Cathodic corrosion protection system with rebar mounting assembly

Abstract

In a method for cathodically protecting and/or passivating a metal section in an ionically conductive material such as steel reinforcement in concrete or mortar, an impressed current or sacrificial anode communicates ionic current to the metal section and a storage component of electrical energy which can be a cell, battery or capacitor is provided as a component of the anode. The storage component can have replacement energy introduced by re-charging or replacing the component from an outside supply. Typically the cell or storage capacitor has an outer case which carries an anode material as an integral outer component. A mechanical clamp is provided to attach the assembly to a rebar. A current limiter is provided which prevents excess current draining the supply.

Claims

1. A reinforced structure comprising: an ionically conductive concrete or mortar material; a generally cylindrical metal reinforcing bar embedded in the concrete or mortar material; an exterior surface of the generally cylindrical metal reinforcing bar being in direct connection with the concrete or mortar material for flow of ionic current therebetween; an anode assembly acting to protect and/or passivate the generally cylindrical metal reinforcing bar, the anode assembly comprising: an anode at least partly embedded within the concrete or mortar material and ionically connected to the concrete or mortar material so that a voltage difference is generated between the anode and the generally cylindrical metal reinforcing bar so as to cause a current to flow through the concrete or mortar material between the anode and the generally cylindrical metal reinforcing bar so as to provide cathodic protection of the generally cylindrical metal reinforcing bar; and a mounting assembly fixedly mounting the anode on the generally cylindrical metal reinforcing bar so as to be supported by the generally cylindrical metal reinforcing bar within the concrete or mortar material and electrically connected to the generally cylindrical metal reinforcing bar such that the electrical current flows from the anode to the generally cylindrical metal reinforcing bar; the mounting assembly comprising: an elongate male threaded rod attached to and extending forwardly from the anode and having a forward end of the elongate male threaded rod forward of the anode, the elongate male threaded rod being electrically conductive so that the forward end is in electrical connection with a first surface portion of the exterior surface of the generally cylindrical metal reinforcing bar; a female threaded nut member into which the elongate male threaded rod engages; an electrically conductive member extends from the female threaded nut portion angularly of the generally cylindrical metal reinforcing bar at least to a position on the generally cylindrical metal reinforcing bar generally diametrically opposed to said first surface portion to form at a least portion of the electrically conductive member in engagement with a second surface portion of the generally cylindrical metal reinforcing bar at said position; the female threaded nut being arranged such that rotation of the elongate male threaded rod therein acts to draw said at least a portion of the electrically conductive member in engagement with the second surface portion toward the forward end of the elongate male threaded rod in engagement with the first surface portion for clamping the generally cylindrical metal reinforcing bar therebetween; wherein the electrically conductive member includes at least two further surface portions each angularly spaced around the generally cylindrical metal reinforcing bar to respective sides of said second surface portion; each said further surface portion being in direct electrical connection with a respective portion of the exterior surface of the generally cylindrical metal reinforcing bar.

2. The reinforced structure according to claim 1 wherein the electrically conductive member comprises first and second parallel plates spaced longitudinally along the generally cylindrical metal reinforcing bar and connected together by a connecting member for common engagement with the metal reinforcing bar, wherein said at least two further surface portions comprise at least four further surface portions, wherein said first parallel plate has a first plate edge with two of said at least four further surface portions thereon and wherein said second parallel plate has a second plate edge with two of said at least four further surface portions thereon.

3. The reinforced structure according to claim 1 the anode is attached to the elongate male threaded rod so that rotation of the anode drives rotation of the forward end of the elongate male threaded rod relative to the first surface portion of the generally cylindrical metal reinforcing bar.

4. The reinforced structure according to claim 1 wherein the forward end of the elongate male threaded rod includes one or more projections biting into the generally cylindrical metal reinforcing bar.

5. The reinforced structure according to claim 1 wherein the female threaded nut member is fixed to the electrically conductive member so that rotation of the elongate male threaded rod causes the electrically conductive member to be pulled toward the anode.

