Einfluss der Alterung auf die innere und äußere Schädigung von Hochleistungsbeton unter Frost- und Frost-Tausalzangriff (English shop)

Forschungsbericht des Instituts für Materialwissenschaft

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In practice, concrete is exposed to various environmental influences that can impair its durability to differing degrees. Ensuring sufficient resistance to freeze-thaw and freeze-thaw with de-icing salt attack is one factor in the construction of structures with a long service life, which is why it is necessary to verify the suitability of a concrete mix with regard to freeze-thaw and de-icing salt exposure. Particularly in the case of special concretes containing additions and admixtures, such testing can be of fundamental importance, since here an assessment based solely on the design concept cannot always be made reliably, depending on the selection of the components.

With the aid of laboratory test methods, the forms of damage to be expected under XF3, XF4 exposure can be simulated in fast motion, and statements about durability can be made after a defined test duration. A test method such as the CDF/CIF test, like other test methods, prescribes a test age of 28 days for reasons of conformity, although in practice components are frequently not exposed to freeze-thaw cycles until a later point in time.

In order to investigate in detail the influence of the test age and the ambient conditions in concretes containing additions, a range of high-performance concretes was examined by means of the CDF/CIF test within the framework of this research work and the results were compared with those of normal concrete. Field tests also made it possible to draw additional conclusions about the behaviour of concrete under real conditions, which were used to examine the transferability of the laboratory results obtained.

Above all, a time-dependent change in the transport mechanisms became apparent, as a result of which internal damage generally sets in earlier. In this context, the surface zone likewise plays an essential role in the damage analysis, since it is the decisive factor for the ingress of moisture within the near-surface regions and, moreover, influences the amount of scaling depending on phase stability and the progress of carbonation. Overall, it could thus be concluded that prolonged storage under laboratory climate evidently does not represent a realistic situation such as concretes experience in practice.