Abstract
In this investigation, six groups of cemented coal gangue-fly ash backfill (CGFB) samples with varying amounts of kaolin (0, 10, 20, 30, 40, and 50%) instead of cement are prepared, and their mechanical properties are analyzed using uniaxial compression, acoustic emission, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. The uniaxial compressive strength, peak strain, and elastic modulus of CGFB samples decreased with the kaolin content. The average uniaxial compressive strength, elastic modulus, and peak strain of CGFB samples with 10% amount of kaolin are close to that of CGFB samples with no kaolin. The contribution of kaolin hydration to the strength of CGFB sample is lower than that of cement hydration, and the hydration products such as ettringite and calcium-silicate-hydrate gel decrease, thereby reducing strength, which mainly plays a role in filling pores. The contents of kaolin affect the failure characteristics of CGFB samples, which show tensile failure accompanied by local shear failure, and the failure degree increases with the kaolin content. The porosity of the fracture surface shows a decreasing trend as a whole. When the amount of kaolin instead of cement is 10%, the mechanical properties of CGFB samples are slightly different from those of CGFB samples without kaolin, and CGFB can meet the demand of filling strength. The research results provide a theoretical basis for the application of kaolin admixture in fill mining.
Highlights
Mine-filling technology processes waste such as coal gangue and fly ash into slurry, which reduces the accumulation of solid waste and pollution in coal mines, and enables effective control of the deformation of overlying strata and surface subsidence in mining areas [1]
Wei et al [17] found that kaolin and other mineral admixtures can improve the early strength of cement mortar in an alkaline environment
The particle size of kaolin is mainly in the range of 0–5 μm, which can be filled into smaller pores of cement paste and be dispersed more evenly, which is conducive to the complete occurrence of chemical reactions
Summary
Mine-filling technology processes waste such as coal gangue and fly ash into slurry, which reduces the accumulation of solid waste and pollution in coal mines, and enables effective control of the deformation of overlying strata and surface subsidence in mining areas [1]. Wei et al [17] found that kaolin and other mineral admixtures can improve the early strength of cement mortar in an alkaline environment. The addition of slag and fly ash is conducive to the diffusion of crystals and destroys the structure of Ca(OH), reducing the porosity of the cement mortar and improving the density of the slurry and filler–matrix interface. The abovementioned research results are of great significance for understanding the effect of kaolin addition on the properties of cement-based materials such as concrete and mortar. The cost of backfilling can be reduced if cement can be replaced with kaolin in cemented coal gangue-fly ash backfill (CGFB) samples. It can provide a new path for resource utilization of kaolin. The results can provide a theoretical basis for application of kaolin admixture in fill mining
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