Study On Stable Dispersion Of Graphene Oxide And Properties Of Composite Modified Cement-based Materials

Cement-based composite materials play an indispensable part of social construction,due to their brittleness,cracks and other problems,they greatly limit the application potential of cement-based materials.The rise of graphene-based nanomaterials provides a new way to solve such problems.Graphene oxide(GO)and thermally reduced graphene(TRGO)are important components of graphene materials.Due to their large specific surface area,ultra-high strength and excellent electrochemical performance,graphene materials mixed with cement-based materials can play a role in strengthening and toughening.However,graphene-based materials are prone to coagulation in the cement pore solution,so the key to their excellent performance is how to improve the uniform dispersion of graphene-based materials in the cement hydration environment.The current research mainly uses polycarboxylic acid type water reducing agent(PC)and ultrasonic to improve the dispersion stability of GO and TRGO in cement media.In this study,effects of the green pure natural substances gallic acid(GA)and sucrose(S)cooperated with PC on the dispersion of GO and GO on the dispersion of TRGO in high calcium and alkaline solution respectively,and the influences of cement-based materials on its mechanical strength,fluidity,durability,electrical and thermal conductivity blending of under high dispersion of GO and TRGO were investigated.The results are as following:(1)Effects of GA on the dispersion of GO and properties of cement composites: GA synergistic dispersion GO in the saturated calcium hydroxide(CH)solution was carried out by using UV-vis spectrophotometer(UV-vis),atomic force microscope(AFM),Zeta potential and particle size distribution.Then it was found that when the mass ratio of GA to GO was 1:1,GO achieved the best dispersion in alkaline cement solution.At the same time,compared with the PC-dispersed GO specimens,when the mass ratio of GA to GO was 1:1 and the content of GO was 0.05%,the flexural and compressive strength of the GO blended mortar with GA and PC dispersed were increased by 17.32%,19.23% at 3d and 19.22%,21.42% at 28 d,respectively.The extra addition of GA could greatly offest the decreased of cement mortar fluidity caused by GO,and make it closer to the fluidity of the benchmark specimen.Scanning electron microscopy(SEM)showed a petal-like compact micro morphology,which proved that the uniform dispersion of GO could better control the morphology and the growth of cement hydration products more complete and regular.Due to this compact internal structure,when the amount content of GO and GA were 0.05%,the mass loss rate and compressive strength loss rate of cement mortar were low,and the fluctuation range was small and cement mortar had the lowest electrical flux.(2)Effects of sucrose on the dispersion of GO and properties of cement composites:The effect of sucrose on the dispersion stability of GO in a saturated CH solution was studied by(UV-vis),AFM,and Zeta potential test.The test results shows that when the mass ratio of sucrose to GO was 2.5:1,the addition of sucrose significantly improved the homogeneous dispersion of GO in cement pore solution.The addition of sucrose could also compensate for the decrease of fluidity caused by GO.But considering the retardation effect of sucrose on the fluidity of fly ash-cement mortar,the mass ratio of sucrose and GO was adjusted during the test.Compared with PC-dispersed GO,the flexural and compressive strength of fly ash-cement mortar with sucrose and PC dispersed GO showed a trend,which firstly increased and then decreased.When the 0.025% of sucrose and the 0.01% of GO,the flexural and compressive strength of GO-fly ashcement mortar were increased by 15.5% and 7.2% at 3d,and 28 d flexural and compressive strength were increased by 17.6% and 16.2% respectively.Scanning electron micrographs(SEM)of cement mortar and the pure slurry showed a petal-like micro morphology,which made the entire internal structure more compact and regular.When the GO content was 0.02% and the dosage of sucrose was 0.03%,the mass loss rate and compressive strength loss rate of fly ash-cement mortar were low,the fluctuation range and the electric flux of cement mortar were the lowest.(3)Effects of GO on the dispersion of TRGO and electrical and conductive properties of cement composites: The best mass ratio of GO disperse TRGO was 3:10 by UV-vis spectrophotometer(UV-vis).When the dosage of GO and TRGO was 0.3% and1.0%,the flexural and compressive strength of the specimen was increased by 49.5%,38.6% at 3d,and 21.34%,34.52% at 28 d.The dense and regular microscopic morphology of the cement mortar confirmed that GO and TRGO could better control the morphology of cement hydration products and make their growth more regular by scanning electron microscope(SEM).Meanwhile,the resistivity of the specimens with additional GO dispersed TRGO was further lower than that of PC-dispersed TRGO.When the content of TRGO was 1.2% and the content of GO was 0.36%,the resistivity of the cement mortar specimens was reduced by 35.9%,compared with the TRGO specimens.And in the firstorder partial conductance data of the resistivity of the cement mortar,the composite material’s resistivity threshold value was the dosage of TRGO of 0.7% and the 3:10 mass raito of GO to TRGO.At the same time,under this dosage,the heating effect of the test piece after 30 minutes of steady-current voltage energization was also the best.When the GO content was 0.36%,the maximum resistance change rate of the cement mortar specimen under load was 2.63%.