Experimental study on mechanical and microstructure properties of cemented tailings-waste rock backfill with continuous gradation

To reduce the risk of engineering disasters and improve the comprehensive utilization rate of solid waste from mines, cementitious tailings-wasted rock filling as a green and safe technology has been widely used in mines. Mechanical properties and microstructural characterization of cementitious tailings-wasted rock backfill (CTWRB) prepared with gradation coefficients (n) of 0.3 ∼ 0.7 and waste rock contents (e.g., 10%, 20%, 30%, 40%, and 50%) were investigated by using UCS (unconfined compressive strength) tests (e.g., peak strength, stress-strain curves, and damage modes), surface strain field analysis and SEM micro-graphs. The results indicate that the UCS value shows an overall "increasing and then decreasing trend" with increasing gradation factor n and waste rock dosage. The UCS value of CTWRB is maximum at 3.94 MPa when n=0.5 and waste rock admixture is 30%. The UCS has increased by 17.96%. The compacting stage of CTWRB is more pronounced under loading. In the post-peak stage, CTWRB has superior resistance to deformation damage. The destruction form of backfill is dominated by the tension destruction parallel to the loading direction. The waste rock constrains the expansion path of cracks inside the specimen, which can effectively improve the UCS of backfill. The grayscale of the strain field in CTWRB shifts towards higher gray levels. The proportion of peaks in the strain field gray histogram changes slowly at first and then rapidly, with the peak stress serving as the boundary. Ettringite/CSH gel are the main hydration products in the backfill material. An overvalue of n leads to worse densification of the specimen and increased voids, which causes the UCS of CTWRB to decrease. The study's results could be a significant guide for ensuring safe mining production.