Semi-selfcompacting concrete (with a water-to-cement ratio of around 40% and a slump flow of around 500 mm) was widely used as filling materials for composite structures such as immersed tunnel. This type of concrete can be provided the required compactability with few supplementary vibrations, and is less costly than self-compacting concrete.
　In this study, to confirm the long-term durability of the concrete under marine environment, long-term exposure test was carried out for 10 years, and various performance were examined after 10 years of exposure.
　Obtained results were as follows:
　1) Compressive strength kept a high strength (around 60 N/mm2) after 10 years of exposure.
　2) Resistance for chloride ion penetration has very excellent performance. Also, The resistance was gradually improved with time. This indicated that the inner part of this concrete gradually became denser.
　3) Deterioration of concrete under marine environment occurred at the only concrete surface, similar to normal concrete.
　4) There was no significant difference in the concrete performance with or without few supplementary vibrations after 1.5 years of exposure.