Flash-Setting Lightweight Material—A First Step to Floating Island Construction

The possibility of constructing a floating island using air/cement/water (ACW), a mixture of water glass solution and foamed cement paste, which shows a flash-setting property and is lighter than water, is studied. The following results obtained through a series of laboratory tests and model placement tests show a high applicability of ACW for floating 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 logarithm of elapsed time, and depends on dry density; (4) viscosity of ACW before gelation is too low to prevent segregation, which can be controlled by bentonite addition; (5) permeability of ACW is dependent on dry density; (6) addition of coal fly ash lowers early strength but enhances long-term strength, and is usable as a partial substitution for the cement; (7) ACW can be directly placed on the water uniformly, and the placed mass on the water settles by its own weight; (8) this settlement ceases within 10 days; and (9) water intake of 30–40 takes place during the flotation, however, this is limited to the underwater part at the placement. This floating island construction is still at the experimental stage; however, the properties of ACW suggest a variety of actual usage such as for structural fills overlaying on very soft ground or embankments for emergency.