Study On Preparation And Performance Of Superhydrophobic Coatings On Cement Base Materials

With continuous implementation of "One Belt and One Road",maritime power and new urbanization strategy,a great deal of infrastructure constructions,such as roads,bridges,high-speed rails and tunnels,are being built at an unprecedented scale.Among all constructions including large numbers of cement-based materials serving in harsh environment,durability is the predominant challenge to be dealt with.Harmful substances,such as chloride ions,sulphate ions,magnesium salts and carbon dioxide,constitute main factors affecting the durability of cement-based materials.These harmful substances are transferred with water by capillary pores to internal of cementbased materials,leading to structural failures.Therefore,preventing water transport is of great importance in improving the durability of cement-based materials.Based on biomimetic superhydrophobic phenomena,two kinds of superhydrophobic materials were fabricated by low surface-energy surfactants.Multi-scale microstructures and surface chemical properties of modified concrete was studied as well as the durability of coated cement-based materials.(1)Preparation of superhydrophobic coatings of GKS and SHCUnder the condition of low temperature and alkali environment,GK was prepared by hydrolytic condensation of siloxane A.Coated with 5wt% GK,cement-based material surface contact angle reached about 136°.By introducing four kinds of nanosilica into GK,WCA of cement base material could be raised above 150°,and the coating of GKS5 with 5wt% nano-silica showed the maximum WCA of 153 °.At room temperature and acidic conditions,the superhydrophobic coating SHC was prepared by siloxane A,hydrogen siloxane(D)and acidic Ludox colloidal silica nanoparticles(AC).The appropriate coating concentration of SHC was 10wt%,and the optimum impregnation time was 40 s.Optimum ratio of siloxane A,D and AC was 7:3:1,while the WCA of cement-based material was 167 °,rolling angle 6.3 °.(3)Chemical action between superhydrophobic coating and cement-based materialSuperhydrophobic coatings grafted onto cement based materials to reduce the surface energy of materials were clarified by Fourier infrared spectrum analysis.The X-ray diffraction patterns showed that the nano-silica of the two coatings reacted with calcium hydroxide in the cement-based materials.(3)Microstructure of superhydrophobic coating of cement-based materialsUsing transmission electron microscopy(TEM),scanning electron microscope(SEM),atomic force microscope(AFM)and digital holographic microscopy(DHM),surface roughness of superhydrophobic cement-based material were investigated in 2D and 3D.The results showed that both superhydrophobic coatings increased the surface roughness of cement-based materials.(4)Effect of superhydrophobic coating on durabilityThe effects of two kinds of superhydrophobic coatings on durability and respiratory properties of cement-based materials were studied by carbonation test,water absorption test and chloride ion penetration test.The results showed that the superhydrophobic coating maintained the respiratory performance of cement base material.The effect of superhydrophobic coatings GKS5 and SHC4 on water absorption rate and chloride ion permeability on cement-based materials of different strengths was observed,chloride ion permeability of C30 and C50 is increased about 16.8% and 29.5% respectively,and above 25% decrease in water absorption rate.