Analyzing microscopic structure and macroscopic strength behavior of cement-based tail fills incorporating fiber by X-ray CT scanning technique

Abstract

Using structurally layered cementitious tailings backfill (CTB) as synthetic roof material for down-cut-and-fill mining can save cost while ensuring mechanical properties. In the current investigation, polypropylene fiber having 0.6 % mass concentration and 12 mm length) was used as a reinforcing agent, and fiber layering height ratio (HR) was used as a variable to prepare fiber layering cement-based tailings backfill (FLCTB). The effects of microscopic parameters (e.g., porosity, sphericity, surface fiber ratio) on strength properties of FLCTB were quantitatively characterized by computerized tomography scan, three-point bending, and scanning electron microscopy. Laboratory findings show that adding fiber can enhance the number, structure and morphology of pores. An escalation in fiber layering height brings about gradual dropping within FLCTB's large porosity while posing a rise in small porosity. Increasing fiber layering could profoundly mend fill's flexural characteristics, and with an increase of fiber layering height, flexural properties show a better trend. For example, using HR-0 and HR-1 as benchmarks, the deflection growth rates for HR-2 are 430 % and 171 %, respectively. The fiberreinforced backfill has significant macro-mechanical properties in academic mining scenarios. This performance is not only due to the fiber's crack resistance and ductility; but also because some fibers form a complex spatial network structure within it, which is conducive to load transfer and dispersion. In this study, a new FLCTB-based artificial roof slab is proposed, and the intrinsic connection between the fibers and pores of FLCTB, as well as the influence mechanism, are investigated from a fine-grained point of view. This FLCTB has low preparation cost and excellent bending and cracking resistance. As a result, the current study suggests a new perspective for the microscopic mechanism of strength features of cementitious backfills reinforced with fiber reinforcing agent, and a theoretical support for FLCTB's practical implementations in underground metallic mines as a solution for developing more sustainable, greener and smarter mining operations.