Study on the Optimization of Filling Ratio and Strength Variation Characteristics of Cemented Backfills Containing Fly Ash

Abstract

The fly ash for underground filling can effectively utilize solid waste, improve the strength of the backfill, and reduce the cost, thus creating good social and economic benefits. Relying on the filling requirements of a gold mine in Jilin, this paper carried out the filling ratio experiments containing fly ash and analyzed the reasons for the variation of the backfill strength based on the hydration characteristics of cement and fly ash and scanning electron microscope. The results show that fly ash has an overall effect on the strength of the backfill, and the strength development is mainly concentrated in the period of 28–56 d; when the filling slurry contains tailings, the excessive amount of fly ash is likely to cause a large number of fine particles to obstruct the hydration of cementitious materials; when the concentration of the filling slurry is 74%, the cement content is 5%, the mass ratio of waste rock-tailings-fly ash is 6:2:3, and the CaO content is 6:3, the strength of the backfill is significantly higher than the current strength of the backfill of the mine, and the cost can be saved by RMB 0.56 per cubic meter; the strength characteristics of the backfill mainly depend on the pore structure; when the filling slurry is better matched, the cement and fly ash hydration generates a large number of C-S-H gel particles, which wraps the aggregate to form a dense structure with less pore structure, and the strength of the backfill increases; the strength variation process of backfill containing cement and fly ash is divided into cement hydration period, fly ash infiltration period, and slurry hardening period. To enhance the strength of the backfill, it is necessary to determine the appropriate cementitious material ratio to maximize the excitation of fly ash hydration during the fly ash infiltration period, and the hydration produces a gel structure with an excellent aggregate ratio. In addition, the slurry hardening reduces the porosity of the backfill. The results can provide basic data and theoretical guidance for further promotion and application of fly ash in mine filling.

Mix proportion and microscopic characterization of coal-based solid waste backfill material based on response surface methodology and multi-objective decision-making

“…In this experiment, the fluidity and bleeding rate are tested. The fluidity of the backfill material is the average diameter of the material flowing freely on the glass plane 26 . The test method refers to the Chinese standard "Test Method for the Homogeneity of Concrete Admixtures" (GBT8077-2000), as shown in Fig.…”

“…Aneke et al 22,23 studied the performance and microstructure of fly ash as a roadbed backfill material, providing reference for the study of the performance of mining solid waste backfill materials. Other scholars have used different methods to optimize the proportioning and performance of backfill materials with different types of solid waste [24][25][26] .…”

The Utilization of Fly Ash in the Mining Sector

“…Fly ash for underground mining backfilling can effectively utilize solid waste, increase the backfill's strength, and lower cost, resulting in positive social and economic outcomes. Using a scanning electron microscope and the hydration properties of cement and fly ash, the causes of the variance in backfill strength were examined by Chang et al [31]. When the concentration of the filling slurry was 74%, the cement content was 5%, the mass ratio of waste rock-tailings-fly ash was 6:2:3, and the CaO substance was 6:3, the strength of the backfill was substantially more significant than the existing strength of the mine's backfill.…”

A Novel Design Concept of Cemented Paste Backfill (CPB) Materials: Biobjective Optimization Approach by Applying an Evolved Random Forest Model

“…The results showed that the high W/C (1.0 and 1.2), low W/S (0.3), 0.05% PAM, and 1.0% PCE can benefit the production cost as well as the physical properties of the CPB. Chang et al [ 32 ] proposed the use of fly ash in CPB to reduce the costs and improve the strength of backfill. The research results show that replacing cement in CPB with fly ash can effectively reduce its cost and have an overall impact on the strength of it.…”