How to Test Chloride Ion Levels in Concrete

How to Test Chloride Ion Levels in Concrete

Testing chloride ion levels in concrete is important to assess the potential for corrosion of embedded steel reinforcement, which can lead to structural deterioration. There are several methods to test chloride ion levels in concrete, including the Rapid Chloride Ion Penetration Test (RCPT) and the Acid-Soluble Chloride Content Test. Here’s how to perform each test:

Rapid Chloride Ion Penetration Test (RCPT):

The RCPT measures the electrical resistance of concrete to the penetration of chloride ions. This test is particularly useful for assessing the concrete’s resistance to chloride ion penetration and is often used for quality control and durability assessment.

Equipment and materials needed:

  • RCPT apparatus
  • Concrete cores or specimens
  • Deionized water
  • Silver-silver chloride electrodes
  • Power supply
  • Testing apparatus calibration standards
  • Safety equipment (gloves, goggles, etc.)


Prepare the concrete specimens:

You’ll need concrete cores or specimens with a specific diameter and length according to the test standard you are following.

Prepare the RCPT apparatus: Assemble the RCPT apparatus and ensure it is calibrated properly.

Wet the concrete specimens:

Immerse the concrete specimens in deionized water for a specified period to saturate them.

Install the electrodes: Insert the silver-silver chloride electrodes into the prepared holes in the concrete specimens.

Connect the apparatus:

Connect the electrodes to the RCPT apparatus, and connect the apparatus to a power supply.

Apply a voltage:

Apply a constant voltage to the concrete specimens using the RCPT apparatus.

Measure current:

Measure the current passing through the specimens over a specific period.

Calculate the chloride ion permeability:

Use the obtained data to calculate the chloride ion permeability of the concrete, typically reported in coulombs.

Acid-Soluble Chloride Content Test:

The acid-soluble chloride content test determines the total chloride content in a concrete sample, which includes both free and bound chloride ions. This test is more suitable for estimating the total chloride content in concrete.

Equipment and materials needed:

  • Concrete core or specimen
  • Acid solution (usually 0.1 N silver nitrate solution)
  • Glass beaker
  • Graduated cylinder
  • Funnel
  • Filter paper
  • Vacuum filtration apparatus
  • pH meter
  • Safety equipment (gloves, goggles, etc.)


Prepare the concrete specimen: Collect a concrete sample, typically by drilling a core from the structure.

Crush the sample:

Crush the concrete sample into small pieces, ensuring that they are representative of the entire structure.

Weigh the sample:

Weigh a portion of the crushed concrete sample.

Prepare the acid solution:

Dilute the 0.1 N silver nitrate solution with distilled water to make it suitable for the test.

Extract chloride ions: Place the weighed concrete sample in a glass beaker and add the acid solution to it.

Filter the solution:

Filter the solution using a vacuum filtration apparatus to separate the solid residue from the filtrate.

Measure pH:

Measure the pH of the filtrate to confirm the acidic conditions.

Titration: Titrate the filtrate with a standard silver nitrate solution until a color change is observed, indicating the endpoint of the reaction.

Calculate chloride content:

Use the volume and concentration of the silver nitrate solution consumed to calculate the chloride content in the concrete sample.

These are the two common methods to test chloride ion levels in concrete. The choice of method depends on the specific requirements and objectives of your assessment. Always follow relevant industry standards and guidelines when performing these tests.