A new system for early chloride detection in concrete

In a national and worldwide context, countless reinforced concrete structures are in an advanced state of deterioration. A principal cause of such degradation is chloride induced corrosion of reinforcement bars. This phenomenon is accentuated in countries where de-icing salts are used for road safety, as well as in maritime zones. To date, no non-destructive method quantifying chloride content during the corrosion initiation phase has been established. Measurement of such a parameter is important for the development of a better understanding of the complexity of corrosion phenomena and, more practically, for better management of existing structures. This paper proposes a new method for non-destructive measurement, for monitoring continuously and in real time free chloride content in concrete pores. In this context, a chemical sensor that employs optical fibers was developed and tested. The sensor functions using the fluorescence of an indicator dye that is sensitive to chlorides. Through fluorescence spectroscopy, variations in the concentration of free chlorides are related to intensity fluctuations of fluorescence. The use of optical fibers also provides an advantage compared with existing electric non-destructive detection systems due to superior electromagnetic stability. Theoretical and experimental studies calibrated and validated the sensor for implementation within mortar samples. Free chloride concentrations between 30 and 350 mM can be detected. Two experiments reproduced climatic variations in a controlled environment. The first test simulated a hot maritime climate and the second test simulated a cold continental climate. These tests confirmed that it is possible to determine with precision the free chloride content. Also, fluorescence spectroscopy with optical fibers offers an innovative means for early and non-destructive detection of free chloride content in concrete. As a result, this new method has potential for improving the science of corrosion process understanding and for planning appropriately for preventive action in practical situations.