| In concrete structures,the corrosion of steel rebars can cause severe structural damage and economic losses.Coating technology is currently a straightforward and cost-effective corrosion protection method,but the performance of existing anti-corrosion coatings is still not satisfactory.This study focuses on the significant demand for corrosion protection of reinforced concrete structures,and based on the novel low-temperature enamel(LTE)coating technology,to explore the related scientific and technical issues associated with the application of LTE coating to steel corrosion protection.Further,to overcome the shortcomings of existing LTE coating,new silicon nitride modified enamel(N-LTE)coating and silicon carbide modified enamel(S-LTE)coating were developed.The findings of this paper revealed that the enamel coating can provide a feasible way to improve the corrosion resistance of steel rebars and prolong the service life of concrete structures.The main work of this paper includes:(1)In view that the enamel coating requires high-temperature sintering,the apparent morphology,metallographic composition,fracture modes,and main mechanical parameters of steel rebars after exposure to different high temperatures and under different strain rates were systematically investigated.The high-temperature exposure and strain rate were discovered to have a coupling effect,and the strength equation and constitutive model of steel rebars were established considering the coupling effect to provide guidance for the sintering temperature selection of enamel coatings.(2)The LTE coating was developed by our research group for steel rebars.The microstructure,phase composition,and basic mechanical parameters of the LTE coating were investigated.Through microstructural,chemical,and mechanical characterization,the adhesion mechanism of the LTE coating/rebar interface was analyzed.Through pull-out test,the quasistatic and dynamic bonding behavior and failure mode of the LTE-coated rebar/concrete interface was analyzed.(3)The N-LTE coating was developed for a thermal shock and corrosion coupled environment.The silicon nitride was added to construct internal pores,thereby reducing and dispersing the internal thermal stress of the enamel coating,which significantly improved the tolerance capacity of the enamel coating under indentation load and thermal shock conditions.It was also found that the filling effect of corrosion products inside the microcracks can effectively reduce the corrosion rate.Furthermore,the corrosion evolution models for cracked and porous enamel coatings were proposed.(4)The S-LTE coating was developed by adding silicon carbide to match the thermal expansion with steel substrate.For S-LTE coatings,the macro residual stress was reduced,and the surface cracking was eradicated.The corrosion behavior of different S-LTE coatings was analyzed by electrochemical and salt-spray tests,and the corrosion rate of S-LTE coated rebar was proved to be more than 10 times lower that that of uncoated steel rebar.In addition,based on the competitive mechanism of electrolyte penetration degradation and corrosion product filling enhancement,the corrosion evolution modes of S-LTE coatings with different microstructures were interpreted.(5)The in-situ tensile-electrochemical corrosion test was employed to evaluate the corrosion resistance of uncoated,epoxy coated,and S-LTE coated steel rebars under different tensile strains.Specifically,the electrochemical impedance spectroscopy characteristics of LTE coated steel rebar under different tensile strains were explored,and the changes in electrochemical characteristic parameters with increasing tensile strains were analyzed. |
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