Doubly-protected reinforcing members in concrete

Abstract

A concrete structure is reinforced with steel rebars coated with essentially pure aluminum in the range from about 0.25 mm to 2 mm thick upon which aluminum coating is an aluminum oxide layer in the range from 0.1 μm to 100 μm thick. This layer of aluminum oxide and/or hydrated aluminum oxide is referred to as a combined aluminum oxide layer, and it is in direct contact with the concrete. The Al-coated rebars may be protected in a galvanic circuit using magnesium or other metal baser than aluminum as a sacrificial anode, but more preferably the rebars are cathodically protected with an impressed cathodic current the current density of which is derived by sensing the corrosion potential at a sensing member of essentially pure aluminum embedded in the concrete, or in concrete outside a zone immediately surrounding the rebars, measuring the corrosion potential at the sensing member relative to a reference electrode until the value stabilizes at a measured stable potential; then providing an impressed current at a potential in the range from about 150 mV to less than 300 mV lower than the corrosion potential of the sensing member.

What is claimed is:  
     
         1 . A method of constructing a concrete structure reinforced with steel rebars, comprising: 
 embedding the rebars in concrete, the rebars having a coating of aluminum in the range of about 0.25 mm to about 2 mm thick upon which coating is an oxide layer in the range of about 0.1 μm to about 100 μm thick, the oxide layer comprising aluminum oxide and/or hydrated aluminum oxide in a combined aluminum oxide layer which is in direct contact with the concrete;    embedding a corrosion potential sensing member of aluminum within the structure;    measuring the corrosion potential at the surface of the corrosion potential sensing member relative to a reference electrode until the value stabilizes at a measured stable potential without measuring the corrosion potential at the rebars;    anodically connecting the source of potential to an anode proximately disposed relative to the rebars;    cathodically connecting the rebars to a source of potential which is sufficiently electronegative with respect to the measured stable potential to repress the cathodic potential of the rebars to within a predetermined range correlatable with a corrosion potential measured at the corrosion potential sensing member; and    continuously maintaining current from the source of electronegative potential at a potential lower than the corrosion potential of the corrosion potential sensing member.    
     
     
         2 . The method of  claim 1 , wherein the coating of aluminum and the combined aluminum oxide layer is in the range of about 0.2 mm to about 1 mm thick.  
     
     
         3 . The method of  claim 1 , wherein the rebars are connected to the source of potential to provide an impressed current at a potential in the range from about −600 mV (−0.6 V) to about −1300 mV (−1.3 V) relative to a HRE.  
     
     
         4 . The method of  claim 3 , wherein the coating of aluminum and the combined aluminum oxide layer is in the range of about 0.2 mm to about 1 mm thick.  
     
     
         5 . A system for the maintenance of a concrete structure reinforced with steel rebars essentially free from corrosion of the rebars, the system comprising: 
 a mass of concrete wherein the rebars are electrically interconnected in a grid;    the rebars having a coating of aluminum in the range of about 0.25 mm to about 2 mm thick upon which coating is an oxide layer in the range of about 0.1 μm to about 100 μm thick, the oxide layer comprising aluminum oxide and hydrated aluminum oxide;    an external power source responsive to a programmable control means to which data is transmitted from a comparator means, connected in serial relationship, the programmable control means being responsive to both the external power source and the comparator means;    measuring means in the comparator means to measure the corrosion potential at the surface of the corrosion potential sensing member relative to a reference electrode until the value stabilizes at a measured stable potential;    means for anodically connecting the external power source of potential to an anode proximately disposed relative to the rebars;    means for cathodically connecting the rebars to the external power source which is sufficiently electronegative with respect to the measured stable potential to repress the cathodic potential of the rebars to within a predetermined range; and    means for continuously maintaining current from the source of electronegative potential at a potential lower than the corrosion potential of the corrosion potential sensing member.    
     
     
         6 . The method of  claim 5 , wherein the coating of aluminum and the combined aluminum oxide layer is in the range of about 0.2 mm to about 1 mm thick.  
     
     
         7 . A corrosion protected structure reinforced with steel rebars, the structure comprising: 
 a mass of concrete wherein a portion of the mass in a zone within a radius of about 10 mm from the surface of a Al-coated rebar has a pH in the range of about 6 to about 9;    the rebars having a coating of aluminum in the range of about 0.25 mm to 2 mm thick upon which coating is an oxide layer in the range of about 0.1 μm to about 100 μm thick, the oxide layer comprising aluminum oxide and hydrated aluminum oxide;    a corrosion potential sensing member of aluminum embedded within the structure;    means to measure the corrosion potential at the surface of the corrosion potential sensing member relative to a reference electrode until the value stabilizes at a measured stable potential;    means for anodically connecting an external power source of potential to an anode proximately disposed relative to the rebars;    means for cathodically connecting the rebars to the source of potential which is sufficiently electronegative with respect to the measured stable potential to repress the cathodic potential of the rebars to within a predetermined range; and    means for continuously maintaining current from the source of electronegative potential at a potential lower than the corrosion potential of the corrosion potential sensing member.    
     
     
         8 . The method of  claim 7 , wherein the coating of aluminum and the combined aluminum oxide layer is in the range of about 0.2 mm to about 1 mm thick.  
     
     
         9 . A corrosion protected structure reinforced with at least one steel rebar, the structure comprising: 
 a mass of concrete containing therein at least one rebar;    the at least one rebar having a coating of aluminum in the range of about 0.25 mm to about 2 mm thick upon which coating is an oxide layer in the range of about 0.1 μm to about 100 μm thick, the oxide layer comprising aluminum oxide and hydrated aluminum oxide; and    a sacrificial anode in galvanic connection with the rebars and proximately disposed relative thereto.    
     
     
         10 . The method of  claim 9 , wherein the coating of aluminum and the combined aluminum oxide layer is in the range of about 0.2 mm to about 1 mm thick.