Application of LA-ICP-MS for meso-scale chloride profiling in concrete

Chloride represents a major risk for reinforced concrete structures because at a certain concentration, it can promote depassivation of the steel bars and initiate corrosion. Therefore it is important to be able to measure the chloride content in concrete. In this paper the application of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for the study of chlorides in concrete is proposed. This scanning technique enables quick multi-element profiling, directly at the sample without the need for further preparation, within a range of sub-millimetre (meso-scale) resolution and with low limits of detection. Optimization of the operating conditions was performed in pressed concrete powder pellets. Linearity of the calibration was verified and limits of detection below 0.05 wt% of cement were determined. Chlorine, calcium and iron distributions were studied in cement based materials of increasing heterogeneity (paste, mortar and concrete). This technique is furthermore proposed for the study of the chloride induced corrosion process, by following element distributions along the concrete-steel interface at the time of depassivation