Preparation of a hydrophobic coating on cement-based materials by fluorinated hybrid nanoSiO2 and study on its UV-resistance performance

In surface treatment technics of cement-based materials, nanoSiO 2 (NS) is effective in refining pore structure while organic water-repelling agents are often used for producing a hydrophobic surface. Due to its advantages of pore refining effect and hydrophobicity, the organic-inorganic hybrid nanoSiO 2 has attracted increasing attention. However, the UV-irradiation can result in photodegradation of organic constituents, leading to deterioration of hydrophobicity. In this study, a novel UV-resistant fluorinated hybrid nanocomposite, NS@TOFS, was synthesized and used for surface treatment on hardened cement-based materials. The water and gas permeability of the treated samples before and after UV-aging were assessed by measuring the water absorption rate, water contact angle and carbonation degree. The experimental results showed that the NS@TOFS treated samples possess enhanced water and gas impermeability after 14 days of exposure to UV rays. A morphological observation of the treated surface revealed that a synergistic effect of organic film and refined pore structure was responsible for the improved surface properties. Findings from this study well demonstrate that the developed fluorinated hybrid nanoSiO 2 holds great promise for enhancing the durability of cement-based materials under UV-irradiations.