HK1121200B - Discrete anode for cathodic protection of reinforced concrete - Google Patents

Description

Discontinuous anode for enhanced concrete cathodic protection

Technical Field

The present invention relates to the field of cathodic protection of reinforced concrete structures and in particular to the design of discrete anodes for cathodic protection, said anodes being suitable for being mounted in holes or slots provided in the concrete.

Background

The phenomenon of corrosion with respect to reinforced concrete structures is well known in the art. Steel reinforcements are embedded in concrete structures to improve their mechanical properties, which generally play a role in passivating systems caused by the alkaline environment of the concrete; however, after a certain time, the movement of ions through the porous structure of the concrete leads to local attacks on the protective passivation film. Of particular concern is chloride erosion, which in fact exists in various environments where reinforced concrete structures are employed, to a greater extent for exposure to brackish water (buildings, bridges, pillars located in coastal zones), antifreeze salts (bridges and highway constructions in cold regions) or even seawater, such as in the case of wharfs and docks. The critical value of chloride exposure is estimated to be about 0.6kg per cubic meter of concrete, beyond which the state of passivation of the reinforcing steel is not guaranteed. Another form of concrete degradation is represented by carbon dioxide saturation, which is the formation of calcium carbonate from the reaction of the cement admixture lime with atmospheric carbon dioxide. Calcium carbonate reduces the alkali content of the concrete (from pH 13.5 to pH 9), leaving the iron unprotected. The presence of chlorides and the simultaneous saturation with carbon dioxide represent the worst protection conditions for building reinforcement grids. The corrosion products of steel are much larger in volume than the steel itself and the mechanical stresses caused by them can lead to delamination and cracking phenomena of the concrete, which translates into huge economic losses, in addition to safety. It is therefore known in the art that the most effective method for extending the life of reinforced concrete structures exposed to atmospheric agents indefinitely, even in the presence of significant salt concentrations, involves cathodically polarizing the steel reinforcement. In this way, the reinforcement becomes a site for oxygen cathodic reduction, thereby inhibiting anodic corrosion and decomposition reactions. Such a system is called cathodic protection of reinforced concrete, which can be implemented by connecting various types of anodic structures to the concrete, which, together with the reinforcement to be protected, acts as a counter-electrode (counter electrode) of the cathodic type; the required current maintained by the external rectifier is conducted through an electrolyte consisting of porous concrete partially soaked with a salt solution. Installation of the cathodic protection system may be performed from the beginning, on newly constructed buildings (in which case "cathodic prevention system" is often used as a reference term) or as a retrofit of old buildings.

