Chloride Ion Migration Coefficient of Cracked Mortar Specimens Using Steady-State Migration Test Method

The primary factor which causes the corrosion of the reinforcing bars, especially in the marine environment is the penetration of chlorides resulting in shortening of the service life of concrete structures. The standard method for calculating the chloride diffusion coefficient is available only for uncracked specimens and there is lack of research for the cracked specimens. This study has been undertaken to understand the tendency of diffusion of the cracked mortar specimens. The major variables for this study were the crack width and the electrical potential difference applied. For this purpose, specimens with real crack widths of 0.1 and 0.3 mm were manufactured in the laboratory and tested to measure the steady-state chloride migration coefficients using the test setup of ASTM C1202 under the electrical potential differences of 12, 24, and 36 V. The steady-state migration coefficients were calculated with the help of Nernst-Planck equation and the effect of crack width and applied voltage on the calculated migration coefficients were explored. The test results confirm that the migration coefficients increase proportional to the crack widths and the applied potential. Under 12 V, the migration coefficients were much smaller than under 24 and 36 V. The low migration coefficients under low potential may be due to the self-healing of cracks during the test because it takes longer time to reach the steady-state under lower potential.