Abstract
To improve the borehole sealing effect, especially that of coal seam with low permeability and micro fissures, this paper takes the expansion rate of the sealing material as the response value and establishes the quadratic model embracing the expansion rate and various experimental factors by designing orthogonal experiments. The response surface is used to further determine the significance order of each key factor according to the expansion rate and adjust the admixture content to obtain the optimal ratio of the sealing material. For the research investigating a sealing material, the optimal ratio of the sealing material is obtained: the content of water reducing agent of 0.5%, the content of retarder of 0.04%, water-cement ratio of 0.8, and the content of expansion agent of 10%. At this time, the expansion rate reaches 3.136%. Besides, a scanning electron microscope is used to observe the microscopic morphology of the material. According to the scanning electron microscopy analysis of new borehole sealing materials, the surface of the new borehole sealing material shows no holes and possesses compactness; and a large amount of ettringite is formed on the surface of the hydration product of hardened cement slurry. The ettringite improves the expansibility of the material. The new sealing material provides a new idea for gas sealing, which is of great significance to improve the efficiency of borehole extraction, improve the utilization rate of resources, and prevent gas accidents.
Highlights
Gas disasters and accidents frequently occur in China and seriously affect production safety in coal mines
Some scholars have developed a CF type expansive cement composed of ordinary Portland cement, aluminum powder, CaO, and gypsum. e expansive cement with good fluidity and high compressive capacity optimizes the expansion performance of cement materials [7, 8]
Ye et al [12] have compared the effects of calcium sulfoaluminate-calcium oxide and magnesium oxide on the expansion rate of Portland cement and found that calcium sulfoaluminate-calcium oxide increases the early strength, while magnesium oxide improves the expansion rate at the middle and late stage
Summary
Gas disasters and accidents frequently occur in China and seriously affect production safety in coal mines. Wang et al [10] have mixed ordinary cement, coal gangue powder, and clay in a certain proportion for a new type of grouting sealing material, whose compressive strength and expansion ratio can be significantly improved. Some scholars have studied the influencing factors of MgO expansive agent effect, which provides a direction for the improvement of expansion performance of sealing materials [16, 17]. Zhou and Wang [18] have studied the influence of the amount of dispersant and expansion agent on the new sealing material based on the compressive strength and expansion ratio and determined the optimal ratio of each factor. Is study focuses on curing cracking of cement materials and the poor grouting effect on micro fissures. All technical parameters and indicators have met the requirements of “Superfine Portland Cement” (GB/T35161-2017). e expansion agent is HCSA with an appearance of off-white powder. e water-reducing agent is PCE with white powder. e retarder used in this experiment is seaweed powder with a white appearance
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