Determination of chlorine, sulfur and carbon in reinforced concrete structures by double-pulse laser-induced breakdown spectroscopy

Abstract

Accurate and reliable quantitative determination of non-metal corrosion agents in concrete is still an actual task of analytical use of LIBS. Two double-pulse LIBS systems were tested as a tool for the determination of chlorine, sulfur and carbon in concretes. Both systems had collinear configuration; a laboratory setup was equipped with an ICCD and two lasers (355/532nm+540nm), but a CCD was a detector for a mobile system with one laser (1064nm). Analytical lines of Cl I at 837.59nm, S I at 921nm and C I at 247.86nm were used to plot calibration curves. Optimal interpulse delays for the laboratory setup were 4μs for chlorine and 2.8μs for carbon, while an interpulse delay of 2μs was optimal for chlorine and sulfur determination with the mobile system. We suggested the normalization of the Cl I line at 837.59nm to the Mg II line at 279.08nm (visible at 837.23nm in the third order) to compensate for pulse-to-pulse fluctuations of chlorine lines. It provided the decrease of the detection limit of chlorine from 400ppm to 50ppm. Therefore, we reported that LIBS can be used to determine main corrosive active substances under ambient conditions in concrete below critical threshold values. Moreover, the application of the mobile system for in-situ qualitative assessment of corrosion way of a steel cage of a swimming pool dome was also demonstrated. It was found that chloride corrosion due to the disinfection of water was the main way for corrosion of the open part steel and the steel rebar inside the concrete.