Effects of Water-Reducing Agents on the Mechanical Properties of Foamed Phosphogypsum

Abstract

In the present experiment, two types of water-reducing agents, naphthalene (FDN) and polycarboxylic acid (PCE), were selected, and their effects on the mechanical properties of foamed phosphogypsum were evaluated. It was shown that when the water-reducing agent contents were increased, the strength of the foamed phosphogypsum first increased and then gradually decreased, and that the dry density of the foamed phosphogypsum first decreased and then gradually increased. The FDN samples had better mechanical properties and a lower dry density than the PCE samples. The effect of the water-reducing agent dose on the apparent viscosity and shear stress of the phosphogypsum slurries was in the order of 0% > 0.4% > 0.3% > 0.5% > 0.2% > 0.1%. The apparent viscosity and shear stress of the gypsum slurry mixed with 0.4% FDN or PCE were the highest. FDN and PCE both enlarged the pore size distribution range, increased the size and proportion of large pores, and decreased the total pore content of foamed phosphogypsum; however, the effect of PCE was more significant. The foamed phosphogypsum slurry mixed with 0.4% FDN had the highest total pore content. Among the samples, the total pore content of foamed phosphogypsum A was able to reach 91% and the total pore content of foamed phosphogypsum B reached 77%; the lowest proportion of large pores for foamed phosphogypsum A and B separately reached 17% and 7%, respectively. The water-reducing agents mainly reduced the water consumption of the phosphogypsum slurries; improved the viscosity and shear stress of the slurries; affected the stability of the foam in the gypsum slurries; influenced the pore size and distribution in the foamed phosphogypsum samples; and caused a difference in the strength and dry density of the foamed phosphogypsum samples. The viscosity of the gypsum slurry doped with 0.4% FDN better matched that of the foam; therefore, it had the highest macro-strength and the lowest dry density.