Study On Properties Of Particulate Materials Modified Graphene Oxide Cement Mortar

Compared to zero-dimensional and one-dimensional nanomaterials,graphene oxide（GO）has better modification effect on cement-based materials and promising application prospects due to the unique properties and preparation advantages of graphene oxide.However,as a nanomaterial,how to not only ensure good interfacial bonding between GO and hydration products,but also ensure the good dispersion of GO is the key problem to give full play to the GO excellent properties.In recent years,researchers have used different particle materials,such as silica fume,fly ash,nano-silica,etc.,in order to promote the dispersion of GO in cement-based materials and improve their mechanical properties.Coal-bearing Metakaolin（CMK）is one materials among them.Coal-bearing metakaolin is a micron-scale particle material with extremely high pozzolanic activity made by high-temperature calcination using coal-series kaolin,which is a industrial solid waste.On the basis of previous work,a surface modification method of CMK was proposed,that is,using Ca（OH）₂solution to change the charged state of the surface of CMK,in order to improve the synergistic dispersion of CMK and GO in cement matrix.The effects and mechanism of surface-modified CMK particles（Ca@CMK）and GO on the mechanical properties of cement mortar were compared and analyzed by mechanical strength test and microscopic test methods.At the same time,the study also comparatively analyzes the effects of the other two nano-particles,nano-silica and nano-calcium carbonate,and CMK particle without surface modification on the mechanical properties of GO-cement mortar.The main research contents and conclusions are as follows:（1）First,the effects of different quality PC/nSiO₂/Ca@CMK particles modified GO solely,as well as different quality nSiO₂/Ca@CMK particles and PC modified GO on GO dispersion in solution-saturated Ca（OH）₂solution were studied by UV-vis.It is concluded that when the mass ratio of PC to GO within the range of 1-2,and the nSiO₂/Ca@CMK particulate materials is equivalent to 4%by weight of cement,is the optimum proportion to improve the dispersion behavior of GO in saturated Ca（OH）₂solution.（2）The fluidity test of cement mortar showed that the fluidity of cement mortar would be reduced whether the four particle materials and GO were mixed single or compound.However,the fluidity of cement mortar is significantly improved when incorporating PC.The results of slump test showed that,when the content of PC is 0.12%by weight of cement,that is,the mass ratio of PC to GO is 2:1,the fluidity of each group of cement mortar has exceeded that of plain cement mortar M.Therefore,the ratio is regarded as the critical ratio of the mechanical strength test of cement mortar.（3）The mechanical strength test of cement mortar showed that at the curing age of 28 d,the strength of cement mortar-GO modified by four different types of particulate materials and PC was improved.Compared with plain cement mortar M,the flexural and compressive strengths of M-G-nCaCO₃,M-G-nSiO₂-P1,M-G-CMK-P1,and M-G-Ca@CMK-P1 cement mortar is increased by 16.5%and 7.1%,30.9%and 29.3%,33.0%and 38.3%,53.6%and49.8%,respectively.It is concluded that GO modified by Ca@CMK and PC is the most beneficial methods to improve the strength of cement mortar.（4）The SEM test showed that M-G-Ca@CMK-P1 cement mortar has a denser microstructure than other cement mortar,and more hydration products is covered on the surface.The interfacial transition zone between the hydration products and the standard sand is staggered by a large number of hydration products,forming a grid-like structure,indicating that the Ca@CMK material can indeed enhance the interfacial bonding force between GO and hydration products of cement mortar.The curves and data obtained from the TG test show that at the curing age of 28 d,the content of bound water in M-G-Ca@CMK-P1 is the highest,and the content of Ca（OH）₂is the least,which shows that the M-G-Ca@CMK-P1could consume more Ca（OH）₂,which is unfavorable to the mechanical properties of cement mortar,the secondary hydration reaction generates more hydration products,improving the mechanical strength of cement mortar.The MIP test found that the pore cumulative volume of M-G-Ca@CMK-P1 cement mortar was the least,indicating that GO modified by Ca@CMK and PC plays a role in refining the pores of cement mortar.