# Suppression Effect of Waterborne Polymer on Soil Used for Backfilling at Construction Site
## 4 Discussions  
According to the wet dust suppression performance of polymers, the drying of the soil for backfilling lasted about 17 h after spraying with the polymer dust suppressant. Due to an increase in humidity and a decrease in temperature at the construction site overnight, as well as the moisture absorption of both the soil and the polymers [34; 35], a high dust suppression effect could be maintained within 24 h. Continuous use of five cycles was equivalent to five days. Therefore, the wet dust suppression performance was evaluated for a continuous duration with a dust suppression efficiency of at least 60%. Taking the test errors and safety factors into account, the determined index was a dust suppression time no less than 5 days. The dust suppression efficiency was calculated based on the average moisture content under constant temperature and humidity conditions using the backfill powder from the construction site. The test objects were the same as the field application \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**PM\({}_{2.5}\)**} & \multicolumn{2}{c}{**PM\({}_{10}\)**} \\ \cline{2-5}
**Time/h** & **Dust Suppression** & **Control Area** & **Dust Suppression** & **Control Area** \\  & **Area** & **Control Area** & **Area** & **Control Area** \\ \hline
0 & 37.00 & 36.50 & 57.75 & 56.50 \\
24 & 15.75 & 34.00 & 18.25 & 56.00 \\
48 & 17.88 & 37.50 & 18.00 & 46.00 \\
72 & 32.75 & 58.00 & 34.75 & 65.00 \\
96 & 26.25 & 34.50 & 41.50 & 55.00 \\
120 & 25.75 & 31.50 & 34.00 & 44.00 \\
144 & 25.25 & 29.00 & 31.00 & 35.50 \\
168 & 47.50 & 51.50 & 48.25 & 54.50 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Concentration of suspended particles at the dust suppression site (\(\upmu\)g/m\({}^{3}\)). Figure 7: (**a**) Dust suppression efficiency at construction sites, and (**b**) surface state of the waste area on day 15 after dust suppression. objects, which reduced the difference between the test data and the real study and helped improve the field stabilization effect. The soil for backfilling exhibited a three-phase structure consisting of mineral particles [36], water, and air. At the saturated moisture content, all the pores were filled with water. During drying, moisture was first released from the soil pores \(\geq\)100 \(\upmu\)m, enhancing cohesion and increasing the compression strength of the soil for backfilling (Figure 5). The bigger pores (>75 \(\upmu\)m) lost moisture from day 3 to day 14 (Figure 8). At this time, the polymer promoted the aggregation of fine particles less than 10 \(\upmu\)m and improved the compression strength [37]. From day 14 to day 21, water loss mainly occurred in the middle-sized pores (30-75 \(\upmu\)m), and bigger particles in the watered samples began to aggregate spontaneously. In Figure 5, the strength of the watered samples on day 21 was 1.94 MPa, reaching 5.38 MPa when the agglutinated powder particles of the polymer and their surfaces were crusted. As the pores did not contain remaining water anymore, the effect became exhausted. The compression strength on day 28 for the watered samples dropped back to 1.26 MPa, while that of the suppressed samples remained at 4.97 MPa. According to deaphology, soil is an aggregate of silt and clay [38]. Therefore, the water-borne polymer dust suppressant can prolong the water evaporation mainly by reinforcing the interaction between powder particles. The average particle size of the aggregate is reduced by anionic carboxyl radicals through the charge repulsion dispersion effect, while the powder cohesion is improved by hydrogen-bonding interactions between the aggregate and the Si-O and Al-O bonds on the powder surface [39]. Figure 9a, b shows the surface morphologies of watered and suppressed samples, respectively. The particles in Figure 9a were more evident and bigger, exhibiting high porosity, rapid volatilization, and low strength compared to the particles in Figure 9b, which were smaller and exhibited dense surfaces due to the dispersion effect and intensified cohesion, respectively.