High-Efficiency utilization of waste shield slurry: A geopolymeric Flocculation-Filtration-Solidification method

A huge amount of waste slurry generated in the shield tunnelling construction process needs to be utilized or disposed properly. A geopolymeric flocculation-filtration-solidification method (G-FFS) was proposed in this paper. The properties and the dewatering efficiency of the waste slurry conditioned by the cementitious agents and the geopolymeric agents were investigated through filtration under multi-stage pressures. The strength of the filter cake and its microstructures were then investigated. Subsequently, the mechanisms of dewatering and solidification of the waste slurry and the advantages of the G-FFS method in terms of environmental friendliness were discussed. The results show that, with the G-FFS method, the waste slurry with a high water content could be dewatered rapidly and transformed into high-strength building materials (2.47–10.31 MPa). The conditioned slurry also demonstrated a low kinematic viscosity and a low capillary suction time, indicating a better pumpability and dewatering ability. The addition of the sodium dodecyl sulfate (SDS) could improve the dewatering performance further. The hydration of the geopolymeric agent and the high-pressure filtration enhanced the strength of the cake. The densified micro-structure of the filter cake and limited water content led to the difficulty of hydration and, thus, limited the increase of the strength. Compared to the traditional method of utilizing the waste slurry through a cementitious agent, the G-FFS method demonstrates its advantages in efficiency, cost-effectiveness, and environmental friendliness.