Study On Different Dispersion Methods Of Graphene Oxide In Cement Pastes

Compared with zero-dimensional and one-dimensional nanomaterials,graphene oxide has a larger specific surface area and excellent mechanical properties,and can be obtained by oxidation from natural graphite flakes,and the cost of obtaining is lower.Graphene oxide plays an important role in enhancing the mechanical properties of cement-based composites by effectively adjusting the microstructure and refining the pore structure of cement-based material hydration products.However,the chelation between calcium ions and graphene oxide surface functional groups makes it very prone to agglomeration.After agglomeration,the elastic modulus and tensile strength of graphene oxide are greatly reduced,and the agglomeration greatly reduces the effective surface area of graphene oxide.Therefore,in order to use graphene oxide more effectively,it is necessary to increase its dispersion in cement-based materials.Coal-bearing metakaolin is a material with extremely high pozzolanic activity made by high-temperature calcination using coal-series kaolin as raw material.Coal-series kaolin is a unique resource of kaolin in my country and is often treated as waste.In this paper,coal-based metakaolin prepared by calcining coal-based kaolin at 600-900℃ is used as a dispersant to test the dispersing effect of coal-based metakaolin on GO and its influence on the mechanical properties and microstructure of cement paste.The comparison of water reducing agent and nano-silica confirms that the coal-bearing metakaolin is effective in improving the dispersion of GO in the cement slurry and the interfacial bonding force between the hydration product and GO.The research contents of this paper are as follows:(1)Within the scope of this experiment,the effect of adding water reducing agents(PC1,PC2 and wood calcium)in different proportions to GO in simulated pore solution-saturated Ca(OH)2 solution and cement paste was studied by spectroscopy.The cement slurry with different ratios of water-reducing agent and GO is cured to 7d and 28 d,and the mechanical strength test is performed to obtain the optimal water-reducing agent content required to disperse a certain amount of GO.Observe the microstructure of the cement paste by SEM.Different water reducing agents are obtained: the optimum dosages of PC1,PC2 and wood calcium are 1:4,1:4,and 1:6 respectively.However,when the curing age is 7d and 28 d,the mechanical strength of the cement paste mixed with different water-reducing agents and GO is lower than the sum of the strength of the cement paste with only GO and only water-reducing agent.Therefore,within the optimum dosage range,the mechanical strength of the cement paste mixed with the water reducing agent and GO does not improve the mechanical strength of the cement paste.(2)Physical modification of GO with two different nano-silicas by physical adsorption,the dispersion of GO with nano-particles adsorbed on the surface in the pore solution and cement paste,and its effect on the mechanical properties of cement paste Impact research.And through the mechanical performance test,the optimal content of amorphous nano-silica and crystalline nano-silica required to disperse a certain amount of GO are 2% and 1.5%,respectively.Use scanning electron microscope(SEM),thermogravimetric difference scanning(TG-DSC),mercury intrusion method(MIP)to observe the microstructure and hydration development of cement paste at different ages.The results show that compared with the cement paste doped with crystalline nano-silica,the addition of amorphous nano-silica has a better dispersing effect on GO in the cement paste.(3)Study on the dispersion of GO in cement paste and its effect on the mechanical properties of cement paste after physical adsorption of metakaolin in coal series.After curing to 3d,7d,14 d,28d,the mechanical strength test is performed to obtain the optimal coal-based metakaolin content required to disperse a certain amount of GO by curing the cement slurry standard of coal-based metakaolin and GO with different proportions.4%.And combined with scanning electron microscope,thermogravimetric analysis,mercury intrusion test to analyze the effect of coal-based metakaolin on the dispersion of GO in cement paste and its effect on the mechanical properties of cement paste.The results show that the addition of coal-based metakaolin is effective for improving the dispersion of GO in the cement paste and the interfacial binding force between hydration products and GO.And the dispersion effect of GO in cement paste is stronger than that of water reducer and nano silica.