Application of LIBS technology for determination of Cl concentrations in mortar samples

Abstract

In a society where the cement and concrete industry is of great importance, the diagnosis of the quality of these materials has become a matter of highest priority. One of the maximum exponents of the deterioration of a reinforced concrete structure is the chloride ion content. In this work it has been shown that its evaluation, traditionally carried out by chemical methods, can also be performed by laser-induced breakdown spectroscopy (LIBS), a much faster and advantageous technique. This work develops an optimal experimental set-up based on the generation of small discharges using a 532 nm Nd:YAG laser of 320 mJ, in a helium atmosphere. The experimental conditions have been optimized and a calibration curve, relating the ratio of intensities of Cl I 837.60 nm and Ca II 849.80 nm obtained from the LIBS and the actual chloride concentration, has been determined from a set of samples with different ion chloride concentrations. These samples have been simultaneously subjected to a traditional chemical analysis, as well as instrumental contrast analysis using energy-dispersive X-ray spectroscopy (EDX). Finally, LIBS technique has been applied to the study of mortar samples that had been submerged in saturated sea salt water for 60 months, and in this way their average ion chloride concentration and their depth profiles have been obtained.