Patent Application
20210095379
This invention relates to anodes for use in protecting reinforced concrete structures from corrosion, methods of galvanic (sacrificial) corrosion protection of reinforced concrete structures and reinforced concrete structures electrochemically protected from corrosion.
Galvanic (sacrificial) anodes and galvanic (sacrificial) protection are used to stop or reduce the corrosion of reinforcing steel in steel reinforced concrete structures. A galvanic anode comprises/includes a galvanic (sacrificial) metal element and a connector. This galvanic (sacrificial) metal element is consumed during the delivery of protection current and, therefore, a galvanic anode has a limited life. It may also include other components. Examples of a reinforced concrete structure include, for example, elements of bridges and buildings.
Discrete galvanic anodes are anodes that are embedded within anode cavities located within the concrete of a concrete structure and distributed across the structure in an array. Typically there will be more than 100 anodes located within anode cavities and distributed across the surface of a single element of a reinforced concrete structure. Typically, the anodes will be spaced between 150 and 700 mm (5.906 and 27.559 inches) apart from one another. The anode cavities, to accommodate the discrete galvanic anodes, are formed by cutting holes in the hardened concrete. Typically the anode cavities are formed by coring or drilling into the hardened concrete. Discrete galvanic anodes then are embedded in anode cavities within an anode backfill.
The anode cavities typically comprise cylindrical holes which are formed in the concrete and have a diameter of between 15 and 70 mm (0.591 and 2.756 inches) and have a depth or length of between 25 and 500 mm (0.984 and 19.685 inches). Generally, the discrete galvanic anodes have a cylindrical exterior shape. The galvanic metal component of the anode is gradually consumed at its outer surface, during the delivery of current, and loses a portion of its cross section as the galvanic metal component is gradually consumed. This limits the life of the anode. To ensure an adequate life of the anode, a galvanic metal component must have an adequate cross-section of material.
Discrete galvanic anodes are connected to each other and to the steel reinforcement by one or more connecting wires to deliver the desired galvanic protection. The connecting wires are buried in interconnecting slots which are cut into the hardened concrete and extend between, and electrically connect, the embedded discrete anodes. The interconnecting slots typically have a width of between 4 to 10 mm (0.157 and 0.394 inches), typically 4 to 6 mm, and a depth of between 10 to 35 mm (0.394 and 1.378 and inches), typically 10 to 20 mm (0.394 and 0.787 and inches), and normally have a length equal to the distance between the anode cavities to be interconnected.
After the anode system is installed, the remaining space in the anode cavities and slots is filled with a concrete repair material that hardens like concrete. The concrete repair material covers the anode system and restores the concrete profile.
Problems with this arrangement arise because discrete galvanic anodes need to deliver a high current density off a small surface area to achieve an acceptable level of protection current at the reinforcing steel. It is to be appreciated that the level of current required increases with the rate at which the unprotected reinforcing steel is corroding. This limits the usefulness of galvanic systems. Drilling more or larger holes into hardened concrete, so as to permit insertion of more and/or bigger anodes to deliver more current, is difficult, expensive and time consuming.
A solution to the problem is to increase the surface area of the embedded discrete galvanic anodes without significantly increasing the volume of concrete that has to be removed in order to embed and install the anode system. This is achieved by installing, within the interconnecting slots cut between the anode cavities, interconnecting galvanic anodes which comprise additional galvanic metal elements with a cross section which is limited by the width of the interconnecting slots. The interconnecting galvanic anodes are preferably connected to wires which are interconnected with the discrete galvanic anodes.
According to one aspect the disclosure, a reinforced concrete structure comprising;
The advantages of this arrangement include the additional surface area of the interconnecting galvanic anodes, located in the interconnecting slots, gives additional protection current at least at the start of the delivery of protection current to the reinforcing steel. This extends the use of galvanic anodes to situations where such additional current will arrest active steel corrosion. As a result of this arrangement, the galvanic metal surface area is increased so as to increase the current density without substantially affecting the ratio of the anode system galvanic metal volume to the volume of concrete removed to accommodate the anode system. The additional volume of galvanic metal, accommodated within the interconnecting slots, delivers a current boost to the anode system. While the interconnecting anodes may have a limited life as a result of their limited cross-section, the life of the system is generally preserved, after corrosion has been sufficiently arrested, by the discrete galvanic anodes. The discrete galvanic anodes continue to deliver current to prevent corrosion from starting again.
The reinforced concrete structure, comprising hardened concrete containing steel reinforcement, may be a complete structure or a component of a structure. For example, it may be an abutment wall or a beam or a column or a section of a reinforced concrete deck. The reinforcement in the structure is any conventional steel reinforcement, examples of which include high tensile steel bars and prestressed steel tendons.
