Mechanical properties and damage evolution of backfill material with variable fly ash content

The mechanical strength of the gangue backfill material is related to the pore volume and its microstructure. To study the mechanical properties and microstructural changes of backfill materials prepared by partially replacing cement with fly ash, the mercury intrusion porosimetry was used to measure the pore volume of the coal gangue cemented backfill. A theoretical analysis was conducted to determine the particle diameter distribution of the coal gangue. Then, the Particle Flow Code in 3 Dimensions was used to conduct numerical simulations on coal gangue backfill with different fly ash replacement ratios. To ensure the authenticity of the specimens, a 3D vector software was used in modelling to generate gangue particles based on the shape of true coal gangue, which were then imported into PFC using the FISH language. The resulting gradation was generated according to a formula and the remainder was replaced with circular particles. Using 3D modeling methods, we investigated the impact of microstructural changes in gangue backfill on its mechanical properties. The results show that the overall performance of the backfill with a fly ash: cement ratio of 2.5 was the best. Based on this optimal formulation, a coal gangue cemented backfill model was established and the pore structure characteristics and meso-damage evolution of the gangue cemented backfill were comprehensively investigated.