Experimental study on cement-based materials for grouting/replacement of broken rock mass in coal mine

Abstract

In deep high-pressure mines, the surrounding rock of soft broken roadways often faces issues such as poor anchorability, support difficulties, high maintenance costs, and the inadequacy of traditional materials for site requirements. To tackle these challenges, this study focuses on grouting reinforcement in coal mine sites and prefabricated bearing arch form (grouting or replacement) under specific conditions, aiming to meet the material requirements. Through an orthogonal test, various properties of cement-based materials were investigated, including fluidity, initial setting time, water separation rate, early (≤1d) compressive strength, fracture strength, and later (28d as a reference) strength. The objective was to develop a cost-effective cement-based material with high strength and toughness, suitable for underground coal mines. The experimental results demonstrate that the self-developed cement-based materials exhibit rapid setting, excellent fluidity, high early strength, and strong durability compared to traditional alternatives. Analyses of the comprehensive properties reveal that the influencing factors, in order of significance, include the mass ratio of cement and sand, water cement ratio, rubber content, and bonding mortar master material content. By employing extreme treatment and efficiency coefficient methods, the comprehensive performance of materials under different ratios was evaluated. Consistent findings were obtained, indicating that the optimal mass ratio of cement-based materials is 500:500:20:15:10:5:8:10 for cement, sand, fly ash, silica fume, mineral powder, steel slag powder, bonding mortar master material, and rubber, respectively. Additionally, the best comprehensive performance was achieved with a water cement ratio of 0.5, which confirms the results of the orthogonal test. Macroscopic failure characteristics and SEM microscopic analysis further validate the superior performance of the materials under the aforementioned ratio. The reaction process of the material can be roughly divided into four stages: initial hydrolysis stage, induction stage, acceleration stage, decay and stability stage, and finally the formation of stone body. A comparison with ordinary materials highlights the advantages of the developed cement-based materials, and suggestions are proposed for the development of field-applicable materials.