The anode cavities are any conventional anode cavity formed in hardened concrete to accommodate discrete galvanic anodes. The anode cavities are typically formed by conventional coring or drilling. The anode cavities are distributed across the concrete generally in the location of the reinforcement that is to be protected. The anode cavities are interconnected by interconnecting slots formed in the hardened concrete typically via a conventional grinding or cutting tool. The anode cavities have a dimension, referred to as a diameter, extending along the plane of the concrete surface and at right angles to the interconnecting slots. The term diameter, as used within this specification, is intended to mean the dimension defined above and is not intended to exclude anode cavities that do not have a circular cross section and that may be formed using concrete cutting equipment. In a reinforced concrete structure there may be, for example, at least 10 anode cavities and associated interconnecting slots or possibly there may be more than 50 anode cavities and associated interconnecting slots.
The interconnecting slots have a width along the plane of the concrete surface and at right angles to a length of the interconnecting slots. The width of the interconnecting slots is less than the diameter of the anode cavities which are interconnected by the interconnecting slot. The width of the interconnecting slot is preferably less than 10 mm (0.394 inches) and more preferably less than 7 mm (0.276 inches). The interconnecting slots and the anode cavities also have a depth that extends into the concrete surface at right angles to the plane defined by the concrete surface. The depth of each of the interconnecting slots is preferably less than the depth of the anode cavities. It is to be appreciated that a wider slot may also be called a chase.
The discrete galvanic anode may be any conventional discrete galvanic anode. Typically each galvanic anode is an individually distinct unit. The discrete galvanic anodes are spaced apart across the concrete structure and electrically connected to each other and the reinforcing steel in the concrete structure to form the anode system. The discrete galvanic anodes preferably will have a circular cross section and further will preferably have a diameter and length in which the diameter of the discrete galvanic anode is less than the length thereof. However, the diameter of the discrete galvanic anode is preferably greater than the width of the interconnecting slots. The discrete galvanic anodes preferably comprise cylinders of galvanic metal connected to a connector.
The interconnecting galvanic anodes have a length and a thickness. Example of typical shapes include ribbons (strips) and wires. A length of the interconnecting galvanic anode is greater than the diameter of the anode cavity. Both the thickness and the width of the interconnecting galvanic anode are less than the width of the interconnecting slot. The thickness of the interconnecting galvanic anode is preferably less than the diameter of the discrete galvanic anode.
According to one embodiment, an interconnecting galvanic anode may comprise a wire or plurality of wires. Preferably the interconnecting galvanic anode may comprise more than two wires or possibly more than 4 wires. The wires will preferably have a thickness (gauge or diameter) of no more than 6 mm (0.236 inches).
In another embodiment, an interconnecting galvanic anode will be in the form of a ribbon having a length, a thickness, and a depth. The depth will preferably be no more than 25 mm (0.984 inches) and more preferably no more than 18 mm (0.708 inches). The depth will preferably be greater than 6 mm (0.236 inches) and will preferably be at least 10 mm (0.394 inches). The thickness will preferably be no more than 6 mm (0.236 inches) and more preferably no more than 3 mm (0.118 inches).
The interconnecting galvanic anodes preferably provide at least 0.01 m2 (more preferably 0.02 m2) of galvanic metal surface per meter of length of the galvanic metal element. The interconnecting galvanic anodes preferably provide no more than 0.2 m2 (more preferably 0.01 m2) of galvanic metal surface per meter length of the galvanic metal element.
The length of an interconnecting galvanic anode may be longer than the length of the interconnecting slot connecting two adjacent anode cavities with one another. For example, the interconnecting anode may have a length of 20 m (787.4 inches) or 50 m (1968.5 inches) or 100 m (3937.0 inches) or more and may include an interconnecting wire running its full length. An anode of this length may be supplied as a coil or roll. The galvanic metal element may be stripped from the interconnecting wire at the location of the discrete anode cavities to facilitate a connection between the connector of the discrete anode and the connector of the interconnecting anode. Alternatively, the interconnecting anode may be a unit that is less than the distance between the discrete galvanic anodes. In this case, it is preferably less than 700 mm (27.559 inches), and more preferably less than 350 mm (13.780 inches). Further, the length of the interconnecting galvanic anode is preferably more than 70 mm (2.756 inches) and more preferably the length is at least 100 mm (3.937 inches) and even more preferably it is at least 150 mm (5.906 inches).
The discrete galvanic anodes are installed in the anode cavities and the interconnecting galvanic anodes are installed in the interconnecting slots by embedding each of the respective anodes within a backfill. The backfill may be any conventional backfill that is used to embed discrete galvanic anodes in concrete.
The discrete galvanic anodes and the interconnecting galvanic anodes are electrically connected together and connected to the reinforcing steel by an electron conducting connector. This electron conducting connector may be any conventional connector used to connect embedded discrete galvanic anodes in concrete. It is to be appreciated that more than one connector may be used.