6. The reinforced structure according to claim 1 wherein the elongate male threaded rod member is rigidly coupled to the anode to fixedly hold the anode at a predetermined distance and orientation relative to the generally cylindrical metal reinforcing bar.

7. The reinforced structure according to claim 1 wherein the electrically conductive member comprises a hook portion which has teeth at an edge of the hook portion for biting into the generally cylindrical metal reinforcing bar.

8. The reinforced structure according to claim 1 wherein the anode assembly comprises a storage component of electrical energy with first and second poles communicating electrical current generated by release of the electrical energy, the first pole having an electrical connection to the anode and the mounting assembly being connected to the second pole for electrical connection of the second pole to the generally cylindrical metal reinforcing bar.

9. The reinforced structure according to claim 8 wherein the anode and the storage component are both at least partly contained in the ionically conductive concrete or mortar material.

10. The reinforced structure according to claim 9 wherein the storage component is connected as a single unit with the anode.

11. The reinforced structure according to claim 9 wherein the storage component is contained within a closed or sealed canister defining the anode on an exterior surface.

12. The reinforced structure according to claim 11 wherein the anode comprises stainless steel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will now be described in conjunction with the accompanying drawings in which:

(2) FIG. 1 is a cross-sectional view of an anode assembly for use in a corrosion protection method according to the present invention.

(3) FIG. 2 is an enlarged view of the current limiting circuit for use with a cell and the mounting of the first abutment on the anode body.

(4) FIG. 2A is a schematic illustration of the current limiting circuit for use with a galvanic anode which uses a battery voltage to generate the reference current.

(5) FIG. 2B is a schematic illustration of the current limiting circuit for use with a galvanic anode which uses two anodes where the second anode is used to generate the reference current.

(6) FIG. 2C is a schematic illustration of the current limiting circuit for use with a system in which both an impressed current anode with the battery supply and a galvanic anode are used and wherein the voltage across the resistor is used to control the FET.

(7) FIG. 3 is a front elevational view of an anode assembly similar to that of FIG. 1 where the anode body uses a sacrificial anode.

(8) FIG. 4 is an isometric view of the anode assembly of FIG. 3.

(9) FIG. 5 is a top plan view of an anode assembly similar to that of FIG. 1 laid in a patch repair in a concrete assembly ready for the addition of fresh unset concrete to be applied to the patch.

(10) In the drawings like characters of reference indicate corresponding parts in the different figures.

DETAILED DESCRIPTION

(11) In the example shown in FIG. 1 there is provided a cell which may be rechargeable, as shown in prior co-pending application Ser. No. 15/341,532 filed Nov. 2, 2016, the disclosure of which may be referenced or is incorporated herein by reference, or may be a simple non-rechargeable cell. The cell may form part of the anode structure or the anode and the cell may be physically separated. As shown in FIG. 1, an anode body 10 is defined by a typical alkaline manganese dioxide-zinc rechargeable cell comprises the following main units: a steel can 12 defining a cylindrical inner space, a manganese dioxide cathode 14 formed by a plurality of hollow cylindrical pellets 16 pressed in the can, a zinc anode 18 made of an anode gel and arranged in the hollow interior of the cathode 14, and a cylindrical separator 20 separating the anode 18 from the cathode 14. The ionic conductivity (electrolyte) between the anode and the cathode is provided by the presence of potassium hydroxide, KOH, electrolyte added into the cell in a predetermined quantity. Other types of rechargeable cells comprise similar main components (can, cathode, anode, separator and electrolyte) but the composition of the components may differ. Some of the types of cell may however be of a different construction such as lead/acid cells or lithium cells.

