Strength evolution and deterioration law of cemented gangue backfill body in acid mine water

Cemented gangue backfill technology is an important backfill mining method. However, the acid mine water environment could seriously affect the strength of the cemented gangue backfill body (CGBB). In this study, CGBB specimens were placed in different environments (air, water, H₂SO₄ solution, and H₂SO₄ solution coupled with load) to test the strength, resistivity, and ultrasonic pulse velocity (UPV) of CGBB at different ages. The acoustic emission (AE) energy of the specimens during loading was monitored, and the microstructure was analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Test results showed that: 1) The strength of CGBB cured in air and water gradually slowed down with age. The strength of CGBB in the H₂SO₄ solution was greater than that of CGBB cured in air or water in the first 90 d. The strength of CGBB under the coupling of the H₂SO₄ solution and load decreased more slowly with age than that of the single H₂SO₄ solution; 2) The resistivity and UPV had a good corresponding relationship with the strength of the CGBB. The failure modes of the CGBB after erosion were various, and the CGBB showed different AE energy characteristics at different stages of loading. The surge of AE energy could be used as a precursor to the failure of CGBB; 3) Erosion products compacted CGBB in the early stages and improved its strength. In the later stage, the CGBB cracked under the action of expansion stress and the strength decreased. Applying a 40% stress-to-strength ratio would resist the erosion of the H₂SO₄ solution. The research could provide a reference for the design of the corrosion resistance of CGBB.