Preparation And Investigation On Functional Prorperties Of Graphene-cement Composites

As the world's most widely used construction materials,cement and concrete present good mechanical performance and durability.With the steady growth of people's living level,the functional and intelligent characteristics of building materials have been drawing increasing attention.As a novel two-dimensional nanomaterial,graphene has excellent mechanical property,electrical conductivity and thermal conductivity,which was added into cement based materials to obtain functional and intelligent peculiarities.This study mainly investigated the preparation of graphene-cement composites and studied their mechanical property,electrical and thermal conductivities,electromagnetic shielding propery and pressure sensitivity performance.The main contents and conclusions of the study are as follows:(1)The dispersibility effects of different dispersants on graphene were quantitatively analyzed by means of ultraviolet-visible spectrophotometer,optical microscope and precipitation method.The results showed that naphthalene sulfonate water-reducing admixture depicted the best dispersion and stability ability and the optimum dosage was equal to the mass of graphene.Compared with the steric hindrance effect,electrostatic repulsion was the main factor that determined the dispersibility of surfactants.In addition,there was mainly physical adsorption between dispersants and graphene,and no chemical reaction occurred.At the same time,it was found that the efficiency and effectiveness of probe-type ultrasound was much higher than that of slot-type ultrasound,and it was a powerful means of dispersing graphene effectively.(2)The grapheme aqueous dispersion was prepared by a high-power ultrasonic dispersion by stages with naphthalene sulfonate water-reducing admixture,which was added into cement materials to prepare graphene-cement composites and mechanical property was studied.It was concluded that both compressive strength and flexural strength of cement mortar were increased firstly and then decreased with increasing graphene.When the amount of graphene was 2.00 wt.%,mechanical property was optimal and compression strength and flexural strength of composites in 3 days were increased by 44% and 49% respectively.It was found that graphene showed more obvious promotion to early strength of cement mortar.It was obtained that enhancement mechanism of graphene was mainly due to the nano-size effect and two-dimensional shape effect.It facilitated to form a network structure in the cement matrix,which led to compacted structure,reduced porosity and simultaneously played a role in pore size refinement.In addition,graphene manifested a strong nucleation effect,which promoted hydration of cement but did not change the type of hydration products.(3)Electrical property of graphene-cement composites was studied by direct current two-probe method.It was concluded that the resistivity decreased firstly and then tended to be stable with increasing graphene.After the dosage of graphene was 2.00 wt.%,the resistivity reached stabilization and decreased by 40% compared to the control group,indicating that cement materials began to form percolation of conductive network.Thermal property of graphene-cement composites was studied by heat-flow steady method,and it was indicated that the coefficient of thermal conductivity increased gradually and then stabilized with increasing graphene.1.00 wt.% of graphene could make mortar composites increased by 23%.The effect of 1.00 wt.% graphene on the electromagnetic shielding performance of cement paste was analyzed by Vector Network Analyzer.It was concluded that 1.00 wt.% of graphene could make imaginary part of dielectric constant increase by 60%,which showed that graphene significantly improved dielectric loss ability of cement based composites to electromagnetic wave,while the electromagnetic shielding effectiveness increased by 30%~45%,indicating that graphene could greatly improve shielding property of cement pastes to electromagnetic wave.(4)The pressure sensitivity of cement based composites with different amounts of graphene was studied by means of response voltage variation regularity and strain and stress sensitivity coefficient under uniaxial compression.It revealed the influence mechanisms of graphene on pressure sensitivity of cement based composites.It was showed that graphene-cement paste samples presented the best pressure sensitivity when the amount of graphene was 1.00 wt.%.However,2.00 wt.% graphene-cement mortar samples revealed the most excellent pressure-sensitivity.The stress and strain sensitivity coefficient of cement based composites increased firstly and then reduced with increasing graphene.The paste materials had better pressure-sensitivity than mortar materials.When the dosage of graphene was 1.00 wt%,paste materials unfolded the largest stress and strain sensitivity coefficient up to 2.52 %/MPa?363.10.