(12) The can 12 is closed at the bottom, and it has a central circular pip 22 serving as the positive terminal. The upper end of the can 12 is hermetically sealed by a cell closure assembly which comprises a negative cap 24 formed by a thin metal sheet, a current collector nail 26 attached to the negative cap 24 and penetrating deeply into the anode gel to provide electrical contact with the anode, and a plastic top 28 electrically insulating the negative cap 24 from the can 12 and separating gas spaces formed beyond the cathode and anode structures, respectively.

(13) The material of separator 20 consists of two different materials, i.e.: a first material 30 made of fibrous sheet material wettable by the electrolyte, and a second material 32 being impermeable to small particles but retaining ionic permeability. An expedient material for the first layer is a sheet material of non-woven polyamide fiber, which is absorbent and serves as a reservoir for electrolyte. The macro-porous structure of the absorbent layer cannot prevent internal shorting by zinc dendrites or deposits during discharge/charge cycling.

(14) Shorting is prevented by the second 32 material which may be a layer or layers of micro-porous or non-porous material which may be laminated to or coated onto the fibrous sheet material. One suitable material is one or more cellophane membranes laminated to the non-woven polyamide sheet. Another is one or more coatings of regenerated cellulose or viscose coated onto and partially impregnating the non-woven polyamide sheet, resulting in a composite material.

(15) Other types of rechargeable cells may be used. In the present arrangement, the type described above is used in a method for cathodically protecting and/or passivating a metal section such as steel reinforcing bar 40 in an ionically conductive material such as concrete 41. The cell therefore includes a first terminal 42 and a second terminal 43 defined by the outer casing 12. The first terminal 42 is connected to the pin or nail 26 which is engaged into the anode material 18. The terminal 42 connects to a connecting wire 42A which extends from the terminal 42 for eventual connection to the steel reinforcing bar 40 as shown in FIG. 1 through the mounting assembly generally indicated at 50 which mechanically and electrically attaches the anode body to the bar 40.

(16) In FIG. 1, an anode 44 is applied as a coating onto the casing 12 of the cell. In this embodiment the anode 44 is of an inert material so that it is more noble than steel. Examples of such materials are well known. Thus the anode material 44 does not corrode or significantly corrode during the cathodic protection process.

(17) In this arrangement the application of the anode 44 onto the outside surface of the casing 12 provides the structure as a common single unit where the anode is directly connected to the cell and forms an integral element with the cell. Anode 44 may comprise one or more layers and may include a mixed metal oxide (MMO), catalytic or sub-oxide layer.

(18) In this embodiment, as the anode 44 is formed of an inert material which does not corrode in the protection process, the anode and the cell contained therein can be directly incorporated or buried in the concrete or other ionically conductive material without the necessity for an intervening encapsulating material such as a porous mortar matrix. As there are no corrosion products there is no requirement to absorb such products or the expansive forces generated thereby. As the process does not depend upon; continued corrosion of a sacrificial anode, there is no necessity for activators at the surface of the anode. As the chemical reaction at the surface of any inert anode during operation generates acid (or consumes alkali) it is beneficial for the anode to be buried in an alkaline material such as concrete or high alkalinity mortar to prevent material near the anode from becoming acidic. If desired, additional alkali may be added to the concrete or other material the anode is in contact with.

(19) The apparatus shown herein includes an anode body generally indicated at 10 which is connected to the reinforcing bar 40 by the mounting assembly generally indicated at 50. In addition, the anode body includes a current limiting system generally indicated at 51 which limits the flow of current from the anode body to the bar 40.

(20) As previously described, the anode body can be defined by a power supply typically in the form of a cell with the anode 44 on the outside surface of the cell and with the other terminal of the cell provided at the end of the cell for connection to the bar 40.

(21) In other embodiments described hereinafter the cell can be omitted in which case the anode body comprises a sacrificial material which is less noble than the steel rebar, such as zinc where a voltage between the anode and the bar comprises the galvanic voltage between the two metal components.

(22) In yet another embodiment, the anode body can comprise a combination of both an impressed current anode and a sacrificial anode.

