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- 2014 (7) (entfernen)
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- LIBS (5)
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- Chloride ingress (1)
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Eingeladener Vortrag
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The 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 and a minimum of required sample preparation investigations of building materials can be conducted quite fast. In combination with a scanning technique (translation stage or scanning mirrors head) the element distributions are evaluated taking in to account the heterogeneity of the material. This is a significant advantage compared to standard procedures. LIBS measurements are also time and cost saving in comparison to standard methods. The automated measurement procedures minimise the liability for errors. All elements are detectable and after calibration results can be quantified. At BAM LIBS has been successfully applied for the investigation of distribution and transport of different ions in building materials. Quantitative measurements are performed for chlorine, sodium, potassium, sulphur, lithium and hydrogen. Beside this the identification of substances and the evaluation of quantitative ratios by means of an integrated marker are possible. An overview about the principle and the possibilities of LIBS investigations of building materials is presented and typical applications are shown. The LIBS technique is on the step from laboratory application to on-site analyses.
Cracks are always present in reinforced concrete structures. In the presented research, influence of mechanical cracks on chloride ingress is studied. A compact reinforced concrete specimen was designed, mimicking the cracking behaviour of beam elements. Cracks of different widths were induced by means of mechanical loading. These cracked specimens were then subjected to weekly cycles of wetting and drying with NaCl solution. After the exposure, the specimens were cut, and chloride distributions were determined using Laser Induced Breakdown Spectroscopy (LIBS), an innovative technique which enables simultaneous determination of different elements with high spatial resolution and minimal specimen preparation. By combining element distributions of different elements, it is possible to discriminate between coarse aggregate particles, and the mortar matrix. It was found that the wider the crack is, the higher the ingress of chloride ions. This was, however, different for two tested concrete mixes. Due to highly inhomogeneous chloride distribution around the cracks, use of fine-scale experimental techniques for chloride mapping is advised, based on the presented study.
Laser Induced Breakdown Spectroscopy (LIBS) is a combination of laser ablation, plasma formation and optical emission spectroscopy. The possibility of direct measurements on the sample surface, the minimum of necessary sample preparation and the automated setup allows for fast investigations of building materials. In combination with a scanning technique (translation stage or scanning mirrors head) the element distribution can be evaluated in consideration of the material's heterogeneity. LIBS measurements are also time-and cost-saving. The ingress profile of chlorine on a 50mm diameter concrete core up to a depth of 50mm can be measured and evaluated in less than 10 minutes. The results are normally referred to the evaporated mass, which is approximately the cement mass of the specific concrete. As a completion to micro XRF measurements also light elements like sodium or hydrogen can be detected. The spatial resolution of the measurement may reach 50 ìm at a maximum measurement frequency of up to 100 Hz. On the basis of calibration curves, results can be quantified.
Laser induced breakdown spectroscopy (LIBS) - visualization of ion transport processes in concrete
(2014)
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 and 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) the element distributions are evaluated with mm resolution. Thus the heterogeneity of the material may be considered. This is a significant advantage compared to standard procedures. LIBS measurements are also time and cost saving in comparison to standard methods. The automated measurement procedures minimize the liability for errors. All elements are detectable. Results can be quantified after calibration. At BAM LIBS has been successfully applied for the investigation of distribution and transport of different ions in building materials. Quantitative measurements are performed for chlorine, sodium, potassium, sulfur, lithium and hydrogen. In addition the identification of substances and the evaluation of quantitative ratios by means of an integrated marker are possible. An overview about the principle and the possibilities of LIBS investigations of building materials is presented and typical applications are shown. The LIBS technique is close to practical application on-site.
Cracks are always present in reinforced concrete structures. In the presented research, influence of mechanical cracks on chloride ingress is studied. A compact reinforced concrete specimen was designed, mimicking the cracking behaviour of beam elements. Cracks of different widths were induced by means of mechanical loading. These cracked specimens were then subjected to weekly cycles of wetting and drying with NaCl solution. After the exposure, the specimens were cut, and chloride distributions were determined using Laser Induced Breakdown Spectroscopy (LIBS), an innovative technique which enables simultaneous determination of different elements with high spatial resolution and minimal specimen preparation. By combining element distributions of different elements, it is possible to discriminate between coarse aggregate particles, and the mortar matrix. It was found that the wider the crack is, the higher the ingress of chloride ions. This was, however, different for two tested concrete mixes. Due to highly inhomogeneous chloride distribution around the cracks, use of fine-scale experimental techniques for chloride mapping is advised, based on the presented study.