| Responding to the strategies of western development and the"One Belt and One Road",railway projects are conducted in northwestern in China gradually.Convenience is provided by the construction mode replacing road with bridge,which helps overcome the difficulties crossing rivers,lakes,ravines and so forth,and makes bridges as the important component of the railway.However,there are a large number of saline soils,salt lakes,and high salt groundwater in western China,which produces a large number of salt soil and water and have further corrosive effects on cement-based materials.This phenomenon raises higher requirements on the durability of bridge pier concrete.Prior studies have shown that organic coating can create a protective layer on piers surface and improve the durability of piers concrete effectively.However,the poor natural conditions,such as complex hydrogeology,high evaporation,large temperature difference,large wind and sand,seasonal drought,and so on,put forward higher requirements for the performance of the anticorrosive coating.Due to the poor performance of the existing anticorrosive coating in the natural condition,problems involving peeling,foaming,and insufficient bond strength often occur,and seriously reduce the effects and service life of the anticorrosive coating.Therefore,optimization of anticorrosion coatings performance urgent to be in serious corrosion areas.Meanwhile,there is a significant implication on similar protection engineering.In the light of the bond performance of the coating film,its key factors are analyzed,and optimization of the anticorrosion coatings is conducted correspondingly.The technical indexes of the anticorrosive coating were determined by analyzing the performance of the coating and the durability of the coated cement-based material.Subsequently,the in-situ test of coated concrete members was conducted on-site,and the degree improved anticorrosion coating match the actual engineering environment was also tested.Finally,the applicability of the anticorrosive coating in bridge pier protection engineering is validated actually.This study achieves contributions as follows:(1)The key factors affecting the adhesion performance of the coating film were analyzed and determined,and the technical indexes of the film optimization are raised correspondingly.On this basis,the performances of the coating film with different technical index values were tested,and the coating viscosity parameter was determined after comprehensive analysis.The results show that reduction of coating viscosity leads to the bond strength of the coating increases first and then decreases.With the reduction of the coating viscosity,the average free volume aperture and free volume fraction of the film decrease first and then increase,and the apparent flatness of the film increases gradually.The tensile strength and elastic modulus of the film increases first and then decreases with the decrease of the viscosity.On the contrary,the elongation after fracture decreases first and then increases.In the five designed groups of coatings,C-20 and C-25 show excellent water resistance.In addition,a new model is proposed to analyze the whole process of water absorption,and presents a higher correlation between experimental data.Finally,taking different viscosity conditions into consideration,the entropy weight was employed to assess the performance indexes of the coatings.The viscosity index was: 1)the initial viscosity should not be less than 221 m Pa·s,2)the viscosity of the coating should be kept within 303 m Pa·s after one hour preparation.(2)The effectiveness of the improved anticorrosive coating involving improving the durability of cement-based materials and the thickness index of the coating film were analyzed and determined by the indoor durability acceleration test.The results show that 1)comparing with non-coated specimens,the impermeability of the coated cement-based composites is enhanced;2)the contents of erosion product in the specimens decreases after erosion;3)the time of corrosion resistance index of the specimens begins to deteriorate delays;4)the corrosion resistance index value of the final test age increases.Meanwhile,a flexural strength predictive model considering the influence of anticorrosion coating was developed,which could calculate the flexural strength of mortar specimens at different test ages accurately.According to the experimental results,the thickness of coating film whose maximum value is 90?m was determined.(3)The degree that improved anticorrosive coating matches the engineering environment was verified by analyzing the overall durability of coated concrete members buried in the engineering environment.Results show that each concrete member has different degrees of sulfate erosion after 3 years buried.Specifically,it shows that the peeling of debris on the surface of the concrete member,the damage of part of the coating film,and the detected erosion products in the concrete member.Notably,the compressive strength and resonance frequency of the concrete member are significantly reduced compared with the initial test values.After adopting the improved anticorrosive coating,the durability of concrete member can be significantly improved.Due to the significant reduction of the concrete members' deterioration,the conclusion that the anticorrosive coating proposed in this study can match the engineering environment better.Besides,it is found that the interface between soil and air presents the most serious erosion in the three test areas of the concrete member.(4)In terms of the research mentioned above,an anticorrosive coating suiting serious corrosion area is proposed.Meanwhile,the effect of the coating is tested on bridge pier actually.Through research and observation in three years,it is found that the proposed anticorrosive coating has higher corrosion resistance,stronger bonding property and better protective effect.The anti-corrosion coating has higher applicability in bridge pier protection engineering and can improve the sulfate corrosion resistance of bridge pier concrete seriously. |
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