# Effects of Water-Reducing Agents on the Mechanical Properties of Foamed Phosphogypsum
## 2 Experimental Section
### Sample Preparation  
Preparation of foam: The foaming agent and purified water were weighed at a ratio of 1:250 and poured into a mixing pot (pot A).  
The rotational speed of the mixer was set to eight gears; pot A was quickly removed after 2 min of stirring.  
Preparation of phosphogypsum slurries: The contents of the water-reducing agent were 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% of the total gypsum content.  
According to the GB/T17669.3-1999 Standard [35] the fluidity of gypsum slurries should reach 180 \(\pm\) 5 mm. The water/gypsum ratio and fluidity of the phosphogypsum A and B samples are presented in Table 4. Pure water, the water-reducing agent, and phosphogypsum powder were poured into a mixing pot (pot B) similar to pot A. The rotational speed of the mixer was first set to two gears for a stirring time of 10 s. Then, the corresponding values were adjusted to four gears and 15 s, respectively.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Type** & **W/C Ratio** & **Fluidity (mm)** \\ \hline A & 0.760 & 180 \\ A-0.1\%FDN & 0.690 & 178 \\ A-0.1\%PCE & 0.720 & 178 \\ A-0.2\%FDN & 0.680 & 178 \\ A-0.2\%PCE & 0.700 & 180 \\ A-0.3\%FDN & 0.670 & 180 \\ A-0.3\%PCE & 0.690 & 178 \\ A-0.4\%FDN & 0.660 & 178 \\ A-0.4\%PCE & 0.680 & 178 \\ A-0.5\%FDN & 0.675 & 180 \\ A-0.5\%PCE & 0.695 & 180 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Water/gypsum (W/G) ratio and fluidity of the phosphogypsum.  
Figure 3: Particle size distribution curves of the phosphogypsum samples. (**a**) Phosphogypsum A. (**b**) Phosphogypsum B.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Sample** & **Standard** & **Initial Setting** & **Final Setting** & **Two-Hour** & **Absolute** & **Two-Hour** & **Absolute** \\
**Tickness (\%)** & **Time (min)** & **Time (min)** & **Flexural** & **Flexural** & **Compressive** & **Compressive** \\
**Strength (MPa)** & **Strength (MPa)** & **Strength (MPa)** & **Strength (MPa)** & **Strength (MPa)** \\ \hline A & 0.76 & 3.20 & 6.20 & 2.7 & 4.2 & 4.8 & 11.8 \\ B & 0.76 & 3.15 & 5.20 & 2.5 & 3.3 & 4.3 & 9.0 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Physical properties of the phosphogypsum samples.  
Preparation of foamed phosphogypsum samples: The as-prepared foam with a mass of 5% of the total phosphogypsum content was poured into pot B. The rotational speed of the mixer was first set to four gears for a stirring time of 10 s. Then, the corresponding values were adjusted to six gears and 15 s, respectively. The evenly mixed foamed phosphogypsum was then quickly poured into a mold of 40 mm \(\times\) 40 mm \(\times\) 160 mm in size. The wet strength, absolute dry strength, and dry density of the gypsum samples were then determined according to the GB/T17669.3-1999 Standard,.  
Furthermore, to characterize the microstructure of phosphogypsum samples, 20 mm \(\times\) 20 mm samples were made; the hydration of these samples was terminated after 2 h and the samples were placed in a sealed container for future use. The flowchart of the foamed phosphogypsum sample preparation is shown in Figure 4.