| The complex factors of bending load and marine environment have caused serious corrosion damage to concrete structure.Surface coating protection technology has attracted wide spread attention as a convenient and effective protective measure.And with the increasing occupation of marine concrete structures,it has become more and more important.How to protect the concrete structure that is used in loads and complex marine environments to ensure its durability has become a hot topic.In this paper,coatings and coating mortars were studied.The properties of chlorinated rubber,polyurethane?urea?and polyurea coating mortars were studied under NaCl solution immersion,erosion in flowing seawater alone and coupling with bending loads.The degradation rule of the macroscopic and microscopic performances of the coating was investigated.The protective effect of the coating on the mortar was verified by the chloride ion permeability,adhesion and electrochemical experiments.The following conclusions were obtained:1.The corrosion resistance of the coating under the conditions of NaCl solution immersion and erosion in flowing seawater showed that the polyurea coating had the best corrosion resistance,and the degradation of mechanical properties and surface properties of the coating after corrosion was from large to small:Chlorination Rubber>Polyurethane?urea?>Polyurea.The FT-IR spectrum revealed that the reason for the above rule was that the corrosive environment caused a large change in the main structure of the chlorinated rubber,which further led to significant deterioration of the coating.The intensity of individual characteristic peaks in the FT-IR spectrum of polyurethane?urea?was weakened,while the polyurea had only a slight breakage of some groups on the surface of the coating,which had only a slight effect on its protective properties.2.The results of mortar strength,chloride ion permeability and interfacial properties under the conditions of NaCl solution immersion and coupling of NaCl solution and bending load showed that,the flexural strength of the uncoated mortar test block and the three coated mortar decreased,the adhesion of the coating decreased.As the corrosion time prolonged,the chloride ion content of the test block increased,the chloride ion diffusion coefficient decreased and stabilized.After immersed for 210 days in the NaCl solution,the chloride ion diffusion coefficient of the uncoated and chlorinated rubber,polyurethane?urea?and polyurea coating mortar was reduced from1.09×10-12m2/s to 0.23×10-12m2/s.The chloride ion diffusion coefficient of the four test blocks after the same time of the coupling condition corrosion showed a gradually smaller changes from 1.17×10-12 m2/s to 0.28×10-12 m2/s.There was no obvious change in the microscopic morphology of the polyurea coating mortar,which was consistent with the results of the anti-chloride ion permeation study.Coupling environment increases chloride ion permeability compared to NaCl solution immersion.3.The results of EIS study under the condition of coupling of NaCl solution and bending load showed that,after corrosion,the low-frequency impedance modulus|Z|0.01Hz,the mortar resistance Rm and the charge transfer resistance Rct of the uncoated and three-coat mortar blocks are reduced.After corrosion for 150 days,the Rct values of the four mortars were 0.05 k?·cm2,0.21 k?·cm2,1.33 k?·cm2 and 2.36 k?·cm2,respectively.At this time,the passive film on the steel rebar was broken down and corrosion initiated.The Rct values of polyurethane?urea?and polyurea coated mortars were reduced to 1.33 k?·cm2 and 2.36 k?·cm2.And the rebar was still in a relatively complete passivated state.The polyurea coating showed better protection performance.4.The results of mortar strength,chloride ion permeability and interfacial properties under the conditions of erosion in flowing seawater and coupling of erosion in flowing seawater and bending load showed that,with the prolonged corrosion time,the flexural strength of the uncoated mortar and the three coated mortar decreased,the adhesion of the coating decreased,the chloride ion content increased,and the chloride ion diffusion coefficient decreased and stabilized.After corrosion for 210 days by erosion in flowing seawater,the chloride ion diffusion coefficient of four kinds of mortar decreases from 1.12×10-12m2/s to 0.35×10-12m2/s.The diffusion coefficient shows a decreasing trend from 1.51×10-12 m2/s to 0.43×10-12 m2/s under the coupling effect of erosion in flowing seawater and bending load.The microstructure of the polyurea coating mortar after corrosion has no significant change,which is consistent with the results of chloride ion diffusion research.The synergistic effect of bending load and erosion in flowing seawater increases the chloride ion permeability of the mortar compared to flowing seawater.5.The EIS study results of erosion in flowing seawater and bending load coupling results showed that,the low-frequency impedance modulus|Z|0.01Hz of the coating mortar,the coating mortar resistance Rm,and the charge transfer resistance Rct is reduced after corrosion.The double layer capacitance Ydl increased.After corrosion for150 days,the charge transfer resistance Rct of the chlorinated rubber coating decreased to 0.16 k?·cm2 with the corrosion time,and the internal steel bars were corrosion.Polyurethane?urea?coating and polyurea coating mortar were reduced to 1.29 k?·cm2and 4.08 k?·cm2 after corrosion for 150 days.respectively.And the rebar inside remained in a passive state over the entire duration of testing.The polyurea coating has a better protective effect compared with other coatings. |
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