In the southern part of the Japanese mainland, many coral limestone rocks have been deposited. In remote islands in such areas, it is desirable to use aggregates manufactured from locally available seawater and coral-derived limestone (hereinafter referred to as "coral aggregates") as concrete materials from the standpoint of economic efficiency and production efficiency. However, the quality of coral aggregate is inferior to that of ordinary aggregate because of the many pores in its structure. In addition, the use of self-filling concrete is expected to save labor in construction, but there has been no study on self-filling concrete using coral aggregate so far.
In this study, the characteristics of coral aggregates collected at Minamitori Island were summarized in order to investigate the applicability of concrete using coral aggregates to marine structures. Coral aggregate was used as the aggregate and seawater was used as the mixing water, and self-filling concrete was investigated experimentally. On the other hand, the marine exposure test of concrete using coral aggregate was started in 1976, and in the present study, the long-term behavior (seawater resistance) of concrete specimens after long-term exposure (after 44 years) was evaluated.
The findings are presented below.
1) It was confirmed that the required flowability and pore passability could be ensured when applied to self-filling concrete. However, since there is a concern about the change in freshness of the aggregate due to pressurized water absorption, it is necessary to keep in mind when pouring concrete by pumping.
2) It was confirmed that concrete after curing had the same level of strength expression as that of ordinary aggregate, and that the shrinkage strain and thermal expansion coefficient were smaller.
3) Even after more than 40 years of exposure to marine and tidal environments, the concrete subjected in this study showed an increase in compressive strength.
The above study shows that coral aggregate has many internal pores and is of low quality in some cases, but it can be sufficiently applied as an aggregate for concrete in the marine environment by using an appropriate formulation based on the characteristics of the target environment.

Key Words: Marine concrete structure, coral aggregate, compressive strength, shrinkage, long term exposure