In-Situ Polymerization Of GO-PCE And Its Effect And Action Mechanism On The Properties Of Cement-based Materials

With the development of modern concrete structure to higher-level,larger-volume,deeper-space,and special functionalization,the requirements of raw materials and properties are more and more diversified.As the most widely used building materials in civil engineering,cement-based materials are widely applied in roads,bridges,nuclear power and water conservancy projects.However,it is a porous material with characteristics of multi-phase and multi-scale,it is easy to cause the temperature inside the matrix to rise due to the hydration reaction of cement,which will cause shrinkage,cracking and chloride ion penetration of hardened cement-based materials,and then lead to leakage,corrosion and other durability problems.Therefore,it is great significance to improve and solve the problems of cracking and chloride ion penetration of cement-based materials,which has always been a research hotspot in this field.The traditional measures to improve the cracking and durability of cement-based materials mainly include adding fiber,nano-materials,expansion materials and so on.However,the addition of fiber and nano-materials will significantly reduce the performance of cement-based materials or delay the construction progress.In recent years,attempt to use graphene oxide(GO)has become a research hotspot in the field of materials to improve the mechanical properties and durability of cement-based materials.GO belongs to two-dimensional nanomaterials,with the small size effect,surface effect and quantum effect,which can significantly enhance and toughen cement-based materials.In this study,the dispersion of GO,the influence of GO on the physical and chemical changes and microstructure changes of cement-based materials,and the influence and mechanism of GO on the shrinkage and impermeability of cement-based materials were systematically studied.Therefore,the following test results were obtained:(1)Based on the GO surface carboxyl activation technology,GO capped polyoxyethylene ether intermediate(GO-IPEG)was synthesized by nucleophilic substitution of GO surface carboxyl group with hydroxyl end group of isoamylenol polyoxyethylene ether(IPEG).FTIR,NMR,Raman and other molecular structure tests showed that the C=O and C-O bonds existed in GO-IPEG molecular structure,which indicated that GO had nucleophilic substitution reaction with IPEG.The covalent bonds are formed between carboxyl groups on GO surface and the upper hydroxyl groups of the IPEG structure.Van der waals in the GO bundles can be overcome by mechanical stirring,which makes the GO nanosheets disperse each other.The absorbance of the GO-IPEG solution increases gradually with the increase of the GO content and the reaction time,which indicates that the number of aggregates in the solution decreases and the dispersion stability increases.Zeta potential results show that GO-IPEG system has lower potential but better dispersion stability mainly due to IPEG steric hindrance.(2)Through the molecular structure design,polycarboxylate modified GO nanomaterials(GO-PCE)were prepared by in-situ radical polymerization of GO-IPEG and acrylic acid.FTIR,NMR,Raman,GPC and other testing results showed that in situ free radical copolymerization reaction was successfully carried out.Dispersion results show that GO-PCE has excellent dispersion stability in both aqueous solution and cement slurry centrifuge solution,and the dispersion has the Tyndall phenomenon,which is better than that of GO in SDS,CTAB,IPEG and PCE.The UV spectrum results showed that the absorbance of GO-PCE solution gradually increased with the extension of the polymerization time between GO-IPEG and AA,the number of GO aggregates gradually decreased,the dispersion stability of GO in the solution improved,and the zeta potential results also indicated that GO-PCE mainly relies on the long side chain of IPEG to overcome the aggregation of GO.DLS and AFM results also show that GO-PCE has larger molecular size.(3)The effects of GO-PCE on the rheological properties of cement-based materials were studied,including the fluidity of cement paste,slump and slump loss of concrete,and rheological parameters of mortar.The mechanism of GO-PCE was revealed by adsorption behavior,zeta potential and thickness of adsorption layer.The results show that the GO-PCE added to the cement slurry can significantly increase its fluidity,and the cement slurry fluidity increases first and then decreases with the increase of the GO content in the GO-PCE and has excellent fluidity maintaining performance.The rheological results of the mortar also show that GO-PCE can significantly reduce the plastic viscosity of the mortar.The rheological curve of cement mortar with GO-PCE accords with the model of Herschel-Bulkley fitting curve and the mortar exhibits a phenomenon of "shear thinning".GO-PCE can significantly reduce the thixotropic ring area of the mortar,indicating that the mortar system needs less time to return to the original state,that is,the viscosity of the slurry is small.The adsorption behavior,zeta potential and DLS results show that GO-PCE relies on the adsorption of PCE and the hydrophobic effect of the two-dimensional grid of GO to form two hydrophilic and hydrophobic adsorption layers on the surface of cement particles,which can thichen the thickness of adsorption layer on the surface of cement particles and then to improve the rheological properties and flow retention properties of cement-based materials.(4)The effects of GO-PCE on the mechanical properties,crack resistance and chloride-resistance of cement-based materials were studied,and the mechanism of controlling the microstructure and improving the chloride-resistance permeability of cement-based materials GO two-dimensional grid structure was investigated.The results show that the addition of GO-PCE can significantly improve the compressive and flexural strength of concrete,and its compressive strength ratio at 28 days reaches 140%.The results show that GO-PCE has better crack resistance,and the reduction rate of total cracking area of concrete is 88.73%.The results show that GO-PCE can significantly improve the chloride ion penetration resistance of concrete,and the permeability index of C40 and C80 concrete reaches “low” and “very low” grades respectively.The shrinkage of concrete increases with the extension of hydration age,and GO-PCE has better effect on improving the shrinkage of high-strength concrete.XRD test results show that GO-PCE promote the 1 d hydration of cement and enhance the diffraction peak strength of calcium hydroxide hydration products in hardened cement stone samples,and the most significant hydration of cement will be obtained when GO content in GO-PCE at one to thouland.SEM microstructure observation and EDS results show that the GO two-dimensional mesh is first laid on the surface of cement particles to form a dense two-dimensional fiber mesh structure,and then as a template to promote the stacking and crystallization of hydration products on the GO surface by GO nanocrystalline nucleation,which makes the microstructure of hardened cement stone more compact and enhance the mechanical properties and crack resistance of cement-based materials.Meanwhile,GO sealing end layer is formed on the surface of cement-based materials,which uses the mechanism of size screening and interlayer percolation og GO sealing end layer to block the transport of chloride ion and sodium ion,and allows free permeation of water molecules,to enhance the chloride ion permeability of cement-based materials.