The Three-dimensional Deterioration Of Non-uniform Corrosion-induced Expansion Damage And The Induced Influence On The Chloride Transport In Reinforced Concrete

Under chloride environments,the steel bars in reinforced concrete structure will be corroded non-uniformly.The non-uniform corrosion of steel bars can cause a graual reduction of bearing capacity even before the designed service life of reinforced concrete structures,leading to an enormous manpower and material losses.Therefore,the research on the durability of reinforced concrete structures under chloride environments is very important.Nowadays,the investigation on the durability of reinforced concrete structures mainly focuses on the invasion of harmful substances in concrete,as well as the temporal and morphology characteristicts of corrosion cracking of reinforced concrete structures.However,the service performance deterioration of the reinforced concrete structures induced by corrosion expansion damage has not been explored compreshensively.The clarification of the three-dimensional damage process of concrete induced by the non-uniform corrosion of steel bars,as well as the influence of three damage field on the transport of chlroides,is helpful for finding appropriate measures in controlling the rapid corrosion and expanding the service life of reinforced concrete structures.In this research,both mortar and concrete were studied from meso-scale to macro-scale.Based on theoretical investigation,experimental analysis and numerical simulation,the three-dimensional damage process of concrete structures induced by non-uniform corrosion was studied at meso-level.And the influence of three-dimensional damage on chlorides transport was also investigated.The main works of this study are listed as follows.(1)Based on thermodynamics theory,an elastoplastic damage constitutive model of mortar was established in considering the compaction coefficient K and the mechanical response under loading.The difference between tensile and compressive properties of mortar materials was taken account in the constitutive model,which could be used to numerically simulate the three-dimensional corrosion expansion at meso-level.(2)Based on X-rayCT scanning technology,the non-uniform corrosion of the reinforced mortar under chloride environments at different times were obtained non-destructively.The three-dimensional displacement fields and strain fields of the specimen at different corrosion times were calculated with the digital volume correlation technology(DVC).The three-dimensional reconstruction of the constituent phases was performed by gray threshold segmentation technology.The volume expansion rate P of the corrosion products under the stress state was obtained.The whole deterioration process of the three-dimensional non-uniform corrosion expansion damage of the reinforced mortar specimen was studied numerically.A comparison between the DVC calculation results and the numerical results was conduced to verify the reliability of the numerical simulation.(3)Based on the X-rayCT scanning technology,the non-uniform corrosion morphologies of reinforced concrete specimen under chloride environments at different times were obtained non-destructively.The three-dimensional displacement fields and three-dimensional strain fields of the specimen at different corrosion times were calculated through DVC technology.The three-dimensional reconstruction of constituent phases was carried out using gray threshold segmentation technology,and the actual spatial distributions of coarse aggregates and pores were obtained.In considering the orginal spatial distribution of coarse aggregates and pores(with the diameter greater than 1mm),a numerical model of reinforced concrete was established to simulate the development of the three-dimensional damage field of reinforced concrete under non-uniform corrosion.The reliability of the numerical simulation was verified by comparing the results with DVC calculations.In addition,the differences of damage rate and morphologis of three-dimensional damge for reinforced concrete specimens between uniform and non-uniform corrosion were comparatively studied.And the research results indicated that non-uniform corrosion would cause greater damage than uniform corrosion.(4)The uniaxial tensile fatigue loading test was used to obtain different tensile damage degrees of reinforced mortar specimens,and the damaged specimens were immersed in chloride salt solution to study the chloride transport process in damaged mortar.The empirical formula between the tensile damage variable D_p of mortar and the chloride ion diffusion coefficient magnification K_f caused by damage was obtained based on the least-square method.(5)Taking the spatial distribution of real three-dimensional aggregates into account,a numerical model was established to simulate the transport of chlorides in reinforced concrete.The validity of the numerical model was verified through experiment.Through the random placement of real coarse aggregates,the influence of the spatial distribution of coarse aggregates on the three-dimensional transport of chlorides in reinforced concrete was studied.And a comparison was furtherly performed with the two-dimensional transprot.The research results show that the chloride ions distributions at different erosion depth caused by the different spatial distribution of coarse aggregate yields to normal distribution,and the spatial effect of the three-dimensional transport cannot be ignored.In addition,the three-dimensional corrosion expansion damage fields of reinforced concrete model were obtained through finite element software Abaqus.The corrosion expansion damage fields were imported into COMSOL software to study the chlorides transport process in damaged concrete.The impact of the three-dimensional damage fields on chloride transport in reinforced concrete was studied and analyzed.