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.

I claim: 
     
         1 . A system for controlling the corrosion of reinforcing steel in a concrete body having a surface, comprising:
 a mixed-metal-oxide (MMO) coated precious-metal anode indirectly bonded to the surface of the concrete body through an electrically non-conductive material; and   a semi-conductive coating covering the anode and at least portions of the surface of the concrete body to distribute cathodic protection current from the concrete surface to the anode without the anode making a direct electrical connection to the concrete body.   
     
     
         2 . The system of  claim 1 , wherein the electrically non-conductive material is a non-conductive adhesive. 
     
     
         3 . The anode of  claim 1 , wherein the anode is composed of carbon, titanium, tantalum, zirconium, niobium, or alloys thereof, or MMO coated titanium, tantalum, zirconium, niobium, or alloys thereof. 
     
     
         4 . The anode of  claim 1 , wherein the coating is composed of oxides of titanium, tantalum, iridium, ruthenium, palladium, or cobalt. 
     
     
         5 . The system of  claim 1 , wherein the anode is in the form of an elongate tape. 
     
     
         6 . The system of  claim 1 , wherein the anode is in the form of an elongate tape having a width of 5 mm or greater and the thickness in the range of 0.001 mm to 1 mm. 
     
     
         7 . The system of  claim 1 , including a plurality of anodes interconnected with a bare metal tape. 
     
     
         8 . The system of  claim 1 , including a plurality of interconnected anodes spaced-apart on the surface of the concrete. 
     
     
         9 . The system of  claim 1 , including a plurality of anodes interconnected with a bare metal tape using an electrically conductive adhesive. 
     
     
         10 . The system of  claim 1 , including a plurality of anodes interconnected to a bare metal tape using spot-welding. 
     
     
         11 . The system of  claim 1 , wherein the semi-conductive coating includes a layer of carbon fibers or passive metal fibers. 
     
     
         12 . The system of  claim 1 , wherein the electrical resistivity of the semi-conductive coating is in the range of 100 ohm-cm to 20,000 ohm-cm. 
     
     
         13 . The system of  claim 1 , wherein the semi-conductive coating is sufficient porous for chlorine gas escape therethrough to atmosphere. 
     
     
         14 . The system of  claim 1 , wherein the anode is in the form of a mesh.