FLASH-SETTING LIGHTWEIGHT MATERIAL - A FIRST STEP TO FLOATING ISLAND CONSTRUCTION

The possibility of constructing a floating island using air/cement/wat er (ACW), a mixture of water glass solution and foamed cement paste, w hich shows a flash-setting property and is lighter than water, is stud ied. The following results obtained through a series of laboratory tes ts and model placement tests show a high applicability of ACW for floa ting island construction: (1) gel time of ACW can be controlled by the quantity ratio of water glass and cement; (2) seawater is also usable , however a larger amount of water glass is needed than for tap water for a given gel time ACW; (3) strength increases linearly with the log arithm of elapsed time, and depends on dry density; (4) viscosity of A CW before gelation is too low to prevent segregation, which can be con trolled by bentonite addition; (5) permeability of ACW is dependent on dry density; (6) addition of coal fly ash lowers early strength but e nhances long-term strength, and is usable as a partial substitution fo r the cement; (7) ACW can be directly placed on the water uniformly, a nd the placed mass on the water settles by its own weight; (8) this se ttlement ceases within 10 days; and (9) water intake of 30-40% takes p lace during the flotation, however, this is limited to the underwater part at the placement. This floating island construction is still at t he experimental stage; however, the properties of ACW suggest a variet y of actual usage such as for structural fills overlaying on very soft ground or embankments for emergency.