Moisture Loss Resistivity Against Evaporation (water retention capacity) of Natural Soil Amended with Raw and Apatite Synthesized Fly Ash.

Coal fly ash (FA) was largely generated from coal-fired power plants. FA recycle as water holding agent is attractive to ameliorate soils in arid areas. FA amendment is usually effective to increase soil water holding capacity, which is measured based on physical water loss by the gravity or controlled pressure under water-saturated condition. In order to simulate soil moisture loss via temperature-driven evaporation by simple drying experiments, this study tested water retention capacity (WRC) which represents moisture loss resistivity against evaporation under unsaturated condition. WRC of decomposed granite soil (DGS), raw FA, apatite-synthesized FA and FA-mixed soil were measured at room temperature and 40 ºC. In apatite treatment of FA, apatite was synthesized on FA surface with P/Ca ratio of 11.67. At room temperature, WRC of almost all pure samples (DGS, raw FA and treated FA) were similar. On the other hand, WRC of raw FA and DGS decreased by around 40 % and 20 % at 40 ºC, respectively. WRC of DGS with raw FA amendment also decreased compared to WRC without FA amendment. This means that FA amendment could not suppress soil moisture loss via evaporation at high temperature. In contrast, WRC of treated FA has almost the same WRC at 40 ºC with that at natural temperature. In addition, treated FA amendment increased WRC of DGS. Surface area of raw and treated FA could not explain positive effect of treated FA amendment on WRC. There was a little difference in surface area between raw FA (about 2.1 m²/g) and treated FA (2.5 m²/g). Pore type of surface micro-structure of raw and treated FA were also the same (slit pore type). Hydraulic properties of treated FA surface, excluding surface area and pore type, seem to affect soil WRC when treated FA is amended.