Posted by Matthew Anderson on March 26, 2025
Chloride in concrete can be a silent killer for steel reinforcement—triggering corrosion that cuts a structure’s life short. If you’re a contractor pouring slabs, a manufacturer supplying precast, or an engineer signing off on specs, knowing how to test for chloride is a game-changer. The good news? You don’t need a fancy lab to get reliable results. With a pH meter, some silver nitrate, and a few basics, you can measure chloride levels yourself. Here’s how I do it.
What You’ll Need
– A pH meter (set to millivolts for endpoint detection)
– Silver nitrate solution (0.1N works well)
– Burette, beaker, stir bar, glass stir rod
– Distilled water
– Nitric acid (diluted to 1 part nitric acid, 3 parts distilled water)
– Concrete sample (powdered—drill or crush it)
– Silver billet electrode
– pH electrode
– Hot plate
Step 1: Prep Your Sample
Start with a dry, powdered, representative concrete sample—ten grams is needed for analysis, but having more can help ensure your sample is representative. Mix your sample well and weigh ten grams of concrete powder into a beaker, recording the weight. If you’re testing water-soluble chloride (what’s free to move around and contribute to corrosion), add 50 mL of boiling water to a beaker containing the concrete powder and mix well by stirring. Allow the mixture sit for 24 hours. For acid-soluble (total chloride, bound or not), add 50 mL of diluted nitric acid to the concrete powder, mix with a stir rod, and bring to a gentle boil on a hot plate. As it begins to boil, remove from the hot plate, stir and let the mixture cool. Filter out the solids— paper filters are commonly used, but coffee filters could work in a pinch. (Curious about the difference between acid-soluble and water-soluble chloride? Check out my last post on chlorides “Why does chloride in concrete matter? What’s the difference between water-soluble chloride and acid-soluble chloride?”
Step 2: Set Up the Titration
Pour your filtered solution into a beaker. Add diluted nitric acid to the filtered solution and mix. The volume is not important for determining the end point, but too much volume can sometimes make it titrate slower. Place your electrodes into the solution and read mV with the millivolt meter. Clamp your burette over the beaker and fill it with silver nitrate solution. You’re ready to titrate.
Step 3: Titrate and Watch the Endpoint
Allow the mV to stabilize and record the initial mV of the solution. Slowly drip silver nitrate into the beaker in 0.2 mL additions, stirring constantly with a stir bar. The chloride ions will react with silver nitrate to form silver chloride, which drops out as a white precipitate. Keep going until about 0.2 mL of silver nitrate drops the mV reading by about 10. Keep adding silver nitrate into 0.2 mL increments and record the mL of silver nitrate added, and the corresponding mV reading. The end point is where the largest drop in mV is recorded for a 0.2 mL addition on silver nitrate (usually 50-100 mV). That’s when all the chloride has been consumed by the silver nitrate.
Step 4: Crunch the Numbers
After completing the titration, the result will need to be calculated. Results are typically reported in %(w/w). Here is an example of data collected during a chloride titration and calculations performed using this example data.
mL mV
1.0 140 (mV1)
1.2 120 (mV2)
1.4 50 (mV3)
1.6 25 (mV4)
First calculate exactly how much silver nitrate was consumed to reach the end point in milliliters. The largest decrease in millivolts is between 1.2 mL and 1.4 mL. So the approximate end point (E1) is 1.2 mL, and the exact endpoint is between 1.2 mL and 1.4 mL. The titration increment (I) used is 0.2 mL. To calculate the exact endpoint the difference between millivolts needs to be calculated between each incremental titrant addition.
D1 = mV1 – mV2
D1 = 140mV – 120mV = 20mV
D2 = mV2 – mV3
D2 = 120mV – 50mV = 70mV
D3 = mV3 – mV4
D3 = 50mV – 25mV = 25mV
D4 = D2 – D1
D4 = 70mV – 20mV = 50mV
D5 = D2 – D3
D5 = 70mV – 25mV = 45mV
Then to calculate the final endpoint (Ef) use the following equation.
Ef = [D4 / (D4 + D5)] × I + E1
Ef = [50mV / (50mV + 45mV)] × 0.2mL+ 1.2mL
Ef = 1.305 mL
The calculated final endpoint of 1.305 mL is the amount of silver nitrate titrant that was consumed to reach the endpoint of the titration. Next use this value to determine chloride content of your concrete sample. It will be assumed the mass of the concrete sample weighed was exactly 10.0000 grams and the normality of the silver nitrate used as the titrant was 0.1000 N. It will also be assumed no sample dilutions were made so the aliquot and dilution volumes will be 1.
Chloride %(w/w) = (Ef) × Silver nitrate normality / Sample mass × Sample aliquot volume / sample dilution × 3.545
Chloride %(wt/wt) = 1.305 mL × 0.1000 N / 10.0000 g × 1 mL / 1 mL × 3.545
Chloride %(wt/wt) = 0.05 %(wt/wt)
For a ten gram concrete sample, this would calculate to 0.05%(wt/wt) chloride. Adjust for your sample size if it’s different. Compare that to specifications.
Why It Works
This setup is lean but effective. The pH meter doubles as a potentiometer, silver nitrate is a tried-and-true reagent, and you will get results quickly. No $20 bargain lab can match the quality and control you get manually titrating samples—or the speed when a job’s on the line.
Need this done for your next project? I can analyze samples at $65 per sample —fast, reliable, and high quality data. Call or email today for a quote. For more information contact Matthew Anderson at 847.306.9240 or manderson@materialsanalyticalgroup.com.
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