Silver nitrate colorimetric method to detect chloride penetration in carbonated concrete: How to prevent false positives

The sprayed silver nitrate (AgNO3) solution colorimetric method allows identifying chloride ion presence in concrete. However, this method gives false positive results in carbonated concrete structures. This work aims to help develop a technique that restrains carbonation interference in silver nitrate solution spraying for detecting chloride ions in reinforced concrete. Calcium hydroxide and sodium hydroxide solutions were applied to raise sample surface alkalinity and act as barrier to carbonated products. Tests were made in carbonated concrete samples and in carbonated concrete samples contaminated with chlorides. A method of spraying sodium hydroxide solution before spraying silver nitrate in concrete was used. Results show that this can eliminate carbonation interference in chloride ion penetration when measuring with the silver nitrate method. This permits the use of the silver nitrate solution colorimetric method in field inspections where structures are exposed to carbonation and chloride attack simultaneously.