Study on the improvement of grouting stone properties in coal mine goafs using combined denitrifying bacteria

• Published in: Royal Society open science Vol. 11; no. 9; pp. 240993 - 18
• Main Authors: He, Hao, Xu, Nengxiong, Qin, Yan, Xu, Tianchi, Guo, Yuxi
• Format: Journal Article
• Language: English
• Published: England The Royal Society Publishing 01.09.2024; The Royal Society
• Subjects: Bacteria; Cement; coal mine goaf; Coal mines; Coal mining; Concrete; Denitrification; Denitrifying bacteria; Engineering; grouted stone body; Heavy metals; Mechanical properties; Metabolism; microbially induced calcite precipitation; Microorganisms; Nitrates; physical and mechanical properties; Physical properties; Pollution; Polyvinyl alcohol; Ratios; Shear strength; Soil erosion; China; microbially induced calcite precipitation; coal mine goaf; grouted stone body; physical and mechanical properties
• ISSN: 2054-5703; 2054-5703
• DOI: 10.1098/rsos.240993

Grouting can effectively reduce residual deformation of coal mine goafs, but fly ash grouting materials suffer from poor flowability and slow early strength development. Microbially -induced calcite precipitation (MICP), with its high environmental compatibility and minimal disturbance to geotechnical bodies, effectively improves the injectability of grouting slurry in goafs. This study combined and to induce calcite precipitation, preparing cement-fly ash slurry with varying water-solid ratios, solid ratios and denitrifying bacteria concentrations. The physical properties of the slurry and the mechanical properties of the grouted stone bodies under sealed curing conditions were measured. Results show that the dual-bacteria MICP improves stone body performance by enhancing cohesive, frictional and interlocking forces, so that the strength of the stone bodies cured by MICP increased rapidly within 7 days, and the strength reached the standard 2.03 MPa at 28 days under conditions of low solid ratio and high water-solid ratio, with the best compressive strength at a denitrifying bacteria concentration with an optical density of 0.8 at 600 nm wavelength. At a water-solid ratio of 1 : 1.2 and a solid ratio of 15%, initial and final setting times were 67.2 and 96 h, respectively, which prolonged the initial setting time and final setting time by nearly 70% and 110% compared with that of the slurry without MICP treatment, indicating that MICP enhances slurry fluidity, providing more time for grouting construction in goafs.