Cathodic protection current distribution method and apparatus for corrosion control of reinforcing steel in concrete structures

Abstract

Mixed-metal-oxide (MMO) coated precious-metal tape is installed directly on concrete surfaces using an electrically non-conductive adhesive with semi-conductive coating or overlay, thereby obviating the need for slots or holes to the concrete structures which are not subject to direct moisture. The tape anodes may be installed on the concrete surfaces exposing metals without developing an electrical short circuit between the anode and the metals due to the non-conductive adhesive. The semi-conductive layer over the metal tape can distribute the CP current uniformly to the entire concrete surface without developing electrical short circuit. Overall the invention provides for quick and low cost installation on many concrete structures. Interconnections between the tape anodes and bare metal distribution elements may be made with conductive adhesive or spot welding.

Description

FIELD OF THE INVENTION[0001]This invention relates generally to corrosion control in reinforced-concrete structures and, in particular, to mixed-metal-oxide (MMO) coated precious-metal tape and mesh that may be installed directly on concrete surfaces without the need for slots, holes, cementitious grout or concrete.BACKGROUND OF THE INVENTION[0002]Cathodic protection (CP) is a method for controlling corrosion of reinforcing steel, including steel structures in chloride contaminated concrete. Various types of impressed current cathodic protection anodes for reinforced concrete structures have been developed in the past. The anode is one of the most critical components for a cathodic protection system, as it is used to distribute cathodic protection current to the reinforcing steel.[0003]One of the most effective and durable anodes is made of a material which is resistance to corrosion, for example a mixed-metal-oxide (MMO) coated titanium substrate. MMO coated anodes are manufactured...

AI Technical Summary

Benefits of technology

The invention allows for the use of a mixed-metal-oxide coated precious-metal tape on dry concrete structures without the need for slots or holes. A semi-electrically conductive and gas-permeable coating is used in combination with the MMO-coated precious-metal tape to improve current distribution at low voltages. The semi-conductive coating prevents the concentration of cathodic protection current discharging to the concrete substrate. The use of a high current discharge capability of the anode system with the semi-conductive coating facilitates electro-chemical chloride extraction from the chloride contaminated concrete. The semi-conductive layer prevents electrical short circuits and shortens the life of the semi-conductive layer when a large current is required for a long time. Passive metal powder or fibers can be used without consumption of the metals.

Problems solved by technology

However, these types of installations add burden to the structure and lead to some durability concerns.

However, when the concrete covers over the reinforcing steel are shallow or congested, such installation procedures are not feasible.

Even if the anodes are somehow installed in the slots or drilled holes, the vicinity of the reinforcing steel near the anodes may cause an electrical short circuit, resulting in malfunction of the cathodic protection system.

This leaves the non-conductive aggregates at the anode-concrete interface and causes the increases of the circuit resistance, diminishing the cathodic protection current.

When highly conductive media is used as an anode to cover the concrete surface, the concentration of cathodic protection current from the local portion of the anode system to shallow rebars develop acid generation, resulting in poor current distribution to a concrete structure.

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