A new material with high content of fly ash named 'Ashcrete' has been developed. To examine the applicability of Ashcrete to marine structures, strength characteristics, resistance to sea water attack, and safety in the marine environment have been studied. And a new manufacturing process has been developed which fluidizing fly ash, cement, admixture and a minimal amount of water mixture by series of vibrations named 'Super fluidizing method'. There are at least following four advantages in the super fluidizing method for Ashcrete production ; (1) increased quality of Ashcrete with homogeneous mixing and least cracking after drying, (2) increased economical efficiency by cutting the amount of cement by 2/3, (3) increased easy handling during operation with minimum adhesion and easy transport, and (4) increased easy mixing design with easy control of water and vibration. As the result of long term studies and underwater observations, the Japanese Govemment has approved the durability of the material, safety in the marine environment and attractiveness to fishes. It is therefore proposed that Ashcrete can be used in constructing large-scale sea mounts named 'Super Ridge' in deep water for the purposes of generating upwelling stream. The project was launched in which Ashcrete blocks were piled onto the seabed to construct a mound-shaped structure. This project is being carried out at a cost of approximately 10 million dollars spaming a period of six years.