Mechanical performance and solidification mechanism of synchronous grouting materials from the reuse of geopolymer-modified shield tunnel muck

The conventional method of preparing synchronous grouting with shield muck usually involves using cement as main binder. However, to enhance environmental sustainability of reusing shield muck in synchronous grouting, developing alternative binders is crucial. Based on the principles of geopolymerisation, this study uses shield muck as the main raw material and mixes it with sand. It also incorporates ground granulated blast furnace slag (GGBS) as a precursor and uses sodium sulfate and hydrated lime serving as activators to develop a new grouting material. Experimental results indicate that the consistency, fluidity, and moisture content of the grout decrease over time. Notably, both consistency and fluidity exhibit pronounced changes in their variation rates at the setting time, with opposite trends observed before and after this point. Additionally, the bleeding rate and bulk shrinkage rate, as well as unconfined compressive strength (UCS), increase with time. The bleeding rate stabilises once the setting time is reached, while the bulk shrinkage rate stabilises after three days. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses reveal the solidification mechanism of the new grouting material. The superior strength of the new grouting material is attributed to differences in hydration processes and the types of products formed. The excellent performance of the newly developed material, with an optimal proportion of 140% moisture, 100% GGBS, and 230% sand, is confirmed by comparing it with traditional grouting materials on site at Nanjing Metro Line 6, and both its economic and environmental benefits in practical application are assessed. • An approach for creating synchronous grout using shield muck was proposed via geopolymerization. • The time-varying characteristics of the new synchronous grouting material were investigated. • The evolution of foams in the silty clay on the new synchronous grouting material was examined. • The solidification mechanism of the novel synchronous grouting material was revealed.