Effect Of Graphene Oxide On Theologicial And Hardened Properties Of Cement-based Materials And Its Strengthening Mechanism On Harden Cement Paste

As the development of nano-materials and nano-technologies,it has been applied gradually in high performance concrete.However,the effect of nanomaterials on the workability of cement-based materials and the strengthening mechanism of mechanical properties are still to be studied.In particular,the re-agglomeration of carbon-based nanomaterials in cement-based materials and the strengthening mechanism of carbon-based nanomaterials in hardened cement-based materials.Therefore,this paper mainly carries on the following experimental research:(1)Exploring the mechanism of dispersion and re-agglomeration of graphene oxide(GO)in cement-based materials.Firstly,the effect of dispersing agents and it to GO ratio were studied and the optimum dispersing agents and ratio were determined.Secondly,the GO with dispersing agents of optimum ratio were dispersed in simulated pore solution in order to clarify the effect of ions on dispersion state of GO.Lastly,the dispersion state of GO in cement suspension was studied.Through a systematic research on the environments of different dispersing agents,a possible mechanism of the dispersion and re-agglomeration behavior of GO in cement suspension was put forward,which lay a foundation for exploring the influence of GO on the rheological properties of cement paste and the strengthening mechanism after hardening of cement paste.(2)Exploring the effect of GO content and GO incorporated dispersing agent on the rheological properties,including shear stress,apparent viscosity,yield stress,plastic stress and thixotropy.The yield stress and plastic viscosity are related to the rheological fitting model.In this study,the applicability of Bingham model,modified Bingham model and Herschel-Bulkley(H-B)model was determined by combining the principle of GO influence rheology and engineering application requirements.(3)The strengthening mechanism of GO on hardened cement paste was investigated thoroughly.Based on the dispersion mechanism of GO incorporated polycarboxylate-based high range water reducer(P-HRWR)in cement paste,the mechanism of GO enhanced hardened cement paste in unniform dispersion and re-agglomeration was studied.The mechanical properties,porosity,hydration products and microstructure were compared to study the strengthening mechanism of GO on hardened cement paste with uniform dispersion and reagglomeration.The results showed that: Homogeneous dispersion of GO in aqueous solution did not guarantee uniform dispersion in cement pastes,because high p H and environment of complex ions would easily lead to GO re-agglomeration and sedimentation.P-HRWR have the potential to prevent GO from re-agglomerating in the cement paste by electrostatic interaction and steric hindrance.GO increased the plastic viscosity and yield stress of cement paste.The dispersing agents mainly changed the spacing of the particles in the paste by increasing the content of free water,which affected the rheology of the paste.Comparing with the results of mercury intrusion porosimetry(MIP),X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FT-IR),scanning electron microscopy(SEM)and energy dispersive spectrometry(EDS),it could see that uniformly dispersed GO could not only promote the hydration of cement paste,reduce the porosity of hardened cement paste,and optimize the pore size distribution,but also strengthen the weak region and limited the development of cracks.