| Cement-based materials are widely used in the field of civil engineering due to their excellent mechanical properties,low cost of raw materials and simple production processes.However,as cementitious materials are covered with capillary pores,they are susceptible to water-mediated oxidative corrosion and freeze-thaw damage in the presence of corrosive media,which reduces the service life of cementitious materials.Superhydrophobic coatings have great potential to be applied to cementitious materials for waterproofing,anti-fouling and corrosion protection because of their hydrophobic and water-repellent properties.With the improvement of living standards,people have new requirements for the application of superhydrophobic surfaces in life,and the preparation of a colourful superhydrophobic coating with both waterproofing and decorative effects has become a new research hotspot.In this paper,a coloured superhydrophobic coating was prepared using the sol-gel method with TEOS as the precursor,PDMS as the low surface energy substance and binder and inorganic iron oxide as the colourant.The effect of PDMS content on sol-gel stability,gelling time and gelling morphology was investigated by varying the amount of PDMS added,and the protective performance of the coating on the substrate was explored under different PDMS content.Based on scanning electron microscopy,X-ray energy spectroscopy and Fourier infrared spectroscopy tests,the microscopic morphology and chemical composition of the coating surface were analysed to reveal the superhydrophobic mechanism of the coating.At the same time,considering the brightness,coloring power,acid-alkali resistance and dispersibility of the colorant,the colorant that can be used for coating preparation was selected.The influence of the type and dosage of colorant on the color saturation,superhydrophobicity and microstructure of the coating was studied,and the physical and chemical stability of the color superhydrophobic coating on the surface of the base was explored.The main conclusions are as follows:(1)The influence law of PDMS doping on the performance of SiO2-PDMS composite sol-gel system was explored.The results showed that with the increase of PDMS content,the stability of sol was weakened and the setting time was increased.When the molar ratio of PDMS to TEOS was 0.2,the composite sol began to show slight delamination,but the overall stability of the sol was relatively good.At this point,the gelling time of the SiO2-PDMS composite solution is approximately 33 h.It can not only ensure that the sol has a certain storage and construction time,but also reduce the wear and tear damage of the coating caused by the long gelling time during construction.After drying under natural conditions for 30 d,the dry gel was basically free from cracking,and the gel had good stability and elasticity.(2)The protective effect of the SiO2-PDMS composite coating on the substrate was studied.The results show that as the molar ratio of PDMS to TEOS increases,the cracks of the coating on the surface of the substrate specimen gradually decrease and the film formation gradually becomes uniform.When the molar ratio of PDMS to TEOS was 0.2,the surface of the composite coating was smooth and basically free of cracks,and the adhesion level of the coating on the surface of the specimen was 4 A.At this time,the contact angle of liquid droplets on the surface of the coating was 152.6°,reaching the superhydrophobic state.The coated specimens reached the saturation state of water absorption at 10 d,and the cumulative water absorption rate was 3.47%,34.28%lower than that of the uncoated specimens.When a certain tilt angle was applied to the substrate,the coating surface droplets can be cleaned of solid particle contaminants and liquid contaminants by external forces such as gravity,and the colour difference value of the specimen surface before and after contamination did not exceed 6.(3)The relationship between colorant content,color saturation and wettability of surface coating was studied.The results showed that for the surface coatings of specimens coloured with inorganic iron oxide pigments,the saturated colour concentration was 10%for the red and green superhydrophobic coatings and 12%for the yellow and blue superhydrophobic coatings.The maximum contact angle of 154.3° and 154.6° was reached for the surface coatings of specimens coloured with iron oxide red and iron oxide green at a colourant content of 8%.When the content of colorant was 10%,the surface coating contact angle of iron oxide yellow and iron oxide blue colored specimens reached the maximum,which were 154° and 153.9°,respectively.At this time,the rolling angles of the surface coatings of the base specimens were 12.1°,12.5°,13.8° and 13.4°,respectively.When drops were added to the surface of the inclined specimens,the drops rolled off in a nearly spherical form under the action of gravity and hardly soaked the surface of the specimens.(4)The physical and chemical stability of the coloured superhydrophobic coating on the surface of the specimen was investigated.The results showed that the contact angle of the coating on the surface of the test piece remained basically unchanged at 40 rounds of sandpaper rubbing.After 100 tape peel tests,the contact angles of the surface coatings on specimens coloured with iron oxide red,iron oxide yellow,iron oxide blue and iron oxide green were 150.2°,150.6°,148.6° and 150.8°,respectively.After 2 h immersion in an acidic solution at pH 0,the surface contact angles of the coatings colored by iron oxide red,iron oxide yellow,iron oxide blue,and iron oxide green were 150.2°,151.1°,146.7°,and 140.9°,respectively.The surface contact angles of the four coatings were 151.3°,150.8°,144.2° and 139.6°,respectively,after 2 h immersion in an alkaline solution at pH 14.After 90 d of immersion in the salt solution,the Cl’ concentration at 22.5 mm inside the specimen decreased by 74%,75%,74%and 79%,respectively.After 20 min of accelerated electrochemical corrosion,the internal reinforcement of the coated specimens remained bright.It shows that the SiO2-PDMS coloured superhydrophobic coating has good physical and chemical stability,and can prevent corrosion damage to the coating surface and internal reinforcement by strong acid and alkali solutions. |
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