Environmental pollution caused by huge amount of generated coal fly ash (FA) without utilization and the deterioration of desertification in arid areas are big social problems. This study investigated the effect of raw coal fly ash amending on water holding capacity (WHC) of decomposed granite soil (DGS), akatama soil (AS) and river sand (RS) with different size distribution. The soil and sand were dried at room temperature and 40 oC, respectively, and their moisture losses were monitored per hour. The experimental results showed that particle size had an effect on WHC. Non-linear relationship appeared between the particle size and WHC of soil or sand. Highest WHC appeared in certain range of particle size and it depends on soil type. One-sided Welch’s t-test suggests that the size dependency of raw FA amendment on WHC was regarded as significant in some cases even when experimental errors were taken into account. If the temperature or mixing ratio is different, however, optimum size range for highest WHC changed. This means that the impact of FA addition on WHC is very complex, depending on many factors such as particle sizes, drying temperature, soil type, and mixing ratio of FA.
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