Study On Natural Iodide Diffusion Coefficient Of Concrete

Chloride diffusion coefficient is an important parameter for evaluating the durability and life of concrete structures.Natural soaking method is a common method to get the diffusion coefficient of concrete.In actual projects,not only the materials used for mixing concrete contain chloride ions but also the chloride ion in the service environment can penetrate into the matrix.Due to the interference of these factors,the results of the immersion test will be biased.In this paper,the iodide ion were used are used to replace the chloride ion to act as the permeating ion.NaI and NaCl solutions were used as the soaking solution in this research.The correlations between the diffusion coefficients of iodine and chloride ions in natural diffusion experiments were compared.The effect of water-cement ratio and fly ash were also discussed.MIP,SEM,and XRD were used to analyze the influence of the iodide and chloride ion on the microstructure of concrete.A test method for natural diffusion of iodide ions was established to evaluate the ion diffusion performance of concrete.The iodide ion diffusion test device and associated program were developed in order to facilitate the application of this method.The main conclusions of this research are as follows:（1）The stability of iodide ion solution in the natural diffusion test can meet the test accuracy requirements.Compared with the iodide concentration change of sodium iodide solution in different environments,sodium iodide solution was found to have the lowest concentration reduction in a dark closed environment.The reduction in iodide ion concentration after 35 days does not exceed 5%.Therefore,once the soaking test was performed in a dark closed environment,the experiment can meet the accuracy requirements of the engineering.（2）The natural diffusion process of iodine and chloride ions in concrete has a good correlation.The experiment shows that the diffusion process of iodide and chloride ions in concrete is in accordance with Fick’s second law.With the decrease of the water-cement ratio or the increase of mineral admixture,the concentration distribution of iodide and chloride ions were reduced greatly.With the increase of the amount of fly ash or slag,the binding capacity of iodide ion and chloride ion of concrete increased first and then decreased.（3）Iodine and chloride ions showed a similar effect on the microstructure of concrete.It was found that the pore structure of the concrete was improved by immersing iodide ions and chloride ions.With the increasing use of fly ash and slag,the pore size was refined.The iodine and chloride ion can react with the hydration products and produced Friedel salt and iodine-containing substance 3CaO·Al₂O₃·CaI₂·8H₂O,respectively.（4）A test method for the natural diffusion of iodide ions was established.The conversion coefficientsλ,μ,andβused to transfer the diffusion coefficients of iodide ions and chloride ions were introduced.A conversion program was approved,and data analysis can be performed automatically with the help of this program.The diffusion coefficient after converting can meet the accuracy requirements of engineering.An iodide ion diffusion test device was designed based on the characteristics of the iodide ion.