Abstract
In a national and worldwide context, countless reinforced concrete structures are in anadvanced state of deterioration. A principal cause of such degradation is chloride inducedcorrosion of reinforcement bars. This phenomenon is accentuated in countries wherede-icing salts are used for road safety, as well as in maritime zones. To date, nonon-destructive method quantifying chloride content during the corrosion initiation phasehas been established. Measurement of such a parameter is important for the development ofa better understanding of the complexity of corrosion phenomena and, more practically, forbetter management of existing structures. This paper proposes a new methodfor non-destructive measurement, for monitoring continuously and in real timefree chloride content in concrete pores. In this context, a chemical sensor thatemploys optical fibers was developed and tested. The sensor functions using thefluorescence of an indicator dye that is sensitive to chlorides. Through fluorescencespectroscopy, variations in the concentration of free chlorides are related to intensityfluctuations of fluorescence. The use of optical fibers also provides an advantagecompared with existing electric non-destructive detection systems due to superiorelectromagnetic stability. Theoretical and experimental studies calibrated and validated thesensor for implementation within mortar samples. Free chloride concentrationsbetween 30 and 350 mM can be detected. Two experiments reproduced climaticvariations in a controlled environment. The first test simulated a hot maritime climateand the second test simulated a cold continental climate. These tests confirmedthat it is possible to determine with precision the free chloride content. Also,fluorescence spectroscopy with optical fibers offers an innovative means for earlyand non-destructive detection of free chloride content in concrete. As a result,this new method has potential for improving the science of corrosion processunderstanding and for planning appropriately for preventive action in practical situations.
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