The large-scale development of urban underground spaces has resulted in hundreds of millions of cubic meters of accumulated shield soil dreg waste, occupying huge amounts of land resources and potentially causing groundwater pollution and soil salinization. In this study, shield soil dreg waste is recycled and activated to substitute cement in ultra-high performance concrete, aiming to promote solid waste management and sustainable construction. The slump, mechanical performance, and autogenous shrinkage of the concrete are investigated through macro-scale tests, and the underlying mechanism is revealed via micro-scale experiments. The incorporation of calcined shield soil dreg reduces flowability and leads to a 10.2 % deterioration in compressive strength of the ultra-high performance concrete while mitigating autogenous shrinkage. The primary reason is due to the low CaO content of shield soil dreg, which limits the formation of calcium silicate hydrate, and its high SiO2/Al2O3 content slows hydration kinetics. The environmental and economic benefits of the concrete are determined via life cycle analysis. Recycling shield soil dreg waste into concrete results in about 35 % reduction in carbon emission and 22 % reduction in energy consumption. According to multi-criteria assessment, the overall performance of the concrete considering economic cost, environmental benefit, as well as physical and mechanical properties increases compared to the pristine concrete, achieving well-balanced economic feasibility, environmental sustainability, and engineering performance. The findings of this study provide an effective approach for recycling shield soil dreg and preparing low-carbon concrete, thus promoting solid waste management and sustainable construction.

This study explored an integrated recycling strategy of utilising a typical excavation waste soil, completely decomposed granite (CDG), in geopolymer production as a sustainable alternative of cement for marine clay improvement. Experimental campaign was conducted to evaluate the effects of composite alkali content and sodium silicate modulus on the mechanical performance of CDG-based geopolymer paste. Test results identified an optimal sodium silicate modulus, while it was also found that the incorporation of magnesium oxide (MgO) in alkali activator could improve the general workability. Moreover, regarding the unconfined compressive strength of marine clay improved, it was demonstrated that the combination of calcined CDG and ground granulated blast furnace slag (GGBS) considerably outperformed cement at the same level of dosage. Finally, multi-criteria assessment based on life cycle analysis (LCA) demonstrated the advantage of CDG-based geopolymer compared to conventional binders, in terms of mechanical properties, environmental benefits, and economic cost.