Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Reexamination Certificate
2000-01-28
2001-07-10
Phasge, Arun S. (Department: 1741)
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
C205S734000, C205S766000
Reexamination Certificate
active
06258236
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for the electrochemical treatment of reinforced concrete.
BACKGROUND OF THE INVENTION
In reinforced concrete the steel reinforcement is normally protected against corrosion by the alkaline environment in the concrete mass. Gradually however the alkalinity is reduced by the action of carbon dioxide and other gases in the atmosphere such as oxides of sulphur. The term given to this process is carbonation and concrete which has been subjected to the action of atmospheric gases is referred to as carbonated.
The effect is a gradual decrease in the pH and, if the process is allowed to continue, the pH will continue to fall and when it reaches a value of about 9.5 the steel is no longer protected against corrosion. Corrosion of the reinforcement may then take place leading to weakening of the reinforcement and spalling of the concrete.
A process for increasing the alkalinity of concrete which has been carbonated has been previously described, for example in European Patent No. 264,421 and U.S. Pat. No. 4,865,702. In this process an electric current is passed between an external electrode which is in contact with an alkaline electrolyte applied to the external surface of the concrete and the internal reinforcement of the concrete as cathode.
During the process there are two effects: the alkaline electrolyte moves into the concrete and the alkalinity is increased in the region of the cathode. The benefit of this is that the steel is repassivated and a layer of electrolyte which has permeated into the concrete maintains a cover zone over and around the steel of sufficiently high pH to keep the steel passive. This process has become known as realkalization.
As the alkaline electrolyte for this process there is proposed in European Patent No. 264,421 an aqueous solution of calcium, sodium and/or potassium salts either in a liquid or absorbed in a porous medium such as rock wool, cellulose, sawdust, sand, clay and the like or the electrolyte can be strongly retarded concrete, mortar, cement grout or lime paste. GB Patent Aplication No. 2,271,123A discloses a process in which sodium carbonate or sodium borate is used in the aqueous electrolyte. However in the operation of the process on a commercial scale the alkaline electrolyte that has been used is an aqueous solution of sodium carbonate.
PROBLEM TO BE SOLVED BY THE INVENTION
Although the results of the process using sodium carbonate solution as the alkaline electrolyte have been generally very successful, the surface of the concrete after the treatment, frequently shows efflorescence. This is a heavy crystalline salt deposit which is unsightly and is unsuitable for the application of a decorative coating. Consequently it is necessary to thoroughly clean the concrete after treatment to remove the efflorescence.
A solution to the above described problem has now been invented in which a solution of potassium carbonate is employed as the electrolyte.
SUMMARY OF THE INVENTION
According to the present invention a process for the electro-chemical realkalization of concrete comprises passing a direct electric current between an anode in contact with a layer of aqueous electrolyte applied to an external surface of the concrete and a cathode which is located internally in the concrete, to cause the internal pH of the concrete to increase and surface layer of the concrete to be impregnated with the electrolyte solution and wherein the electrolyte layer contains an aqueous solution of potassium carbonate at a concentration at least 0.3 Molar.
ADVANTAGEOUS EFFECT OF THE INVENTION
The advantage of the present invention obtained by the use of an aqueous solution of potassium carbonate as the alkaline electrolyte is that efflorescence on the external surface of the concrete after treatment is reduced or eliminated. This advantage could not have been predicted from the prior art and is therefore unexpected.
REFERENCES:
patent: 5320722 (1994-06-01), Miller
patent: WO 87 06521 (1987-11-01), None
patent: WO 94/04474 (1994-03-01), None
Fosroc International Limited
Nixon & Vanderhye P.C.
Phasge Arun S,.
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