Investigating the seepage control and plugging capabilities of polyurethane-cement composites: A comprehensive study on material properties

Composite grouting materials are increasingly becoming the focus of seepage control and plugging research in civil engineering. To improve their mechanical properties and delay the hydration repair effect without compromising their workability, polyurethane (PU)-cement composite grouting materials, in which cement is not the main component, require a finer particle size and good shape. In this study, ball-milled cement was prepared and combined with waterborne PU (WPU) and oil-based PU (OPU) to create a new PU-cement composite grouting material. The particle size distribution, early strength, and microstructure of the ball-milled cement were analysed, and the best preparation process was determined as follows: a ball-milling time of 120 min and 0.03% grinding-aid doping. The viscosity, swelling rate, bond strength, Fourier transform infrared spectroscopy, X-ray diffraction, and microstructure (via scanning electron microscopy) of composites with different ratios of polymer/cement (P/C) and OPU/WPU were then examined. A new method for evaluating the impermeability of repair materials was proposed based on moisture distribution. The function of ball-milled cement in the composites and the interaction mechanism between ball-milled cement and PU were investigated. The results showed that the best performance was achieved with P/C ratios of 3:1 and 4:1 and an OPU/WPU ratio of 2:1 or 3:1. This indicates that PU-cement grouting material is an ideal choice for seepage control and plugging of underground structures.