Reinforced concrete structures in harbors or sea shores are typically contacted with sea waters and exposed to brine and humid environment from the start of the construction stage thus erosion in the durability of the structures are aggravated. Especially, the SOC structures suffered drying shrinkage accompanying the through cracks, facilitate the penetration of chlorine ion. In this study, the durability improving admixture(DIA) mixed with oligomer condensate and Si/Al composition was developed. The DIA countervails the drying shrinkage of concrete and mortar, fixes the chlorine ion, and prevents the erosion from the sulfate ion. In the experiments of this study, the mortar having excellent resistibility against salt damage was produced by mixing the DIA with the binder replaced the fine blast-furnace slag and cement. The whole 3 mixtures including the one mixed only with the cement (OPC) and another one replaced the blast-furnace slag (BSC), and the other one mixed with the DIA were tested. Using the 3 mixtures, the experiments to identify restraint drying shrinkage, chlorine ion penetration and the erosion from the sulfate ion were conducted. In all conducted experiments, the excellent resistibility against salt damages and drying shrinkage were identified in the order of DIA, BSC, and OPC.