Improved Rapid Chloride Migration Test for Chloride Diffusion Coefficient of Concrete Based on the Image Processing Technique

The point average method (PAM) is commonly used in rapid chloride migration (RCM) tests to measure the average depth of chloride migration in concrete specimen. In this article, a spatial average method (SAM) was presented to improve the accuracy and stability of results tested on the basis of an image processing technique. There are 74 groups of concrete specimens prepared with different mix proportions and tested by the RCM technique with varying voltage applied. The area of the chloride migration region on the longitudinal section of the concrete specimens was captured by the image processing technique firstly, and then both the average depth of chloride migration and the diffusion coefficient of concrete were accordingly determined. Furthermore, the spacing of measuring points and the range and amplitude of the edge effect in the RCM test were determined by detailed analysis of the test data, thereby improving results from the PAM and the SAM. It was demonstrated that the edge effect should be taken into consideration in the RCM test for determining the chloride diffusion coefficient of concrete, and the spacing of measuring points for the PAM in current codes and guidance is so large that they should be modified. The general validity, satisfying stability, and high accuracy of the proposed SAM were evidentially proved by comparing it with the test data of the PAM.