Improved water and efflorescence resistance of flue gas desulfurization gypsum-based composites by generating hydrophobic coatings

Flue gas desulfurization gypsum blocks were prepared using polymethylhydrosiloxane as a waterproofing and antiefflorescence agent, flue gas desulfurization gypsum as the matrix, and fly ash as the mineral admixture . The mechanical properties, water absorption, softening coefficient, surface contact angle, phase composition, and microstructure of the flue gas desulfurization gypsum blocks were determined with a universal testing machine, contact angle tester, X-ray diffractometer , Fourier-transform infrared spectrometer, and scanning electron microscopy. The salt crystallization phenomenon on the block surfaces was also observed to evaluate antiefflorescence performance. Results showed that flue gas desulfurization gypsum blocks containing 0.4 wt% polymethylhydrosiloxane had optimal overall properties. The compressive and flexural strength values were 16.03 and 6.80 MPa, respectively; the water absorption rate was 3.25%; the softening coefficient was 0.83; and the contact angle with water was 121.75°. The introduction of polymethylhydrosiloxane improved water resistance for flue gas desulfurization gypsum blocks, which also discharged water from the blocks and removed soluble salt , effectively prevented efflorescence.