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

Abstract

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 floatation, 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.