Anodes are commonly used to enhance the cathodic protection of concrete, consisting of a titanium matrix coated with a transition metal oxide or other type of catalyst for anodic oxygen evolution (evolution). As a matrix, it is possible to use other valve metals-pure or alloyed-pure titanium is still the main preference for cost reasons. From a system design point of view, the cathodic protection of the enhanced frame structure can be accomplished in two distinct ways, namely with distributed or with discontinuous anodes. A protective structure with distributed anodes provides coverage of the concrete envelope surface to be protected reinforced, said envelope surface being covered with anodes consisting of (suitably prepared) highly expanded mesh bodies; the anode is then covered with a new cement layer of a few centimeters in thickness. Alternatively, mesh or solid strips may be installed inside the enclosure in cutouts in the pipe (which are not deep enough to reach the iron) and then the pipe filled with cement grout (cement mortar). In newly constructed buildings, the anodes, typically anode mesh strips, can finally be mounted directly on the reinforcing cage and kept electrically insulated from the iron by plastic or concrete-like insulation means. When pouring concrete for construction, the anode system is buried in the building. Provided that the reinforcement has a very simple and regular shape, a small direct current (typically from 1mA to 30mA per square meter of reinforcement) is applied to all anodes distributed throughout the building, said direct current applying the same cathode voltage to the reinforcement to be protected. Conversely, if the reinforcement has a complex shape and exhibits portions that are smaller than others, or has a different steel density per unit surface, or other types of irregularities, it is ensured that all the reinforcement portions are sufficiently reinforced without supplying additional current to the other portionsProtection can be difficult. Discontinuous anode type protective structures can overcome this difficulty by using separate anodes, for example in the form of bars, plates, rods, mesh or pieces of strips, etc., which are mounted in suitable holes or cut-outs in the concrete and reinforced with cement mortar after arrangement. The discrete anodes may be arranged as desired, increasing their number or decreasing their spacing where more current must be supplied. For some constructions, a combination of mesh and strip anodes and discrete anodes may ultimately be provided to achieve the best protection. The maximum current density applicable to the anodes of the above type (mesh, strip or discontinuous anodes) is defined by the need to prevent excessive concrete acidification in the environmental territory in which they are located; in fact, said acidification causes several types of damage, in which the gradual accumulation of reaction products in the defined area around the anode and the consequent mechanical action that damages the surrounding cement slurry due to inevitable soaking raise the interfacial resistance. Effective regulations provide up to 110mA/m²The maximum current density is per the effective active surface of the anode (i.e. the effective active surface refers to the sum of the two faces). Thus, in order to be able to provide the necessary protection current at maximum current density, it is appropriate to maximize the anode surface per unit length without adding too much installation and raw material costs associated with making deep holes or cuts in the concrete. On the other hand, in order to limit the installation cost, it is also necessary to improve the convenience of transportation and assembly of the anode as much as possible. Finally, it is necessary to determine the electrode geometry, so as to increase as much as possible the adhesion of the anode to the cement paste used for its fixation. The electrode geometry of the discontinuous anodes of the prior art has significant drawbacks in all these respects, for example, since an increase in the surface of the anode per unit length is only possible by an increase in its diameter or length. Furthermore, it may prove very difficult to install cylindrical or mesh or solid strip-type anodes in vertical surfaces or on building roofs, where such anodes must be suitably fixed to the new slurry before it is covered therewithIn holes or cut-outs provided in the concrete to prevent them from falling under the influence of gravity.

Disclosure of Invention

A first object of the present invention is to provide a discontinuous anode for cathodic protection systems of reinforced concrete structures that overcomes the drawbacks of the prior art.

In particular, it is an object of the present invention to provide a discontinuous anode for cathodic protection systems for reinforced concrete structures, characterized in that it has a high active surface per unit length, is easy to transport, store and install and has a high adhesion to the cement slurry.

A second object of the present invention is to provide a cathodic protection system for a discontinuous anodic reinforced concrete structure.

Another object of the present invention is to provide an installation method of a cathodic protection system for a discontinuous anode type reinforced concrete structure.

These and other objects will be clarified by the following description which is purely exemplary in purpose and is not intended to constitute a limitation of the present invention.

The anode of the present invention comprises a planar substrate of corrugated titanium or other valve metal welded to a current collector and having surface catalytic activity suitable for rolling upon itself to form a cylinder.

As is evident from the description of the invention, the term "cylinder" is therefore generally used for surrounding surfaces that are generally approximately cylindrical, in particular ignoring deviations caused by wrinkles.

The corrugated substrate is preferably formed of a thin corrugated mesh body and the current collector is preferably a rod or bar, for example welded to the center of the active substrate or along one edge of the active substrate.

Thus, the term "corrugated substrate" is generally used to refer to a substrate having a profile forming corrugations or folds of any shape suitable to define a fluted surface, including folds having continuous bends and folds having sharp corners, optionally in combination with flattened ends.

The substrate must be thin enough to easily withstand the cylindrical folding, which is preferably performed parallel to the major dimension of the current collector; on the other hand, the thickness of the matrix must be sufficient to maintain permanent surface corrugations and to give the cylindrically folded anode an elastic behavior.

