# Effects of Water-Reducing Agents on the Mechanical Properties of Foamed Phosphogypsum
## 3 Results and Discussion
### Discussion on the Effect of the Water-Reducing Agents on the Foamed Phosphogypsum Sample  
The addition of water-reducing agents manifests a certain effect on the rheology of gypsum slurries; the bubble size distribution in foam is strongly correlated with the rheology of gypsum slurries. Therefore, in this section, the effects of the water-reducing agents on the rheological properties of the phosphogypsum slurries are discussed. 3.1 Effect of the Water-Reducing Agents on the Rheological Properties of the Foamed Phosphogypsum Slurries  
Figures 6 and 7 display the apparent viscosity curves and shear stress curves of the foamed phosphogypsum A and B pastes mixed with different water-reducing agents, respectively. It can be seen in Figure 6 that the apparent viscosity of the phosphogypsum slurries gradually and rapidly decline with the increase in the shear rate under the same water-reducing agent content. When the shear rate was in the range of 1-50 s\({}^{-1}\), the apparent viscosity of the slurries significantly decreased. When the shear rate was large, the variation in the apparent viscosity tended to be flat. At the same shear rate, the effect of the water-reducing agent content on the apparent viscosity of the phosphogypsum slurries was in the order of 0% > 0.4% > 0.3% > 0.5% > 0.2% > 0.1%. In comparison to the apparent viscosity of the phosphogypsum slurry doped with 0.4% PCE, the apparent viscosity of the slurry mixed with 0.4% FDN was closer to that of the slurry with no water-reducing agent. Figure 6: Apparent viscosity curves of the phosphogypsum slurries mixed with different water-reducing agents. (**a**) Phosphogypsum A doped with FDN. (**b**) Phosphogypsum A doped with PCE. (**c**) Phosphogypsum B doped with FDN. (**d**) Phosphogypsum B doped with PCE. Figure 7 reveals an approximately linear relationship between the shear stress and shear rate of the slurries. The shear stress of the slurries increased with the increase in the shear rate under the same water-reducing agent amount. At the same shear rate, the effect of the water-reducing agent content on the shear stress of the phosphogypsum slurries was in the order of 0% \(>\) 0.4% \(>\) 0.3% \(>\) 0.5% \(>\) 0.2% \(>\) 0.1%. In comparison to the shear stress of the phosphogypsum slurry doped with 0.4% PCE, the shear stress of the slurry mixed with 0.4% FDN was closer to that of the slurry with no water-reducing agent. With the increase in the water-reducing agent content from 0.1% to 0.4%, the water consumption of the gypsum slurries significantly decreased, causing an increase in the viscosity of the slurries; thus, greater shear force was required to maintain the same shear flow rate. When the water-reducing agent content was 0.5%, the water consumption of the gypsum slurry was between 0.2% and 0.3%. Therefore, the apparent viscosity and shear stress of the phosphogypsum slurries mixed with 0.4% of the water-reducing agents were closer to those of the slurry with no water-reducing agent. The phosphogypsum slurries mixed with PCE had lower apparent viscosity and shear stress than the slurries doped with FDN under the same water-reducing agent dosage due to their slow coagulation by PCE. 3.2 Effect of the Water-Reducing Agents on the Pore Structure Distribution of the Foamed Phosphogypsum Samples  
Figure 8 displays the pore size distribution curves of the foamed phosphogypsum samples doped with FDN and PCE. The pore size of both foamed phosphogypsum samples followed a bimodal distribution; the pore size distribution was mainly concentrated in the range of 100-3000 nm. FDN and PCE both enlarged the pore size distribution range of foamed phosphogypsum and increased the size and proportion of large pores; however,  
Figure 7: Shear stress curves of the phosphogypsum slurries mixed with different water-reducing agents. (**a**) Phosphogypsum A doped with FDN. (**b**) Phosphogypsum A doped with PCE. (**c**) Phosphogypsum B doped with FDN. (**d**) Phosphogypsum B doped with PCE. the influence of PCE was found to be more significant.