LAUSR

Abstract This paper discusses the application of construction demolition waste (CDW) in the field of backfill mining as an efficient way of increasing the CDW utilization rate. But much of the research on cemented paste backfill (CPB) with the CDW has been conducted in the laboratory which cannot accurately explain the spatial differentiation characteristics and mechanism of onsite CPB. To this end, this study uses fractal theory, image processing, and scanning electron microscopy (SEM) to analyze the spatial stratified heterogeneity (SSH) of recycled aggregates and the mechanical properties of the CPB under the natural flow of slurry. The spatial distribution mechanism of the CPB’s performances is also explained. The results indicate that the compressive strength reaches a maximum of 4.07 MPa on the top of the upper segment and a minimum of 1.6 MPa on the bottom of the upper segment, with a mean value of 2.4 MPa in the whole tunnel. This satisfies the requirements of field applications. The maximum and minimum mean particle sizes appear on the bottom of the upper segment and the lower segments of the tunnel, and the multifractal parameters are shown to indirectly reflect the distribution of recycled aggregate size. According to the test results of sampling point, the spatial distribution of CPB’s strength and recycled aggregate along the flow direction of slurry are regressed, allowing the tunnel to be divided into five distinct regions. Finally, the PSD of recycled aggregates and microstructures has a profound impact on the mechanical properties of CPB, but the motion characteristics of the recycled aggregates are the main reason for the SSH of the CPB properties.