Study On The Durability Of Concrete With Modified Nano Composite Inorganic Coating

As a building material,concrete is widely used in various construction fields.A large number of pores and cracks are distributed on the surface and interior of concrete.Various harmful ions migrate from the surface to the interior of the concrete matrix,resulting in carbonization,freeze-thaw,and steel corrosion of concrete.Concrete surface treatment technology is a recognized economical and effective method to improve concrete durability.Based on a water-based compound silicate surface strengthening materials that can improve the impermeability and durability of concrete,this paper proposes to use nano-SiO₂ particles as a reinforcing material to further enhance it is strengthening effect on the concrete surface.Because the nano-SiO₂ particles are difficult to disperse in an aqueous solution matrix,the methyl acrylate was reacted with KH550 and KH590 silane coupling agents based on the Michael addition reaction,and the ester bonds that can be hydrolyzed under alkaline conditions were introduced into modified coupling agent molecules.Then the surface modification of nano-SiO₂ particles was carried out,and the ester bonds were hydrolyzed by the alkaline conditions of the compound silicate solution,to give the nano-SiO₂ particles good water dispersibility in the inorganic silicate solution,and the nano-composite silicate surface strengthening material was obtained.Through the dispersion experiment and particle size analysis in the mixed silicate solution,the dispersion of nano-SiO₂ particles modified by KH550 was the best.Firstly,the effects of different contents of nano-SiO₂ particles in the compound silicate solution on the water absorption,water vapor permeability,water penetration height,and freezing-thawing resistance of different mortar ages were investigated.The results show the impermeability of nano-composite-treated mortar is better than that of composite silicate-treated mortar.When the content of nano-SiO₂ particles is 1%,the performance of the composite coating is the best.Compared with the composite silicate-treated,the water absorption,water vapor permeability,water penetration height,strength loss rate,and mass loss rate of the 28d age mortar after nano-composite treatment decreased by 47.3%,25.1%,25.0%,6.9%,and 0.16%,respectively.The mechanism of the nano-composite system on the improvement of the impermeability of mortar was investigated by scanning electron microscopy,Fourier transform infrared spectroscopy and X-ray diffraction spectroscopy.It is found that nano-SiO₂ particles can accelerate the secondary hydration of cement,and have a synergistic effect with silicate to generate more hydrated calcium silicate gel,which improves the surface compactness,but excessive nano-SiO₂ particles will lead to a decrease in surface compactness.Finally,the nano-composite system was applied to the surface layer of concrete with different strength grades of C30 and C50,and its influence on chloride ion permeability,carbonation resistance and freeze-thaw resistance of concrete with different strength was studied.The results show that the nano-composite system has a better effect on the durability of C30 concrete than that of C50 concrete.The 6h electric flux of C30 concrete and C50 concrete decreases by 35.5%and 10.7%respectively,and the carbonation depth decreases by37.5%and 19.2%respectively.After 100 freeze-thaw cycles,the frost resistance level of C30 concrete increases from F25 to F75,the mass loss rate decreases by 44.8%,the relative dynamic elastic modulus of C50 concrete increases by 16.1%,and the mass loss rate decreases by 42.1%.