Gerd Wilsch

LIBS for non-destructive testing of element distributions on surfaces

Abstract A laser-based technique for the quasi non-destructive evaluation of surfaces of building materials is presented. Laser-induced breakdown spectroscopy (LIBS) is an analytical tool to determine the chemical composition of laser evaporated material. After the material has been vaporized by the high energy laser pulse the elements emit their specific fluorescence. This radiation is used to identify the elements in the evaporated material by spectroscopic methods. The mass of the evaporated material is of the order of micrograms; this means LIBS is a quasi non-destructive method for building applications. The main advantages of LIBS are the direct measurement without any preparation and the possibility to measure on site and to obtain on-line results. LIBS is a well-known technique which has been successfully applied in the areas of material testing, medicine and industrial process control. This article reports on the progress of LIBS applications for building materials by the use of some examples: identification and analysis of the main components of concrete; determination of salt concentrations in building materials; and measuring the relative element composition to a depth of up to 10 mm with high geometrical resolution.

Imaging laser analysis of building materials - practical examples

The Laser induced Breakdown Spectroscopy (LIBS) is supplement and extension of standard chemical methods and SEM‐ or Micro‐RFA‐applications for the evaluation of building materials. As a laboratory method LIBS is used to gain color coded images representing composition, distribution of characteristic ions and/or ingress characteristic of damaging substances. To create a depth profile of element concentration a core has to be taken and split along the core axis. LIBS was proven to be able to detect all important elements in concrete, e. g. Chlorine, Sodium or Sulfur, which are responsible for certain degradation mechanisms and also light elements like lithium or hydrogen. Practical examples are given and a mobile system for on‐site measurements is presented.

Quantitative Determination of Chloride-to-Cement Content of Concrete by Laser-Induced Breakdown Spectroscopy (LIBS)

Laser-induced breakdown spectroscopy (LIBS) is a combination of plasma generation on the sample surface by a high power laser pulse and optical emission spectroscopy (OES). It is a direct measurement method without an extensive sample preparation. Concrete is a multi phase system. With LIBS it is possible to distinguish the different phases and based on that to correlate the chloride content to the cement mass. This is done by scanning the surface with a resolution of up to 0.1 mm. The high measurement frequency of 100 Hz or even higher allows the in-situ visualization of the chloride content over the measured area. With a calibration a quantification of chloride concentration is possible. As an example the LIBS measurement on a 50 mm by 70 mm area with a resolution of 0.5 mm and the visualization of the chloride distribution takes only 10 minutes. Additionally it is possible to evaluate the carbonation depth from the same measurement. Examples of practical application to determine the chloride-to-cement-content on concrete samples are presented. The possibilities and the limitations of LIBS are discussed.