Study On The Effect And The Mechanism Of Graphene Oxide Modified Silane Composite Emulsion On The Waterproof Performance Of Foamed Concrete

With the acceleration of urbanization and the improvement of people’s quality of life,the total energy consumption of China’s buildings has been rising year by year.At the present stage,the total energy consumption of China’s buildings has accounted for about one-third of the total energy consumption of society,and such a large proportion will inevitably affect the economic development of China.Based on the background of implementing the sustainable development strategy of building energy saving and achieving the national energy saving planning target,the application field of foamed concrete is expanding by its excellent thermal insulation performance,but its durability is affected and its service life is shortened due to its high water absorption rate and poor water resistance.In this paper,silane was selected as a waterproof material and combined with graphene oxide nanomaterials(GO)to prepare a graphene oxide/silane(Silane/ GO)emulsion.Internal doping and surface coating were used to improve the waterproofing performance of foamed concrete,and the waterproofing mechanism was analyzed at the molecular level using molecular dynamics simulation methods.The results of the study showed that:(1)Silane(EI)emulsion and graphene oxide/silane(EG)emulsion were prepared by the sol-gel method,and the two silane emulsions were incorporated into the mix as admixtures at 0.5%,0.75% and 1% of the mass ratio with cement to prepare foamed concrete test blocks,and the basic properties of foamed concrete,such as dry density,thermal conductivity,compressive strength and pore structure were tested,the study found that the admixture of silane emulsion intensified the defoaming process of foamed concrete,and the large amount of discharge of foam liquid film promoted the hydration of high-belite sulfoaluminate cement,which changed the pore structure of foamed concrete,so that its porosity decreased,dry density increased,thermal conductivity increased,compressive strength increased,and mass water absorption decreased,and with the increase of silane admixture,the larger the contact angle on the surface of foamed concrete,the the better the waterproofing effect.Scanning electron microscope(SEM)and X-ray diffraction(XRD)analysis results show that the degree of cement hydration peaked when the silane emulsion admixture was 0.75%;when the EI emulsion admixture was 1%,the cement hydration process was inhibited;when the EG emulsion admixture was 1%,EG promoted the cement hydration process.(2)In order to enhance the waterproof performance of foamed concrete without changing its pore structure,surface treatment was used to coat the surface of foamed concrete with silane composite emulsion.The penetration depth test found that if only the surface of foamed concrete was coated with silane emulsion,with the penetration and diffusion of silane emulsion,the foamed concrete only appeared as a waterproof layer in the middle part with thicknesses of 9.6 mm(EI)and 10.2 mm(EG),and neither the exterior nor the coated surface was waterproof,but the volumetric water absorption of foamed concrete still decreased by 82% and the surface contact angle reached 124.5°.However,if the treatment of soaked silane emulsion was used,the overall waterproofing of foamed concrete could be achieved with almost 0 mass water absorption.Microstructure test results showed that the silane in graphene oxide/silane emulsion reacted with C-S-H in the cementitious material and formed a waterproof layer on the surface of the cementitious material,and graphene oxide combines with silane in a Si-O-C covalent bond to promote the hydration of foamed concrete.The waterproof layer was formed earlier and thicker,it had excellent hydrophobic effect.(3)In order to improve the dispersibility and fluidity of silane emulsions,PVP/silane(VI)and PVP/graphene oxide/silane(VG)were prepared by using polyvinylpyrrolidone(PVP)as a new dispersant,and rheological tests were conducted on four kinds of composite silane emulsions(EI,EG,VI and VG),and it was found that after the incorporation of PVP,the The rheological properties were improved.The results of waterproof performance test showed that VI and VG could reduce the volumetric water absorption of foamed concrete by 82% and 88%,respectively,and the waterproof performance was better than EI and EG,respectively.(4)By studying the effect of different coating times of silane emulsion on the waterproofing performance of foamed concrete,it was found that foamed concrete coated with silane emulsion followed by GO/Silane emulsion had a larger waterproof layer thickness,smaller volumetric water absorption and better waterproofing performance than foamed concrete coated with Silane emulsion only.However,compared with the foamed concrete coated with GO/Silane emulsion only,the waterproof layer thickness of the foamed concrete coated with GO/Silane emulsion and then coated with Silane emulsion increased while the volumetric water absorption increased,and the waterproofing effect was poorer.(5)The molecular dynamics method was used to simulate the transport process of water molecules in C-S-H gel pore channels after the combination of silane and graphene oxide/silane with C-S-H was simulated,and it was found that the Silane/GO model in which GO was connected to C-S-H with a solid ionic bond of Os-Ca-O and a more stable molecular structure,the number of Silane molecules washed away by water in the model was reduced,the hydrophobic Alkyl groups were the most abundant,water transport was the slowest,and the hydrophobic effect was the best.