Influence Of Cracks On The Corrosion Mechanism And Cathodic Protective Effect Of The Reinforced Concrete Structures Contaminated By The Chloride Salt

Reinforced concrete structure is one of the typical structural types in the field of construction engineering.Its durability is related to the service safety of the structure.Chloride ion is an important factor to promote the corrosion of steel bars.The existence of cracks provides a convenient channel for the transmission of corrosive media.The corrosion of steel concrete structures is affected by singularity of local defects in cracks.Therefore,in this paper,different characteristic cracks are fully considered,and their effects on the corrosion mechanism and process of the steel-concrete structure and the protection effect of the forced current cathodic corrosion under chloride environment are studied.On this basis,the comprehensive anti-corrosion measures for the steel-concrete structure with cracks are proposed.The main contents are as follows.Firstly,the influence of cracks on the natural corrosion mechanism and process of steel-concrete structure is studied.Based on the Nernst-Plant equation,considering the influence of diffusion,convection and electromigration on mass transfer,and combining with the mass transfer theory of porous media of concrete materials,a mesoscopic ion transfer model of water saturation reinforced concrete members with cracks under natural corrosion condition is established.The cracks with different width,depth and spacing are prepared by non-destructive method,and the natural corrosion test of reinforced concrete members with cracks is carried out.The comparison between numerical simulation and test results shows that the crack parameters have little influence on the concentration distribution of potassium ion;when the crack spacing is 10 mm,the amount of sodium ion,chloride ion and hydrogen oxide ion transfers into concrete from erosion solution increases,and the migration speed of calcium ion and sulfate ion to erosion surface increases.The established material transport model can accurately predict the natural corrosion process of the cracked and saturated steel-concrete structure under the corrosive environment.Secondly,the influence of cracks on the effect of ICCP is explored.From the point of view of corrosion dynamics and thermodynamics,based on the particle field transport model in concrete and combined with the boundary conditions of electrochemical reaction on the electrode surface,the material transport model in the saturated reinforced concrete structure under the action of the active electric field of forced current cathodic corrosion protection is established,and then the development of the ion field in the saturated reinforced concrete structure under the action of the crack on the corrosion control electric field is revealed.The resultsshow that with the increase of crack width,the concentration of potassium ion near the crack increases,the aggregation degree of sodium ion and calcium ion increases,and the migration of chloride ion to anode accelerates.The current concentration phenomenon exists in the crack area,which makes the current density of oxygen consumption and hydrogen evolution reaction on the surface of steel increase,but the order of magnitude does not change.The electrode reaction on the surface of steel is mainly oxygen consumption reaction,and the applied electric field can completely control corrosion.The numerical model can effectively predict the material transport of reinforced concrete members with cracks under the action of the electric field coupling erosion environment.Corrosion control electric field can effectively control chloride ion erosion.Finally,a synergistic anticorrosion method for electric drive of cracked steel-concrete structure and corrosion inhibitor is proposed.Using the corrosion control electric field as the driving force of the rust inhibitor,the typical organic and inorganic rust inhibitors are selected.Based on the coupling model of electric field and particle field,combined with the experimental results in literature,the concentration distribution of organic rust inhibitor on the surface of steel concrete members with cracks is analyzed.In addition,the deposition state of inorganic rust inhibitor in the cracks of saturated steel concrete members driven by electric field is compared and analyzed based on the results of literature test.The results show that with the increase of crack width,the higher the concentration of rust inhibitor on the surface of steel bar,the faster the transmission of deposition products.The proposed method of electric drive and corrosion inhibitor cooperation can effectively control the corrosion of steel concrete structures with cracks.