Synthesis and Water Repellency Evaluation of Hydrophobic Modification Materials for Silt Subgrade

Silt subgrade is often deformed and damaged due to poor water stability, which poses a threat to the safe operation of highways. To address these issues, a new nanotype hydrophobic material (NT-HM) was synthesized in this study. The synthesis and application parameters of NT-HM were optimized using single-factor tests and the response surface method. The hydrophobic properties of NT-HM-modified silt were then investigated through macro- and microexperiments, revealing the mechanism of hydrophobic modification by NT-HM. The experimental results show that NT-HM synthesized under the conditions of 51°C temperature, pH=9, nanosilica sol concentration of 4.5%, and organic silicon content of 95.5% yields the best performance. By adding just 0.5% of NT-HM synthesized under these conditions, the surface contact angle of silt can reach 150.4°, which reduces its permeability by 97% and effectively prevents the occurrence of capillary action. Hydrophobic modification did not significantly alter the morphology or particle size of the silt, and no new chemical compounds were formed. NT-HM enhances the hydrophobic properties of silt by forming a hydrophobic oil film around the silt particles and filling the pore structure within the sample. The research results provide a valuable reference for the modification of silt subgrades.