Abstract: The stockpiling of massive muck produced by shield tunnelling construction easily triggers a series of environmental and safety problems, including land resource occupation, dust pollution and slope sliding. Most existing studies on ceramsite prepared from shield tunnelling muck focus merely on single formulation schemes, while systematic analyses on the modification laws of different admixtures (e.g., fly ash and straw) and their microstructural regulation mechanisms are still insufficient. In this research, shield muck sourced from the Jiluo Road Yellow River Tunnel Project was adopted as the primary raw material. Fly ash and straw were separately incorporated as admixtures to fabricate three types of ceramsite, namely pure muck ceramsite, fly ash composite ceramsite and straw composite ceramsite. The effects of sintering temperature, holding time and material proportion on the key properties of the prepared ceramsite, including loss on ignition (LOI), bulk density and compressive strength, were systematically investigated，combined with scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and nuclear magnetic resonance (NMR) pore tests, to reveal the internal correlation between the microstructural characteristics and macroscopic performance. The results showed that the pure muck ceramsite achieved the optimal compressive strength of 10.8 MPa at a sintering temperature of 1 100 °C with a particle size of no more than 10 mm. The fly ash composite ceramsite with a fly ash content of 50 wt% delivered excellent mechanical performance with a compressive strength of 18.2 MPa within the sintering temperature range of 900~1 100 °C. In addition, the straw composite ceramsite with a straw content of 10 wt% could be successfully formed at a low temperature of 250 °C for a holding time of 20 min, with a water absorption rate of 27.69%. The three types of ceramsite exhibit distinctly different microstructures, which were characterized by dense structure, uniform cementitious structure and loose porous structure, respectively. The elemental composition was closely correlated with raw material components and sintering process parameters. This research provides a novel technical approach for the resource utilization of shield tunnelling muck.
