Preparation and Anti-Corrosion Properties of Hydrophobic Geopolymer Coatings

To lower the water absorption capacity and enhance the anti-corrosion performance of geopolymer coatings, methyltrimethoxysilane (MTOS) was adopted as a hydrophobic modifier to synthesize hydrophobic geopolymer coatings, and their anti-corrosion behaviors were systematically investigated. The results reveal that increasing MTOS content gradually improves the fluidity and setting time of fresh coatings while reducing their bonding strength. MTOS effectively strengthens the surface hydrophobicity of the coatings, decreases the water absorption of coated concrete substrates, and remarkably boosts chloride ion penetration resistance. The modified coatings achieve the optimal anti-corrosion performance at an MTOS dosage of 8 wt.%. Under this optimal condition, the surface water contact angle reaches 135.1°. After 28 days of chloride ion erosion, the chloride ion concentration is 45.0% lower than that of the unmodified counterpart. Meanwhile, the coating exhibits the minimum water absorption rate of 2.06% and the lowest average chloride penetration rate of 0.41 × 10−3 mg/(cm2·d), which accounts for only 41% of the standard threshold value. This study demonstrates that MTOS-based hydrophobic modification can significantly upgrade the anti-corrosion capability of geopolymer coatings, which provides a valuable theoretical basis and practical guidance for improving the durability of concrete structures.