Rmeability Evaluation Method Of Concrete Based On The Transport Characteristics Of Iodide Ions

Chloride permeability has great significance for service life prediction, durability design and construction of concrete structure. However, the conventional RCM (Rapid Chloride Migration) method for chloride permeability assessment is no longer applicable for concrete structure which has contained chloride ions. To overcome the influence of the interior chloride ions on the test result and realistically assess the service life of chloride-carrying concrete structure, this thesis proposes to use iodide ions as migrating ions, instead of chloride ions, in migration tests for permeability evaluation. In light of concrete material science, physico-chemistry and other basic principles, based on comprehensive macroscopic tests and microscopic analyses, the transport process and binding mechanisms of iodide ions in concrete are investigated and compared with that of chloride ions. Based on this study, a new concrete permeability evaluation method is developed, i.e. RIM (Rapid Iodide Migration) test.Main results of the present study are drawn as follow:(1)The influences of iodide ions and chloride ions on the pore structure, surface-layer sorptivity and paste micro structure are systematically studied, and it is found that the effects of these two kinds of ions are similar. Since there is no iodide ions neither in surrounding environment nor inside the concrete, iodine ions can be used as migrating ions instead of chloride ions in migration tests for permeability assessment.(2)Starch-potassium iodate colorimetric method is proposed to test the penetration depth of free iodide ions in concrete.(3)The effectiveness of the starch-potassium iodate colorimetric method for the determination of iodide penetration depth, and the influences of w/c and fly ash amount on the colorimetric boundary concentration of iodide ions are deeply examined. The correlation between the iodide colorimetric boundary concentration and the chloride colorimetric boundary concentration based on AgNO3colorimetric method is discussed.(4)In consideration of the binding capacity, time-dependency of diffusion coefficient, service environment and ion characteristics, an immersion leaching factor and the diffusion coefficient are used to build a new equation describing the diffusion process of ions in concrete. This new equation can be used to describe the diffusion of different ions, and has been validated by experimental results of the diffusion of iodide ions and chloride ions.(5)This research comparatively studies the evolutions of the deposition amount and penetration depth of chlorine ions and iodine ions in concrete under natural immersion condition. It is found that, with the same penetration depth, the cumulative deposition of iodide ions is greater than chlorine ions, and the different between them increases following the increase of w/c; with the increase of the penetration depth, the cumulative deposition amount of chlorine ions and iodine ions becomes closer; the penetration depth and the water-cement ratio are closely related, and a power function taking w/c as a variable can be used to reflect the evolution law of the penetration depth.(6)Based on the transport characteristics of iodide ions in concrete and the principles of RCM test, RIM test method which evaluates permeability of concrete using iodide ions is developed. A colorimetric depth correction factor is proposed to translate RIM test results to RCM results. It has been proved that, RIM method can be effectively used to evaluate the permeability of concrete containing interior chloride ions.