Effect of the Initial Air Content in Fresh Slurry on the Compressive Strength of Hardened Cemented Paste Backfill

Youzhi Zhang,Zhenlin Xue,Sheng Hu,Xun Chen,Deqing Gan,Erol Yilmaz

doi:10.1155/2020/8838572

Abstract

Filling mining method can dispose of the tailings into filling slurry, which can be transported to the stope through pipelines to manage the ground pressure and protect the environment. To improve the flowability of filling slurry, additives are used more and more widely. However, some additives can increase the air content in the slurry. The air in the slurry will become pores in the hardened cemented paste backfill (CPB). Therefore, it is necessary to explore the influence of initial air content in fresh slurry on the compressive strength of CPB. In this paper, sodium dodecyl sulfate (SDS) was used to regulate the air content in the fresh slurry. After measuring the initial air content, the slurry was made into test blocks. Then, the uniaxial compressive strength (UCS) of CPB at 28 d age was tested, and the distribution of CPB microscopic pores was observed by scanning electron microscope (SEM). The results show that as the initial air content in fresh slurry increases, the UCS of CPB first increases and then decreases. Before the initial air content in fresh slurry is 6.03%, the CPB pores distribution is relatively uniform. However, after exceeding this value, “discontinuous contact” structures, pore groups, and macropores occur in CPB. Through the CPB microscopic force analysis, the mathematical model describing the effect of initial air content on UCS of CPB should be a combination of logarithmic function and quadratic polynomial. This work can provide a supplement to the theory of CPB strength.

Highlights

Filling mining method can discharge all or most of the tailings into the underground stope, which can effectively manage the ground pressure of stope, and relieve the environmental and economic pressure of tailings surface depositing [1,2,3,4,5,6,7]
After stirring by a mixer, the slurry will contain a certain amount of air, so that there will be some pores in the hardened cemented paste backfill (CPB) [12, 13]. e slurry is transported into the stope through a pipeline, so the slurry flowability has an important influence on the filling mining efficiency
In order to improve the flowability of high-concentration slurry, pumping agents are widely used in slurry pipeline transportation. e pumping agent is generally mainly composed of water-reducing agent and airentraining agent (AEA)

Summary

Introduction

Filling mining method can discharge all or most of the tailings into the underground stope, which can effectively manage the ground pressure of stope, and relieve the environmental and economic pressure of tailings surface depositing [1,2,3,4,5,6,7] Under this background, the mechanical properties (i.e., compressive strength, tensile strength, and flexural strength) of cemented paste backfill (CPB) have attracted wide attention. It can be seen that past researches have analyzed the relationship between porosity and compressive strength from a qualitative perspective They did not propose a mathematical model that can use the initial air content in fresh slurry to quantitatively analyze the CPB strength. Combined with the CPB microscopic force analysis under compression, a quantitative mathematical model will be proposed. is work will make a useful supplement to the theory of CPB strength

Materials and Methods

Results and Discussion

Fluctuations

Conclusions e main conclusions of this paper are as follows: