Research on the Frost Resistance of Polyurethane-Modified Sulfoaluminate Cement

The development of cementitious materials with superior frost resistance remains a critical requirement for ensuring the durability of concrete structures. In this study, waterborne polyurethane was used to modify sulfoaluminate cement. The influence of waterborne polyurethane on the frost resistance of cement specimens was investigated through water and salt freeze–thaw cycle tests by monitoring variations in surface appearance, mass, and relative dynamic elastic modulus. Microstructural changes were analyzed using scanning electron microscopy, X-ray diffraction analysis, Fourier transform infrared spectroscopy, mercury intrusion porosimetry, and nanoindentation. The results indicated that incorporating an appropriate amount of waterborne polyurethane not only mitigated the freeze–thaw damage on the specimen surface but also reduced mass loss and relative dynamic elastic modulus loss to 0.8% and 7.9%, respectively, after 300 water freeze–thaw cycles. Moreover, the specimens exhibited excellent durability under the combined influence of salt and freeze–thaw cycles, successfully withstanding over 200 cycles. The internal pore structure of specimens containing waterborne polyurethane was significantly optimized, characterized by an increased number of small pores. Waterborne polyurethane effectively inhibited the propagation of microcracks within the specimens, forming a polymer film and an interlaced network structure throughout the matrix, thereby improving internal structural integrity. Waterborne polyurethane did not chemically react with sulfoaluminate cement; however, it delayed the cement’s hydration process. These results demonstrate that the addition of waterborne polyurethane can effectively enhance the frost resistance of sulfoaluminate cement, offering significant benefits for practical engineering applications.