Experimental investigation on diffusive behavior and microstructural modifications induced by free iodide and chloride ions in concrete incorporating with fly ash

This study investigates the use of iodide as a substitute for chloride in rapid migration tests for assessing chloride migration in marine reinforced concrete (RC) contaminated by seawater. It explores the effect of fly ash (FA) content (0 %, 15 %, 30 %, 60 %) and curing ages (28 and 150 days) on chloride ions and iodide ions concentration, penetration depth, and diffusion coefficient. The study also uses SEM, EDS, XRD and MIP to analyze migration mechanisms. Results show that FA content affects migration behavior, with 30 % FA optimizing resistance to ion penetration due to increased C S H and calcite minerals and micropore volume. Long-term curing (150 days) reduces free chloride and iodide ions concentration, improving matrix compactness. A relationship between diffusion coefficient of chloride ions and iodide ions is proposed, allowing for accurate prediction of diffusion coefficient of chloride ions based on diffusion coefficient of iodide ions. This novel method provides a reliable approach for evaluating chloride migration in concrete exposed to seawater or de-icing salts.