Internal pore evolution and early hydration characterization of fly ash cement backfill

The early internal hydration process and pore evolution of backfill have a significant influence on its performance and strength. In this paper, Lf-NMR is used for 72 h continuous detection of fly ash slurry to observe the changes of internal gel water and capillary water, and analyze the pore structure combined with fractal dimension. UCS tested the fly ash cement backfill (FACB), and the composition and microstructure evolution of hydration products were analyzed by combining porosity and SEM. Results confirm that the influence of FA on the hydration process increases gradually with time. Fly ash has abilities of delaying solidification and hardening cement slurry. The proper proportion (10%) of FA has a lower fractal dimension and complexity of pore structure. Excessive FA proportion leads to the reduction of cementing products (C-H, etc.), increased surface roughness, high porosity, the decline of strength, and enhanced ductility.