Die Anreicherung des Alkaligehalts im Zementstein infolge von Taumittel-Beaufschlagung kann mit einem neu entwickelten Trennverfahren bestimmt werden. Die an Betonfahrbahnen nachträglich ermittelten Alkaligehalte werden mit den Alkaligehalten verglichen, welche in aktuellen Prüfverfahren zur Prüfung der AKR-Empfindlichkeit eingetragen werden. Dadurch wurden Informationen darüber gewonnen, ob in Performance-Tests Alkaligehalte simuliert werden, wie sie in Verkehrswegen maßgebend sind. .
Subsequent take-up of alkalis by the concrete surfaces on traffic routes and by the test pieces in performance tests for the alkali reaction due to the application of de-icing agents.
The aim of this practical DAfStB research project was to determine the increase in the alkali content of the hardened cement paste in concretes due to the application of de-icing agents. The alkali contents measured subsequently in carriageways were compared with the alkali contents which are employed in current methods for testing the sensitivity of aggregates and concretes to the alkali-silica reaction. This provided information about whether the alkali levels used in performance tests actually occur in concrete roads. The investigations described here use a separation method developed at TUUH (Hamburg-Harburg Technical University) for subsequent analysis of the hardened cement paste in concrete. In this method the hardened cement paste is comminuted mechanically and separated by the density separation method. The alkali content is determined by atom emission spectroscopy (ICP-OES). In alternative methods for determining the Na2O-equivalent the pore solution is expressed from the concrete and the alkali content of the hardened cement paste is calculated or the content of soluble alkalis is determined by extraction with water. With the method developed at the TUHH the Na2Oequivalent can be determined directly on the hardened cement paste from concrete. This enables the total alkali content of the hardened cement paste to be determined subsequently in accordance with the standardized analysis of the cement.