Study On Non-destructive Testing Method For Chloride Ion Penetration Process Of Cement Material

Ordinary Portland cement,as a basic component of concrete,physically and chemically protects the pre-embedded steel from corrosion.However,the lack of durability of the concrete material due to aggressive media in the environment has prevented the building structure from reaching its normal service life.During the deterioration of concrete,chloride ions are the main cause of the decrease in durability of concrete structures.The intrusion of chloride ions accelerates the corrosion of steel in the structure and has a great impact on the concrete in the coastal environment.Therefore,studying the penetration process of chloride ions in cement-based materials is of great significance to the durability of concrete structures.Currently,there are many methods for assessing chloride ion transport properties,chloride ion content,and predicting the long-term service life of cement-based materials,but most are destructive,time-consuming,and labor intensive.Therefore,this paper mainly uses electrochemical impedance spectroscopy?Electrochemical Impedance Spectroscopy,EIS for short?and X-ray Tomography Technique?XCT?to nondestructively study the chloride ion permeation process and penetration in cement-based materials.The main researches and results are as follows:?1?Through the electrochemical impedance spectroscopy test of cement-based system,the experimental data fitting shows that the improved model has good applicability to the electrochemical impedance spectroscopy of cement-based materials.The electrochemical parameter R_ct1 of the chloride ion permeation process is established as a function of the chloride ion penetration depth,and the known value predicts the late chloride ion penetration depth.This relationship is applicable to the cement-slag-fly ash system.The error between the predicted result and the actual test result is less than 14%.?2?By studying the different water-cement ratios,the effects of different concentrations and different mineral admixtures on the electrochemical results,it is shown that reducing the water-cement ratio and increasing the slag fly ash replacement rate of the sample can improve the chloride ion impermeability.Through the establishment of triangular and other maps,the influence of different admixtures on the penetration depth is obtained,and the results have a certain guiding effect on the actual project.?3?Visually track and characterize the two-dimensional and three-dimensional evolution of the iodide ion penetration depth of cement samples with different water-cement ratios over time using XCT technology.Based on the average gray value method,it can accurately determine and quantify different penetration times.The concentration distribution during the non-destructive testing of iodide ion permeation was verified by verifying the comparative test.?4?The concentration distribution of partial sections of iodide ion and chloride ion under the same infiltration time was analyzed by XRF technique.The study found similarity between chloride ion and iodide diffusion behavior.Therefore,the XCT test can be carried out by using iodide ion instead of chloride ion and visually characterizing the migration relationship between the transport process and quantitative analysis of moisture in the cement-based material,and finally the concentration distribution curve of chloride ion is obtained.