term performance of reference electrodes for cathodic protection of steel in concrete | |
EP0197981A1 (en) | Catalytic polymer electrode for cathodic protection and cathodic protection system comprising same. | |
Davison et al. | Electrochemical systems for repair of reinforced concrete structures | |
PSA | 30 CATHODIC PROTECTION OF PORTCULLIS HOUSE: PSA 5-YEAR TRIAL PROVES THE SYSTEM CC MORTON PSA Specialist Services, DCES, Croydon, UK | |
NO170291B (en) | CATHODIC PROTECTED, STEEL ALARMED CONCRETE CONSTRUCTION AND PROCEDURE FOR AA INSTALLING A COATED VALVE METAL ELECTRODE A CATHODIC PROTECTION SYSTEM FOR SUCH A CONSTRUCTION |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
PUAI | Public reference made under article 153(3) epc to a published international application that has entered the european phase |
Free format text: ORIGINAL CODE: 0009012 |
|
AK | Designated contracting states |
Kind code of ref document: A1 Designated state(s): AT BE CH DE FR GB IT LI LU NL SE |
|
17P | Request for examination filed |
Effective date: 19860905 |
|
17Q | First examination report despatched |
Effective date: 19870911 |
|
RAP1 | Party data changed (applicant data changed or rights of an application transferred) |
Owner name: EBONEX TECHNOLOGIES, INC. |
|
GRAA | (expected) grant |
Free format text: ORIGINAL CODE: 0009210 |
|
AK | Designated contracting states |
Kind code of ref document: B1 Designated state(s): AT BE CH DE FR GB IT LI LU NL SE |
|
ITF | It: translation for a ep patent filed |
Owner name: BARZANO' E ZANARDO MILANO S.P.A. |
|
REF | Corresponds to: |
Ref document number: 50291 Country of ref document: AT Date of ref document: 19900215 Kind code of ref document: T |
|
ET | Fr: translation filed | ||
REF | Corresponds to: |
Ref document number: 3575953 Country of ref document: DE Date of ref document: 19900315 |
|
PGFP | Annual fee paid to national office [announced via postgrant information from national office to epo] |
Ref country code: FR Payment date: 19901030 Year of fee payment: 6 |
|
PGFP | Annual fee paid to national office [announced via postgrant information from national office to epo] |
Ref country code: LU Payment date: 19901107 Year of fee payment: 6 |
|
PGFP | Annual fee paid to national office [announced via postgrant information from national office to epo] |
Ref country code: GB Payment date: 19901119 Year of fee payment: 6 |
|
PLBE | No opposition filed within time limit |
Free format text: ORIGINAL CODE: 0009261 |
|
STAA | Information on the status of an ep patent application or granted ep patent |
Free format text: STATUS: NO OPPOSITION FILED WITHIN TIME LIMIT |
|
ITTA | It: last paid annual fee | ||
PG25 | Lapsed in a contracting state [announced via postgrant information from national office to epo] |
Ref country code: LU Free format text: LAPSE BECAUSE OF NON-PAYMENT OF DUE FEES Effective date: 19901130 |
|
PGFP | Annual fee paid to national office [announced via postgrant information from national office to epo] |
Ref country code: NL Payment date: 19901130 Year of fee payment: 6 Ref country code: AT Payment date: 19901130 Year of fee payment: 6 |
|
PGFP | Annual fee paid to national office [announced via postgrant information from national office to epo] |
Ref country code: BE Payment date: 19910114 Year of fee payment: 6 |
|
26N | No opposition filed | ||
PGFP | Annual fee paid to national office [announced via postgrant information from national office to epo] |
Ref country code: CH Payment date: 19910207 Year of fee payment: 6 |
|
EPTA | Lu: last paid annual fee | ||
PG25 | Lapsed in a contracting state [announced via postgrant information from national office to epo] |
Ref country code: GB Effective date: 19911129 Ref country code: AT Effective date: 19911129 |
|
PG25 | Lapsed in a contracting state [announced via postgrant information from national office to epo] |
Ref country code: LI Effective date: 19911130 Ref country code: CH Effective date: 19911130 Ref country code: BE Effective date: 19911130 |
|
BERE | Be: lapsed |
Owner name: EBONEX TECHNOLOGIES INC. Effective date: 19911130 |
|
PG25 | Lapsed in a contracting state [announced via postgrant information from national office to epo] |
Ref country code: NL Effective date: 19920601 |
|
NLV4 | Nl: lapsed or anulled due to non-payment of the annual fee | ||
GBPC | Gb: european patent ceased through non-payment of renewal fee | ||
PG25 | Lapsed in a contracting state [announced via postgrant information from national office to epo] |
Ref country code: FR Effective date: 19920731 |
|
REG | Reference to a national code |
Ref country code: CH Ref legal event code: PL |
|
REG | Reference to a national code |
Ref country code: FR Ref legal event code: ST |
|
PGFP | Annual fee paid to national office [announced via postgrant information from national office to epo] |
Ref country code: SE Payment date: 19921116 Year of fee payment: 8 |
|
PGFP | Annual fee paid to national office [announced via postgrant information from national office to epo] |
Ref country code: DE Payment date: 19921212 Year of fee payment: 8 |
|
PG25 | Lapsed in a contracting state [announced via postgrant information from national office to epo] |
Ref country code: SE Effective date: 19931130 |
|
PG25 | Lapsed in a contracting state [announced via postgrant information from national office to epo] |
Ref country code: DE Effective date: 19940802 |
|
EUG | Se: european patent has lapsed |
Ref document number: 85308692.4 Effective date: 19940610 |