As noted above, a galvanic anode comprises a galvanic (sacrificial) metal element and a connector. The connector, which is typically integrated into the interconnecting galvanic anode, may be a conductor that is used to electrically connect adjacent discrete galvanic anodes to one another. A connector integrated into one discrete galvanic anode may extend a sufficient distance from the galvanic metal element of the discrete galvanic anode such that the connector may also be integrated into an interconnecting galvanic anode over a portion of its length.
The discrete galvanic anodes and the interconnecting galvanic anodes both include a galvanic metal element less noble than the steel reinforcement so that the galvanic anodes gradually oxidize so as to protect the steel reinforcement. The galvanic metal element may be of any conventional metal used in the sacrificial protection of steel in concrete including, for example but not limited to, zinc and zinc alloys.
According to another aspect this disclosure, a method of forming the reinforced concrete structure set out in the first aspect of this invention as substantially disclosed herein and part of this disclosure.
This invention is now illustrated further with reference by way of example to the drawings in which:
It will be appreciated that the combinations of features shown in individual figures and described with reference to specific examples below are purely by way of exemplary. As those skilled in the art will readily understand, specific features of any of the examples described and shown may be used in combination with a feature, or a subset of features of any other specific examples to the extent that it is technically feasible.
As shown in
As shown for example in
A conventional backfill (e.g., plaster also known as gypsum) is used to embed each one of the discrete galvanic anodes 15 and each one of the interconnecting galvanic anodes 16. Typically the space above the backfill/plaster in the cavities and slots is filled with a sand cement mortar with a ratio of 1 to 1 so as to completely cover each one of the embedded discrete galvanic anodes 15 and interconnecting galvanic anodes 16.
A 10 ohm resistor is installed between a discrete galvanic anode 15 and the connecting wires 19, and between the interconnecting galvanic anode 16 and the connecting wires 19 and used as a current sensor to measure the current off each one of the discrete galvanic anodes 15 and each one of the interconnecting galvanic anode 16 to ensure sufficient electrical connection.
In the arrangement described above, following installation, each one of the discrete galvanic anodes 15 and each one of the interconnecting galvanic anodes 16 can deliver 2 mA. The current was integrated to calculate the charge delivered. This is shown in
By way of example the following text in this section headed “Industrial Applicability” may be used in a technical data sheet describing a specific galvanic interconnecting anode product and its installation in a use of the above described invention.
General Description
Galvanic interconnecting anodes are located in slots (e.g., chases) between conventional discrete galvanic anodes 15. The galvanic interconnecting anodes 16 provide an additional high current phase to galvanic corrosion protection systems. The galvanic interconnecting anode 16 increases the initial restorative properties of a galvanic system and arrest corrosion in sound but contaminated reinforced concrete (BS EN1504 section 9 Principle 10). The galvanic interconnecting anode 16 is to be embedded into the interconnecting slots 12 which are normally formed between adjacent discrete galvanic anodes 15 and connected to the steel reinforcement 13 via a recessed feeder wiring or connector 19.
The galvanic interconnecting anode 16 may be ribbon shaped and have a width of 10 mm (0.394 inches), a length of 250 mm (9.843 inches) and a thickness of 1.5 mm (0.059 inches) with a continuous, uncoated, stainless steel wire or titanium wire protruding from both opposed ends of the galvanic interconnecting anode 16. This wire will act as the wiring for the conventional discrete galvanic system that the galvanic interconnecting anode 16 will be used in combination with.
One galvanic interconnecting anode 16 preferably has a minimum charge capacity of 30 kC (kilo coulombs) and preferably contains a minimum of 11 grams of zinc alloy. If desired, the galvanic interconnecting anode may be coated with an activator. The galvanic interconnecting anode 16 may be pre-connected to a stainless steel or titanium wire 9. The galvanic interconnecting anode 16 may be supplied as a string of pre-connected anodes.
It is to be appreciated that the embedment material (e.g., the backfill), for the galvanic interconnecting anodes, may be pre-mixed, single component specially formulated mortar provided in sealed tubes. The embedment material preferably remains pliable for more than 48 hours following installation. The backfill preferably has sufficient ionic conductivity to facilitate current delivery from the anode unit for the intended and designed service life. The backfill dispensing equipment preferably has a nozzle to allow the application of the backfill to the base of the interconnecting slot 3, 12 to dispel any air from the base of the interconnecting slot 3, 12.
