Effects of Foaming and Drainage Behavior on Structure and Properties of Polyurethane/Water Glass (PU/WG) Grouting Materials for Coal Mines

Abstract

During the grouting operation in the underground coal mine, abnormal curing behaviors such as foaming and drainage often lead to the loss of reinforcement effect of the polyurethane/water glass (PU/WG) materials on coal walls and even cause safety accidents. Herein, three kinds of PU/WG grouting materials were successfully prepared by changing the type of catalysts, which were the normal sample (C7), the foaming sample (C14), and the sample with drainage (C17) during curing. The structure, thermal stability, and compressive strength of the three samples were characterized by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetry-differential thermal analysis (TG-DTA), and pressure testing machine. The results showed that the abnormal curing behavior had little effect on the thermal stability of the material, but it had a significant effect on the microstructure and compressive strength of the consolidated body. C7 exhibited a typical three-phase distribution, in which the polysilicate microspheres encapsulated by acicular carbonate were embedded in the polymer continuum. The structure of C7 had high rigidity and hardness, and the compressive strength was up to 43 MPa. The three-phase structure of C14 disappeared gradually with the increase of catalyst content, the hard block material and matrix are porous, and the compressive strength was only 2.7 MPa. The organic polymer of C17 existed in the form of microsphere and distributed irregularly in the continuum composed of inorganic components, and the compressive strength was 4.9 MPa. The abnormal solidification behavior such as foaming and drainage made the water glass/polyurethane material lose its basic mechanical properties, which cannot meet the needs of grouting reinforcement in coal mines. Therefore, the type of catalyst had a significant impact on the stability of the system, and it is necessary to avoid selecting catalysts that are likely to cause abnormal solidification during formulation research.