Study of hydrophobic cemented paste backfill (H-CPB) to prevent sulphate attack

One of the challenges encountered in mining is acid mine drainage (AMD) in sulphurous ores in response to rainfall and groundwater. CPB one of the most prevalent waste management systems addresses this issue today. Nevertheless, in the long term, the concretion in CPB may become ineffective because of external factors, such as groundwater and rainfall. The relevant sources in the literature have no mention of AMD problems that may occur in the long term with CPB, particularly in metallic ores. Most studies indicate that the issue which can be prevented by using cement. However, due to the destructive effects of nature, cement alone would be insufficient. Consequently, the research's principal aim is to form CPB hydrophobic, thereby reducing the interaction between CPB and water. In the study, stearic acid was chosen as the hydrophobic agent and application method to the CPB and the changes in load-bearing capacity were studied. Specimens were tested by ion chromatography, X-ray diffraction (XRD), elemental analysis by combustion, water absorption, uniaxial compressive strength (UCS), and scanning electron microscopy (SEM). There was a decrease in the load-bearing capacity while gaining the hydrophobic properties of the material. The results confirm the validity of the selected agent and method and reveal that the effect of sulphate decreases with increasing hydrophobicity yet, there is no significant decrease in the 7, 14, and 28-day UCS tests. The optimal results were achieved when Stearic Acid (SA) was used at a concentration of 1.25 % for 7 % Portland cement and 0.75 % for 11 % Portland cement, with a UCS strength of 1.223 and 2.008 MPa, respectively. The expected benefit of stearic acid was realized as the water absorption value of the reference sample was 2.50 times higher in 7 % cement and 4.25 times higher in 11 % cement than the same value in Hydrophobic Cemented Paste Backfill (H-CPB). These results indicate that AMD formation can be prevented in the future with H-CPB. The results demonstrate that stearic acid, with the new methodology, forms the CPB hydrophobic, while only an acceptable strength loss was observed. Additionally, the outcomes point out that the methodology adopted does not consider a significantly adverse impact on hydration phase of concretation and can be utilized as an environmentally friendly backfilling method, thereby being evaluated as the cleaner backfilling for further CPB applications.