This page presents a general description on applying Chloride Extraction.  Incorporated within the page is also a tool to calculate the total cost of applying Chloride Extraction.

ECE is also referred to as chloride extraction (CE) or desalination.  The fundamental principle involved in ECE is similar to that of Cathodic Protection.  The only major differences are the period and level of current application.  ECE is a temporary treatment where a much higher current density in the range of 0.5-2.0 A/m² of steel is applied over a period of weeks.  The chloride ions migrate to the concrete surface where they are removed.

Early work in the 1970’s, at Battelle Columbus Laboratory and BRE, showed that the electrochemical removal of chloride from reinforced concrete was possible.  The studies concentrated on removing chloride over a relatively short timescale by using high voltages and current densities that were not practical for large-scale applications and also resulted in increased permeability of the concrete.   Furthermore, high current densities could result in the production of toxic concentrations of chlorine gas, which necessitated the collection of chloride ions before reaching the anode.

Certain factors has to be taken into consideration to check if Chloride Extraction is suitable for the structure in question.  

To find out if  it is suitable, activate this tool Check List . The Check List tool present a list of criteria which should not exist within the structure, if Electrochemical Chloride Extraction  is to be used.  If any of the criteria is checked, then it is our recommendation that it should not be applied.

Activate this tool Chloride Extraction  to calculate the cost of using Chloride Extraction.

The two main inputs expected are the 'Cost of Technique'  and 'Area to be Treated' . 

Multiplication of the two main inputs generates a total cost for the specified technique.  This cost is then added to the 'Fixed Cost' to produce a total cost for applying the technique from conception to finish.

The first and last two inputs which is the'Name of the Technique',  'Maintenance Cost' and 'Life of Technique' are essential if the user requires the output generated by this tool for future reference.

The generated output is presented in a report format which contains the specified technique as well as other details relating to the calculation .

The output produced within the Total Cost text area can then be copied and pasted within a report or a document for future reference.

The commercial processes use lower current densities of typically 1 A/m² of steel and the chloride extraction from one treatment area can take up to 12 weeks.  The rate of extraction will depend upon:

•  The amount of chloride.
• The temperature.
• The permeability of the concrete.
• The amount of reinforcement.
• The depth of the reinforcement.
• Whether the chloride was cast-in 

The application of ECE

The process requires that the surface of the concrete is made good but does not require otherwise sound chloride-contaminated or carbonated concrete to be replaced. The electrical continuity of the reinforcement is checked and electrical connections are made to it with at least one connection per 50 m² of concrete surface.  In a typical set-up, sealed cassette shutters are used with the anode mesh suspended in the electrolyte within. The anode mesh is most commonly titanium based, as mild steel varieties would rapidly corrode away. 

The electrical connections are made to the mesh with one connection per 10 m² of mesh, or per cassette shutter. The electrolyte used is usually water with an addition of calcium hydroxide to reduce acidification of the electrolyte during the extraction process.

The steel reinforcement is connected to the negative terminal of a DC transformer rectifier unit and the mesh to the positive terminal.  Once switched on the system is usually operated at a nominal current density of 1 Am^-2 of steel, although this is dependent upon several factors including;

·         The ratio between the steel and concrete surface areas.

·         Resistivity of the concrete.

It may be decided to effect the treatment on the basis of a fixed run time of say 1500 Ahrs/m² of steel surface.