Study On Non-uniform Corrosion Model Of Steel Rebar In Concrete Under Heat-Moisture-Chlorine-Oxygen Multifield

Under marine environment,chloride ions reach to the surface of steel rebar through transport,and destroy the passive film,which furtherly induce the corrosion.In order to achieve a comprehensive understanding on the corrosion behavior of steel rebar in concrete under complex climate conditions,a dynamic self-balancing electrochemical model of steel corrosion in concrete under thermal-wet-chlorine-oxygen multi-fields was established in this research.This model took into account the coupling of temperature and humidity in concrete,the transmission and consumption of chloride ions and oxygen.Based on the corrosion polarization equation deduced from the coupling effect of macrocell and microcell,the influence of environmental temperature and humidity,chloride ions and oxygen concentration on the corrosion potential,corrosion current density and distribution of rust layer thickness on steel surface were analyzed.And the dynamic characterization of steel depassivation,corrosion propagation and evolution of rust layer distribution on steel surface in natural climate environment was realized.The corrosion processes of steel in constant temperature and humidity environment and time-varying temperature and humidity environment were verified by experimental data.The numerical solution of accelerated galvanic corrosion was given.The effects of impressed current density and environmental chloride solution concentration on the time ratio when the steel rebar reach the same corrosion ratios under two corrosion methods were discussed.The differences in the radial corrosion depth and the distribution of rust layer thickness between the two corrosion methods were compared.The main work of this paper includes:Based on the mass transfer and heat transfer theory of porous media and the thermal-wet coupling model of early-age cement-based materials,the moisture adsorption curve of mature concrete was applied to improve the calculation of mass convection exchange coefficient.And a temperature-wet coupling model was established to bridge the connection between the internal microenvironment of concrete and the external macro environment.The diffusion characteristics of cement paste phase and ITZ phase were studied,and the effects of environmental temperature and humidity on the diffusion,convection and combination of chloride ions were explored.The influence of a series factors,such as the environmental temperature and humidity,the oxygen content on the surface of concrete cover,the balance between gaseous oxygen and dissolved oxygen in concrete pores,the oxygen consumption during corrosion cathode reaction et al.,on the transmission and consumption of oxygen were discussed.The dynamic self-balance relationship between the area ratio of cathode to anode corrosion cell and the non-uniform distribution of chloride ions concentration on steel surface was analyzed using the corrosion polarization equation coupled with macrocell and microcell.The influence of environmental temperature,humidity,external chloride ions and oxygen concentration on the corrosion potential,corrosion current density,and rust layer distribution on steel surface was discussed.The dynamic characterization of steel depassivation,corrosion propagation and rust layer distribution on steel surface in concrete under natural climate environment was achieved.(2)In considering the uniform distribution of temperature and humidity in the internal microenvironment of concrete under constant external temperature and humidity environment,the steel corrosion model under the combined actions of temperature,humidity,chloride ions and oxygen was optimized to establish a steel corrosion model under constant temperature and humidity environment.The calculation results of oxygen concentration,chloride ions concentration,corrosion current density and rust layer thickness distribution of the model were verified by the experimental data in the literature and in this study.The transmission performance and concentration distribution of chloride ions and oxygen in the process of steel corrosion,the area ratio of cathode and anode of corrosion cell,and the distribution of concrete resistivity were discussed.The effects of environmental temperature and humidity,oxygen and chloride ions concentration distribution on the corrosion process and results were studied.(3)The steel corrosion model suitable for time-varying temperature and humidity environment was established,and the relationship between the temperature and humidity field in the external macro environment and the internal micro environment of concrete,the transmission of oxygen and chloride ions and the concentration distribution field was established.The calculation results of temperature field,humidity field,oxygen and chloride ions concentration distribution field,corrosion current density and rust layer thickness distribution in concrete under time-varying temperature and humidity environment were verified using the experimental data in the literature and the experimental data in this study.Under the time-varying temperature and humidity in the external macro environment,the mechanism of temperature and humidity response in concrete,the transmission field and concentration distribution field of chloride ions and oxygen,the corrosion current density of steel,and the distribution and evolution of rust layer on steel surface were deeply explored,and the dynamic change process and results of steel corrosion in periodic temperature and humidity environment were studied.(4)A half-soaking accelerated corrosion model was established to numerically characterize the ions concentration,corrosion current density and rust layer thickness distribution on the steel-concrete interface and inside the concrete.The test data were used to verify the calculation results of the rust layer thickness and steel corrosion ratio of the model.The quantitative relationship between the time ratio of natural corrosion and accelerated galvanic corrosion was discussed when the two methods reach the same corrosion ratio.The effects of impressed current density and Na Cl solution concentration on time ratio were studied.The distribution differences of corrosion depth and rust layer thickness between the two methods were explored under the same corrosion ratio.