In a preferred embodiment, the base body is an undulating mesh body having an initial thickness of between 0.2mm and 2mm, a length of between 30mm and 300mm, and a number of grooves per linear meter of between 20 and 2000. After the corrugation treatment, which defines the groove geometry, the final thickness is preferably between 1mm and 30 mm.

The cathodic protection system of the invention comprises a plurality of anodes of the invention folded into a cylindrical shape, said anodes being forcibly inserted and fixed with a cement slurry in suitable cylindrical holes or channels made in the appropriate areas of concrete surrounding the metal reinforcement to be protected.

The anode of the cathodic protection system of the present invention may also be provided with an outer insulating ring or other equivalent means to prevent shorting to the surrounding exposed rebar, as is well known in the art.

Alternatively, the anode may be pre-filled with cement paste or other porous electrically insulating material before the anode is inserted into the appropriate hole.

According to another embodiment, the anode may be pre-welded into a cylindrical shape prior to installation in concrete. This configuration is particularly preferred when drilling of the associated bore hole is likely to cut across the reinforcing rod, and installation of an open cylindrical anode may cause a short circuit between the anode cylinder and the reinforcing rod exposed by the drilling process. When cathodic prevention is employed in the construction of concrete structures, a pre-welded cylindrical anode may be suitably used. Such pre-formed cylinders may be mounted on rebar cages separated by insulating spacers.

In particular, the anode cylinder can be accurately mounted near the high steel density area of the reinforcement cage to ensure optimal local current distribution. The anodes of the invention can also be installed without cylindrical folding, i.e. in a planar state or in an intermediate curved open state (position), for example folded in a semicircular or crescent and the like, in suitable cut-outs provided in the concrete.

The advantages of this type of structure will be apparent to those skilled in the art: the corrugated substrate has a larger active surface (e.g., 1.5 times or more) than the projected surface, so that the total current provided per unit length specification increases by a large factor, preferably 50% or more. The anode is easy to activate and transport because it can be coated with a catalyst and carried like a flat sheet, and it is rolled into a cylindrical shape without difficulty in use; the current collector may be fixed before or after transportation as needed. The anode may be manually rolled and optionally held in a cylindrical shape by a clamp and optionally forced into a hole provided in the concrete with the aid of a plastic conduit, which is subsequently pulled out of the site.

The elastic properties of the anode contribute to a good fixation to the walls of such holes; in setting, a cement slurry is set which is then poured or sprayed into the hole and optionally also applied to the anode before the anode is inserted into the hole, this setting of the cement slurry benefiting from the surface of the anode corrugations.

Drawings

For a better understanding of the invention, reference may be made to the following drawings which have the purpose of illustrating some preferred embodiments thereof, which do not constitute any limitation of the invention.

Figure 1 shows a plan view and a cross-section of a first embodiment of an anode of the present invention.

Fig. 2 is a plan view of a second embodiment of the anode of the present invention.

Fig. 3 shows a detail of the corrugated substrate of the anode of fig. 1 secured to a current collector.

Figure 4 is a top view of the discrete anodes of the present invention installed within the corresponding cathodic protection system of a reinforced concrete structure.

Detailed Description

Figure 1 shows in detail a plan view of an anode according to the invention, machined on a planar substrate, in the specific case a corrugated mesh body (100); for clarity of the drawing, the wavy mesh pleat is schematically indicated as (101), without reproducing its surface pattern. (100') shows a cross-section of the same undulating mesh body. The undulating mesh body is just one possible corrugated matrix in which the invention can be implemented, however, many other geometries are suitable for the said range, which in addition include solid, perforated or expanded sheets, metal foams and various combinations obtained by juxtaposing elements of this type, solid or preferably mesh (foaminus); the decisive factors for the choice of the geometry of a particular corrugated substrate are given by: easy to roll into a cylinder, elastic properties and easy to obtain and maintain a durable wrinkle. The anode substrate (100) is activated by means of a catalytic coating known to the person skilled in the art, preferably containing a catalyst for the oxygen evolution reaction, such as a mixture of: noble metals such as iridium, platinum, palladium, ruthenium, their oxides and/or oxides of other transition metals such as titanium, tantalum, niobium, zirconium, molybdenum, cobalt and other metals. In the embodiment of fig. 1, the current collector (200) is welded to the corrugated substrate (100) in a central position; in this case, the collector is rod-shaped, but it may also be constituted by a rod-shaped, strip-shaped or other longitudinal collector known in the art.

