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Electrochemical chloride extraction (ECE) is a method of concrete treatment to prevent future corrosion of steel. The electrochemical chloride extraction is a treatment process where chloride ions are removed from chloride-contaminated concrete through ion migration. Unlike a cathodic protection system, the ECE is temporary and removed from the structure after completion of the treatment process.
The chloride extraction process is considerably advantageous to reduce the chloride below the level at which the corrosion process initiates. It can be utilized for various reinforced concrete structural members to not only increase their service life but also reduce maintenance work and cost. The ECE is employed to treat beams, columns, pier caps, decks, magnesite floors, and car parks.
The ECE removes chloride ions from contaminated concrete and reintroduces the passivity of steel reinforcement. As a result, the ECE process increases the service life of a structure.
ECE Treatment Process
The ECE treatment process is conducted by using a temporary electric field between reinforcements and an anode, which is externally attached to the concrete surface.
ECE can be applied to both vertical and horizontal concrete surfaces, and it provides extended service life and minimum disruption of traffic. The negative terminal of a DC power supply is connected to the reinforcing steel in the concrete. In contrast, the positive terminal is connected to an anode embedded in an electrolyte medium applied to the surface of the concrete.
Chloride ions move toward the anode, which is outside the concrete. These chloride ions leave the concrete and accumulate in the electrolyte media around the anode.
The chloride content of the concrete is reduced, particularly on and around the negatively charged reinforcing steel. During the electrolysis process, the production of hydroxyl ions at the reinforcing steel surface results in a high pH highly alkaline concrete environment after completion of the process.
This alkaline environment protects the steel against future chances of corrosion. The duration of ECE is between 3 to 8 weeks based on several factors, including treatment density, quantity and distribution of chloride ions, reinforcing steel quantity, and concrete properties such as permeability and electrical resistivity.
The system works at relatively low current densities and has a life varying between 5 and 20 years. The most commonly used electrolyte is calcium hydroxide because it is more alkaline.
The endpoint is determined by the reduction in the current, specifying chloride contents by taking samples from concrete, chloride content near the anode, or based on the calculation of total charge. The two side effects of chloride removal are an increase in alkali-silica reactivity (ASR) and reduction in bond strength of plain bars.
Factors Influencing ECE Performance
- Cement type
- Chloride binding
- Current density
- Rebar configuration
- Reduce corrosion activity and extended service life.
- The ECE is environmentally friendly.
- It offers an effective treatment for the whole area of application.
- It is a non-destructive method for reinforced concrete treatment.
- It doesn't need a permanent system for monitoring.
- Employ temporary power supply
- It does not replace corroded steel.
- The ECE can cause hydrogen embrittlement of the high-strength steels.
- Unsuitable for prestressed concrete members.
- The reinforcing steel must be electrically continuous for ECE to function.
- The removal efficiency may be different in areas close to reinforcing steel and between it.
- Pier caps
- Magnesite floors and car parks
- It can be used to treat marine structure in the seawater splash zone that causes the accumulation of chloride, but the provision of further protection against chloride is highly recommended.
FAQs on the Electrochemical Chloride Extraction?
It is a process that extracts chloride from chloride contaminated concrete members. The electrochemical chloride extraction employs the electrical field between steel bars and an external anode. It reduces chloride levels in concrete and re-establish the passive conditions of steel bras.
The ECE removes chloride ions from contaminated concrete and reintroduces the passivity of steel reinforcement.
Reduce corrosion activity, environmentally friendly, non-destructive method for reinforced concrete treatment, no requirements for a permanent system for monitoring, and employ temporary power supply.
Cause hydrogen embrittlement of the high-strength steels, not able to replace corroded steel, unsuitable for prestressed concrete members, reinforcing steel must be electrically continuous for ECE to function, and the removal efficiency may be different in areas close to reinforcing steel and between it.
The ECE applied to treat different concrete structural members such as beams, columns, pier caps, decks, magnesite floors, and car parks.