Analysis of Strength and Microstructural Characteristics of Mine Backfills Containing Fly Ash and Desulfurized Gypsum

Abstract

The utilization of solid wastes (SWs) as a potential resource for backfilling is not only conducive to environmental protection but also reduces the surface storage of waste. Two types of SWs, including fly ash (FA) and desulfurized gypsum (DG), were used to prepare cementitious backfilling materials for underground mined-out areas. Ordinary Portland cement (OPC) was used as cement in mine backfill. To better investigate the feasibility of preparing backfill materials, some laboratory tests, such as uniaxial compressive strength (UCS), scanning electron microscopy (SEM), and energy dissipation theory, were conducted to explore both strength and microstructural properties of backfilling. Results have demonstrated that the main components of FA and DG in this study are oxides, with few toxic and heavy metal components. The ideal ratio of OPC:FA:DG is 1:6:2 and the corresponding UCS values are 2.5 and 4.2 MPa when the curing time are 7 days and 14 days, respectively. Moreover, the average UCS value of backfilling samples gradually decreased when the proportion of DG in the mixture increased. The main failure modes of various backfilling materials are tensile and shearing cracks. In addition, the corresponding relations among total input energy, dissipated energy and strain energy, and stress–strain curve were investigated. The spatial distribution of oxygen, aluminum, silicon, calcium, iron and magnesium elements, and hydration product are explored from the microstructure’s perspective. The findings of this study provide both invaluable information and industrial applications for the efficient management of solid waste, based on sustainable development and circular economy.

Influence of Fe2O3, MgO and Molarity of NaOH Solution on the Mechanical Properties of Fly Ash-Based Geopolymers

“…The mechanical strengths of the samples obtained, comparable to Portland cement, justify the use of these geopolymer pastes in the production of geopolymer concretes and in the production of precast concrete. Results obtained in the current study are in accordance with results previously obtained in the literature, while completing the knowledge about the production of alkaline-activated geopolymer materials [ 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 ].…”

Investigation on Dynamical Mechanics, Energy Dissipation, and Microstructural Characteristics of Cemented Tailings Backfill under SHPB Tests

“…In this study, the value of solid content and the cement-tailings ratio of the manufactured CTB samples was constantly set to 75 wt.% and 0.25. The experiment personnel used a standard electronic scale to weigh the tailings, cement, and tap water and fully stirred the materials in the mixer for 180 s [33]. The content of each component is 34.5 g of cement, 138 g of tailings, and 57.5 g of water.…”

Experimental and Analytical Investigation into the Synergistic Mechanism and Failure Characteristics of the Backfill-Red Sandstone Combination

“…In the process of underground filling, the surrounding rock and filling form a kind of heterogeneous, discontinuous and nonlinear special support. The surrounding rock and filling work together to bear the load of overburden, which has complex mechanical properties and deformation and failure mechanisms [1][2][3]. Therefore, it is necessary to establish the common bearing mechanical model of backfill-surrounding rock combination (BSRC) and study the damage evolution characteristics of surrounding rock and backfill after reasonable matching, which 2 of 19 has an important reference value for exploring the damage and failure mechanism of the BSRC model in deep mining.…”