(23) In this way the anode body is constructed and arranged so that when the anode is ionically connected to the concrete, a voltage difference is generated between the anode 44 and the bar 40 so as to cause a current to flow through the concrete between the anode and the bar 40 so to provide cathodic protection and/or passivation of the reinforcing bar in the concrete.

(24) In the embodiment shown in FIGS. 1, 3 and 4, the mounting assembly 50 comprises a first abutment 52 in the form of a threaded rod 53 which is attached at one end to the anode body 10. An opposed end 54 of the threaded rod forms a front face for engaging one side face of the bar 40. As shown in FIGS. 2 and 4, the end face 54 of the threaded rod 53 includes a peripheral circular edge 55 and intervening projections 56 which are arranged to bite into the surface of the bar 40 when in compressed contact therewith.

(25) The mounting assembly 50 further comprises a second abutment 57 for engaging generally the opposed the face of the bar 40 at a surface 58. In general the second abutment forms a hook member which contacts the opposite or rear surface of the bar 40 at least at two positions 59 and 60 on either side of a diameter 61 extending through the bar 40 from the face 54. In this way the bar 40 is contacted by three points 54, 59 and 60 which are spaced around the axis 62 of the bar system to provide a stable engagement.

(26) The hook member defined by the surfaces 59 and 60 forms a part of a C-shaped structure 63 with a bottom crossmember 64 and a top crossmember 65 carrying the surfaces at 59 and 60. These cross members are interconnected by an outwardly extending leg 66 which extends parallel to the threaded rod 53. The crossmember 64 includes a flange 67 at right angles to the threaded rod 53 with a threaded hole 68 through the flange which acts as a nut on the threaded rod so the rotation on the threaded rod causes the nut to be driven toward the anode body to pull the surfaces 59 and 60 toward the surface 54 to clamp the bar 40 therebetween.

(27) The surfaces 59 and 60 can also be formed with teeth or other projections 59A or a sharp cutting edge 59B which bite into the surface of the bar 40 and cooperate with the teeth 55 and 56 of the face 54. In this way a strong physical connection is provided between the first and second abutment and the bar 40 and also a strong electrical connection is provided between the rod 53 and the bar 40. These teeth or sharp cutting edges on some or all contacting surfaces can bite into any contaminant such as corrosion or concrete residue on the surface of the rebar to ensure an effective engagement and electrical contact with the metal of the rebar. That is each of the first and second abutment members includes components for cutting into a surface of the reinforcing bar thus avoiding the necessity to clean the surface of the bar.

(28) In accordance with another independent feature of the invention, in order to ensure that the projections and cutting edges provide the necessary engagement with the metal of the rebar, a sensor can be provided which measures the effectiveness of the connection. This can be done for example by measuring the resistance across the connection by bridging the rebar and a point on the connection to ensure that the resistance of the connection meets the necessary low level of resistance. This output is provided to an indicator to output to the installer an indication for example visually or audibly as to whether the connection properly meets the set standard.

(29) The hook member can comprise a single body on one side of the rod 53. However as best shown in FIG. 4, typically the hook member is formed by two separate hook portions 68 and 69 connected by a backplate 70. In this way the rod 53 is contained between the portions of 68 and 69 and in front of the backplate 70. The hook portions of 68 and 69 each include surfaces 59 and 60 which engage the rear surface of the bar 40. Thus the forces pulling the second abutment member toward the anode body pull on both hook portions and on both surfaces 59 and 60 providing four points of engagement which cooperate with the single point of engagement from the surface 54 of the rod 53.

