Influence of Hydrophobic Coating on Freeze-Thaw Cycle Resistance of Cement Mortar

Due to the porous characteristics of cement-based materials, they are often corroded by salt solutions, which results in decreased durability, especially against damage under freeze-thaw cycles (FTCs). Improving surface properties is an effective way to improve the durability of these materials. In this study, a hydrophobic coating was applied to the surface of cement mortar by chemical modification of low surface energy materials. Fourier transform infrared spectroscopy (FT-IR) showed that low surface energy substances are linked to hydration products through chemical bonds. A water contact angle test indicates that the surface of cement mortar changed from hydrophilic (theta = 14 degrees) to hydrophobic (theta = 140 degrees) after chemical modification. The cumulative water uptake of hydrophobic samples decreased by 90%. Meanwhile, the wear resistance of the hydrophobic coatings was excellent. Compared with the baseline sample, mass loss rate, flexural strength, and compressive strength of hydrophobic coating samples increased several-fold in the FTC test. Microstructural changes of the mortar were characterized by scanning electron microscopy. The results show that a hydrophobic coating can significantly improve the freeze-thaw resistance of cement-based materials. The formation of a hydrophobic layer on the surface of cement-based materials can improve their durability. The research results not only have applications in civil engineering but will also have great impact in the restoration of historic structures.