Study On Iodide Diffusion Coefficient Of Concrete Mixed With Mineral Admixture

The chloride diffusion coefficient is an important parameter for evaluating the durability of concrete.At present,the rapid electromigration method(RCM)is commonly used to measure the chloride diffusion coefficient of concrete.However,in the case of concrete containing chloride ions,the internal chloride ions will seriously affect the accuracy of RCM method.In this paper,the rapid iodide ion electromigration method(RIM)is used in this paper.replacing chloride ion with iodide ion.The effects of mineral admixtures on the penetration depth and diffusion coefficient of iodide ion and chloride ion in concrete are studied,and the distribution of free iodide ion and chloride ion in concrete is compared and analyzed.The effects of iodide ion and chloride ion on the pore structure and micro-morphology of concrete with mineral admixture were compared and analyzed.The correlation equation between diffusion coefficients of iodide ion and chloride ion in concrete is established.The main research contents and results are as follows:(1)Compared with concrete specimens without chloride ion,RCM method is no longer accurate in measuring chloride ion penetration depth,free chloride ion concentration and chloride ion diffusion coefficient when chloride ion is already contained in ordinary concrete,slag and fly ash concrete,and the results are distorted.However,the penetration depth and diffusion coefficient of iodide ions measured by RIM method are basically not affected by internal chloride ions.(2)The diffusion coefficients of iodide and chloride ions in concrete with mineral admixtures have good correlation.RIM and RCM methods were used to study the effect of slag and fly ash on the diffusion coefficient of iodide ion in concrete with different dosage and age.The results show that the penetration depth and diffusion coefficient of iodide ions are slightly larger than chloride ions in concrete of the same mix ratio.With the increase of slag content,the penetration depth and diffusion coefficient of iodide and chloride ions decrease gradually;with the increase of fly ash content,the penetration depth and diffusion coefficient of iodide and chloride ions decrease first and then increase.(3)The diffusion process of free iodide ion and chloride ion in concrete has a good correlation.With the increase of penetration depth,the concentration of free iodide ion and chloride ion decreases gradually,and the concentration of free iodide ion at the same penetration depth is slightly higher than the concentration of chloride ion.Through mercury intrusion and scanning electron microscopy tests,it is found that iodide ion and chloride ion have similar effects on the pore structure and micro-morphology of concrete with mineral admixtures.(4)The relationship between diffusion coefficient of iodide ion and chloride ion in concrete with mineral admixture was established.The diffusion coefficient of iodide ion in slag concrete is 1.074-1.184 times that of chloride ion,and that of fly ash concrete is1.085-1.294 times that of chloride ion.The adjustment coefficient ??????? are introduced,the correlation equation between mineral admixture content and adjustment coefficient ??????? is fitted by Origin,the iodide ion diffusion coefficient of concrete can be converted into chloride ion diffusion coefficient and used to evaluate the permeability of concrete.