Patent Application
20060065519
The present invention relates, in general, to repairing cracks in chloride contaminated reinforced concrete structures and, more particularly, to the application of technology to electrodeposit a chemical composition into a crack to fill the crack and to repassivate the steel reinforcing rods in the concrete structure.
Steel reinforcing rods contained within concrete are protected against corrosion by the alkalinity of the cement within the concrete. The cement contains alkali, alkali earth, metal oxides and hydroxides that typically result in concrete having a pH of between 12 and 14 depending upon the source of the cement and its age. In a highly alkaline environment, the steel reinforcing rods are passivated by the formation of a surface oxide film that protects the steel from corrosion. This protective oxide film is relatively stable at pH values greater than approximately 12.5 in a chloride free environment. The pH value required to stabilize the protective oxide film increases as the chloride content within the concrete increases. If this protective film is broken, corrosion can commence on the steel reinforcing rods. This may occur as a result of the ingress of sufficient chlorides into the concrete matrix to initiate corrosion. The chlorides may originate from the use of deicing salts, exposure to a marine environment, or through the use of a concrete admixture that contains chlorides. Alternatively, or in combination with the ingress of sufficient chlorides, carbonation of the concrete can occur. Carbonation, which is the reaction of CO and CO2 in the air with available alkali in the concrete, causes the pH of the concrete to decrease over time. Once the pH of the concrete is below 9.5, the protective oxide film starts to break down resulting in the commencement of corrosion of the steel reinforcing rods and the deterioration of the concrete structure. The deterioration of such structures has become a concern in the concrete industry. This concern has become so important that the issue of concrete durability has replaced the issue of concrete strength as the most pressing problem facing the concrete industry.
The objective of any type of concrete repair is for the repair to be relatively low in cost and durable in nature. In addition, variations in the repair should be limited and predictable over time and the repair should not deteriorate over time. Typically, there are several approaches to rehabilitate chloride contaminated reinforced concrete. One approach is to remove the damaged concrete and replace it with patch materials. Another approach is to utilize electrochemical means to minimize or eliminate future corrosion of the steel reinforcing rods within the concrete. Electrochemical chloride extraction typically involves the application of relatively high direct electrical currents to the concrete over a period of 10 to 50 days. The objective of this approach is to remove 20-50% of the chlorides from the concrete.
Another approach which is referred to as cathodic protection involves the passage of a small direct electrical current through the concrete. The objective of this approach is to reduce the rate of reinforcing rod corrosion to very low levels that are not of engineering significance. To apply an electrical current to the concrete, an anode is attached to the concrete and a voltage is applied between the anode and the steel reinforcing rods causing a direct current to flow through the concrete. With the cathodic protection approach, it is generally assumed that the protective current must be continually provided to the steel reinforcing rods.
Even though electrochemical approaches have been utilized to minimize or eliminate future corrosion of the steel reinforcing rods in concrete, such an approach does not fill the cracks within same. To fill such cracks, the injection of epoxy into same or routing and sealing the cracks or placing grout into the cracks are several of the approaches that have been utilized. Alternatively, electrodeposition of material into the cracks has been suggested. Such an approach, however, requires the crack to be immersed completely in an electrolyte solution. In many instances, immersion of the crack into an electrolyte solution is not possible.
In view of the foregoing, it has become desirable to develop an apparatus to electrodeposit a chemical composition into a crack in a chloride contaminated reinforced concrete structure in order to fill same while repassivating the steel reinforcing rods within the structure, even though the crack is not totally immersed in an electrolyte solution.
The present invention solves the problems associated with the prior art approaches to repair cracks in chloride contaminated reinforced concrete structures and other problems by applying technology to electrodeposit a chemical composition into the crack filling same. Such electdeposition requires the use of a dam (reservoir) which is placed over the crack to be filled, an electrolyte received with the dam (reservoir), a direct current power source and a steel mesh electrode which is received within the electrolyte and acts as an anode. The steel reinforcing rods within the concrete structure act as the cathode. The electrolyte is comprised of a composition of dialkylamino alkanoate zinc salt in isopropanol and natural spirits, and barium methaborate. Application of direct current by the power source to the steel mesh electrode and the steel reinforcing rods within the concrete structure causes the electrodeposition of a chemical composition into the crack in the concrete structure filling the crack and the repassivation of the steel reinforcing rods within the concrete structure.
Referring now to the Figures where the illustrations are for the purpose of describing the preferred embodiment of the present invention and not intended to limit the invention described herein,
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From the foregoing, it is apparent that the present invention can be successfully applied to reinforced concrete structures that are not totally immersed in electrolyte permitting the filling of cracks that are located in any area of the structure. In addition to filling the cracks in the concrete structure, the present invention repassivates the steel reinforcing rods within the structure. Thus, the present invention restores the integrity of the reinforced concrete structure by filling the cracks therein and by repassivating the steel reinforcing rods within the structure, and coats the concrete surface with chemical compounds that provide a physical barrier to the further intrusion of corrosive material into the concrete.
Certain modifications and improvements will occur to those skilled in the art upon reading the foregoing. It is understood that all such modifications and improvements have been deleted herein for the sake of conciseness and readability, but are properly within the scope of the following claims.
