Investigation of natural diffusion behavior in concrete using iodide replacing chloride ions: The impact of mineral admixtures types and dosages

The chloride natural diffusion (CND) test is often used in concrete-related field to analyze the chloride diffusion behavior in concrete and chloride diffusion coefficient (D(Chloride)) is an important parameter for durability assessment of RC structures. Thus, CND and iodide natural diffusion (IND) tests were performed to obtain the diffusion depth and concentration and D(Chloride)/D(Iodide) in concrete with different mineral admixture types and dosage to verify the feasibility of IND to replace the CND test under condition that some concrete exposed in marine environment. It is found that IND test need to conduct under air-isolated dark environments with lower iodide oxidative behavior effectively. Besides, with the increase of FA amount, the concentration of chloride/ iodide decreased and then increased, while the chloride/iodide binding capacity increased and then decreased. However, with the increase of GGBFS content, the chloride/iodide concentration gradually decreased, while the chloride/iodide binding capacity increased. Meanwhile, a good linear relationship was shown between the free ion concentration and bound ion concentration. Although the chloride or iodide diffused into the concrete can prompt the generation of complex compounds, namely 3CaO center dot Al2O3 center dot CaCl2 center dot 10H2O and 3CaO center dot Al2O3 center dot CaI2 center dot 8H2O, iodide seems to hinder secondary hydration of FA/GGBFS and lower the compactness of matrix and increase the proportion of harmful gels, compared to chloride. With the increase of mineral admixture dosage, there are more hydrates, the porosity gradually decreases, and the proportion of harmful pores also drops. Moreover, a quadratic relationship between D (Chloride) and D (Iodide) was studied, a direct correlation between FA/GGBFS dosage and conversion coefficient was given, and there is a plane function relationship between D(Chloride)/D(Iodide) and total porosity, FA/GGBFS dosage. Overall, this study gives a new idea of IND replacing CND test to assess the durability of RC marine structures.