The Study On Surface Modification Of Cement-based Materials By Nano-silica

The surface quality of cement-based materials directly affects many properties of the substrate,such as carbonization resistance,chloride ion resistance,permeability,water absorption,etc.The improvement of the surface quality of the substrate reduces the intrusion of harmful substances and the deterioration and corrosion of cement-based materials and steel bars inside the matrix,prolonging the service life of cement-based materials.Due to their high permeability,high activity and excellent functionality,nanomaterials can be used as new surface treatment agents to improve the performance of cement-based materials while imparting functionality?such as self-cleaning,air purification,bacteriostatic and electromagnetic shielding?.It basically meets the new demands placed on the structure and functionality of building materials due to the improvement of people's living standards.However,most of the nanomaterials are directly applied to the surface of cement-based materials,and their poor adhesion to the substrate results in poor durability.Nanomaterials with pozzolanic activity,such as nano-SiO₂,can undergo pozzolanic reactions with the matrix.Using this feature,it is combined with functional nanomaterials to improve the performance of cement-based materials,impart functionality,and enhance the durability of nanomaterials.This thesis focuses on nano-SiO₂,functional nanomaterials?such as wave-absorbing and photocatalytic nanomaterials?and their composite materials?Fe₃O₄@SiO₂,TiO₂@SiO₂,SiO₂@TiO₂ and BiOBr@SiO₂?to treat the surface layer of cement-based materials,studying its effects on the properties,functionality and durability of cement-based materials.SiO₂ oligomer has the advantages of small size,high surface hydroxyl content and low viscosity,which has the effect of increasing the application depth and increasing its pozzolanic activity.In this study,the sol-gel method was used to synthesize SiO₂ oligomers with excellent properties in acidic and alkaline environments by adjusting the experimental parameters.After treatment on the surface of cement-based materials,the water absorption of the samples was significantly reduced.Under the induction of magnetic field,the excellent magnetic properties of Fe₃O₄nanomaterials can be used to penetrate the surface of cement-based materials.The SiO₂ shell can improve the dispersibility,oxidation resistance and wave absorption of Fe₃O₄nanomaterials.The sample treated with the Fe₃O₄@SiO₂ core-shell nanomaterials has a small reflectivity and is less reflective than the pure Fe₃O₄ treated sample.The pore structure of the cement-based material can be improved,and the water absorption of the substrate reduces due to the volcanic ash activity of SiO₂.Commercial TiO₂ has high photocatalytic activity.Using this material as core material,TiO₂@SiO₂ core-shell nanomaterials were prepared by using nano-SiO₂ as shell layer.Nanocomposites with different shell thicknesses were prepared by adjusting experimental parameters.The nanocomposites were applied to the surface of cement-based materials to test the photocatalytic effects of direct treatment,curing and rain simulation.After simulating the raining process,the photocatalytic properties of cement-based materials treated with TiO₂@SiO₂ core-shell nanomaterials were reduced.SiO₂ shells can effectively stabilize the photocatalyst.In order to reduce the influence of other materials on the surface of photocatalyst on photocatalytic performance,SiO₂ was used as the core material,and TiO₂ was attached to the surface of SiO₂.SiO₂@TiO₂ composite was with two different deposition densities were formed by controlling experimental parameters.After spraying two samples on the surface of the cement paste,the sample has excellent photocatalytic performance under both ultraviolet light and sunlight.After curing and simulating rain,the photocatalytic performance of SiO₂@TiO₂ treated cement-based materials did not decrease,indicating that the core material SiO₂ can effectively stabilize the photocatalyst.The reaction mechanism of the sample in the cement system is proposed by reacting with important components in the cement and hydration products.The application of BiOBr catalytic material under visible light greatly improves the utilization of sunlight,and in practical applications,the photocatalytic efficiency can be greatly improved.The SiO₂ shell was prepared by St?ber method,and the content of SiO₂precursor was controlled during the preparation to form BiOBr@SiO₂ composite with different shell thicknesses.It is applied to the surface of the cement-based material,and still has relatively excellent photocatalytic performance.The porosity of 0.01-0.2?m is obviously reduced relative to the untreated cement paste.The surface of the BiOBr@SiO₂-cem sample increased with the increase of the shell content,and the surface became dense and smooth after curing for 28 days.The research in this paper provides a technical approach for the functionalization of cement-based materials,providing theoretical basis and support for the design and application of other similar structures.