Experimental and Mechanism Study of a Polymer Foaming Grouting Material for Reinforcing Broken Coal Mass

To study the mechanism of grouting reinforcement of broken coal mass, simulation experiments on grout reinforcing of broken coal mass were performed by using traditional materials, namely, Superfine Cement (SC) and Aluminate Cement (CA), and selfdeveloped Polymer Foaming (PF) grouting material. The macromechanical test results of the different grouting reinforced specimens showed that the residual strength of broken coal increased by different degrees after grouting, and the reinforcement effect was improved most notably by the PF material, which caused obvious plastic deformation characteristics of the coal mass that highly adapted to the deformation of the surrounding rocks, moreover, the long-term reinforcement effect was beneficial. Scanning Electronic Microscopy (SEM) showed that the grout-coal interfaces of the SC and CA materials were relatively loose and mainly affected by the types, quantities, and existence forms of cement hydration products, but had little relation to the properties of the injected medium. However, SEM showed a close combination at the interface with the PF material, which presented acceptable molecular compatibility. Moreover, FTIR indicated that some chemical grafting reactions occurred between the PF and coal mass, thereby leading to a firm polymer coating on the coal surface; thus, the grouting reinforcement effect of the broken coal mass was improved.