Performance evaluation of the sludge treated by industrial waste slag and recycled solid waste

Abstract Large amounts of sludge produced are difficult to dispose of, and thus, its solidification can effectively address the environmental pollution and resource scarcity issues. In this study, dredged sludge, industrial slag, and recycled solid waste were processed, and the performance of flowable solidified sludge (by cement slag powder, and slag–recycled waste) was investigated. Solidified sludge under different solidifier ratios was prepared, and the resulting compressive strength, water stability, and freeze–thaw resistance were determined. The results showed that the 28-day compressive strength of the solidified sludge by the synergistic solidification of 12% slag powder and 18% recycled solid waste was 72.9% and 99.3% higher than that of the solidification by 12% cement and 12% slag powder, respectively. The sludge solidified by slag—recycled solid waste had greater porosity, and the strength loss after 24 h water immersion was greater than that of the other two solidifying agents. However, the final compressive strength was still 1.2% higher than that of cement-solidified sludge. Recycled solid waste also affected the mechanical properties of sludge solidified during freeze–thaw cycles. The strength loss after 15 freeze–thaw cycles was 15.2%, though the residual strength was 3.9% higher than that of cement-solidified sludge for the same number of freeze–thaw cycles. The results elucidate that sludge solidified by the synergistic use of slag powder and recycled solid waste meets the requirements of engineering applications, reduces cement consumption, and provides a design basis for solidification projects using large amounts of industrial waste and recycled solid waste to treat dredged sludge.