SiO2/TiO2 and PDMS modified self-cleaning coating and its application in decorative UHPC surface

Decorative ultra-high performance concrete (UHPC) is easily contaminated with organic and inorganic pollutants owing to its hydrophilicity. Long-term pollution causes the aesthetics of UHPC to diminish gradually. The antifouling ability of decorative UHPC can be improved by adding functional coatings. However, the decorative UHPC surface is smooth and dense. An ordinary superhydrophobic coating offers a single function, and cannot adhere stably to the UHPC surface. The coating detachesis easily off after long-term use, thus causing the material to lose its self-cleaning performance. In this study, a multifunctional self-cleaning coating with a double-layered structure is designed. Polydimethylsiloxane (PDMS) is used as the bottom layer, which increases the adhesion of the coating to UHPC and provides hydrophobicity to the coating. The surface layer is a nano-SiO2/TiO2 superhydrophobic layer modified with polymethylhydrosiloxane. Nanoparticles form a regular micro/nano composite structure on the surface of the UHPC via self-assembly. The introduction of TiO2 imparts excellent photocatalytic performance to the coating. Experimental results show that the prepared multifunctional coating not only prevents the adhesion of inorganic pollutants, but also effectively decomposes organic pollutants, such as methylene blue, and significantly improves the self-cleaning performance of UHPC. When the SiO2:TiO2 ratio is 2:3 and the PDMS content is 2.5 wt%, the static contact angle of the coating surface is 157.2° and the sliding angle is 2.1°. The coating exhibits excellent superhydrophobic photocatalytic performance, wear resistance, water erosion resistance, acid and alkali resistance, and ultraviolet light stability. In addition, the excellent superhydrophobicity and mechanical stability of the coating are explained based on chemical characterisation and micro-area morphology analysis.