Coal fly ash amendment to mitigate soil water evaporation in arid/semi-arid area: An approach using simple drying focusing on sieve size and temperature

Abstract Coal fly ash (FA) utilization as water retention agent to ameliorate soil is attractive in arid/semi-arid area. FA amendment was expected to make void pore networks in soil better for water retention. The purpose of this study is to investigate FA amendment effect on weight-based water holding capacity (WHC) and evaporation mitigation capacity (EMC) of soils and sands. EMC represents water loss mitigation capacity against physical evaporation using drying experiments at room temperature and 40 °C. Because this study hypothesized that particle size of soil/sand mainly controls WHC and/or EMC, sieved soil/sand samples were tested. FA amendment effect was significant to increase WHC but much smaller than sieve size effect. On the other hand, statistical tests suggested that FA addition had no significant effect on EMC, which was contrast to sieve size and temperature effects. Significant interaction was also found between sieve size and temperature. Contrast to the initial hypothesis, sieve size effect on EMC was not derived from physical particle size of soil/sand but from organic matters contained in sieved samples. Organic matter concentration had a good correlation with the variation of EMC. In addition, it showed opposite trends at room temperature and 40 °C. It means that organic matters mainly control EMC. This study concludes that FA amendment can increase the amount of water remaining water in soil but is not effective to make water retention longer. FA modification using appropriate organic compounds is necessary and it should be designed carefully considering temperature dependency.