Abstract
The aim of this study was to examine the microstructure of cemented paste backfill (CPB) during its development and relate the characteristics of the microstructure to the physical and mechanical properties of CPB. The geometry and morphology of the microstructures of CPB were observed by the scanning electron microscopy (SEM). The characteristics including pore size, pore shape, and orientation of the microstructures of CPB at different curing times were analyzed based on the SEM images. The porosity, fractal dimension, and probability entropy were characterized using the Particles and Pore Recognition and Analysis System (PPRAS). It was found that the pore size, pore shape, and orientation of the microstructure of CPB significantly change as the curing time increases, resulting in the increase of UCS. Meanwhile, the arrangement of the pores affects the mechanical properties of CPB. At the early age of CPB development, the probability entropy is above 0.96, indicating a chaotic pore distribution and no obvious orientation. At the late age of CPB development, the probability entropy becomes smaller and the order and orientation of the pore distribution are enhanced, leading to an increase in USC. The UCS of CPB is also greatly affected by the characteristics of the pore morphology. During the development of CPB, the pore shape becomes smoother. The UCS of CPB approximately linearly improves with an increase in the average roundness of pores.
Highlights
E aim of this study was to examine the microstructure of cemented paste backfill (CPB) during its development and relate the characteristics of the microstructure to the physical and mechanical properties of CPB. e geometry and morphology of the microstructures of CPB were observed by the scanning electron microscopy (SEM). e characteristics including pore size, pore shape, and orientation of the microstructures of CPB at different curing times were analyzed based on the SEM images. e porosity, fractal dimension, and probability entropy were characterized using the Particles and Pore Recognition and Analysis System (PPRAS)
It was found that the pore size, pore shape, and orientation of the microstructure of CPB significantly change as the curing time increases, resulting in the increase of UCS
Zhou et al studied the microstructure of Guangzhou soft soil during the consolidation process using the Environmental Scanning Electron Microscopy (ESEM) and found that the increase of consolidation pressure resulted in the scale increase of structural units of the soil and the orientation, and the decrease of the soil porosity and the fractal dimension [13]
Summary
E particle size distribution (PSD) of tailings is presented, which shows that d10, d50, d60, and d90 are 4.96 μm, 23.84 μm, 32.00 μm, and 71.30 μm, respectively, and the nonuniformity coefficient of the tailing particles is 6.45 It could be classified as a gap gradation type, indicating that the tailings used relatively lack of large particles. The main chemical compositions of tailings were tested in Beijing General Research Institute of Mining & Metallurgy (BGRIMM), and the details are listed, indicating that the high content of sulphide has some damaging effect on the quality (e.g., strength deterioration) of cement-based backfill materials [18]. Portland cement (P.O. 32.5) is selected as the binder for CPB, and the main physical properties and chemical compositions are shown in Tables 3 and 4, respectively
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