In Japan, the island country, many concrete structures are located under marine environment.These structures are exposed in severe conditions, where heavy deterioration is generally observed due to chloride attack by seawater splashing and sea breeze. Therefore, a lot of studies on durability enhancement of reinforced concrete structures under marine environment were carried out. On the other hand, the tidal and submerged parts of marine concrete structures are generally covered with marine aquatic organisms. Empirically, deterioration of organically covered concrete is not so severe.It can be presumed that the layer of organisms may inhibit penetration of substances such as chloride ions into concrete. In this study, this hypothesis is examined through laboratory and field exposure tests for about two years. This study will contribute to not only durability enhancement of marine concrete structures, but also preservation of marine ecological systems. The following conclusions were drawn by this study.
(1) The membrane layer of barnacles was mainly composed of calcium carbonate with protein. The layer is denser than cement paste matrix. A chloride ion diffusion coefficient of the membrane layer is about 1/l00 as that of concrete.
(2) Low alkaline mix of concrete is suitable for the marine fouling organisms to attach to concrete surface at the earlier stage of attachment. After the earlier stage, concrete with much voids is suitable for promoting the attachment.
(3) The chloride ion diffusion coefficient, the oxygen diffusion coefficient and the corrosion rate of rebars decreased as the amount of marine fouling organisms increased. Also, the corrosion of rebars decreased with increase in the length of the crack right above the rebars covered by marine fouling organisms.
(4) On the basis of the time-dependent deterioration progress model of reinforced concrete structures, it is made clear that the lifespan of structures can be extended by attachment of organisms.
(5) Technical methods of marine fouling organisms attachment to real concrete structures were proposed. Also, life cycle maintenance method of organically covered structures were discussed.