Novel Superhydrophobic Cement-based Materials Achieved by Construction of Hierarchical Surface Structure with FAS/SiO₂ Hybrid Nanocomposites

This work aims at developing novel superhydrophobic cement concrete by applying a tridecafluorooctyltriethoxysilane/nanosilica (FAS/SiO₂) hybrid nanocomposite onto surfaces of hardened concrete. The hybrid nanocomposite was synthesized and characterized using TEM, TGA and NMR. The performance of the FAS/SiO₂ treated cement paste/mortar samples were evaluated using a water contact angle (WCA) test, lab-raining detachment test, 3D image analysis, and UV irradiation test. The results indicate that the core-shell spherical structured composite had a particle size of about 200 nm and shell thickness of about 50 nm, displayed high pozzolanic reactivity, and enable to polymerize C-S-H gel of the concrete, thus lowing surface energy and modifying surface structure. The WCA of the FAS/SiO₂ treated-concrete samples was larger than 150, signifying a superhydrophobicity. The FAS/SiO₂ hybrid composite had superior anti-detachment performance, proposing that the treated concrete surface would have a long-term high water-proofing performance. A hierarchical structure observed from the 3D image analysis might be primarily responsible for the increase in the hydrophobicity of the hardened cement-based materials. The 800-hour UV irradiation test results suggested a good stability of superhydrophobicity under severe weathering conditions. It is concluded that the FAS/SiO₂ hybrid nanocomposite has a great potential for improving durability of existing concrete structures.