Effect of Temperature and Sulfate Ions on the Mode I Fracture Toughness of Waste-Based Cemented Paste Backfill With/Without Superplasticizer

Waste-based cemented paste backfill (WCPB) is a green mining method that has been implemented in many mines in China. However, the backfilling body is exposed to many dynamic loadings, including blasting and rock cutting, which in turn affect the stability of the underground structure. The Mode I fracture toughness (K_IC) of WCPB exposed to thermal and chemical loadings is experimentally investigated in this research. The results indicate that the mechanical response and K_IC of WCPB are time dependent. The temperature-induced enhancement in cement hydration improves the fracture toughness, while the increasing sulfate content poses negative impacts on the fracture toughness, with the exception of the 2500-ppm sample cured for 28 days. Besides, the temperature-induced acceleration of cement hydration counteracts the inhibition effect caused by sulfate ions. Moreover, superplasticizers improve particle repulsion but weaken cement hydration. These findings provide a better understanding of the fracture properties of WCPB and significantly impact the operation safety and productivity of coal mines.