Study on the settlement and delamination mechanism and acoustic emission characteristics of mixed aggregate cemented backfill

To study the effects of waste rock (WR) contents on the delamination and mechanical characteristics of the cemented backfill, the backfill specimens with 40%-80% WR content were prepared based on the stacking density of mixed aggregate. The characteristics of the WR distribution inside the cemented backfill with various WR contents were examined by scanning the sections images of the specimens. The strength and damage properties of the cemented backfill were investigated by uniaxial compression acoustic emission (AE) tests, and the strength and damage evolution mechanisms were explained by microstructure testing experiments. The results show that the viscosity and yield stress of the filling slurry gradually decreased with the contents of WR increased, and the WR settlement and delamination more obvious. The uniaxial compressive strength (UCS) has the same trend as the stacking density of the mixed aggregate, showing the trend of "increased first and then decreased" with the content of WR increased. When the content of WR was 60%, it had the highest UCS. As the content of WR increased, the fracture area at the interface of WR and cementitious matrix gradually increased, and the extrusion between coarse aggregates became more obvious, leading to more complex crack extension and higher AE cumulative energy. The main products of hydration in the cemented backfill were calcium silicate hydrated (C-S-H gels), ettringite (AFt), and calcium hydroxide (Ca(OH)2). The specimens with higher content of hydration products have better cementation among aggregate particles, denser microstructure, and higher compressive strength of cemented backfill.