Investigations of the Freeze-thaw and De-icing Resistance of Fly Ash Concrete with the Modified CDF-method for Exposure Class XF2
Project Number 330
Fly ash is used as a concrete addition in Germany for more than 30 years and it is integrated in guidelines and standards. Due to numerous research results it is now possible to take fly ash into account in the concrete composition for concrete exposed to freeze-thaw attack with de-icing salt (exposure classes XF2 and XF4). This opens a new field for the use of fly ash in concrete.
In order to achieve a comprehensive application of fly ash in this new field all normative requirements regarding the freeze-thaw de-icing salt resistance have to be fulfilled. There are different exposure classes according to the various forms of frost attack (XF1 to XF4). The exposure classes XF1 and XF2 describe a frost attack without and with de-icing salt at moderate water saturation and the classes XF3 and XF4 classify a frost attack at high water saturation.
The problem of missing evaluation criteria for the use of concrete according the exposure class XF2, as for example the abutment or the columns of a bridge still has to be solved. Test methods are only available for the evaluation of concrete under extreme conditions that means high water saturation without and with de-icing agents (XF3 and XF4). The resistance against the exposure at moderate water saturation is proofed with the stronger test method at higher water saturation. Due to the pozzolanic reaction of fly ash especially the fly ash concretes are misjudged by this test method and because of that these concretes are not used in this field of application.
In the framework of the research project concrete with fly ash is analyzed with different frost test methods. The evaluation of the concretes is made by the scaling and the internal damage.
Starting in October 2009 and finishing in February 2010, the project is carried out by the Institute of Building Materials Research of RWTH Aachen University (ibac), and it is technically supervised by the Technical Committee Power Plant By-products. The project is assigned to the VGB research programme "Waste Management of Coal-fired Power Plants and Waste Incineration Plants" (ERKOM).