Fig. 2 shows a plan view of an embodiment of the anode of the invention, which is identical to the anode of fig. 1, except for the current collector (200) which is welded in a lateral position with respect to the planar substrate (100). In both cases, the invention provides a planar substrate which is preferably folded by connecting two parallel edges to the current collector to form a cylinder when mounted.

Fig. 3 shows details of the mounting of the corrugated mesh body as anode base (100) to a collector bar (200) by welding (300) performed according to the known art of the anode base (100).

Figure 4 shows a top view of a discontinuous anode of the invention installed in a cathodic protection system for reinforced concrete structures; the corrugated substrate (100) is wound in a cylinder having an axis parallel to the current collector (200), and the anode is forcibly embedded in a hole (400) provided in the concrete (500). After installation, the anode is fixed by applying a cement paste (not shown). A plurality of anodes are installed according to an equivalent embodiment, distributed and anodically polarized according to the protection requirements of the steel reinforcement and constituting the discontinuous anodic cathodic protection system of the present invention. The corrugated substrate (100) shown in fig. 4 has a continuously curved profile, however, it will be apparent to those skilled in the art that the invention can be practiced with other types of corrugated structures, for example with corrugated structures having sharp corners, the top view of which appears as a star profile once rolled into a cylinder, without departing from the scope.

Examples of the invention

A thickness of 0.6mm and a thickness of 5m²The net structure of the small-width mesh body is suitable forThe precious metal catalytic coating, which worked in concrete, was activated and subsequently corrugated and cut into several 150mm wide and 200mm or 400mm long blocks. The anode thus obtained had a maximum current density of 110A/m²The current capacity (current capacity) is 6.7mA or 13mA respectively. Such current supply represents a higher value than prior art anodes for current densities for specific applications. A titanium rod as a current collector was spot-welded to each of the obtained blocks at a central position. The anodes thus shaped are placed at the site of the building where cathodic protection systems must be installed for the uprights and the top layer (ceiling) of bridges, in particular in the drainage sections of the sidewalks covering the roads where corrosion by chlorides occurs. These areas requiring very high currents are limited to the parts most susceptible to corrosion (anodic areas).

Holes 250mm deep and 65mm or 130mm wide, spaced approximately 500mm apart, are made in the top layer and cylinder of concrete for easy installation of the anode of the invention inside, suitably rolled by hand inside the cylinder. To facilitate the mounting on the wall of the column, plastic conduits are embedded in holes provided in the concrete, the diameter of the conduits being slightly smaller than the diameter of said holes. The anode folded into a cylindrical shape is inserted into the guide tube. The conduits are removed as each anode is positioned. The remaining anode is thus well fixed to the wall of the hole, making it easy for the operator to fill the hole. To mount the anode on the top layer, the anode is molded inside the cylinder and the cylinder shape is stabilized by using metal or plastic clips to allow sufficient elastic margin of the cylinder itself. Also in this case, once mounted inside the hole of the protected top layer, the cylindrical anode is well fixed to the inner surface of the hole itself. In other areas of the bridge to be protected, which are more accessible, the anodes can be installed after manual crimping into the cylinders, without the need for pipes or for metal or plastic clamps. After installation, the anodes are suitably connected to a rectifier by suitable wiring. A silver/silver chloride reference electrode was also installed to monitor the degree of protection.

The cathodic protection system was activated for a period of approximately 30 days, and then a 100mV depolarization test was successfully performed as generally specified by standards for measuring the correct operation of the system.

