FIBEROPTICAL SENSORS IN CONCRETE |
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| S.Wiese, J. Wichern, W. Kowalsky, W. Grahn |
- Abstract:
- Buildings of reinforced concrete are exposed to a variety of damaging influences. In particular, moisture has an important influence on the lifetime of concrete structures. This is caused by the involvement of free water in corrosion of the steel and the fact that water acts as a transport medium for damaging ions such as chloride, sulfate, carbonate and ammonium. Thus, we have developed fiberoptical moisture sensors, which allow an in-situ non-destructive long-term monitoring of concrete structures. As indicator we use a pyridinium-N-phenolat betain (Reichardt’s dye), which shows a high solvatochromic behavior. The dye is embedded in a polyacrylonitrile polymer matrix whose polarity is enhanced by free water diffusing into the sensor. This leads to a continuously hypsochromic shift of the absorption spectrum in dependency on the water concentration. Without moisture the sensor shows a peak-wavelength in the absorption spectrum at 602 nm. The wavelength is shifted about 40 nm to 562 nm by a maximum relative concentration of water in the matrix (28 wt%). This behavior is fully reversible. We use the same sensor concept to measure the pH-value in the concrete by using an azo-dye as pH-indicator. So we applied fiberoptical moisture sensors as well as pH sensors to observe chemical attack at a concrete testing structure. The structure has been developed in a cooperation with different research groups of chemists, electrical engineers and civil engineers in a collaborative research project to study the damaging influences of moisture and different ions on concrete.
- Keywords:
- fiberoptical sensor, moisture sensor, pH sensor, polymer, concrete
- Download:
- IMEKO-WC-2000-ST-P476.pdf
- DOI:
- -
- Event details
- Event name:
- XVI IMEKO World Congress
- Title:
Measurement - Supports Science - Improves Technology - Protects Environment ... and Provides Employment - Now and in the Future
- Place:
- Vienna, AUSTRIA
- Time:
- 25 September 2000 - 28 September 2000