(30) In this embodiment the female threaded portion is provided by a threaded hole through the flange 67. A screw action pulling the second abutment member toward the anode body is therefore provided by rotating the rod 53. This can most effectively be done by grasping manually the anode body and using it as a handle to turn the rod 53. Of course this requires a strong connection between the bottom end of the rod 53 and the anode body. In the arrangement shown in FIG. 2, this connection is provided by a base plate 71 attached onto the bottom end of the rod 53 and engaged firmly into the upper end of the anode body. In an arrangement using a solid anode 74 of a sacrificial material, the rod 53 can be cast into the interior of the anode body to provide the necessary structural and electrical connection. In FIG. 3, the solid anode body 74 includes a conventional covering of a mortar material 75 for purposes of retaining corrosion products and of carrying conventional activating materials described herein before.

(31) In another arrangement (not shown) the female threaded portion engaged on the rod 53 can be formed by a separate nut which itself can rotate relative to the second abutment member on the flange and 67. In this embodiment rather than rotate the rod, the nut can be rotated to drive the flange 67 toward the anode body. Other arrangements of threaded connection are also possible to drive the second abutment member toward the anode body. In another example, the hook is part of the anode body and the screw is turned to press the rebar against the hook.

(32) A sensor 401 is provided which measures the effectiveness of the connection for example by measuring the resistance across the connection by terminals 403, 404 bridging the rebar and a point on the connection to ensure that the resistance of the connection meets the necessary low level of resistance. This output is provided to an indicator 402 to output to the installer an indication for example visually or audibly as to whether the connection properly meets the set standard.

(33) Turning now to FIG. 2, there is shown in more detail the connection between the terminal 42 of the cell and the rod 53 which is electrically connected to the bar 40 as described above.

(34) The terminal 42 is connected to a wire 42A which in turn is connected to a transistor 78. An output wire 79 of the transistor 78 is connected to the base plate 71 connected to the rod 53.

(35) The transistor 78 can be a conventional transistor in which case a base of the transistor 78 has a control current provided by a wire 80 connected through a resistor 81 in turn connected through a wire 82 to the positive terminal of the battery connected to the anode 44.

(36) The transistor 78 can also be an FET in which case the wire 80 controls a gate of the FET through the resistor 81.

(37) As the transistor 78 is connected to the steel bar 40 and the wire 82 is connected to the anode 44, the control current to the transistor 78 is determined by the voltage across the cell and the resistance of resistor 81. As this voltage is typically relatively constant at least until the cell is in its later stages of life, this constant control current controls the amount of current flowing through the transistor from the cell to the bar 40. As is well known the resistor 81 can be selected to provide a control base current to the transistor which sets the current flow through the transistor to a maximum value. This maximum value is retained regardless of the conductivity between the anode 44 and the bar 40 through the concrete. As the conductivity through the concrete is very high, for example during an initial installation, the current is maintained at the maximum value. As the conductivity through the concrete falls to a lower level, the current is maintained at the desired level until the maximum voltage of the cell is reached. If the conductivity falls to a yet lower level, the current through the transistor also falls dependent upon the conductivity and is not maintained by the action of the transistor. The simple circuit therefore provided by the resistor and the transistor does not act as a regulator but instead merely acts as a current limiter.

(38) FIGS. 2A and 2B show applications of the current limiting device in use with a galvanic anode.

(39) FIG. 2A shows galvanic anode 86 connected to transistor 78. A separate battery 87 is connected to resistor 81 and is connected to transistor 78 to provide the control current to the transistor such that the transistor controls the maximum current flowing to the bar 40.

(40) FIG. 2B shows a galvanic anode 88 connected to transistor 78. In this case the control current to the transistor is provided by a second galvanic anode 89 and resistor 81. As in the example described above, the control current controls the maximum current flowing to the bar 40.

(41) FIG. 2C shows a current limiting circuit for use with a system in which both an impressed current anode 10 with the battery supply and a galvanic anode 90 are used and wherein the voltage across the resistor 81 is used to control the FET 78. The output from the anode 10 and the anode 90 is added downstream of the FET and the current from the anode 10 generated by the battery is limited using the current limiting circuit. In this way the current from the impressed current anode is used to top up the current from the galvanic anode to maintain a current which is adequate to provide the required protection. As is known the current from the anode 90 can vary due to changing conditions in the concrete so that the top up from the battery is used only when required. As the current taken from the battery is now limited, the system can be designed such that the life of the battery can match the life of the anode 90.

