X-ray CT three-dimensional reconstruction and discrete element analysis of the cement paste backfill pore structure under uniaxial compression

In order to explore the patterns of porosity evolution during the bearing failure of cement paste backfill (CPB), medical X-ray CT and small loading device were employed to carry out the real-time uniaxial compression scanning test, obtaining the two-dimensional CT images under different stress states. Through three-dimensional reconstruction of CT images and discrete element simulation, CPB's three-dimensional multi-component structure and porosity values under different stress conditions were obtained. Results showed that, at low amount of waste rocks, the porosity values increased along with the stress values; beyond 80% of the stress peak, the porosity increased drastically, and the pores were mainly distributed in an X-shaped conjugate plane. When the waste rock content was increased to 50%, the initial primary porosity in CPB increased to 3.12%. The pore Volumes were 4.36%, 5.64%, and 8.64% at 40% and 80% of stress peak and post-peak, significantly greater than that at 30% waste rock content; moreover, the fractures were primarily in the overall form, failing to form an X-shaped conjugate shear plane. For CPB under uniaxial compression, the early stage was mostly featured by tensile failure, while the middle and late stages were partly featured by shear failure. In general, the entire process of CPB failure was divided into 4 stages: no microcrack region, initiation and aggregation of microcrack, connection of microcrack, and formation of macroscopic fracture region. During the process of bearing, shear deformation of microscopic void cell within CPB occurred under forces, eventually leading to the destruction of CPB. (C) 2017 Elsevier Ltd. All rights reserved.