Geopolymeric flocculation-solidification of tail slurry of shield tunnelling spoil after sand separation

•Geopolymeric flocculation and solidification of the tail slurry was conducted.•Model test simulated the dewatering process of the slurry on construction sites.•Geopolymeric flocculation-solidification agent performed better in treating slurry.•The effects of flocculation and solidification mutually interacted with each other. Geopolymeric flocculation-solidification of the tail slurry of shield tunnelling spoil after sand separation was investigated to replace the low-efficient flocculation and filter-pressing method currently adopted on site. The geopolymeric flocculation-solidification agent (GBFS-FS) consisting of flocculation component and geopolymeric solidification component (granulated blast-furnace slag (GBFS) activated by alkali) was prepared and investigated through flocculation-sedimentation test, dewatering model test, unconfined compression test, SEM test, etc. In the flocculation-sedimentation test, the GBFS-FS agent demonstrated the best flocculation effect as compared with other cementitious flocculation-solidification agents. The dewatering model tests revealed that adding the GBFS-FS agent into the slurry can not only dewater the slurry efficiently, but also generate solidified clayey sediments with quickly-increased strength. The solidified clayey sediments with GBFS-FS showed strengths 3.5 times higher than others with cementitious agents at a 28-day curing age. The GBFS-FS agent can also facilitate to make controlled low-strength material (CLSM) using the tail slurry. The fluidity and strength of CLSM with GBFS-FS were distinctly better than those of other groups. SEM test shows that the components of the GBFS-FS agent can interact to avoid large flocs and support each other in strength growth.