Effect Of Graphene Oxide-based On Microstructure Of Cement-based Materials

Graphene oxide(GO)is an oxide of graphene,and its structure is characterized by the formation of carboxyl,carbonyl,hydroxyl and epoxy groups on the two-dimensional layer of graphene.These functional groups which render the GO hydrophilic,thus facilitate the application at aqueous solution.In the preliminary study of the research group found that the incorporation of GO into the cement-based materials not only can control the hydration products and microstructure of cement,but also improve the mechanical properties of cement-based materials.However,GO nanaosheets are prone to agglomeration in aqueous solutions and can not be uniformly dispersed in cement-based materials.In addition,the content of various oxygen-containing functional groups can not be quantitatively controlled,so GO cannot qualitatively regulate the microstructure of cement.In this paper,modified graphene oxide(MGO)was prepared by the combination of acrylic acid and GO to enhance the dispersibility in the cement slurry.The effects of GO and MGO on the microstructure of cement-based materials were studied,which provided a theoretical base for studying the microstructure of cement-based materials.(1)GO nanometer lamellar was prepared by Hummer method and ultrasonic stripping,and its chemical structure,nanometer size and interlayer distance were characterized.The results show that the GO structure had carboxyl group(-COOH),carbonyl group(-C=O),hydroxyl group(-OH)and epoxy group(-O-).The thickness of GO nanosheet was 1.23 nm and its size was 200 nm to 500 nm.The The distance between GO layers after freeze drying was increased from 0.34 nm to 0.86 nm.At the same time,the dispersibilities of GO in different solvents and different pH environments were studied.The results showed that GO had poor dispersibility in common organic solvents(ethanol,acetone)or strong acid and alkali environments,and was better in water and surfactant solutions.(2)The modified graphene oxide(MGO)was formed by polymerization of acrylic acid and graphite oxide,where N,N-methylene bisacrylamide is used as a crosslinking agent and graphite oxide was prepared by Hummer method.The structure and dispersibility of MGO nanosheet were characterized and tested.The results showed that the oxygenated functional groups on the MGO nanosheets were the same as those of GO,but the contents of-COOH and C=C were increased by 2.56% and 5.26%,respectively.The size of MGO nanosheet was 100 nm to 500 nm,and its thickness was 0.67 nm,which thinner than the GO nanosheet.In addition,MGO nanoscale sheets cannot exhibit agglomeration under neutral and alkaline conditions.(3)The relationship between the apparent density and the water absorption,the change of the microstructure,the pore structure and the mechanical properties of the cement-based materials after the incorporation of GO and MGO were studied.The results showed that the addition of 0.03% GO or 0.05% MGO can improve the water absorption of the foamed lightweight cement composites,but the increase of MGO was larger.Compared with the variety(petals,thread-like,bird-like and multi-faceted)of the microscopic morphology of cement-based materials with the content of 0.03% GO,the formation microscopic morphology of cement-based materials with 0.05% MGO was mainly patterned.The incorporation of GO and MGO could lower the porosity of cement stone,reduce the occurrence of cracks,and improve the compressive strength and flexural strength of cement-based materials.(4)Through the discussion of the mechanism of GO and MGO affecting the microstructure of cement-based materials,it can be found that GO is favorable for the growth of hydrated crystals,and the increase of carboxyl group is more favorable for the formation of hydrated crystals.The effect of oxygen-containing functional groups of GO nanosheet on the hydration products of cement is competitive and selective.