• Sterz, Karl Leonard
• Galan, Isabel
• Juhart, Joachim
• Sakoparnig, Marlene
• Vallazza-Grengg, Cyrill
• Müller, Bernhard
• Mittermayr, Florian
• Mayr, Torsten

Abstract

Introduction<br/>Corrosion-related damages on concrete infrastructure account globally for several billion US dollars annually. Roughly 38% of these costs could be saved by the application of optimized materials and/or more efficient monitoring technologies. Currently, the most commonly used methods to assess the state of a concrete structure in terms of carbonation and chloride penetration, are phenolphthalein coloration and silver nitrate titration, respectively. However, the accuracy of the methods and the correlation of the obtained results with the actual state of the considered structure in terms of potential damage are constantly being questioned.<br/><br/>Methods <br/>Optical chemical sensors are applied based on luminescent pH and chloride sensitive dyes, to quantitatively access the pH evolution and chloride concentration of cement-based construction materials. Dual lifetime referencing was applied for chemical imaging and sensor probes. For this method a fluorescent pH or chloride indicator dye (short lifetime) is combined with a phosphorescent reference dye (long lifetime) with similar spectral properties. <br/><br/>Results<br/>We present high resolution pH imaging, demonstrated on various real concrete samples with different levels of carbonation and a comparison with the standard method (phenolphthalein coloration). We show that the imaging method provides high alkalinity pH-profiles of carbonation with a higher level of information than the standard method. Using this technique, we critically discuss crucial aspects of pH measurement, which have to be reconsidered when determining the pH of concrete structures. We also show an optical chloride sensor suitable for the measurement of released chloride from concrete powder samples and point out the challenges of sample preparation. <br/>The promising results show that the application of this novel methodology will allow for a better assessment of the concrete structures’ state and for a better understanding of the processes taking place in cementitious matrices during hydration and exposure to the environment. The methodology has the potential to enable field measurements with a faster detection and on-sight decision making on the status of buildings. <br/><br/>Innovative aspects <br/>•pH-imaging provides detailed carbonation profiles of concrete samples<br/>•pH-probes for high alkalinity measurements without alkalinity error. <br/>• Field method for accurate measurement carbonation and chloride concentration in concrete<br/><br/>Acknowledgements<br/>The authors gratefully acknowledge funding by the Austrian Research Promotion Agency FFG (LumAConM Project-No. 879008), the Austrian Society for Construction Technology ÖBV and the industry partners.<br/>

Topics

• impedance spectroscopy
• silver
• corrosion
• cement
• titration
• pH measurement