<p>Polyurethane polymer grouting materials with rapid expansion and solidification characteristics have been widely applied for infrastructure repair and reinforcement. An accurate characterization of the chemical reaction process of the slurry is essential for investigating its grouting mechanism. However, the high concentration of isocyanate groups in such polymer systems causes a “flat-top phenomenon” in Fourier transform infrared (FTIR) spectroscopy, rendering it difficult to accurately determine the conversion rate. To address this issue, a real-time method for measuring the reaction conversion rates of slurry components was proposed. The polyol conversion rate was obtained by tracking the integral area changes of the C—O bond peak in the carbamate product relative to the internal standard. The total slurry volume was determined at different time intervals using light detection and ranging (LiDAR)-based point cloud scanning, from which the gas volume was estimated. Combined with the solubility curve of the physical blowing agent and ideal gas law, the conversion rate of the chemical blowing agent was calculated. The isocyanate conversion rate was indirectly inferred based on the measured polyol and chemical blowing agent conversions. This method was applied to a polyurethane grouting material used in an engineering project, and the time-resolved conversion curves of all components throughout the reaction were obtained. The results revealed a three-stage evolution: a slow initial increase, a rapid rise in the middle stage, and a gradual deceleration in the later stage. The foaming reaction proceeded consistently faster than the gelation reaction did. These findings provide a foundation for further research on the diffusion mechanisms of polyurethane polymer slurries.</p>