The influence of different fly ash-cement replacement ratios on the pressure drop of a horizontal backfilling pipe

Abstract

Fly ash (FA) is a kind of harmful by-product in thermal power generation plants, and finding a way to enhance the utility of fly ash has been widely discussed among civil engineering and mining sectors. To investigate the possible optimal ratios of replacing usually used bind agent namely Portland cement (PC) with fly ash, this paper designed different test groups with varying PC-FA replacement ratio. To identify the physical and chemical characteristics of mixing materials used to produce the backfilling slurries, a rheological experiment and X-ray diffraction test have been conducted. Rheological tests show all these three replacement ratio groups (60%, 65%, 70% respectively) are yield pseudoplastic fluid. Computational fluid dynamics as an efficient and money-saving method also has been introduced in the present research to duplicate the flow behaviors and calculate the pressure drop (PD) in the backfilling pipe circuits. The simulation results suggested that all these three RR categories experience an increasing tendency in pressure drop with increasing flow velocity, but in the velocity range of 2 m/s - 2.4 m/s, the increasing tendency is gentle until flow velocity reaches 2.6 m/s, the PD increase evidently. Furthermore, when the RR = 65%, the pressure drop is significantly lower than that of RR = 60% or RR = 70% at all the corresponding investigated flow particle sizes have significant impact on the pressure drop across a pipe and is dependent on solid fraction and flow rate and velocities. Therefore, we can conclude that a proper dosage of FA in mixing backfilling slurries can reduce pressure drop obviously and thereby decrease the expenses in bind agent. Given the FA’s significant effect on pressure drop, and comprehensive considering the backfilling capacity and backfilling cost, the combination of RR = 65% and velocity = 2.6 m/s is optimum.