Recycling of calcareous shield tunnel muck and industrial solid waste for preparation of self-consolidating backfill slurry: Perspectives on fluidity, mechanical properties, and carbon footprints

Recycling calcareous shield tunnel muck (STM) and industrial solid waste promotes a sustainable economy. In this research, all-solid waste cementitious materials (CBF) were designed using calcium carbide residue (CCR), slag (BFS), and coal fly ash (CFA) to cement STM for preparing backfill slurry (CBFSM). The results indicated the optimal ratio of CBF was 15% CCR, 20% CFA, and 65% BFS. With 15% addition of the optimal CBF binder, the CBFSM slurry had fluidity of 22.6 cm, setting time of 240-510 mins, bleeding rate of 2.73%, and 28d strength of 2.92 MPa, which was 1.80 times the cement. The microscopic mechanism revealed that the abundant hydrated silicon aluminate calcium (C-A-S-H) gels filled pores, densifying the matrix and enhancing strength. Meanwhile, calcareous STM not only promoted C-A-S-H formation but ensured sufficient free water to maintain fluidity. 1 m 3 of CBFSM slurry reduces costs by 5.56 USD and CO 2 emissions by 76.04 kg per unit of strength compared to cement -based slurry. This work presents a sustainable and cost-effective approach for repurposing STM and industrial wastes in construction backfilling. ● Develop a backfill slurry from calcareous shield tunnel muck (STM) and waste binder. ● STM’s calcium supplement and low water absorption promote waste binder hydration. ● All-waste slurry has great engineering performance, low carbon, and economic benefit.