Mechanical properties and damage evolution law of cemented-gangue–fly-ash backfill modified with different contents of recycled steel fibers

Abstract

The cemented-gangue – fly-ash backfill (CGFB) prepared from coal-based solid waste materials commonly exhibits high brittleness, leading to an increased susceptibility to cracking. Uniaxial compressive strength (UCS), acoustic emission (AE), and scanning electron microscopy tests were conducted on CGFB samples with recycled steel fiber (RSF) contents of 0, 0.5%, 1.0% and 1.5% to assess the mechanical properties and damage evolution law of the CGFB. The research findings indicate that: 1) When RSF contents were 0.5%, 1%, and 1.5%, respectively, compared to samples without RSF, the UCS decreased by 3.86%, 6.76%, and 15.59%, while toughness increased by 69%, 98%, and 123%; 2) The addition of RSFs reduced the post-peak stress energy activity and increased the fluctuations in the b-value; 3) As the RSF dosage increased from 0 to 1.5%, the per unit dissipated strain energy increased from 5.84 to 21.51, and the post-peak released energy increased from 15.07 to 33.76, indicating that the external energy required for the CGFB sample to fail increased; 4) The hydration products, such as C-S-H gel, ettringite, and micro-particle materials, were embedded in the damaged areas of the RSFs, increasing the frictional force at the interface between the RSF and CGFB matrix. The shape variability of the RSFs caused interlocking between the RSFs and the matrix. Both mechanisms strengthened the bridging effect of the RSFs in the CGFB, thereby improving the damage resistance capability of CGFB. The excellent damage resistance occurred at an RSF content of 0.5%; thus, this content is recommended for engineering applications.

Keywords

recycled steel fibers / cemented-gangue – fly-ash backfill / acoustic emission / crack development / energy evolution

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