Study on mechanical properties of a roadbed rehabilitation polyurethane grouting material after freeze-thaw cycles

The mechanical properties of roadbed rehabilitation polyurethane grouting material (RhPU) under freeze-thaw cycles are the theoretical basis for evaluating its long-term performance in cold regions, but are currently not well understood. Freeze-thaw cycle tests were conducted on RhPU grouting materials of different densities using a rapid freezing method to investigate the effects of damage characteristics of RhPU. The experimental results indicate that the frost damage of RhPU is a fatigue failure process from the outside to the inside. During the freeze-thaw cycle, water-filled cells experience compression damage due to freezing expansion and interconnected, forming more water seepage channels, accelerating the internal damage of RhPU. Therefore, the dynamic elastic modulus, longitudinal wave velocity, rigidity, and compressive strength of RhPU all decrease with an increase in freeze-thaw cycles. Moreover, at the same freeze-thaw cycles, the lower the density of RhPU, the greater the loss rate of the dynamic elastic modulus, longitudinal wave velocity, rigidity, and compressive strength. The square of the longitudinal wave velocity of RhPU samples before and after freeze-thaw cycles correlates well with density, and the longitudinal wave velocity loss rate better quantifies the internal damage of RhPU samples. Through scanning electron microscopy, the microstructure of RhPU after freeze-thaw cycles was observed, revealing that the lower density of RhPU exhibits more severe freeze-thaw damage compared to higher density RhPU, attributed to its larger cell diameter and greater contact area between adjacent cells. This indicates poorer freeze resistance performance for low-density RhPU.