Dispersion Of Graphene And The Mechanical Properties Of Graphene Reinforced Cement-based Composites

As a new carbon nanomaterial,graphene has attracted immense attention and researches of scholars all over the world.Depending on its distinctive mechanical properties,graphene,as a reinforcing material,has been applied to polymers,ceramics and rubbers to improve the toughness of the matrixes.With the reinforcing and toughening effects,graphene can enhance the tensile strength and toughness of cement-based composites,which possesses significant engineering application value.However,the researches of graphene reinforeced cement-based composites are rare,and the mechanisms of graphene in cement matrix are indefinite.In this paper,the dispersibility of graphene in aqueous solution is studied,and the optimum dispersing method is confirmed through comparing non-covalently chemical functionalization with covalently chemical functionalization.On the basis,the flexural strength,compressive strength and bending toughness of graphene/cement composites are investigated.Finially,the mechanisms of graphene reinforcing mechanical properties are explored by means of various micro testing teniques.Main research achievements and conclusions are as follows:(1)The optimum dispersing method of graphene: a nonionic surfactant polyoxyethylene(40)nonylphenylether(CO890)was as dispersant,and opimum mass ratio of CO890 to graphene was 5:1;meanwhile,the optimum sonication power and minimum sonication time were 360 W and 20 min,respectively.Results indicated that CO890 could adsorb on the interfaces of graphene and reacted with residual functional groups at the edges of graphene,resulting in the formation of steric hindrance.Finally,the stable grpahene dispersions were prepared.(2)The mechanical of graphene/cement paste composites increased at first and then decreased with the increase of graphene contents.At the age of 28 d,water-cement ratio of 0.30,the flexural strength and compressive strength of 0.05 wt% graphene/cement paste composite were increased to 13.4 MPa and 95.6 MPa,increasing by 25.5% and 3.7%.In addition,the introduction of 0.05 wt% graphene by weight of cemet could reinforce the flexural toughness and the breaking point displacement of graphene/cement paste sample,increasing by 55.9% and 52.1%,respectively.(3)Besides,graphene also enhanced mechanical properties of cement mortar.At the age of 28 d,the introduction of 0.05 wt% graphene could increase flexural strength and compressive strength by 24.0% and 13.6%,respectively.When the content of graphene was 0.08 wt%,the flexural toughness of graphene/cement mortar composite was 357.7 N·mm,increasing by 77.6%;the breaking point displacement was close to 0.313 mm,increasing by 58.9%;the maximum load value was 2549.7 N,increasing by 39.3%.(4)Micro measurement results indicated that graphene could fill pores of cement in a twist to decrease the initial cracks,reduce porosity of matrix and refine the pore size distribution.Graphene could absorb and disperse effectively energy load through prolinging the propogation paths of cracks,leading to the improvement of mechanical strength.Moreover,graphene could promote the formation of calcium silicate hydrate(C-S-H)at early age and influence the generation and development of C-S-H;meanwhile,crystallization and regularity of calcium hydroxide(CH)was promoted by the addition of graphene.