## 3 Results and Discussion
### Chloride Transport Properties
For unsaturated specimens (S = 60%), however, the accumulation of chlorides seems to have been less apparent, and the chloride peak disappeared in the outermost part of the specimen, in particular for the early drying-wetting cycles. The chloride content of the unsaturated specimens shows a slight decrease first and then a rapid drop with the depth. In the wetting process of the unsaturated specimens, capillary absorption predominated the transport phenomena, and the effect of capillary absorption seems to have been pronounced with the first increase in the drying-wetting cycles. As such, the chlorides could hardly be accumulated in the skin layer. On the other hand, the saturation level of the unsaturated specimen became higher with the continuous increase in the drying-wetting cycles, given that water evaporation caused by drying is much slower than water absorption caused by wetting. There may possibly be a critical saturation level, above which the influential depth of cyclic drying-wetting on chloride penetration tends to be decreased. The accumulation of chlorides in the skin layer of the unsaturated specimens (S = 60%) could be observed after 50 drying-wetting cycles. For unsaturated specimens, the convection owing to cyclic drying-wetting played a significant role in the chloride penetration, and the chloride contents were considerably higher than those of the saturated specimens. This suggests that marine concrete in tidal zones should be cured with as much saturation as possible to avoid drastically rapid penetration of chloride at an early age of service. To quantitatively describe the effect of drying-wetting cycles on chloride penetration, the experimental data of the total chloride profiles were fitted with [PERSON]'s second law (Equation (2)). The apparent chloride diffusion coefficient \(D_{\text{a}}\) as a function of the drying-wetting cycles is displayed in Figure 9. It has been recognized that both capillary absorption and chloride diffusion influence the chloride penetration of specimens exposed to cyclic drying-wetting conditions. The \(D_{\text{a}}\) values given in Figure 9 were used primarily for comparative studies. The surface chloride content \(C_{\text{s}}\) does not have a consistent trend of change with increasing drying-wetting cycles according to the best-fit results using Equation (2). The \(D_{\text{a}}\) value, nevertheless, generally shows a decreasing trend with the increased cycles of drying-wetting exposure. A drastic drop in the \(D_{\text{a}}\) value can be seen at the early stages of the drying-wetting cycles, and a slightly slow decrease in the \(D_{\text{a}}\) value  
Figure 8: Total chloride profile of saturated (S = 100%) and unsaturated (S = 60%) mortar specimens. was observed at later stages. The \(D_{\text{a}}\) value was considerably higher for the binders with lower saturation levels. The slag-blended binders exhibited markedly higher resistance to chloride penetration than the OPC binders, as reflected by the lower \(D_{\text{a}}\) values. It is interesting to note that the differences in the \(D_{\text{a}}\) values were diminished for 65% slag binders of various saturation levels. This was the same case for OPC binders. The \(D_{\text{a}}\) value may become quite similar for a particular binder even with a different initial saturation level after sufficient exposure to drying-wetting cycles. The chloride transport at early drying-wetting cycles, as indicated by the \(D_{\text{a}}\) value, seems to have been much more sensitive to the initial saturation level for the slag-blended binders than for the OPC binders. In the early days of drying-wetting exposure, capillary absorption played an important part in the chloride penetration of unsaturated binders. A lower saturation of the binder corresponded to higher capillary absorption, leading to a higher \(D_{\text{a}}\) value. The saturation level of unsaturated binders increased rapidly at the early exposure and then tended to increase gradually.