Effect of aggregate size distribution and confining pressure on mechanical property and microstructure of cemented gangue backfill materials

The use of gangue, cementitious materials, and water mixed to make cemented gangue backfill material (CGBM) can achieve solid waste recycling while reducing environmental problems caused by its accumulation. In this paper, the fractal dimension of particle size distribution (PSD) and the confining pressure were investigated on the compressive strength, elastic modulus, stress–strain behavior, dilatancy deformation, and failure mode of CGBM using uniaxial compression, conventional triaxial compression, and microscopic scanning tests. The mechanism of the PSD fractal dimension on the mechanical properties of CGBM was revealed from a microscopic perspective. The results demonstrate that the compressive strength and elastic modulus of CGBM are quadratic polynomial and positively linearly related to the PSD fractal dimension and confining pressure respectively, with the PSD fractal dimension characterizing the maximum compressive strength of CGBM ranging between 2.4150 and 2.6084. The volume strain variation of CGBM diminishes as the PSD fractal dimension grows and increases dramatically when the confining pressure rises. The PSD fractal dimension has a quadratic polynomial relationship with both the cohesive force and the internal friction angle of CGBM. A reasonable PSD fractal dimension can optimize the microstructure of CGBM, reduce the distribution of defects such as microcracks and micropores, and enable hydration products to effectively fill the defects, guaranteeing that the CGBM has sufficient load-bearing capacity.