A study of the factors affecting the surface chloride maximum phenomenon in submerged concrete samples

The chloride content analysis of the concrete exposed to chlorides often shows an initial increase in the concentration of chlorides to a maximum point within the first layers from the concrete surface, followed by a gradual reduction in the concentration of chlorides at the lower depths. A review of literature shows that very little attention has been given to the depth (Δx) at which the maximum chloride concentration (C_max) occurs and its potential impacts on the numerical estimation of the apparent chloride diffusion coefficient (D_a) and surface chloride concentration (C_s). This paper studies the influence of water-to-cement ratio (w/c), the concentration of chlorides in the environment, the time-to-exposure, and exposure duration on C_max and Δx. Results show that w/c does not have a significant influence on C_max. However, a significant increase in Δx is observed with an increase in the w/c. Results also show that while C_max has time-variant properties and it increases nonlinearly with the exposure duration, exposure duration has minimal impacts on Δx. In addition, the time-to-exposure and the concentration of chlorides in the exposure environment are found to be significant factors influencing both C_max and Δx. The findings of this study show that Δx has a significant impact on the numerical estimation of D_a and C_s. Because Δx is not limited to the first millimeter of the concrete surface, as specified in ASTM C1556, care must be taken to exclude the layers that correspond to Δx.