(42) If the electrical circuit includes a normally closed FET, the FET can allow current to flow unimpeded from the galvanic anode 86 to the bar 40 after the separate battery or separate galvanic anode described above ceases to function.

(43) This limitation of the current to a maximum value set during manufacture by the selection of the resistor 81 can ensure that the current remains during the life of the system at a relatively low level so as to dramatically increase the lifetime of the cell from a typical value in the absence of the current limiter which could be of the order of one year up to a more suitable lifetime of 10 years for example. In this way the current is maintained at a value which is suitable for cathodic protection but at no time is there any excess current over and beyond this desirable value which may damage the concrete or deplete the cell prematurely such that corrosion protection is not provided for the desired timeframe.

(44) This arrangement is particularly valuable in relation to an arrangement which uses a non-sacrificial impressed current anode and a cell as the power supply for generating the required voltage. In such an arrangement the current generated between the anode 44 and the bar 40 can in some circumstances significantly exceed the desirable value. In addition the mechanical mounting of the anode body on the reinforcing bar provides an effective electrical connection. Furthermore the strong physical connection between the anode body and the bar ensures that the anode body can be located at a required orientation relative to gravity such as where the anode body is to one side of the bar or above the bar as required.

(45) In order to connect the terminal 42 to the rod 53, there is provided an insulating or protective collar 83 surrounding the transistor 78 and the resistor 81. The bottom end of the collar is attached to the top end of the cell and the top end of the collar receives the base plate 71 in a suitable receptacle portion. The collar 83 is attached to the cell 44 by a surrounding insulating layer 84 of a suitable plastic material. Inside the collar 83 is provided a conventional potting material 85 which surrounds the electrical components and wires to maintain connection and to prevent damage from moisture penetration. The structure is thus sufficiently strong to ensure that the base plate 71 is attached to the cell in a manner which allows the cell to be grasped manually and rotated as an operating handle to rotate the rod 53.

(46) As shown in FIG. 5, and anode body generally indicated at 90 is mounted within a patch repair 91 in a concrete material 92. The anode body includes a mounting assembly 50 as previously described including a rod 53 and a hook portion 57. In this embodiment the anode body 90 is formed of a cell 93 and portion 94 of a sacrificial material. The cell 93 has an outer surface 95 which acts as an impressed current anode. The cell has a terminal 96 which is attached by a wire 97 including a diode 98 which transmits voltage from the terminal 96 to the rod 53. During an initial operating period, therefore, the system operates primarily as an impressed current system where the cell generates a majority of the flowing current between the anode at 95 and the bar 40. However when the cell is depleted, the cathodic protection is taken over by the sacrificial anode 94 which is directly connected to the rod 53. In this arrangement the diode 98 prevents the reverse flow of current through the cell 93 which could act to reverse the sacrificial process and instead more actively corrode the steel. The cell 93 and the anode 94 are suitably connected by a structural mounting element 99 shown only schematically which physically attaches the cell to the anode 94 sufficiently to prevent the cell from breaking away from the anode during installation.

(47) As shown in FIG. 5, the anode body 90 stands outwardly to one side of the bar 40 horizontally within the patch. In this way the anode body is supported at a spaced position from the bar 40 defined by the length of the rod 53 and the mechanical connection of the clamping assembly. The mechanical connection of the clamping assembly ensures that the anode body remains in its horizontally extending orientation during the filling of the patch 91 with additional concrete. During the setting of the additional concrete, the current limiting system described above prevents the generation of gases at the surfaces of the anode and the rebar which can enter the setting concrete and cause significant damage to the concrete.

(48) Since various modifications can be made in my invention as herein above described, and many apparently widely different embodiments of same may be made within the spirit and scope of the claims without department from such spirit and scope, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense.