Insights into mechanical property and damage evaluation of a novel waste-based coal gangue-filled backfill

•The mechanical properties of CGFBs were correlated to multi-phase structure.•The AE technology was employed to monitor the damage process of CGFBs under loading.•The damage evolution mechanism of CGFB was analyzed at multiple scales. The cemented backfill is a multi-phase cementitious composite material, which is widely used in the backfilling industry of mined-out areas. To investigate the mechanical properties and damage mechanism of a novel waste-based coal gangue-filled backfill (CGFB) under the action of overburdened rock, in this study, the uniaxial compressive test and microscopic analysis were conducted, the damage process of CGFB samples under loading was monitored by the acoustic emission (AE) technique. The results show that the compressive strength of CGFB samples mainly depends on the mechanical behavior of the cement-tailings grout (CTG) and the microscopic features of the interfacial transition zone (ITZ) between the coal gangue (CG) aggregate and CTG matrix. The response of ringing counts and AE energy to the development of stress shows a clear time-varying response law. The b-value results reveal the macro and micro-crack development of the CGFB samples during different damage stages. The tensile failure predominates in the failure process according to the analyses of average frequency (AF) and RA (Risetime/ Amplitude) values. The damage variable increases slowly first and then develops rapidly with the increasing stress. The failure modes of CGFB samples with low water-to-cement (w/c) ratios were CG aggregates and ITZ damage, while ITZ damage was dominant for those with high w/c ratios. The results of the study can provide a theoretical basis for the reinforcement and modification of the novel CGFB material.