Corrosion Behavior And Mechanical Property Degradation Model Of Coated Steel Bar In The Environment Of Western Salt Lake

The climatic environment in the western salt lake area is very bad,in which the air and soil contain a large number of ions which cause erosion to steel and reinforced concrete structures,which seriously shortens the service life and durability of buildings and structures.However,the zinc-rich epoxy resin coating can well protect the steel bar from serious corrosion,and the magnesium oxychloride cement concrete itself without modification has excellent anti-halogen corrosion performance,so the combination of the two can show a strong applicability in the western salt lake area.At present,how much thickness of steel surface coating,both to meet the corrosion resistance and to save resources and has not yet been determined;The bond property of magnesium chloride cement concrete is greatly weakened because of the corrosion of steel bar.If the above two problems can be solved,a new application field will be opened up in the western salt lake area as structural materials,so as to reduce the "magnesium damage" caused by the development of potash fertilizer in salt lake area.In this paper,based on the project of national natural science foundation of China(magnesium reinforced concrete foundation research based on the problem of "magnesium damage" in western salt lake,project no.Main research contents of this paper:(1)Based on the actual environment in the western salt lake region,three accelerated corrosion test schemes were designed for coated rebar of different thicknesses(6 coated rebar of different thicknesses plus exposed rebar as the control group)in three salt fog environments(chloride solution,sulfate solution and chlorine-sulfate mixed solution).The polarization curve,open circuit potential and corrosion current density of coated steel bars were analyzed by electrochemical corrosion principle.The results show that the coating with different thickness has a certain protection capability,and the protection effect tends to decrease with the increase of coating thickness.Specifically,the time required for T0～T6 coated steel bars to reach the serious corrosion degree is 4d,16 d,16d,24 d,36d,36 d and 40 d respectively in the chloride environment.14 d,28d,40 d,60d,68 d,70d and 76 d in sulfate environment;In the compound salt environment,16 d,20d,26 d,38d,48 d,58d and 72 d were used.(2)By analyzing and studying the corrosion behavior of steel bar coated with different thickness and considering the particularity and economy of the salt lake environment in western China,it is concluded that using the coatings with thickness of 0.4mm,0.3mm and 0.3mm respectively in the chloride environment,sulfate environment and composite salt environment is conducive to avoiding the possibility of serious corrosion of steel bar as early as possible.(3)Accelerated corrosion tests were carried out on coated rebar in three spray environments,from the consumption of the coating,the corrosion pattern of the rebar surface and the bond property of the coating with the rebar after corrosion of the specimen.The results show that the corrosion process from pitting to small pitting and then to large pitting occurs on the surface of the coating,which leads to the corrosion process from pitting to small pitting and then to large pitting.(4)Through the reinforcement drawing test of the uncorroded coated reinforced magnesium chloride cement concrete,this paper mainly studies the bonding strength value of the members corresponding to the coating of different thickness sprayed on the steel surface.The results show that the bonding strength of the members with coating thickness of 0.3mm is the highest,that is,the optimal coating thickness.(5)Three solutions(chlorine salt,sulfate and chlorine-sulfate mixed solution)were used as electrolytes to conduct constant current accelerated corrosion test on the reinforced concrete coated with magnesium oxychloride cement(the optimal coating thickness),and the drawing test of coated steel bar and magnesium oxychloride cement concrete under different corrosion current densities was completed.The influence of corrosion current density on bond strength and slip amount of coated rebar was analyzed from the drawing failure pattern and corrosion degree of the specimen.The results show that with the increase of the corrosion current density,the bonding strength between the coated steel bar and the magnesium oxychloride concrete increases first and then decreases.Based on the analysis of the experimental data,the expression formula of bond strength reduction coefficient and slip ratio is put forward,and according to the bond-slip constitutive relation of the reinforced concrete in the current code,the bond-slip constitutive model of the reinforced concrete coated with magnesium oxychloride cement is obtained.