Effects of red mud additions on gangue-cemented paste backfill properties

Abstract To research the influence of red mud (RM) on gangue-cemented paste backfill (GCPB) properties, GCPB samples with different proportions of RM and Portland cement (PC) were prepared. The macroscopic strength and microstructure evolution of GCPB were analyzed by uniaxial compression tests, X-ray diffraction, Scanning electron microscope, and Fourier transform infrared spectroscopy. The results show that RM has a considerable effect on the strength and hydration products of GCPB. The optimal GCPB samples were RP03 which contained 1/4 RM + 3/4 PC. The uniaxial compressive strengths of GCPB samples after being cured for 7 and 28 days were 0.23 MPa and 0.95 MPa, respectively, which were 7% and 13% higher than that of control samples, respectively. It was found that GCPB mixed with RM can meet the requirements of mine filling and shows obvious advantages in terms of strength and cost-efficiency compared with the GCPB with pure PC used in mines. In other words, replacing a quarter of the PC with RM would achieve the same strength and reduce the cost of the GCPB by about 23%. The hydration products of GCPB mixed with RM are mainly composed of gismondine (CaAl2·Si2O8·4H2O), calcium-silicate-hydrate (C-S-H) gel and ettringite (AFt). These hydration products are closely agglomerated and cross-linked with raw materials, which makes the internal microstructure denser. Furthermore, this leads to the key reason for the improvement in the macroscopic strength development of GCPB.