Preparation And Research On Mechanical Sensitivity Of Graphene Cement-based Composite

With the development of large-scale,super high-rise and intelligent modern concrete structures,cement-based materials have also developed from a single mechanical property to the integration of structure and intelligence.As a new type of two-dimensional nanomaterial,graphene has excellent mechanical,electrical and thermal properties.When added into cement-based materials,it can improve its electrical conductivity and obtain stable mechanical sensitive.This performance is reflected in the regular change of material resistance with external load changes,which can be used for real-time monitoring of large-scale concrete structure damage and provides important support for the intelligent development of concrete.In this paper,two different oxygen content reduction graphene oxide(RGO)and two different plate diameter graphene microchips(GNP),first studied graphene in deionized water and cement hole solution dispersion.On the basis of good dispersion,graphene cement-based composite material with well mechanical properties was systematically studied to study the effects of test methods,dispersants,graphene types and dosing,ambient humidity,stress loading mode and other factors on its conductive and mechanical sensitivity properties,the main conclusions are as follows:(1)In the system of deionized water and cement hole solution,polyurethane high-efficiency water reducing agent(PCE)dispersion effect is optimal,polyoxyethylene(20)sorbitol monophyl laurel(TW-20),sodium xyl sulfonate(SDS),sodium xyl benzene sulfonate(SDBS)in cement hole solution dispersion efficiency decreased significantly.Further research shows that the dispersion efficiency with lower charge density PCE is best,while the dispersion efficiency with higher charge density and longer side chain PCE is poor.(2)The graphene composite mortar with PCE has optimal hydraulic and micro properties,due to the action of gasation,SDBS and SDS will affect the microporous structure of the cement substrate,thereby reducing the strength of the cement mortar resistance to folding pressure.Graphene has no obvious effect on the hydration process,but it can refine calcium hydroxide crystals.(3)Using AC two-electrodes method,cement-based composites were tested with minimal resistivity and the most stable pressure-sensitive properties.The DC two-electrodes method causes the resistivity to increase gradually over time and the pressure sensitivity to be unstable due to the polarization effect.(4)Graphene cement-based composites with PCE have the lowest resistivity and optimum pressure-sensitive properties,and graphene cement-based composites with SDS have the greatest resistivity and the worst pressure sensitivity.(5)Test block moisture content has a significant impact on mechanical sensitivity performance,with the reduction of water content of the test block,graphene cement-based composite material resistivity gradually decreased,and pressure sensitivity with the decrease of water content first increased and then decreased,to achieve the optimal pressure sensitivity when the water content of 2.5%.(6)Under the same mass content,the conductivity and smart performance of cement-based materials with high oxygen content graphene(RGO-HO)are better than those with low oxygen content graphene(RGO-LO),The conductivity of cement-based materials of large-diameter graphene micro-sheets(GNP-L)is better than that of small-diameter graphene micro-sheets(GNP-S).When the optimal dosage is reached,the two GNP cement-based composite smart materials have little difference in smart performance.In addition,compared with the small diameter RGO,the cement-based composite material mixed with GNP has better smart performance.(7)With the increase of graphene doping,the conductivity decreased significantly,and the mechanical sensitivity increased first and then decreased.For pressure-sensitive properties,the best doping of four graphene(RGO-LO,RGO-HO,GNP-S,GNP-L)is 0.05 wt,0.05 wt,0.12 wt,and 0.08 wt,respectively.For tension-sensitive the best doping of the four graphenes(RGO-LO,RGO-HO,GNP-S,GNP-L)was 0.05 wt,0.07 wt,0.12 wt,and 0.12 wt,respectively.(8)Under different levels of cyclic loading forces and different loading speeds,the resistance change rate of graphene cement-based composites has a sensitive response and stability to compressive/tensile stress loads.