**5. Conclusion**

As electricity generation using coal-fired power shows an increasing trend, dealing with fly ash is an important issue. However, some developing, and developed countries are not utilizing fly ash effectively. On the other hand, backfill mining shows a considerable scope where fly ash can be utilized in a win-win situation. In three types of backfill materials, fly ash can be an essential component and can enhance the effectiveness and minimize the cost.

Fly ash has a considerable positive impact on the fluidity of the backfill slurry, as shown by the quick drop in shear stress that occurs with increasing fly ash replacement of cement. This property may produce the ball-bearing phenomenon, a lubricating effect that results in a frictionless flow in stowing tubes. Even whilst the fly ash content stays the same, the rheological qualities change noticeably when the curing temperature changes. The amount of polymer formed by hydration and the rate at which fly ash reacts to hydrate are generally acknowledged in the scientific community to be strongly influenced by temperature.

Fly ash positively influences the backfill's strength in mining, with the strength improvement focusing primarily on 28–56 d. However, too much fly ash may result in many fine particles in the backfill when the filling material comprises tailings, which will impede the hydration of cementitious material and impact the growth of backfill strength. Workability is affected by the solid mass concentration, fine gangue ratio, and fly ash content. When the mass ratio of the waste rock-tailings-fly ash mixture is 6:2:3, the paste backfill material exhibits greater strength.
