Properties and Engineering Applications of a New Goaf Grouting Filling Material

Abstract

In the treatment of goafs in traffic engineering, technical problems such as those related to large-volume grouting and the precise control of material properties are often encountered. To address these issues, we developed a new composite material comprising cement-fly ash-modified sodium silicate (C-FA-MS). The setting time, fluidity, unconfined compressive strength, and microstructure were varied for different proportions of cement-sodium silicate (C-S) slurry, cement-fly ash-sodium silicate (C-FA-S) slurry, and C-FA-MS slurry, and their performances were compared and analysed. The experimental results showed that the initial setting time of the slurry was the shortest when both the original sodium silicate volume ratio ( $V_{\text{S}}$ ) and modified sodium silicate volume ratio ( $V_{\text{MS}}$ ) were 0.2. The final setting time of the C-S and C-FA-S slurries tended to decrease but then increased with decrease in $V_{\text{S}}$ , while that of the C-FA-MS slurry increased with lower $V_{\text{MS}}$ . The fluidity of the C-FA-S and C-FA-MS slurries decreased with decrease in $V_{\text{S}}$ or $V_{\text{MS}}$ at different fly ash admixture ratios. The consolidation compressive strength of C-S increased with decreasing $V_{\text{S}}$ , while that of C-FA-S showed a considerable increase only when $V_{\text{S}}$ decreased from 0.4 to 0.2. Meanwhile, the compressive strength of the C-FA-MS concretions first increased and then decreased with decrease in $V_{\text{MS}}$ . Microstructural analysis revealed that there were more cracks in the C-S agglomerate, the fly ash in the C-FA-S agglomerate reduced the relative density of the skeletal structure, and the stronger cross-linking in the C-FA-MS agglomerate improved the strength of the agglomerate. Under the condition of unit grouting volume, the cost of the C-FA-MS slurry was approximately 44.7% and 31.3% lower than that of the C-S and C-FA-S slurries, respectively. The new C-FA-MS material was applied for the treatment of the goaf in the Wu Sizhuang coal mine. Core drilling detection and audiofrequency magnetotelluric survey revealed that the goaf was sufficiently filled.