Anode assembly for cathodic protection

Abstract

The cathodic protection of a reinforced concrete structure utilizes sacrificial anodes such as aluminum or zinc as well as alloys thereof. Each anode is embedded or substantially covered in a material consisting of a hydrophilic non-cementious open-cell foam. An activating agent such as one or more lithium salts is contained within the cells of the foam to maintain the anodes in an electrochemically active state. The activating agent may be immobilized in the cells using an aqueous gel such as agar. One or more metallic conductors electrically connect the anodes to the metal reinforcing members.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application claims the benefit of and priority to provisional patent application Ser. No. 61 / 849,291, filed on Jan. 24, 2013, entitled “ANODE ASSEMBLY FOR CATHODIC PROTECTION which is incorporated herein in its entirety by reference.BACKGROUND OF THE INVENTION[0002]1. Technical Field[0003]This invention generally relates to the field of galvanic cathodic protection of steel embedded in concrete structures, and is particularly concerned with the performance of embedded sacrificial anodes, such as zinc, aluminum, and alloys thereof.[0004]2. Description of Prior Art[0005]The problems associated with corrosion-induced deterioration of reinforced concrete structures are now well understood. Steel reinforcement has generally performed well over the years in concrete structures such as bridges, buildings, parking structures, piers, and wharves, since the alkaline environment of concrete causes the surface of the steel to “passivate” such th...

AI Technical Summary

Benefits of technology

The present invention is about improving the performance and lifespan of embedded anodes used for cathodic protection of reinforced concrete. The invention achieves this by using a non-cementitious hydrophilic open-cell foam covering material for the anode, which is impregnated with an activating salt that breaks down the passive film on the anode surface and prevents corrosion. The activating salt can be one of several salts, such as nitrates or bromides, and can be immobilized within the foam using a gel or semi-solid jelly-like material. This invention provides a better method of cathodic protection for reinforced concrete, ensuring longer performance and service life of the embedded anodes.

Problems solved by technology

Unfortunately, since concrete is inherently somewhat porous, exposure to salt (NaCl) over a number of years results in the concrete becoming contaminated with chloride ions.

When the chloride reaches the level of the reinforcing steel, and exceeds a certain threshold level for contamination, it destroys the ability of the concrete to keep the steel in a passive, non-corrosive state.

When this tensile force exceeds the tensile strength of the concrete, cracking and delaminations develop.

With continued corrosion, freezing and thawing, coupled with traffic pounding, the utility or integrity of the structure is finally compromised and repair or replacement becomes necessary.

Reinforced concrete structures continue to deteriorate at an alarming rate.

Structurally deficient bridges are those that are closed, restricted to light vehicles only, or that require immediate rehabilitation to remain open.

The damage on most of these bridges is caused by corrosion.

Of these techniques, only cathodic protection is capable of controlling corrosion of reinforcing steel over an extended period of time without complete removal of the salt-contaminated concrete.

This type of cathodic protection has been generally successful, but problems have been reported with reliability and maintenance of the power supply.

Problems have also been reported related to the durability of the anode itself, as well as the concrete immediately adjacent to the anode, since one of the products of reaction at an inert anode is acid (H+).

Acid attacks the integrity of the cement paste phase within concrete.

Finally, the complexity of ICCP systems requires additional monitoring and maintenance, which results in additional operating costs.

Many of these means involve driven pins, impact tools, and other specialized techniques, with attendant drawbacks.

But some embodiments, such as the use of high pH to maintain the anode in an electrochemically active state as described by Page, result in protective current that is small and often inadequate to mitigate corrosion.

Also, some of the chemicals used to maintain the zinc anode in an electrochemically active state render the corrosion products of zinc largely insoluble.

In this case the expansive corrosion products apply stress to the surrounding concrete, and when this stress exceeds the tensile strength of the concrete, cracking of the concrete can occur.

Although several potential solutions have been proposed, including the ionically compressible conductive matrix described in U.S. Pat. No. 7,160,433, cracking remains a problem in some cases.

It is noteworthy that, although one or two patent applications in this field have been broadly worded, there have been no commercial applications or reported positive results utilizing anything other than a cementitious covering material for the sacrificial anode.

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