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The laser-induced breakdown spectroscopy (LIBS) is a fast method to provide multi-elemental analysis of any sample. At the Federal Institute for Materials Research and Testing (BAM) the LIBS technique is applied on building materials to measure ingress profiles of harmful species like chloride and alkalis. The ingress depth and the quantitative amount is important for the evaluation of the potential for damage processes like the alkali-silica reaction or chloride-induced corrosion. Concrete as an example is a highly heterogeneous material with 1/7 cement (major component CaO) and 6/7 aggregates (SiO2) with different grain sizes. Due to a scanning procedure a two dimensional element distribution of a concrete surface can be measured. In order to have an automated Separation method to evaluate heterogeneous materials, different cluster algorithm have been tested. Best results have been achieved with the Expectation-Maximization-Algorithm (EM-Algorithm).
Laser-induced breakdown spectroscopy (LIBS) is a combination of laser ablation and optical emission spectroscopy. Due to the possibility of direct measurements on the sample surface with a minimum of sample preparation investigations of building materials can be conducted quite fast. In combination with a scanning technique (translation stage or scanning mirrors head) 2D element distributions of harmful species like chlorides and alkalis are evaluated with a sub-mm resolution. By scanning a surface of typically 100 mm x 100 mm the heterogeneity of the material may be considered. LIBS is capable to identify hot spots in element concentration with a resolution of 0.1 mm or even smaller. A LIBS-system for the on-site application on building materials is, in cooperation with system developers and companies which will use this technique for investigation on real structures, under test at BAM. We present an example. Further work will focus on providing guidelines to establish LIBS as a standard procedure for chemical investigations of building materials.
LIBS is on the step from a laboratory application to on-site analysis. A validated mobile LIBS-system for on-site application on building materials is under development at BAM in cooperation with industrial partners (system developers and companies), who will use this technique for investigation on building structures like bridges and parking decks. The system is designed to measure the content of harmful species like chlorine, sulfur or alkalis, to give the engineer a tool for the estimation of the condition of concrete structures and for quality assurance during concrete repair work on-site. In these work results of on-site measurements on a chloride contaminated bridge are shown. Further work will focus on providing guidelines to establish LIBS as a standard procedure for chemical investigations of building materials.
Die Laser induzierte Breakdown Spektroskopie (LIBS) bietet für die Analyse heterogener, mineralischer Baustoffe, wie z. B. Beton, deutliche Vorteile gegenüber konventionellen Methoden. Sie ermöglicht neben der Quantifizierung von Elementgehalten und -verteilungen im Baustoff auch die Differenzierung von Elementkonzentrationen innerhalb einzelner Phasen im Baustoff. So können beispielsweise die für die Alkali-Kieselsäure-Reaktion (AKR) interessanten Natriumkonzentrationen bestimmt und hinsichtlich ihrer Verteilung aufgelöst werden. Es lassen sich Natriumgehalte, welche sich in der Gesteinskörung befinden, separat von denen der Betonmatrix bestimmen. Der vorliegende Artikel befasst sich mit den Vor- und Nachteilen von LIBS als alternative Methode für die chemische Analyse von Baustoffen. Anhand von Beispielen aus der Praxis wird der derzeitige Stand der Technik dargestellt und ein Vergleich mit etablierten Messmethoden vorgenommen. Compared to conventional methods the Laser Induced Breakdown Spectroscopy (LIBS) provides significant advantages for analysis of heterogeneous, mineral building materials as e.g. concrete. Besides providing the possibility to quantify element concentrations and distributions in building materials, this technique enables also to differentiate concentrations within different phases of the material. It is possible to determine sodium concentrations and distribution directly, which e.g. is important when regarding Alkali-Silica-Reaction (ASR). Sodium contents provided by the aggregates can be distinguished from those provided by the concrete matrix. The present article is concerned with the advantages and disadvantages of LIBS as alternative method for chemical analysis of building materials. On the basis of samples from practice the current state of the art is shown and different measurement techniques will be compared.
The information about the chemical composition of coal is of great interest during mining, sorting and processing. Due to great variations of the soil layers the quality of coal suffers great fluctuations during mining because of adjoining rocks [1-6]. To provide on-site analysis of coal the application of LIBS as a multi-element method has been tested. Therefore different qualities of coal have been chemically analyzed to get reference values for the water content as well as for the major (carbon) and minor components (ash = Ca, Mg, S, Si). For the LIBS analysis a system using a low energy laser with a wavelength of 1064 nm, pulse energy of 3 mJ, pulse length of 1.5 ns and a repetition rate of 100 Hz have been used. A compact czerny turner spectrometer operating in the UV range (Δλ = 170 nm – 350 nm) have been applied. To provide quantitative concentrations different calibration curves have been evaluated using chemometrics. The system has been validated using internal cross-validation as well as an external set of samples. For the evaluation of the method different figures of merit will be presented. After applying LIBS for coal analysis in the laboratory a LIBS system for the on-site analysis has been tested during the mining process.
In civil engineering the information about the quantitative ingress of harmful species like Cl⁻, Na⁺ and SO²⁻₄ is of great interest to evaluate the remaining life time of structures. These species are triggering different damage processes like the alkali-silica reaction (ASR) or the chloride-induced corrosion of the reinforcement. For the evaluation of the heterogeneous concrete it is necessary to discriminate between the different phases mainly cement matrix and aggregates. The transport processes are only proceeding in the cement matrix therefore the measured concentrations should be regarded to the cement content. For the 2D evaluation of element distributions different multivariate cluster-algorithms like k-means and Expectation-Maximization-algorithm (EM-algorithm) have been tested. The methods are compared and different figures of merit will be presented. After phase separation non-relevant information of the aggregates can be excluded. The ingress of harmful species is then quantified using chemometrics. Due to concrete cores from a parking deck the methods have been validated and verified with standard methods of wet-chemistry.