Effect of nano-silica and silicone oil paraffin emulsion composite waterproofing agent on the water resistance of flue gas desulfurization gypsum

Abstract This paper indicates the influence of nano-silica and silicone oil paraffin emulsion mixed with flue gas desulfurization (FGD) gypsum on its water resistance. Nano-silica was mixed with FGD gypsum to explore the influence of nano-silica particle size and content on the waterproofing and mechanical properties of FGD gypsum while also analyzing its waterproofing mechanism. In addition, silicone oil paraffin emulsion was mixed along with nano-silica into FGD gypsum to study its effect on FGD gypsum. The results show that nano-silica can improve the water resistance of FGD gypsum. When the particle size of nano-silica is 50 nm and the mass fraction is 0.4%, the softening coefficient of FGD gypsum reaches 0.92. Nano-silica and organic composite emulsion can play a synergistic role and further enhance the performance of FGD gypsum. The water resistance and mechanical properties of gypsum further increased when mixed with nano-silica and silicone oil paraffin emulsion. The water absorption rate decreased to 13.62%, and the compressive strength reached 13.71 MPa. Combined with the microscopic morphology analysis of the gypsum sample, the appropriate size of nano-silica fills the crystal pores, reduces porosity, and, to a certain extent, changes the structure and morphology of gypsum crystals. Silicone oil paraffin emulsion can be wrapped on the surface of gypsum crystals forming a dense oil hydrophobic membrane. It produces a compact gypsum structure together with nano-silica, hindering the entry of water molecules into gypsum, thereby improving the performance of FGD gypsum.