Feasibility experimental study on performance of cemented filling materials prepared with red sand

In view of the problem of shortage of gangue raw materials in mining area, a large amount of natural red sand was used to substitute gangue to prepare cemented backfill. The properties of gangue-red sand cemented materials with different red sand replacement rates (mass ratio of red sand instead of gangue), gangue based and red sand based cemented materials with different concentrations were tested, and to analyse the feasibility of preparing cemented filling material with red sand instead of gangue. With the increase of red sand replacement rate, slurry slump flow and bleeding rate both increased, rheological parameters (yield stress, viscosity coefficient) and backfill density decreased, and uniaxial compressive strength (UCS) and ultrasonic wave velocity increased first and then decreased. The content of clay minerals in red sand is less than that of gangue, the particles of red sand are fine and well graded, which increased the fluidity of slurry and reduced the fluctuation range of shear stress value of rheological curve. The slurry shear stress curve conformed to Bingham constitutive model.The fine red sand could better fill the pores of the backfill, and the hydration products could wrap the fine particles quickly, therefore the strength increased. The internal structure of red sand particles is not as dense as that of gangue, as the red sand continued to be added, the backfill strength was slightly reduced. The UCS was positively correlated with ultrasonic wave velocity. The microstructure and density of the backfill showed that the UCS was not only related to the density, but also to the internal particle structure of the backfill. After adding red sand, the peak strain of the backfill did not change significantly, the final strain decreased, red sand mainly affected the post-peak deformation stage, and this effect weakened with the growth of curing age. Under the same concentration, the slump flow and bleeding rate of red sand based slurry were larger than that of gangue based slurry, and the rheological parameters were smaller than gangue based slurry. With the increase of concentration, the difference of bleeding rate of two kinds of slurry gradually decreased, and the difference of rheological parameters gradually increased. The UCS of red sand based backfill was higher in early stage, but slightly lower in late stage than gangue backfill. The transportation performance and mechanical properties showed that red sand could better replace gangue to prepare cemented filling materials, which provided an alternative cemented filling material for coal mine.