In Situ Polymerization Of Waterborne Coatings Modified By Graphene Oxide For Concrete Anticorrosion

Highway bridge concrete is easily eroded by water molecules,chloride ions,sulfate ions,oxygen,carbon dioxide and ultraviolet rays affected by the environmental corrosion factors during service.Causing the internal volume expansion,skin cracking and peeling on the concrete surface.In the winter,large amounts of chloride ions are brought by spreading deicing salts to prevent roads from freezing.Chloride ion and freeze-thaw cycle form double corrosion,which intensifies the damage of concrete structure.Therefore,the development of concrete surface corrosion protection has important engineering application value.In view of the problem of insufficient environmental protection and durability of the concrete surface protection materials in the deicing salt environment,four waterborne graphene oxide modified polymer nanocomposite coatings were prepared by introducing the two-dimensional in situ graphene into the emulsion polymerization process of designing a waterborne copolymer emulsion,and the influence law and mechanism of graphene content on the performance of composite coatings were studied.The research contents are as follows:（1）The effect of surface modification of coupling agent on the dispersion of graphite oxide（GO）in polymer emulsion was studied.KH560 and A151 were used to modify GO to obtain KGO and AGO,respectively.Microscopic characterization methods such as infrared spectroscopy,XRD,thermogravimetry and SEM were used to compare the GO structure,particle size,thermal stability and surface morphology before and after modification.The graphene oxide was sonicated in a mixture of absolute ethanol and deionized water（3:1）and dried and ground after 5 h of hydrothermal reaction with an appropriate amount of coupling agent,the Si-O-C absorption peaks appeared in the infrared spectrum,indicating that the silane coupling agent was successfully modified.The introduction of Si-O bonds also improved the thermal stability of GO.XRD and SEM showed that the layer spacing of the modified AGO nanosheets increased.There were obvious folds and the stacking phenomenon of the modified nanosheets was improved.（2）In order to improve the adhesion between the coating and the concrete surface,the polar functional group structure in the epoxy structure was used to copolymerized with acrylic acid,Epoxy resin（E-44）,methacrylic acid,methyl methacrylate and butyl acrylate were used as the main raw materials,Different amounts of GO（FGO:0.025wt%,0.05wt%,0.075wt%,0.10wt%）were introduced by in-situ polymerization method to prepare GO/WEP emulsion.GO/WEP coating was prepared with an appropriate amount of pigment filler and additives.The results showed that the addition of FGO improved the thermal performance of the composite coating.The comprehensive performance of 0.05wt%KGO-WEP is better.The pencil hardness of the composite coating is 5 H.The impact strength is?50 cm.The bonding strength is 1.79MPa.The water absorption rate is 1.06%.The contact angle is 78.05°.The chromatic aberrationΔE after 1000 h UV aging is 0.75.The gloss GU is maintained well at 9.7.The coating morphology is maintained well after 240 h of chemical resistance.The chloride ion permeability of the coating is 0.34×10^-3 mg/（cm²·d）.（3）Considering the resistance and isolation of the chemical characteristics of the coating surface to the corrosive medium,the copolymerization of acrylates with fluorine-containing monomers was used.Dodecafluoroheptyl methacrylate（DFMA）,methacrylic acid,methyl methacrylate and butyl acrylate were used as the main raw materials.GO（FGO:0.025wt%,0.05wt%,0.075wt%,0.10wt%）was introduced by in-situ polymerization method to prepare GO/FC emulsion.GO/FC coating was prepared with an appropriate amount of pigment filler and additives.The results show that the addition of FGO improved the thermal performance of the composite coating.0.075wt%AGO-FC composite coating has the best comprehensive performance.The pencil hardness 6 h.The impact strength?50 cm.The bonding strength 4.74MPa.The water absorption 0.25%.The contact angle 128.16°.The chromatic aberrationΔE after 1000 h UV aging is 0.35.The gloss GU remains high at 13.2.The morphology remains intact after 240 h of chemical resistance.The chloride ion permeability of the coating is 0.3×10^-3 mg/（cm²·d）.（4）The 0.05wt%KGO-WEP and 0.075wt%AGO-FC coatings in the above study were applied to concrete mortar blocks.Salt freeze cyclic corrosion tests were performed compared with an uncoated concrete mortar block,and a blank control group was set.The freeze-thaw corrosion conditions simulated experimentaly were 5%commercially available deicing salt solution.The blocks were frozen for 3 h,taken out and wiped dry and allowed to stand for 1 h as a cycle.After every 5 cycles,the mass growth rate,the bonding strength of the coating,the compressive strength,and the resistance to chloride ion permeability of the test block after absorption of the deicing salt solution were evaluated.The results showed that after 40 salt-freezing cycles,the comprehensive performance of 0.075wt%AGO-FC coating is the best.The AGO nanosheets were uniformly dispersed in the polymer matrix.The adhesion between the coating and the concrete substrate was good.The surface hydrophobicity and the corrosion resistance of AGO-FC coating was improved.