Study on macro-meso mechanical properties of cemented tailings backfill with high fly ash content

The use of cement and fly ash (FA) to prepare cemented tailings backfill (CTB) lowers backfill mining costs while also reducing pollution caused by the accumulation of waste materials like tailings and FA, making it a green backfill mining process. While adding FA to CTB may reduce costs, too much FA might weaken CTB's strength property. Mechanical tests were used to explore the effects of FA content and curing time on the uniaxial compressive strength (UCS) and deformation modulus of CTB in this research. The effects of FA content on failure modes, strain energy, and crack evolution of CTB were studied using a numerical model that considered FA content and particle contact mode. The influence mechanism of different FA contents on CTB was also revealed at the microscopic level. The results demonstrate that the UCS of CTB has a quadratic polynomial and a linear relationship with FA content and curing time respectively, and that the elasticity modulus and secant modulus of CTB increase and then decrease with FA content under different curing times. The peak strain energy of CTB increases and subsequently declines with the FA content, and crack propagation inside CTB may be limited by regulating the FA content. A reasonable content of FA can optimize the size and distribution of CTB microscopic defects, enabling them to exhibit superior strength property. This study systematically explores the mechanism of different FA contents on the strength property of CTB from a macro-micro perspective, providing an essential reference value for improving the recycling of FA and waste residues such as tailings.