Use of Hard Coal Fly Ash as Concrete to Avoid a Damaging Alkali-silica Reaction with Alkali-sensitive Aggregates
Project Number 245
For many years, international experience with fly ash in concrete has shown, that fly ash can be successfully used against damages to alkali-silica reactions (ASR). In concrete constructions with alkali-sensitive aggregates a damage caused by an alkali-silica reaction could often be avoided by the partial replacement of alkali-rich cements with fly ash.
According to the Alkali Guideline of the German Committee of Reinforced Concrete (DAfStb) it is allowed to add fly ash to concrete mixtures. However, the reducing or preventing effect of the alkali-silica reaction has not been acknowledged so far. By taking into account this ASR preventing effect fly ash could be used in combination with alkali-rich cement for the production of concretes with alkali-sensitive aggregates instead of a cement with a low alkali content.
In the research project concretes and mortars with different fly ashes and cements of different alkali contents with alkali sensitive aggregates will be tested according to the Alkali Guideline of the DAfStb. Apart from opal sandstone/flint, so-called slow/late rocks as greywacke or broken gravel from the upper Rhine region will be examined.
The concrete and mortar samples will be stored in the fog chamber (40 °C; 99 % of humidity) and outdoors. The samples will be examined by the measurement of expansion and ultrasonic velocity. The formation of gel by ASR will be investigated via thin section microscopy. The alkali contents in the pore solution of the mortar samples will also be examined. For these tests the pore solution will be gained by high-pressure treatment of the mortar samples.
The project is assigned to the VGB research programme "Waste management of coal-fired power plants and combustion plants" (ERKOM). Starting on May 1, 2003 and finishing on October 31 in 2005 the project is carried out by the Institute of Building Materials and Construction at the Technical University of Munich and is technically supervised by a working group of the working panel "Power Plant By-products".