Engineering properties and mechanistic insights of fluid fill material derived from multi-source solid wastes

The synergistic resource utilization of solid waste represents a critical scientific challenge in the field of environmental engineering. This study innovatively proposes a solid waste-based fluid-filled material (FFM) to address the significant physicochemical differences among multi-source solid wastes, including drinking water treatment residues (DWTR), mixing station sediments (MSS), recycled fine aggregates (RFA), and mud. The results demonstrate that by precisely controlling the fluidity (160-200 mm), water-to-solid ratio (0.52-0.87), and wet density (1.47-1.68 g/cm³) of the material, FFM with excellent mechanical properties can be obtained, exhibiting 7-day and 28-day compressive strengths of 0.20-1.20 MPa and 0.40-1.40 MPa, respectively. Under the premise of meeting performance requirements, the mechanical properties of FFM significantly improve with increasing proportions of low-carbon composite cementitious material (LCCCM) and RFA, as well as with extended curing age. Through systematic optimization, the optimal mix ratio for FFM was determined as Lime∶ DWTR∶ MSS∶ RFA∶ mud∶ LCCCM = 1∶ 5∶ 5∶ 10∶ 67∶ 12, achieving a 28-day compressive strength of 0.70 MPa, which complies with the engineering requirements specified in the standard. Furthermore, micro-characterization technology techniques, including scanning electron microscopy (SEM) and X-ray diffraction (XRD), demonstrate that: (1) the multi-component materials form a densely packed structure, significantly enhancing mechanical properties; and (2) hydration products effectively fill pores, dramatically improving material durability. These findings provide theoretical guidance for the design and development of low-carbon flowable solidified soils.