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In order to explore the interactional relations of internal chloride and external chloride-binding amongst the cementitious materials, the chloride-binding capacity of mortars composed of marine sand (MS) or washed marine sand (WMS) were investigated. Results indicate that more external chloride can penetrate and diffuse more deeply into the WMS mortar than that in the MS mortar. This phenomenon suggests that the external chloride migration resistance due to WMS is lower than that caused by MS. The distribution trends of the bound chloride content in the two types of mortars are the same at different immersion times. However, a significantly decreased area of the bound chloride content exists at the border of the external penetration area (EPA) and the external unaffected area (EUA) at the immersion ages of 3 and 7 d, and then it disappears gradually with immersion time. The WMS mortar can bind more external chloride, whereas the MS mortar can bind more internal chloride, at different immersion times. The distributions of bound chloride conversion rate in the EPAs of the two types of mortars differ across immersion times. The distribution firstly decreases, and then it increases at the immersion ages of 3 and 7 d. The distribution was from increase, then decreases, and increase again at the immersion ages of 28 and 56 d. The bound chloride conversion rate in the WMS mortar is affected more greatly by external chloride penetration than that in the MS mortar. The amounts of the Friedel's salt tend to increase with prolonged immersion time. Finally, the penetration of external chloride can increase the amount of fine capillary pores smaller than 100 nm in the WMSmortar exposed for 56 d in the chloride salt solution (WMS-E) specimen. [ABSTRACT FROM AUTHOR]