Microstructure and performances of sludge soil stabilized by fluorogypsum-based cementitious binder

As the byproduct in fluoride production, fluorogypsum is of slow hydration and poor concreting, playing a role of threat to environmental safety. Microstructure and performances of sludge soil stabilized by fluorogypsum-based cementitious binder were investigated in comparison with the solidified sludge blended with quicklime (LM) and PC32.5 cement (PC32.5) in this paper. The water content (wt%), pH value, unconfined compressive strength (UCS) and strength loss after soaking in water for 24 h of the solidified sludge with different solidifications were discussed. The solidified sludge blended with fluorogypsum-based cementitious binder (FB) possessed the lowest wt% of 9.24% (14 days, solidification agent dosage as 19%) indicating the good compressibility and potential to be a roadbed material. The pH value of 9.67 for FB (14 days, solidification agent dosage as 19%) was closer to neutral than LM and PC32.5. The UCS of FB stabilized for 14 days arrived at 4.7 MPa with the solidification agent dosage as 19%, which was 1.6 and 6.4 times as much as that of PC and LM, respectively, which further proved the good compression performance of FB. SEM and FT-IR demonstrated the formation of ettringite, portlandite and other hydration products, and explained the phenomenon that FB had sufficient early strength. The FB has not only a big specific surface area of 6.02 m2 g−1, but also a great pore volume of 2.25 × 10-2 cm3 g−1, which would improve the FB activity and accelerate hydration reaction. Based on the above characterization and analysis, the FB solidified sludge soil was clarified as a roadbed material and potential adsorbent.