Experimental Study On Chloride Ion Erosion Of Concrete Under Carbonation, Freeze-thaw And Load Coupling Action

Under the effects of freeze-thaw damage,carbonization,chloride ion erosion and other factors,the durability of reinforced concrete structures is becoming increasingly serious,Among them,the erosion of chloride salts is an important factor leading to steel corrosion.Therefore,chloride ion erosion in concrete is the main line,and the effects of carbonization,load,freeze-thaw damage,and their coupling on chloride diffusion are studied in this paper.The main contents are as follows:(1)The concrete was assumed as a two-phase composite material of aggregate and mortar.The spherical and ellipsoidal random aggregate delivery algorithms were designed respectively,and the corresponding program was compiled by using MATLAB to realize the generation of three-dimensional mesoscopic random concrete geometric model.The program named mat2 scr 2017 was developed based on MATLAB to read the graphic file data from the MATLAB into the SCR script file,thus the conversion of MATLAB graphics to CAD graphics was realized,and the generality of stochastic concrete model is greatly enhanced.Combining the software COMSOL with MATLAB,the finite element mesh analysis of the concrete geometric model was carried out.The results show that the aggregate content of the random aggregate model can reach a high level,and the aggregate size and delivery position meet the randomness requirements;The ellipsoid random aggregate delivery algorithm is simple and efficient,and guarantees the randomness of the ellipsoid's dip angle;The model is applicable to the generation of arbitrary graded concrete,and the continuous graded concrete aggregate is delivered according to different grading sections,thus ensuring the volume ratio of the aggregate at all levels;The mesh generation of random concrete can achieve better results and meet the needs of finite element analysis;This research provides a reliable foundation for further study of the mechanical and physical properties of three-dimensional concrete from meso level.(2)Based on Fick's second law,the diffusion equation of chlorine ion was proposed on the basis of the former considering factors such as effect of chloride binding capacity,time dependence of chloride diffusion,surface chloride concentration,effect of electrostatic field of ion,and influence of temperature.(3)Concrete carbonation and freeze-thaw cycle tests were designed.Then,chloride ion erosion tests were conducted on concrete specimens with different ages of carbonization,different cycles of freeze-thaw cycles,and different load levels.A modified model of the chloride diffusion coefficient of the above durability factors was established and the parameters were determined.The calculated results of the numerical model agreed well with the experimental results.(4)based on the macroscopic numerical model of chloride ion erosion and the established three-dimensional concrete mesoscopic model,the law of chloride ion transmission in the saturated concrete was explored from the meso level.The results show that the chloride ions contents in concrete with the same depth are different.The transport of chloride ions is impeded by the aggregate.The transmission path of chloride ion in concretc is changed because of the aggregate.The chloride ions transfer around the aggregate.