# Utilization of Thermal-Activated Coal Gangue to Enhance the Properties of Sandy Soil Composites
## 3 Results and Discussion
### Analysis of Water Holding/Retention Properties of Composite Soils  
As can be seen from Figure 6, the application of gangue significantly enhanced the water-holding capacity of mixed sandy soil. In comparison with CK, the water absorption of mixed soil with different dosages was obviously improved. The water absorption of mixed sandy soil with a 20% dosage of raw coal gangue reached 448.5 mL, which was enhanced by 136.8%. The evolution of water content changes in samples during the evaporation process is shown in Figure 7. After 24 h of evaporation at 110 \({}^{\circ}\)C, the change in water content in different treated sandy soils was similar. All samples exhibited a decrease in water content with the increasing of evaporation duration. Taking the raw coal gangue-modified sandy soil as an example, the water content of mixed sandy soil after mixing 5%, 10%, 15%, and 20% admixture was 33.1%, 34.5%, 37.2%, and 40.1%, while CK was 25.9% after 12 h, respectively. According to the measurement of water content after 24 h tending to complete evaporation, the water content of the CK group was 0.38%, while the water retention of 5%, 10%, 15%, and 20% dosed mixed sandy soil was 3.32%, 5.3%, 7%, and 8.5%, respectively. The water absorption of the soil composite increased with the increase in gangue admixture, indicating that the application of coal gangue and calcined coal gangue can effectively enhance the adsorption capacity of the composite soil to water molecules. Comparing the water absorption of mixed soil with 20% of different calcined coal gangue. For example, the application of 600 \({}^{\circ}\)C calcined coal gangue in sandy soil resulted in water absorption of 472 mL, which was increased by 148.8% compared to CK. At the same time, 850 \({}^{\circ}\)C calcined coal gangue-modified sandy soil contributed to the water absorption of 464 mL, which was increased by 143.8% compared to CK. On the other hand, the calcination treatment also improves the performance of coal gangue in mixed sandy soil during the water evaporation test. Moreover, 20% of raw coal gangue mixed with sandy soil exhibited a water content of 40.1% and 9.8% after 12 h and 24 h, respectively. Meanwhile,  
Figure 5: (a) Raw coal gangue effect on soil aggregate composition (a: dry sieve method, b: wet sieve method); (b) 600 \({}^{\circ}\)C gauge effect on soil aggregate composition (a: dry sieve method, b: wet sieve method); and (c) 850 \({}^{\circ}\)C gauge effect on soil aggregate composition (a: dry sieve method, b: wet sieve method). the sample mixed with 600 \({}^{\circ}\)C calcined coal gangue reached a water content of 44% and 13% after 12 h and 24 h, respectively. However, the increased calcination temperature of coal gangue showed a limited improvement in water-holding capacity. Mixed sandy soil with 850 \({}^{\circ}\)C calcined coal gangue exhibited a water content of 41.8% after 12 h and 11.6% after 24 h, which were lower compared to samples mixed with 600 \({}^{\circ}\)C calcined coal gangue particles. These observations indicate that calcination pre-treatment of coal gangue can effectively promote the water retention capacity of mixed sandy soil. By testing both water holding and retention, a more complete picture of the effect of gangue material application on soil properties can be seen. Morover, it can be seen that the resulting effect is a combination of both the amount of material incorporated and the treatment temperature. Combining the results of the two tests, when the gangue material mixing amount is 20% and the treatment temperature is 600 \({}^{\circ}\)C, the most excellent enhancement of the performance of sandy soil. To further confirm the water absorption ability of calcined coal gangue mixed sandy soil, the isothermal water absorption was conducted and will be discussed in the following section. Figure 6: Changes in water uptake of mixed soils with different treatments. Figure 7: (**a**) Changes in water content of mixed soils modified with raw coal gangue.