# Utilization of Thermal-Activated Coal Gangue to Enhance the Properties of Sandy Soil Composites
## 3 Results and Discussion
### The Modification of Calined Coal Gangue on the Aggregation of Sandy Soil  
Soil aggregates can be categorized into macroaggregates R\({}_{0.25}\) (>0.25 mm) and microaggregates (<0.25 mm) based on particle size, which is considered one of the most important factors in evaluating soil physical properties [19]. Furthermore, water-stable aggregates are structural units of soil structure that can maintain their morphology and not disperse immediately after water immersion. This stability is one of the most important indicators of soil structure, which reflects the ability of soil to resist water erosion and dispersion [20]. Due to the strong interaction force between particles within the water-stable agglomerates, the joint effect makes the agglomerates remain stable under the action of water, which can effectively prevent water infiltration and erosion and improve the soil's resistance to erosion. It is generally believed that the greater the number of soil aggregates, the greater the stability of the soil body [21].  
Firstly, the mechanical composition of aggregates of different grain sizes in composite sandy soil was determined using the dry sieve method. The original coal gangue was selected as a reference (CK), and composite sandy soil doped with 5% of gangue compared to CK treatment (Figure 5a), the proportion of aggregates with grain sizes of 0.075-0.15 mm and 0.075 mm \(<\) was increased by 5% and 9%. When the amount of doped amount reached 20%, the proportion of aggregates with grain sizes of 0.075-0.15 mm and 0.075 mm \(<\) the proportion of particle size agglomerates increased by 12% and 16%. The content of > 0.25 mm particle size agglomerates in each treatment increased by 2%, 4%, 5%, and 7%. When TACG was applied, the composite sandy soil with >0.25 mm particle size agglomerate content under 600 \({}^{\circ}\)C and 850 \({}^{\circ}\)C (Figure 5b,c) treatments was not significantly increased. When the dosage reached 20%, both were increased by 1%.  
Using the wet sieve method, determining the distribution of water-stable aggregates in mixed soils with different grain sizes. Taking the original gangue as a reference (CK), the effect of different admixture amounts on the water stability agglomerate distribution of mixed sandy soil is more significant. Compared with the CK treatment, the proportion of the grain size agglomerate of 0.075-0.15 mm and 0.075 mm\(<\) in the composite sandy soil admixture with 5% gangue is increased by 11% and 12%. The content of >0.25 mm grain size agglomerate of each treatment is increased by 12%, 24%, and 20%. When the amount of doped amount reached 20%, the proportions of 0.075-0.15 mm and <0.075 mm particle size agglomerates increased by 12% and 24%. The content of >0.25 mm particle size agglomerates in all treatments increased by 4%, 7%, 7%, and 8%.  
Similarly, comparing the sand soil mixed with TACG (600 \({}^{\circ}\)C and 850 \({}^{\circ}\)C) and the original gangue, when the dosage reaches 20%, the content of >0.25 mm particle size agglomerates does not change significantly. For the composition of water-stable agglomerates, the change trend in sand soil after mixing with TACG is the same as that of mixing with the original gangue. From a comprehensive point of view, the application of gangue material has a positive effect on the aggregate structure composition of sandy soil, and the dosage of coal gangue plays a dominant role in it.