The above description is not intended to limit the invention, which may be used according to different embodiments without departing from the scope thereof, and whose extent is univocally defined by the appended claims.

Throughout the description and claims of this application, the term "comprising" and its various modifications, such as "comprises" and "comprising," are not intended to exclude the presence of other elements or additives.

Claims (17)

1. Cathodic protection system for reinforced concrete structures comprising a metal reinforcement embedded in concrete, characterized in that it comprises a plurality of anodes, each of said anodes comprising a corrugated metal planar matrix welded to a current collector, said anodes being forcibly seated in a plurality of holes provided in the concrete, wherein said anodes are rolled into an open cylinder, having an axis parallel to said current collector, being forcibly seated in a plurality of holes provided in the concrete.

2. The cathodic protection system of claim 1, wherein the metallic planar substrate comprises a valve metal, the valve metal being coated with a catalytically active layer.

3. The cathodic protection system of claim 2, wherein the valve metal is pure titanium.

4. Cathodic protection system according to claim 2 or 3, wherein the catalytically active layer comprises noble metals and/or oxides thereof and/or oxides of other transition metals.

5. The cathodic protection system of claim 1, wherein the metallic planar substrate is selected from the group consisting of: mesh bodies, solid, perforated or expanded sheets, metal foams, and stacked mesh bodies, sheets or foams.

6. Cathodic protection system according to claim 5, wherein said metallic planar substrate is a mesh body having an initial thickness comprised between 0.2mm and 2mm and a final thickness after corrugation comprised between 1mm and 30 mm.

7. The cathodic protection system of claim 5, wherein the corrugations of the metallic planar substrate define a plurality of grooves, the number of grooves being between 20 and 2000 grooves per linear meter.

8. The cathodic protection system of claim 1, wherein the current collector is a metal rod or strip.

9. Anode according to claim 1, characterized in that it is pre-welded in cylindrical shape.

10. Anode according to claim 1, characterized in that the anode is further provided with an outer insulating ring.

11. Cathodic protection system for reinforced concrete structures comprising metal reinforcements embedded in concrete, characterized in that it comprises a plurality of anodes, each of which comprises a corrugated metal planar matrix welded to a current collector, said anodes being forcibly seated in a plurality of holes provided in the concrete, wherein said anodes are forcibly seated in a flattened or curved open condition in a plurality of notches drilled in the concrete.

12. The cathodic protection system of claim 11, wherein said anode is embedded in said hole or said notch in the concrete by applying a cement slurry.

13. Method for installing a cathodic protection system within a reinforced concrete structure comprising a metal reinforcement embedded in concrete, said method comprising

A plurality of holes are arranged in the concrete,

forcibly placing an anode of a cathodic protection system according to any one of claims 1 to 12 in each of said holes, said anode being folded in a cylindrical state and having an axis parallel to said current collector,

and the anode is fixed in the hole by applying cement slurry by casting or spraying.

14. A method for installing a cathodic protection system within a reinforced concrete structure comprising a metal reinforcement embedded in concrete, the method comprising:

a plurality of holes are arranged in the concrete,

forcibly placing a hard plastic conduit within each of said holes,

inserting in each of said conduits an anode of a cathodic protection system according to any one of claims 1 to 12, said anode being rolled in a cylindrical state and having an axis parallel to said current collector,

the catheter is pulled out to leave the anode,

and the anode is fixed in the hole by applying cement slurry by casting or spraying.

15. A method according to claim 13 or 14, wherein the folded anode is stabilized in the cylindrical state by a metal or plastic clamp.

16. The method of claim 13, wherein each of said anodes is pre-filled with a porous electrically insulating material before said anodes are forcibly positioned within said cavities.

17. Method for the cathodic protection of reinforced concrete structures, characterized in that it comprises applying an anodic potential to the anode of the cathodic protection system according to any one of claims 1 to 12.