Experimental Study on Performance Optimization of Grouting Backfill Material Based on Mechanically Ground Coal Gangue Utilizing Urea and Quicklime

Abstract

Previously conducted studies have established that grouting backfill in mining-induced overburden bed separation and mined-out areas with broken rocks provides an efficient strategy to control strata movement and surface subsidence caused by underground mining. Grouting backfill materials (GBMs) based on coal gangue (CG) are highly desirable in coal mining for accessibility to abundant CG and urgent demand for CG disposal. However, CG is generally employed as coarse aggregate due to rather rigid and inert properties, limiting its application in GBMs. Herein, to reduce reliance on fine aggregates, such as fly ash and clay, cemented GBM formulations using ground CG powder as a dominant component were proposed. Urea and quicklime were utilized as additives to optimize slurry transportability and compressive strength. Besides typical grinding without additives, CG powder was also prepared via grinding with urea, intending to enhance the hydrogen bonding (HB) interaction between urea and minerals contained in CG. The effect of grinding time and urea on CG particle size and phase composition was investigated. Then, the dependence of slurry transportability and compressive strength on grinding time, solid concentration, urea, and quicklime dosage were revealed. It has been experimentally proved that grinding for 30~90 min significantly decreased CG particle size and even induced crystal deformation of dolomite and kaolinite. For GBMs, urea improved slurry flowability, possibly caused by decreased water absorption on the CG surface and the release of water encapsulated in hydrated cement particles. Moreover, quicklime strengthened GBM bodies, which could be explained by an accelerated pozzolanic reaction between CG powder and additional CH supplied by quicklime hydration. G60U3-based GBM-B2 with 5% quicklime provided a stable and smooth slurry with a bleeding rate of 1.25%, a slump flow of 205 mm, and a hardened body with a seven-day UCS of 1.51 MPa.

Experimental Study on Ratio and Performance of Coal Gangue/Bottom Ash Geopolymer Double-Liquid Grouting Material

“…According to the reference [44], the reinforced impermeable material needs a certain shear strength to prevent the slurry stone body from being squeezed out of the fissure by water pressure, so as to resist the seepage failure of high water pressure. This performance can be checked with the Buckingham-Reiner formula:…”

Performance comparison of geopolymer and clay-cement grouting pastes and goaf effect evaluation of grouting backfilling method

“…For example, the material is conveniently inserted to gap via piping, effectively occupying goaf cavity as well as significantly mitigating the potential for surface subsidence resulting from goaf collapse (Xu et al, 2020;Shrestha et al, 2022). Wang et al proposed a new method of using coal gangue powder as the dominant component in grouting backfill materials for underground mining with optimized slurry transportability and compressive strength using urea and quicklime as additives (Wang et al, 2023). Yuan et al used molecular dynamics simulations for relationship between crosslinking degree as well as properties for polyurethane grouting materials, providing insights into their microstructure and thermomechanical properties (Yuan et al, 2022).…”

Experimental Study on Preparation of Dry-Mixed Mortar from Coal Gangue

“…Zhang et al [10] replaced cement with a part of gangue ground to fine ash to prepare concrete, and the results showed that when the replacement rate was approximately 15%, the properties of the concrete were almost the same as those of pure cement concrete. Chen et al [11] reviewed the current research progress of domestic and foreign scholars on the mechanical properties and durability of gangue, pumice, and ceramic light aggregate concrete, obtained different types of hard bone materials, particle size, shape, and substitution rate and introduced the effects of the mixture and aggregate activation on the mechanical properties and durability of concrete [12][13][14]. However, the preparation of dry-mixed mortar from coal gangue and its application have not been reported.…”