Application of the colorimetric method to chloride diffusion evaluation in concrete structures

The purpose of the present study are to properly estimate diffusion coefficient and determine the concentration of sprayed silver nitrate (AgNO3) that corresponds with the critical chloride amount. We also propose a suitable guide for application of the colorimetric method through indoor and field tests.According to the results, the colorimetric method using AgNO3 showed distinguished change to white reaction (AgCl) from brown reaction (AgOH). Any concentration (more than 0.05 N) of AgNO3 is useful in evaluation of the diffusion coefficient and is available regardless of age. The model equation for the relationship between Da (the concentration profile according to distance from the surface) and Dc (the penetration depth of the colorimetric method) is also proposed. When AgNO3 of 0.1 N is sprayed, free chloride amount (0.045%/1.08 kg/m3) of the color-change border is similar to the critical chloride content where corrosion is observed. Measurement of penetration depth by the colorimetric method is not appropriate when the pH of concrete is below 11.

► The colorimetric method can be an easy and practical alternative means to estimate the penetration depth of chloride ion.
► To use a silver nitrate concentration exceeding 0.05 N is recommended if the penetration depth of chloride ion is measured.
► The measurement of penetration depth by the colorimetric method is not practical if the pH of concrete is below 10.