Abstract
Reinforcement corrosion is major reason for concrete structures deterioration. Chlorides from external sources such as seawater and de-icing salts penetrate in the concrete and as soon as a critical threshold reaches the reinforcement level corrosion processes start. Therefore, the characterization of the chloride ingress resistance in form of the rapid chloride migration (RCM) coefficient, DRCM is crucial to classify concretes for given applications and to enable full probabilistic service life prediction. To measure DRCM of chloride-contaminated concrete, a rapid iodide migration test was developed using iodide as penetration ion and an iodine–starch reaction for penetration depth indication. This indicator mixture has the disadvantage that it is not applicable on sulfide containing concretes such as ground granulated blast furnace slag concretes. In this paper, the reason for the unsuitability of this indicator is examined and alternative oxidation agents are found and validated to overcome this problem. The new indicator mixtures with hydrogen peroxide (H2O2) or/and potassium persulfate (K2S2O8) as oxidation agents are not only insensitive to sulfide contamination but are also applicable to common concrete compositions and could replace the existing indicator universally.
Highlights
The major reason for concrete structures to deteriorate is the chloride-induced reinforcement corrosion, for instance when the structure is located in marine environment or exposed to de-icing salts
Two alternatives for KIO3 as oxidation agents for iodide are presented in this paper, which are not iodine containing but having the same oxidation power as IO3-: hydrogen peroxide (H2O2) is known to be a strong oxidation agent, it is a mass product with good availability and very riskless reaction products: water (H2O) and oxygen
By adding 6 drops of the KIO3 solution as oxidation agent to the salt solutions, a color change from milky turbid to blue is observed independent of the type of salt
Summary
The major reason for concrete structures to deteriorate is the chloride-induced reinforcement corrosion, for instance when the structure is located in marine environment or exposed to de-icing salts. Suitable and reproducible test methods are required to characterize the chloride transport in concrete These test methods should be usable for performance specifications and quality control. The Dapp(t) can be determined by chloride profiles from field data and/or laboratory diffusion tests [3, 4] These diffusion tests take several weeks while the determination of the rapid chloride migration (RCM) coefficient of concrete DRCM by RCM test is a suitable alternative [5]. Drilled on-site concrete cores can already contain chlorides before the RCM test starts if a structure has been exposed to marine environment or de-icing salts. Chlorides can be introduced to the concrete by chloride contaminated aggregates or water with chlorides Since these internal chlorides migrate together with chlorides from the test solution, the RCM test is no longer applicable. Other byproducts of the reaction are sodium and potassium acetate (NaAc/KAc)
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