Freeze-Thaw Cycle Characteristics of Solidified Sludge with Composite Rapid Soil Stabilizer

A composite rapid soil stabilizer (CRSS) is used to rapidly solidify sludge, endowing it with characteristics of fast setting, fast hardening, and high strength. The effects of freeze-thaw (FT) cycles, CRSS content, and moisture condition of the sample on physical and mechanical properties of the solidified sludge were studied through FT cycle tests, and the microscopic evolution mechanism during FT cycles was analyzed. The research results showed that with the increase of FT cycles, the mass of solidified sludge gradually increased, and the unconfined compressive strength (UCS) first increased and then decreased. With the increase in CRSS content, the appearance of the sample was more complete, and final losses in the mass and strength were smaller. After 25 FT cycles, the DR20 sample lost only 0.33% in mass and only 6% in strength. The moisture condition of the samples before FT cycles had a significant effect on the durability against FT cycles, and increasing the content of CRSS could offset the FT erosion caused by high moisture content. After 25 FT cycles, the number of pores in the sample, the most probable pore size, and the cumulative pore volume increased. Macroscopic and microscopic analyses revealed the microscopic evolution mechanism, especially the strength evolution mechanism, of the solidified sludge resistance to FT cycles. Thus, CRSS-solidified sludge exhibits good durability against FT cycles, which lays a theoretical foundation for its application.