# Suppression Effect of Waterborne Polymer on Soil Used for Backfilling at Construction Site
## 2 Materials and Methods
### Experimental Instruments and Test Methods  
Contact angle: A pellet with a diameter of 13 mm and a height of 3 mm was made from 0.8 g soil dust under 20 MPa pressure. The contact angles between droplets and soil dust were measured with an optical contact angle instrument (DAS30, Kruss Ltd., Hamburg, Germany) at a titration speed of 100 \(\upmu\)L/min and a droplet volume of 4 \(\upmu\)L.  
Zeta potential: The Zeta potential was measured using a nanoparticle size and potential analyzer (Nano-ZS90, Malvern Ltd., Leamington Spa, UK), and the mass concentration of the powder suspension was 0.1 wt.%. Moisture content: Soil for the backfilling powder with an initial mass \(W_{s}\) of 20.0 g was filled and leveled out in a culture plate with a diameter of 100 mm and sprayed with a dust suppressant solution until the sample surface was fully wet. The obtained samples were referred to as suppressed samples, and the mass of the dust suppressant was 1.05%. Other \begin{table}
\begin{tabular}{c c c} \hline \hline
**Name** & **Purity** & **Manufacturer** \\ \hline Acrylic acid (AA) & Industrial grade & Hebei Richu Chemical Co., Ltd., Cangzhou, Hebei, China \\ Butyl acrylate (BA) & Industrial grade & Hebei Richu Chemical Co., Ltd., Cangzhou, Hebei, China \\ Methyl methacrylate (MMA) & Industrial grade & Hebei Richu Chemical Co., Ltd., Cangzhou, Hebei, China \\ Styrene (St) & Industrial grade & Hebei Richu Chemical Co., Ltd., Cangzhou, Hebei, China \\ Emulsifier (EC) & Industrial grade & Hebei Richu Chemical Co., Ltd., Cangzhou, Hebei, China \\ Ammonium persulfate (APS) & Industrial grade & Hebei Richu Chemical Co., Ltd., Cangzhou, Hebei, China \\ Polyacrylic acid resin (PMMA) & Industrial grade & Hebei Richu Chemical Co., Ltd., Cangzhou, Hebei, China \\ Sodium peroxide (NaOH) & Analytically pure & Hebei Richu Chemical Co., Ltd., Cangzhou, Hebei, China \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Main experimental reagents. Figure 1: Particle size distribution of soil for backfilling. dust samples were sprayed with the same amount of distilled water as a control group, referred to as watered samples. The watered samples were placed in an incubator (WS-70 constant temperature and humidity incubator, Shanghai Zhuli Instrument Ltd., Shanghai, China) with constant temperature and humidity of 35 \({}^{\circ}\)C and 45% RH, respectively. The mass \(W_{t}\) (g) at different times \(t\) was recorded, and the moisture content \(P\) at time \(t\) was expressed as follows:  
\[P=\frac{W_{t}-W_{s}}{W_{s}}\times 100\% \tag{1}\]  
where \(P\) is the moisture content (%), \(W_{s}\) is the initial mass of the soil for the backfilling powder (g), and \(W_{t}\) is the mass of the suppressant sample or watered sample at different drying times (g). Compression strength: A total of 50.0 g of dust suppressant solution with a concentration of 3.0% was mixed and stirred with 141.0 g of soil for the backfilling powder, poured into a brass mold (40 mm \(\times\) 40 mm \(\times\) 40 mm) to form, and then stripped before being dried at room temperature. For comparison, the above operation was repeated with the same amount of distilled water. After 1, 3, 7, 14, 21, and 28 days, the compressive strength was tested with a microcomputer-controlled electron universal testing machine (UTM-5305, Shenzhen Sansi Testing Technology Ltd., Shenzhen, China) following the _GB/T 17671-1999 Method of Testing Cements-Determination of Strength (ISO)_.  
Microstructure: The morphological structure of the soil for backfilling was examined using a field emission scanning electron microscope (Nova Nano SEM450, FEI Ltd., Hillsboro, OR, USA), and the sample surface was sputtered with Au before measurement. Field application: The meteorological information, including the particle concentration, temperature, and humidity at a height of 2.5 m on the construction site, was monitored in real-time with an online dust-monitoring system produced by Shijiazhuang Zhaorong Technology Co., Ltd. (Shijiazhuang, China). The dust suppressant was sprayed with a multipurpose anti-dust truck.