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Due to the ageing of the infrastructure facilities, a reliable assessment of the condition of concrete structures is of great interest to plan timely and appropriate measures. In concrete structures, pittingcorrosion of the reinforcement is the predominant deterioration mechanism affecting serviceability and eventually structural performance. Determination of quantitative chloride ingress is not only necessary to obtain valuable information on the current condition of a structure, but the data obtained can also be used to predict future developments and the associated risks. An overview of the progress and the possibilities of the application of laser-induced breakdown spectroscopy for concrete analysis in daily civil engineering practice is given. High-resolution 2D measurements of drill cores to determine the penetration of harmful species into concrete is presented. Furthermore, the application of a mobile LIBS system in a parking garage is shown. The system consists of a diode-pumped low-energy laser (3 mJ, 1.5 ns, 100 Hz) and a compact NIR spectrometer. A scanner allows two-dimensional element mapping. Progress towards the establishment of LIBS in a leaflet for the analysis of chlorine ingress into concrete in civil engineering is presented.
To conduct a reliable, repeatable and accurate LIBS analysis, the optimization of the experimental setup is an important task. Hardware parameters of lasers and spectrometers used in the setup as well as additionally required components such as optics or process gas pipes must be carefully aligned and adjusted because factors like (i) focal conditions of the optics, (ii) alignment of the sample, (iii) process purge gas (types, flow rate) or (iv) measurement settings (integration time, accumulation of pulses) have a big impact on the signal quality. Therefore, in most cases the effect of different factors is evaluated empirically due to changing one factor at a time while keeping the overall configuration the same. In the end, the optimal configuration is selected based on the best parameters for each influencing factor. During optimization, a configuration of the experimental setup is aimed at, which allows e.g. the highest signal intensity or the lowest variation. In most cases, cross-correlation, interference and interaction among the various factors are not considered. For this reason, the possibilities of using Design of Experiment (DoE) to optimize a LIBS experiment will be shown and advantages of (i) reduction of testing plans using a feature space, (ii) identifying and considering cross-correlations and interactions, (iii) evaluating individual impacts on the measurement (e.g. contour and surface plots) as well as (iv) multivariate models for prediction of impacts will be presented.
High-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS-GF-MAS) was employed for determining adsorbable organic chlorine (AOCl) in water. Organic chlorine was indirectly quantified by monitoring the molecular absorption of the transient aluminum monochloride molecule (AlCl) around a wavelength of 261.42 nm in a graphite furnace. An aluminum solution was used as the molecularforming modifier. A zirconium coated graphite furnace, as well as Sr and Ag solutions were applied as modifiers for a maximal enhancement of the absorption signal. The pyrolysis and vaporization temperatures were 600 °C and 2300 °C, respectively. Non-spectral interferences were observed with F, Br, and I at concentrations higher than 6 mg L-1, 50 mg L-1, and 100 mg L-1, respectively. Calibration curves with NaCl, 4-chlorophenol, and trichlorophenol present the same slope and dynamic range, which indicates the chlorine atom specificity of the method. This method was evaluated and validated using synthetic water samples, following the current standard DIN EN ISO 9562:2004 for the determination of the sum parameter adsorbable organic halides (AOX) for water quality. These samples contain 4-chlorophenol as the chlorinated organic standard in an inorganic chloride matrix. Prior to analysis, organic chlorine was extracted from the inorganic matrix via solid-phase extraction with a recovery rate >95%. There were no statistically significant differences observed between measured and known values and for a t-test a confidence level of 95% was achieved. The limits of detection and characteristic mass were found to be 48 and 22 pg, respectively. The calibration curve was linear in the range 0.1–2.5 ng with a correlation coefficient R2 = 0.9986.