Installation of Galvanic Interconnecting Anodes
Good practice requires that the reinforcement continuity should preferably be proven on site by measuring the electrical resistance between reinforcing steel bars 13 exposed in locations across the structure, including between reinforcing steel bars 13 exposed during concrete repairs or other works, following the method and acceptance criteria as specified in BS EN 12696:2016, clause 7.1. It is important to ensure that any electrically discontinuous steel should preferably be made continuous. The location of steel reinforcement, in the areas to be protected, should preferably be established to confirm that the detail in a design is appropriate. The concrete cover over the steel to be protected should preferably be determined to ensure a minimum cover, 30 mm (1.181 inches) in this example, for the purposes of installing the galvanic interconnecting anodes 16.
It is to be appreciated that the electrical connections, to the reinforcing steel 13, may be formed by removing a small area of the concrete cover to expose a small section of this steel 13, drilling a 4 mm (0.157 inches) diameter hole, for example, into this steel 13 and then riveting the feeder wire or connector 19, via a 3 mm (0.118 inches) stainless steel pop rivet (not in shown), in this drilled hole. Good practice requires that preferably a minimum of two steel reinforcement connections are made per zone of galvanic anodes 15, 16. The continuity between the feeder wire or connector 19 and steel reinforcement 13 should preferably be checked using a multimeter. Generally, electrical continuity is confirmed if a resistance of less than 1 ohm is measured.
The interconnection slots 3, 12 (e.g., chases), having width of 4 mm (0.157 inches) and a depth of 25 mm (0.984 inches) for linking or connecting the conventional discrete galvanic anode cavities 11 to one another, may be prepared to receive the galvanic interconnecting anodes 16 and the connection wires or connectors 19. All of the interconnecting slots 12 should preferably be free of dust, debris and/or rubble, prior to installation of the galvanic interconnecting anodes 16 and embedment materials or backfill within the interconnection slots 12 (e.g., chases).
The galvanic interconnecting anodes 16, in this example, are to be installed in these interconnecting slots 12 and used to link or connect conventional discrete galvanic anodes 15. One galvanic interconnecting anode 16 may be placed generally in the center of an interconnecting slot 12 between first and second adjacent discrete galvanic anodes 15. A wire connector 19 attached to the length of an edge of the galvanic interconnecting anode 16 may be located within the interconnecting slot 12 on the concrete surface side of the slot.
Prior to installation, a spray bottle, or some other suitable water dispensing device or apparatus, technique or method, may be used to pre-soaked each of the interconnecting slots 12 with water for a minimum of 15 minutes. Excess water, contained in the base of the interconnecting slots 12, should preferably be removed prior to the application of the backfill thereto. The backfill may be applied into each one of the interconnecting slots 12 using a sealant gun and a small diameter nozzle to allow access to the base of the interconnecting slot 12. A spatula may be used to press and force the backfill into the interconnecting slot and assist with expelling any entrapped air from the base of the interconnecting slot 12 and ensure good electrical conductivity.
After injection of the embedment material or backfill at each anode site, the galvanic interconnecting anode 16 may be placed into the interconnecting slot 12 and inserted such that the backfill (embedment material) completely encapsulates the entire galvanic interconnecting anode 16, ensuring that the material (backfill) preferably flows to about 15 mm (0.591 inches) from the plane defined by the concrete surface. Each end of the connecting wire 9, 19, extending from opposed ends of the galvanic interconnecting anode 16, is then preferably utilized to connect to one of the adjacent discrete galvanic anodes 15 located on either side of the interconnecting slot 12. In this preferred example, the connector wires 19, of the galvanic interconnecting anode 16, act as the wiring to connect to other components, e.g., the anodes, the steel, etc., to assist with completing the anode system.
It is to be appreciated that the installation of the associated conventional discrete anodes should otherwise preferably be undertaken in accordance with their conventional installation requirements.
To complete installation in this example, the remaining 15 mm (0.591 inches) or so at the top of each interconnecting slot 12, plus the cavities formed, for example, to expose the steel reinforcement 13 in order to make steel connections, should preferably be filled with an appropriate low shrink BS EN 1504 compliant repair mortar applied and cured as per the manufacturer's instructions.
Note, the above example covers a specific installation and specific galvanic interconnecting anode design. The installer should preferably satisfy himself/herself that the details above apply to his/her particular work environment and that the same is in compliance with all relevant regulations and standards.
Examples of suitable backfills, for use with the present disclosure, are disclosed in U.S. Pat. No. 8,002,964. The backfill may also be a powder mixed with water to produce a paste when installing the sacrificial anode assembly, an example of which would be a weak air entrained cement mortar paste. The backfill preferably retains its viscous and pliable properties for at least 48 hours and more preferably the backfill retains these properties for a longer period of time (e.g., at least one week and more preferably at least one month) as this feature renders the backfill practical for storage within a container, such as a cartridge, for an extended period of time. One example of such a suitable backfill is a lime mortar paste.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1914014.4 | Sep 2019 | GB | national |
